US20030213005A1 - Biological control - Google Patents

Biological control Download PDF

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US20030213005A1
US20030213005A1 US10/148,041 US14804102A US2003213005A1 US 20030213005 A1 US20030213005 A1 US 20030213005A1 US 14804102 A US14804102 A US 14804102A US 2003213005 A1 US2003213005 A1 US 2003213005A1
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lethal
organism
sex
male
female
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Luke Alphey
Dean Thomas
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Oxford University Innovation Ltd
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Oxford University Innovation Ltd
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Assigned to ISIS INNOVATION LIMITED reassignment ISIS INNOVATION LIMITED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ALPHEY, LUKE, THOMAS, DEAN
Publication of US20030213005A1 publication Critical patent/US20030213005A1/en
Priority to US11/733,737 priority Critical patent/US20080115233A1/en
Priority to US13/942,601 priority patent/US9125388B2/en
Priority to US14/836,863 priority patent/US20160044902A1/en
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    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01K—ANIMAL HUSBANDRY; AVICULTURE; APICULTURE; PISCICULTURE; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
    • A01K67/00—Rearing or breeding animals, not otherwise provided for; New or modified breeds of animals
    • A01K67/033—Rearing or breeding invertebrates; New breeds of invertebrates
    • A01K67/0333—Genetically modified invertebrates, e.g. transgenic, polyploid
    • A01K67/0337—Genetically modified Arthropods
    • A01K67/0339—Genetically modified insects, e.g. Drosophila melanogaster, medfly
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01K—ANIMAL HUSBANDRY; AVICULTURE; APICULTURE; PISCICULTURE; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
    • A01K67/00—Rearing or breeding animals, not otherwise provided for; New or modified breeds of animals
    • A01K67/033—Rearing or breeding invertebrates; New breeds of invertebrates
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01K—ANIMAL HUSBANDRY; AVICULTURE; APICULTURE; PISCICULTURE; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
    • A01K67/00—Rearing or breeding animals, not otherwise provided for; New or modified breeds of animals
    • A01K67/033—Rearing or breeding invertebrates; New breeds of invertebrates
    • A01K67/0333—Genetically modified invertebrates, e.g. transgenic, polyploid
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
    • C12N15/09—Recombinant DNA-technology
    • C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
    • C12N15/09—Recombinant DNA-technology
    • C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
    • C12N15/79—Vectors or expression systems specially adapted for eukaryotic hosts
    • C12N15/82—Vectors or expression systems specially adapted for eukaryotic hosts for plant cells, e.g. plant artificial chromosomes (PACs)
    • C12N15/8216—Methods for controlling, regulating or enhancing expression of transgenes in plant cells
    • C12N15/8237—Externally regulated expression systems
    • C12N15/8238—Externally regulated expression systems chemically inducible, e.g. tetracycline
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
    • C12N15/09—Recombinant DNA-technology
    • C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
    • C12N15/79—Vectors or expression systems specially adapted for eukaryotic hosts
    • C12N15/82—Vectors or expression systems specially adapted for eukaryotic hosts for plant cells, e.g. plant artificial chromosomes (PACs)
    • C12N15/8241—Phenotypically and genetically modified plants via recombinant DNA technology
    • C12N15/8261—Phenotypically and genetically modified plants via recombinant DNA technology with agronomic (input) traits, e.g. crop yield
    • C12N15/8271—Phenotypically and genetically modified plants via recombinant DNA technology with agronomic (input) traits, e.g. crop yield for stress resistance, e.g. heavy metal resistance
    • C12N15/8279—Phenotypically and genetically modified plants via recombinant DNA technology with agronomic (input) traits, e.g. crop yield for stress resistance, e.g. heavy metal resistance for biotic stress resistance, pathogen resistance, disease resistance
    • C12N15/8285—Phenotypically and genetically modified plants via recombinant DNA technology with agronomic (input) traits, e.g. crop yield for stress resistance, e.g. heavy metal resistance for biotic stress resistance, pathogen resistance, disease resistance for nematode resistance
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01K—ANIMAL HUSBANDRY; AVICULTURE; APICULTURE; PISCICULTURE; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
    • A01K2217/00—Genetically modified animals
    • A01K2217/05—Animals comprising random inserted nucleic acids (transgenic)
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01K—ANIMAL HUSBANDRY; AVICULTURE; APICULTURE; PISCICULTURE; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
    • A01K2227/00—Animals characterised by species
    • A01K2227/70—Invertebrates
    • A01K2227/706—Insects, e.g. Drosophila melanogaster, medfly
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
    • Y02A40/10—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in agriculture
    • Y02A40/146—Genetically Modified [GMO] plants, e.g. transgenic plants

Definitions

  • the present invention relates to a method for controlling the population of an organism.
  • SIT requires some mechanism for insect sterilisation.
  • SIT commonly also employs separation of males from females, with the release of only one sex. This is desirable in the case of an agricultural pest, such as the medfly, where the female damages fruit, even if the female is sterile. Similarly, only the female mosquito bites humans. As such, release of the female insect is preferably avoided in these cases.
  • Fryxell and Miller disclose an alternative strategy for insect control, using Drosophila containing a dominant conditional lethal gene which is expressed under appropriate cold conditions in the wild.
  • this method can be ineffective due to varying field conditions, where the environment does not provide suitably cold conditions.
  • organisms that live in a range of temperature habitats may not be controlled under all conditions.
  • DeVault et al. disclose a two-stage process which is a modification of the SIT procedure. Insects are initially separated by expression of a stably inserted female specific promoter linked to a lethal gene, which is expressed to kill females and to produce just one sex. The remaining males can then be sterilised by irradiation or chemical treatment and released into the environment.
  • this method suffers from the drawback referred to above, in that released flies have reduced fitness due to the sterilisation treatment.
  • the DeVault article discloses use of this genetic sexing step in combination with a second genetic system which may serve to sterilise or retard the hardiness of the natural population.
  • the present invention sets out to overcome such problems.
  • the invention relates to a non-human multicellular organism carrying a dominant lethal genetic system the lethal effect of which is conditional, wherein the lethal effect of the lethal system occurs in the natural environment of the organism.
  • the invention relates to an organism viable in a laboratory under controlled conditions.
  • Controlled conditions are conditions that do not occur in the natural environment of the organism. As such, the conditions are typically artificial. Removal of the controlled conditions permits expression of the lethal genetic system.
  • the organism may be autocidal, in that it will be killed after release into the environment.
  • the organism can transmit a lethal element to at least some of its offspring, such that at least some of these offspring are also killed.
  • the organism of the invention can be used in population control to pass on the lethal genetic system through mating, and also to block potentially productive mating of wild type organisms. Distribution of the organism of the present invention into the environment thus initiates a biological control system. The organism of the present invention does not need to be sterilised, thus avoiding problems with sterilisation through irradiation and loss of genetic fitness.
  • the invention provides a method of biological control, comprising:
  • the lethal genetic system is made to be sex-specific.
  • the lethal genetic system is preferably a conditional dominant sex-specific lethal genetic system, which is expressed in the restrictive conditions of the natural environment of an organism.
  • the expression of the lethal genetic system may be controlled under permissive conditions in a laboratory, factory or other regulated system, for example, to allow growth of a normal populations, e.g. insect stock with both sexes.
  • the conditions Prior to release of the factory or laboratory stock into the environment the conditions can be manipulated to ensure only single sex populations of the organism are distributed into the environment. No additional irradiation of the organism is required and the arrangement removes any requirement for use of two separate genetic systems (i.e. those employed by De Vault et al, for sexing and, for example, sterilisation). Only one genetic system needs to be constructed and inserted into the organism, which renders the methodology easier and quicker.
  • the multicellular organism carries a dominant sex-specific lethal genetic system which is conditional, and does not have a dominant sex-specific lethal genetic system which is unconditional and is expressed in every individual.
  • the lethal genetic system in the organisms of this invention is not expressed, and a stock of organisms can be bred. Imposition of restrictive conditions then allows one sex (for example, females) to be killed The remaining sex (males) can be released to the environment, and the genetic system is passed on to at least some offspring resulting from any sexual reproduction between said males and a wild-type organism of the same species.
  • the conditional dominant lethal genetic system is selected such that expression of the lethal system occurs in the natural environment.
  • the stock of organisms grown under permissive conditions can be released into the environment, without imposing the restrictive conditions to kill off one sex before release.
  • This variation permits the possibilities of using a timing mechanism, e.g. life cycle stage, in creating a biological control agent. That is, the imposition of the restrictive condition is programmed by an event other than, for example, a pre-determined change in factory/laboratory conditions prior to release into the environment For example, release of a normal population of larvae creates a useful time-scatter or delayed release agent.
  • the present invention provides a method of biological control for an organism, the organism having discrete sexual entities, the method comprising the steps of:
  • a normal population i.e. containing both sexes
  • a certain stage of the life cycle of the organism e.g. larvae
  • the invention relies on expression of a conditional dominant lethal genetic system capable of sex specific lethality, in order to eliminate one sexual entity.
  • the conditional expression of the lethal gene is such that the lethal effect occurs in the natural environment of the organism to cause the biological control.
  • the invention accordingly involves a third step
  • the invention further provides a method of biological control, comprising:
  • the invention also relates to organisms comprising a conditional dominant lethal genetic system for use in a combined method of sex separation and biological control as herein defined.
  • the invention further provides a multi-phase lethal system having lethality at more than one life cycle stage.
  • the invention provides an organism or single sex population for use in biological control, wherein the organism or single sex population produces no viable progeny when mated with the wild-type opposite sex under restrictive conditions, e.g. in the natural environment.
  • the invention provides a male population which produces no viable male or female progeny. This contrasts with the situation in which a male only population produces no female progeny but viable male progeny.
  • the invention further provides a method for the sex-separation of organisms, wherein the expression of a sex specific dominant conditional lethal system is used to kill one sex to leave either an essentially pure male or female population, or a population in which organisms comprise either male or female tissues, or a population in which organisms are unable to produce functional male gametes or female gametes (or both) which they would have been able to produce but for expression of the lethal genetic system.
  • the invention further provides a method of biological control in which the growth of a stock of organisms under permissive conditions, once initiated, is self-sustaining and requires no additional pool of organisms for its maintenance.
  • the invention further provides a method of biological control in which the expression of the lethal genetic system occurs in the absence of a substance which is absent from the natural environment of the organism, thus ensuring effective biological control when the organism is released.
  • the lethal genetic system is suitably comprised of a lethal gene and controlling and/or regulatory elements.
  • the lethal system may be comprised simply of a lethal gene, sufficient to produce the lethal effect.
  • the dominant genetic system suitably includes a dominant gene whose effect is phenotypically expressed in the heterozygous state. This dominant effect ensures that, if an organism only receives one copy of the lethal genetic system, then the lethal effect of that system will nevertheless be exerted in the host in the natural environment of the organism.
  • the lethal genetic system may be sex-specific or non-sex specific, the former being generally preferred. In the case of a sex-specific lethal system it is possible to carry out a genetic sex-selection before release of organisms for biological control.
  • the lethal effect is female specific.
  • a male specific lethal effect may be required in certain situations.
  • the sexual entities need not be discrete organisms, but parts of the same organism.
  • the present invention may thus also be applied to plants, wherein one sexual entity of a plant is killed.
  • the conditional dominant lethal genetic system is permitted to be expressed during growth cycles before release, and the plant then distributed.
  • no such permissive expression might be needed before release, for instance in the case of seed distribution with the lethal effects only manifesting once the plant reaches a certain further stage in its life cycle in the environment.
  • distributing the organism typically occurs by release of the organism into the environment.
  • distributing typically occurs by planting of mature plants, seedlings or seeds, or any suitable form of the organism in the environment.
  • conditional effect of the dominant lethal genetic system is seen except under defined permissive conditions.
  • restrictive conditions occur in the natural environment of the organism, and are those conditions which allow the lethal effect of the lethal system to be expressed.
  • permissive conditions which allow the survival of the organism are only present when adopting permissive conditions in the regulated growing environment.
  • expression of the dominant lethal genetic system is conditional upon the presence of a substance or condition not found in the natural environment, such as an artificial or synthetic compound, suitably an antibiotic, antibiotic analogue or derivative.
  • a substance or condition not found in the natural environment such as an artificial or synthetic compound, suitably an antibiotic, antibiotic analogue or derivative.
  • an artificial substance or condition is suitably always absent from the natural environment, that is, it is never or only rarely present in the natural environment in sufficient abundance or concentration to inactivate or functionally repress the lethal genetic system.
  • absence of the substance or condition results in expression of the lethal effect of the lethal system.
  • the natural environment of the organism is generally the environment in which the population to be controlled is located, or may survive. Additionally, the natural environment is also an environment which provides the necessary restrictive conditions.
  • the universal nature of the invention allows universal application of the methods used in the invention, and the natural environment may thus be any world environment in which biological control is needed, without restriction.
  • the lethal genetic system of the present invention may be any genetic element or combination of elements which is capable of producing a lethal effect.
  • the lethal genetic system comprises a DNA sequence encoding a potentially lethal gene product (a lethal gene) and controlling elements such as promoters, enhancers or trans-activator components.
  • the elements which regulate the gene may be located on the same chromosome as the lethal gene, which is preferred, or on a different chromosome.
  • the lethal system is a lethal gene the expression of which is under the control of a repressible transactivator protein.
  • the lethal system may simply be the lethal gene alone, or in combination with its native promoter.
  • the organism of the present invention has only one lethal genetic system, the system wing conditional on environmental factors. More preferably the system has only one conditional lethal gene.
  • the use of a simple genetic system minimises the chance of genetic complication when producing or carrying out the invention.
  • the organism contains no transgenes or other non-natural gene or DNA arrangements, other than that of the lethal genetic system of the invention.
  • the invention thus relates to a method for the field testing of tansgenic crops, comprising the Step of growing a transgenic plant comprising the conditional lethal dominant system of the invention under permissive conditions, and then distributing the plant into the environment where it is exposed to restrictive conditions.
  • a field test is generally any test carried out on a transgenic plant to asses its characteristics, such as its commercial suitability as a crop or foodstuff, for example.
  • the invention also extends to plants having the conditional lethal dominant system of the invention in combination with one or more transgenes.
  • the lethal effect may also be targeted to a specific life cycle stage of the organism.
  • life cycle specificity we prefer that the lethality of the invention is embryo specific lethality.
  • the lethal phase suitably ends before the developmental stage at which the organisms are released, or they may lose fitness or die following release.
  • embryonic lethality ensures that no larvae emerge to damage crops or animals. Whilst this is less important in the case of disease vectors such as mosquitoes, where only the adult stages transmit the disease, it is important in the case of many crop pests where it is the larvae that cause economic damage.
  • Embryo-specific lethality allows the last and biggest mass-reared generation to be reared on food lacking the repressor, reducing costs.
  • Embryo-specific lethality can also be combined with later sex-specific lethality, e.g. female-specific lethality. In this case we demonstrate that this allows the construction of a strain in which both sex-separation and “sterilisation” are automatic consequences of the withdrawal of permissive conditions from the last generation prior to release.
  • the lethal expression is such that individuals die before they cause the damage which it is intended to prevent.
  • mosquitoes it is desirable to reduce disease transmission.
  • the earliest that a female mosquito can transmit disease is the second blood meal (having picked up the parasite/virus in the first blood meal and so become infectious). Therefore, the mosquito can be killed as late as shortly after the first blood meal.
  • mosquito feeding is also undesirable, and preferably killing is effected shortly before or just after the first blood meal.
  • the lethal gene of the lethal genetic system may be any genetic element which is capable of causing the death of, or leading to the fatality of, the host.
  • the term covers gene fragments capable of exerting a lethal effect, and is not limited to full length genes. Any element capable of exerting a lethal effect which may be conditionally controlled is covered by this term.
  • lethal genes are those described in the Examples herein, the hid gene [see Heinrich and Scott, P.N.A.S Jul. 18 2000, volume 97, 15, 8229-8232], and the Nipp1Dm gene, a Drosophila homologue of mammalian NIPP1 (see Example 7).
  • Other possibilities for lethal genes include sex-determination genes which may act to tnansform the sex of the organism.
  • transformation of females to sterile males would also enable biological control to be achieved, and the lethal gene is lethal to the population as such and not specifically to the organism.
  • highly toxic gene products such as diphtheria toxin and ricin A, we prefer that the genes are only expressed at levels sufficient to kill the organism, but with minimum environmental impact.
  • a preferred lethal gene for use in the invention has a threshold of toxicity—below a certain level it is harmless while above it is lethal. Additionally, to reduce the possibility of resistance, the lethal gene preferably has multiple essential targets. Nipp1Dm generally fulfils these criteria It encodes a highly conserved protein present in all cells at a significant level. Modest over-expression is therefore unlikely to have any adverse consequences. It is a potent inhibitor of three essential genes in Drosophila, each of which have highly pleiotropic effects. Accordingly, because of the high level of conservation of this protein between C. elegans, D. melanogaster and mammals, Nipp1Dm is a preferred lethal gene for use in the present invention.
  • the conditional nature of the lethal system allows recombinant organisms to be bred under conditions permissive for organism survival, for example in a factory or laboratory, and then released into the natural environment
  • the lethal effect of the lethal system is controlled such that the released organisms are able to breed, and sexual reproduction allows the lethal system to be passed into the wild type population, killing all or a defined group of these organisms.
  • the target class may be, for example, females, i.e. 50% of the progeny.
  • the lethal effect results in killing of greater than 95% of the target class, still more preferably 99% and most preferably 100% of the target organisms in the environment.
  • the conditional nature of the lethal system may be conditional on any suitable factor, such as temperature, diurnal cycle (with light duration and/or intensity being factors) or pheromones, for example.
  • the recombinant stock could be reared at the permissive temperature, and released into an environment having a restrictive temperature.
  • the lethal effect occurs at a temperature which is at least 5° C., more preferably 10° C., more preferably 20° C., within the extremes of the temperature range known to occur in the environment of the organism across the world, such that there is always expression of the lethal effect in the environment.
  • the lethal effect of the lethal system is inherently insensitive to temperature variations or fluctuations which occur in the natural environment of the organism.
  • the expression of the lethal system is not conditional on temperature but is temperature sensitive to any extent, we prefer that greater than 90% of the organisms are killed in the natural environment, more preferably at least 95%, preferably at least 98%, preferably at least 99% or more.
  • the lethal genetic systems of the present invention are generally not susceptible to temperature to any significant extent, so that for example, the difference in lethal effect at 1° C. and 29° C. is less than 5%, preferably less than 1%.
  • the preferred lethal genetic systems of the invention are suitably functional across a broad temperature range, such as may occur naturally within the environment where the organism is found. Examples of typical temperature ranges are 0° C. to 50° C., more usually 10° C. to 45° C., such as 15° C., 20° C. or 25° C. 40° C.
  • the lethal effect is exhibited in at least 95% of organisms across this whole temperature range, in that 95% of organisms are killed at any given temperature in the range, more preferably 98%, 99% or even more. More generally, the highest survival rate at any temperature is preferably less than 10%, suitably 5%, 2%, 1% or less.
  • the lethal effect of the lethal system is preferably expressed in the natural environment when the organism is distributed into its natural environment or any naturally occurring environment, irrespective-of the natural conditions which can occur or which prevail in that environment.
  • the lethal effect of the lethal system is conditional upon a dietary additive, such as a food or water additive, which is not a normal food component for the target species.
  • a dietary additive such as a food or water additive
  • the recombinant stock to be grown on food or water containing the additive, which prevents the lethal effect.
  • the organism On release into the wild, the organism has no exposure to the additive, and the lethal effect of the lethal system is expressed in the progeny of a mating with the recombinant organism of the invention. It may also be expressed in the parent organism under certain circumstances, although the released organism must survive long enough to mate.
  • antibiotics such as tetracycline and non-antibiotic tetracycline analogues and derivatives thereof, which function with the preferred tetracycline repressible system of the present invention.
  • Non-antibiotic compounds are especially preferred to avoid potential problems with antibiotic accumulation in the environment.
  • Suitable analogues include epioxytetracycline and anhydrotetracycline, although other suitable analogues may also be employed, as appropriate.
  • the lethal effect is conditional upon a dietary additive, it may be that the progeny will survive without themselves ingesting or absorbing the dietary additive.
  • the progeny might retain sufficient of the additive from their parents or from an earlier life cycle stage without feeding, or at the least the additive may be slowly lost from the progeny. This effect might pass through one or more generations before the lethal effect is fully expressed under restrictive conditions.
  • the recombinant multicellular organism of the present invention contains a dominant lethal system the lethal effect of which is conditionally suppressible, In this way, the lethal effect is suppressed under controlled conditions, but not suppressed in the natural environment of the organism.
  • conditional expression for example, conditional activation
  • the repressible expression system is a tetracycline repressible system in which tetracycline, or an analogue or derivative thereof, is used to inhibit expression of the lethal systems
  • tetracycline or an analogue or derivative thereof
  • One suitable system is described in detail in the examples herein, in insects. This tetracycline system has also been shown to work in plants (see Zuo and Chua, 2000, Curr. Opin. Biotech. 11:146 and references therein).
  • the repressible lac repressor system is less preferred, as the inducer (IPTG) is less diffusible and more toxic than tetracycline.
  • an inducible system may be based upon the constitutive expression of a toxin and inducible expression of a repressor of the toxin.
  • a chimeric transcription factor which is normally inactive (sequestered by binding to Hsp90).
  • the inducer a steroid hormone or analogue, e.g. dexamethasone
  • the transcription factor is released from Hsp90 and can drive gene expression.
  • the tapetum-specific A9 promoter may be used.
  • the tapetum is a tissue required for production of functional pollen The system is then ‘off’ in all tissues except the tapetum.
  • the toxin and the transcription factor are both expressed.
  • the inducer here dexamethasone
  • the antidote is also expressed. So plants treated with dexamethasone arc normal, but those not treated with dexamethasone produce no pollen.
  • barnase and barstar (Hartley, R W, 1988, J. Mol. Biol. 202:913, Hartley, R W, T.I.B.S. 14: 450-454, 1989) may be used as toxin and antidote, respectively.
  • barnase and Barstar are suitable examples of a toxin/repressor pair, the invention is not so limited, and a suitable repressor could act at a transcriptional (or other) level, and the toxin itself does not have to be a protein.
  • the invention includes the possibility of conditional control both at the level of lethal gene expression, and by control of the activity of the lethal gene product. As such, the invention includes the case in which the lethal gene product is being produced but the effect of which is masked in some way.
  • the method of the invention uses only organisms with a single conditional dominant lethal genetic system.
  • this system is the only recombinant element present in the organism.
  • the organism contains only one type of lethal gene, but it is possible to envisage multiple lethal genes under the same regulatory control, giving the integrated genetic construct concept but a more efficient lethality of the system.
  • This single lethal gene may be under the control of just one promoter in the genetic system, or more than one promoter.
  • the organism of the invention is preferably recombinant, which refers generally to any organism whose genetic material has been altered by genetic manipulation.
  • the organism is modified by insertion of a gene, gene fragment or genetic element (such as a promoter or enhancer) from another species, to produce a transgenic organism.
  • the transgenic component is generally the lethal system which produces a conditional lethal effect.
  • a conditional lethal effect may also be generated using genetic components derived from the same (host) species. For example, a promoter derived from a different gene in the same species; when placed in front of a gene which is only normally expressed at low levels, may result in a lethal effect.
  • the recombinant organism is thus either a transgenic organism or one in which the host genetic material has been modified to produce a lethal system.
  • the multicellular organism may be any organism, such as a plant or animal. Indeed, the invention is generally only limited to those organisms having a sexual component in their life cycle, which enables the lethal system so be transferred from one organism to another. For example, the invention is also applicable to fish, such as the sea lamprey, against which sterile male release techniques have been employed.
  • the multicellular organism of the invention is an insect, with insect pests being particularly preferred
  • An insect pest may be either a direct or an indirect pest
  • Direct pests are those insects which cause damage at one or more stage of their life cycle by, for example, eating crops or damaging animals
  • the New World screw-worm fly Cochliomyia hominivorax for example, is a direct pest of cattle.
  • Indirect pests are those insects which are vectors of human diseases, such as mosquitoes which carry malaria Indirect pests of organisms other than humans, such as livestock or plants are also known.
  • Preferred insect targets for the present invention include Crop (arable and forestry) pests animal pests and disease vectors.
  • Examples of specific organisms which potentially may be used in the present invention include, but are not limited to: Australian sheep blowfly (Lucilia cuprina, Asian tiger mosquito (Aedes albopictus); Japanese beetle ( Popilla japonica ), White-fringed beetle (Graphognatus spp.), Citrus blackfly ( Aleurocanthus woglumi ), Oriental fruit fly ( Dacus dorsalis ), Olive fruit fly ( Dacus oleae ), tropical fruit fly ( Dacus cucurbitae, Dacus zonatus ), Mediterranean fruit fly ( Ceratitis capitata ), Natal fruit fly ( Ceratitis rosa ), Cherry fruit fly ( Rhagoletis cerast ), Queensland fruit fly ( Bactrocera tryoni ), Caribbean fruit fly ( Anastrepha suspensa ), imported fire ants ( Solen
  • the transgenic stock is released into the environment at appropriate sites and times.
  • the procedure is slightly different.
  • the gametes themselves are released, e.g. as pollen, or plants are dispersed, e.g. at field margins, to pollinate wild weeds and so reduce their reproductive potential.
  • the present invention is of particular use in the control of those weeds, such as rye grass, which are not well controlled by current herbicides, or against weed types which have developed herbicide tolerance.
  • the invention is preferably such that expression of the lethal genetic system will always occur in the environment in which the organism is released for biological control, and is unaffected by natural variation in environmental factors. In this way, biological control is always achievable using the present invention, irrespective of the site of release, time of release, or any other environmental conditions. Where the factor controlling conditional expression is artificial, then it is immediately clear such a factor cannot, by definition occur in the natural environment.
  • the present invention is essentially pandemic, in the sense that it may be universally applied over the whole of a country or the world environment.
  • any natural environment itself provides the restrictive conditions for the organism, resulting in the biological control.
  • the restrictive conditions are guaranteed to occur upon organism release, and there is no concern that local environmental conditions will affect the action of the lethal system.
  • the natural environment of the organism provides the absence of a controlling factor or condition, which then results in expression of the lethal genetic system in the environment.
  • the multicellular organism of the present invention preferably has a lethal system homozygous at one or more loci.
  • a lethal system homozygous at one or more loci.
  • at least one copy of the system will be passed to any offspring during sexual reproduction. Therefore, the dominant lethal effect will be exerted, except in permissive conditions.
  • the present invention may be carried out using a heterozygote for the dominant lethal system. However, in this case, not all the offspring will have a copy of the lethal system, and the effect on the population is reduce.
  • the lethal system can also function when controlling elements are present at different genetic loci to the lethal gene, if controlling effects of these elements are exerted in trans, for example. In that event, the genetic system is still effective if the controlling and lethal elements are also homozygous, and at least one copy of each is transferred to the offspring.
  • the invention relates to a non sex-specific system, in which both males and females are killed by the lethal genetic system.
  • a non sex-specific system in which both males and females are killed by the lethal genetic system.
  • Such an approach is preferred in certain organisms.
  • one advantage of the invention lies in the avoidance of sterilisation by irradiation.
  • mixed sex releases are preferred in pink bollworm (a lepidopteran pest of cotton), but irradiated moths are estimated to suffer at least a 10 fold reduction in effectiveness as a consequence of the irradiation due to loss of vigour and reduced life span. Similar advantages are predicted in other organisms.
  • irradiated males are about 50% less effective than the non-irradiated equivalent in competitive mating tests and they live 3-5 days instead of the non-irradiated 10-15. This gives a composite 410 fold potential performance improvement by avoiding irradiation.
  • the method of the invention alternatively uses a sex-specific lethal system to achieve sex separation before or after release of organisms into the environment.
  • the multicellular organism is an insect containing a homozygous dominant lethal system, the lethal effect of which is lethal only to females.
  • males released into the natural environment will not be killed
  • female offspring will contain at least one copy of the dominant system and be killed.
  • male offspring 50% of which contain the dominant system viable and may mate with further females. In this way, the dominant system may be transmitted to subsequent generations, although without further artificial introductions the system will eventually be lost from the gene pool.
  • Sex-specific lethality may be achieved in a number of different ways. For example, it is possible to use a sex-specific lethal gene as part of the lethal system, whose gene product is toxic only in one sex. This approach will allow killing of a single sex even if expression of the lethal gene of gene product is not sex specific.
  • Candidates for female sex-specific lethal genes include genes from the sex determination pathway, for example normally active only in males and toxic in females, or genes derived from sexual differentiation or gametogenesis systems.
  • expression of the lethal gene or gene product may be controlled so that it is expressed or produced only in one sex (or in only one gamete or sexual organ of a hermaphrodite).
  • sex-specific promoters or enhancers may be used, either in combination with sex-specific lethal genes or non-specific lethal genes. Sex-specific splicing provides another mode for sex-specific gene expression. All possible combinations of non-specific lethal genes, sex-specific lethal genes, non-specific promoters and sex-specific promoters are envisaged by the present invention.
  • other sex-specific factors which control the lethal effect of the lethal gene are included in the present invention.
  • the present invention also includes a method of biological control in which the lethal effect may be sex-specific at one stage of the life cycle, but be lethal to both sexes at another stage.
  • the lethal system may be female specific in an adult organism, but be lethal to both males and females in the larval stage.
  • one sex may be killed by expression of the lethal system in the adult form.
  • both males and females can be killed.
  • Such an effect can be achieved by a promoter which is sex specific at one life cycle stage, but not at another, or by placing the lethal gene under control of two different promoters, for example. Multiple lethal systems might also be employed.
  • a lethal effect manifested at an embryonic or larval stage will not affect adult organisms, if they are grown under permissive conditions through this stage.
  • organisms may be distributed into the environment after the lethal life cycle stage, allowing the lethal system to be passed into the wild-type population through sexual reproduction.
  • Other life cycle stages, such as the adult stage may also be targeted by selection of genes or promoters expressed at specific life cycle stages, if appropriate.
  • the multicellular organism of the present invention has a copy of the lethal genetic system at more than one locus.
  • the lethal system is homozygous at more than one locus.
  • the approach will clearly be more effective if more than 50% of this next (second) generation of male offspring were to inherit the lethal genetic system.
  • the lethal genetic system is homozygous at more than one, not tightly linked locus, e.g. on more than one chromosome, then the proportion of these males carrying the lethal genetic system will increase.
  • the lethal genetic system homozygous at two unlinked loci, the first generation males will be heterozygous at both loci, 75% of the second generation males will carry at least one copy of the lethal genetic system.
  • all of the first generation and 75% of the second generation females will die.
  • SD chromosome is preferentially inherited from males heterozygous for SD and a normal (+) SD-sensitive chromosome.
  • SD/+males transmit SD-bearing, to the virtual exclusion of +-bearing, homologues; as many as 99% of the functional sperm may carry SD.
  • Segregation distortion/meiotic drive systems are known in a wide range of insect and non-insect species.
  • a third way of ensuring >50% inheritance of the lethal genetic system in the second generation is to link the lethal genetic system to insecticide resistance and use the insecticide to eliminate some or all of the second (and subsequent) generation progeny which do not carry the lethal genetic system and hence do not carry the linked resistance gene.
  • the lethal system may be located on any chromosome, either an autosome or sex chromosome. In species where sex is determined by the X or Y chromosome content and where elimination of the transgene from the gene pool is desired, then we prefer that the lethal system is located on the X chromosome.
  • the lethal system is specific for females.
  • a male organism (XY) having the lethal system on the X chromosome mates in the wild with a female wild type organism (XX).
  • the male offspring must derive their Y chromosome from the recombinant male and their X chromosome from their mother. These males are viable and have no lethal gene.
  • Female offspring must derive one X chromosome from the recombinant male and, thus, contain the lethal genetic system—they are killed. As such. the lethal system is eliminated from the gene pool, which may be preferable if this element is a transgene.
  • the present technology also provides a method for the selection of males or females per se, comprising producing a organism as described herein containing a conditional dominant lethal system, wherein the lethal effect of the lethal system is sex-specific. Sex selection is achieved by allowing expression of the lethal effect of the lethal system, to eliminate one sex.
  • the individual male or female population may then be used for any desired purpose, not being limited to biological control.
  • the present invention also relates to a method of producing a recombinant multicellular organism for use in the present invention, wherein the organism is transformed with a vector or vectors containing a dominant lethal system, or a suitable sequence for site specific mutation.
  • the present invention further relates to a vector or vectors comprising a dominant lethal system as described herein.
  • vectors comprising the conditional dominant lethal genetic system of the invention, wherein the components of the vector (such as the genes or regulatory elements, in particular the lethal gene) are genetically insulated from one another. Preferbly there is no cis cross-talk between the different elements of the lethal genetic system of the vector.
  • insulator sequences derived from vertebrate DNA which prevent such cross-talk.
  • Such insulators have been reported to work in Drosophila, for example [Namciu, S. J., et al., (1998) Mol. Cell. Biol. 18: 2382-91 and Chung, JH., et al., (1993) Cell 74:505-514], and by extension are likely to be effective in other insect species at least.
  • the vector of the invention comprises a tetracycline repressible system.
  • a lethal gene is located on the same DNA sequence or vector as this system, optionally with a reporter gene.
  • a suitable tetracycline based lethal system comprises two key components, a lethal gene and a tTA gene which activates expression of the lethal gene Tetracycline, or analogue thereof, then blocks activation of the lethal gene by the tTA.
  • enhancer-blocking insulators are used to isolate one component from the next, namely the lethal gene from the tTa, the lethal gene from the reporter and the tTa from the reporter gene.
  • a particularly preferred vector in which the genetic elements are separated and modular is presented in the Example 7 herein
  • This vector comprises a dominant lethal tetracycline repressible. genetic system, wherein at least somne of the genetic components of the system are separated by genetic insulator sequences.
  • the lethal gene is the Nipp gene from Drosophila
  • This modular vector may be adapted by replacing the BmA 3 promoter with any suitable promoter to allow the construct to be used in any organism of interest.
  • the invention provides a modular template vector as described herein, where the BmA 3 promoter module may be replaced by any promoter, for use in any suitable organism.
  • the invention also extends to variants of this specific modular vector, in which the functional elements have been replaced with other elements which perform equivalent functions, such as other insulators or lethal genes, and to DNA encoding such variants.
  • the invention also relates to a method of constructing a vector appropriate for imparting a dominant lethal genetic system to an organism, comprising the steps of:
  • the lethal genetic system of the vector is modular in that there are components which can be individually replaced by functionally equivalent genetic components, appropriate for the lethal system to function in an organism of interest.
  • a modular vector allows the lethal gene or promoter sequences to be replaced, for example, without the need to generate an entirely new vector.
  • the individual genetic components may be separated by insulator sequences and still function together to cause a lethal effect.
  • the vector comprises at least one insulator sequence, preferably two such sequences.
  • the invention also relates to vectors obtained and obtainable by the above method
  • the present invention also extends to polynucleotide sequences encoding a conditional dominant lethal genetic system according to the present invention, preferably being a DNA sequence.
  • the invention relates to DNA encoding the lethal genetic system of the Examples, in particular the modular transformation vector of Example 7 herein, and to mutants and variants of such DNA having minor changes such as substitutions, deletions or additions, but wherein the function of the vector or lethal genetic system are not substantially affected, and the vector is able to cause the lethal effect of the invention as required.
  • multiple vectors may be used to transform the organism with the necessary elements of the lethal system, if necessary. It is also possible that control elements and enhancers used to control, for example, a transcription factor which acts on the lethal gene, may also interfere with the lethal gene expression itself It may, therefore, be necessary to separate the components using silencer elements, or other genetic insulating elements to avoid unwanted gene expression problems.
  • the effect of a promoter or enhancer upon a gene normally requires the elements to be present on the same stretch of DNA
  • the effect of a transcription factor may be exerted in trans, and may be located on, for example, a different chromosome.
  • the invention is not limited to integration of the controlling elements on the same chromosome.
  • the construction of a recombinant multicellular organism may require use of a transformation system for the target species (the species which is to be controlled).
  • the specific nature of the transformation system is not a critical feature of the invention, and transformation protocols for a number of, for example, insects are already known.
  • Vectors may be constructed using standard molecular biology techniques in bacteria such as E. coli .
  • the vector used for transformation contains a selectable marker, such as genes producing G418 resistance or hygromycin resistance.
  • Alternative genes other than those related to antibiotic resistance characteristics, such as green fluorescent protein (GFP) may also be used.
  • GFP green fluorescent protein
  • this protein can be visualised simply by illuminating with a suitable excitatory wavelength (e.g. blue) and observing the fluorescence.
  • a suitable excitatory wavelength e.g. blue
  • Such a marker would also allow easy identification of trapped insects in release-and-recapture experiments.
  • the invention also extends to cells, such as bacterial cells, transformed with a vector of the invention.
  • cells such as bacterial cells
  • Suitable cell lines for maintenance and/or propagation of such vectors, for example, are well known to the person skilled in the art.
  • the resulting flies have significantly higher fitness than the rest of the stock and so their numbers tend to increase rapidly.
  • the breakdown product discharge of all or part of the transposon
  • the breakdown product has no great advantage over the intended stock, when reared on media containing Tc.
  • it would take several independent events i.e. loss of each insertion, to make the stock completely ineffective.
  • the lethal genetic complex may be further stabilised. Suitable methods include deleting one end of the transposon after integration or secondary mobilisation of the system out of the transposon into another site, using a site-specific recombination system such as ERT/F1lp or cre/lox. Both of these systems are known to work in Drosophila.
  • FIG. 1 illustrates a modular vector for organism transformation
  • FIG. 2 illustrates a model of a meiotic drive system of the present invention
  • FIG. 3 illustrates a model of population control using multiple unlinked loci
  • FIG. 4 illustrates a model of a meiotic drive system according to the present invention
  • FIG. 5 illustrates a model of population control using multiple unlinked loci
  • FIG. 6 illustrates a further model of a meiotic drive system of the present invention
  • FIG. 7 illustrates model of population control using multiple unlinked loci
  • FIG. 8 illustrates models of population control using the parameters of FIGS. 2, 6 and 7 , but wherein the first two releases are doubled in size.
  • a two-part system may be used to produce a conditional lethal effect.
  • This system is based upon the repressor (tetR) of the transposon-1-derived tetracycline (Tc) resistance operon of E. coli .
  • Tc transposon-1-derived tetracycline
  • the use of this repressor for repressible gene expression in eukaryotes has been developed by Manfred Gossen and Hermann Bujard (reviewed in Gossen, et al., TIBS 18 471-475 1993).
  • the tetR gene product is fused to the acidic domain of VP16, to create a highly efficient Tc-repressible transactivator (tTA).
  • the first part of the system is the tTA expressed under the control of a suitable promoter, and the second part is a dominant lethal gene expressed under the control of the tTA. Overall this gives expression of the dominant lethal in a Tc-repressible fashion.
  • the tTA activates the lethal gene.
  • tetracycline When tetracycline is present, it binds to the tTA and prevents activation of the lethal gene by tTA This lethal system is under the control of a promoter of choice.
  • Tc-analogue One further level of control can be exerted by the choice of which Tc-analogue to use for repression: different analogues will have different half-lives in the insect leading to induction of the killer gene more or less promptly after the repressor is withdrawn from the diet.
  • a non-bactericidal analogue should be used, so as not to encourage tetracycline resistance in environmental micro-organisms.
  • Use of a non-bactericidal analogue is in any case essential for species such as tsetse fly, which have symbiotic bacteria essential for reproduction of the fly which are killed by antibiotics.
  • this one system may be varied to provide a flexible tool for population control. Greater flexibility may be achieved by combining two or more promoters or enhancers. For example, medfly control might use expression in the adult female (to prevent release of egg-laying females), and in early embryonic development (to prevent larval growth within the fruit). Since this means expression before the embryo starts to feed for itself, it would be important for growing the stock that a relatively stable Tc analogue is used, so that the embryos survive because of the maternal contribution of Tc. Larval expression could be also used as an alternative, but with greater damage to the fruit.
  • stage-specific expression may be identified by subtractive hybridisation or other known methods.
  • Insertion of the lethal gene or system into the chromosome of the transgenic orgasm may be at any suitable point. It is not necessary to determine the location of the lethal gene on the chromosome. Even though inserted elements may respond to control elements in adjacent chromatin this not an issue for the tRE-killer lines, where lines giving inappropriate expression will probably not survive.
  • the present invention has been exemplified in the model insect species Drosophila melanogaster . Though D. melanogaster is not an economically important pest, it is experimentally tractable.
  • the tTA system in general has been demonstrated in Drosophila (Bello, B., et al., 1998, Development 125:2193-2202).
  • Hsp26tTA Heat shock protein 26-tTA Low basal level, heat-shock inducible to higher level, not sex-specific.
  • Hsp26 promoter region with a portion of the translated region was fused to a tTa coding region isolated as an EcoRI/BamHI fragment from pUHD 15-1. neo followed by the transcription termination sequence of the Hsp70 gene.
  • Act5C-tTA Actin 5C-tTA. Strong, constitutive, ubiquitous promoter, not sex-specific.
  • the tTA coding region was excised as an EcoRT/PvuII fragment then end filled using T4 DNA polymerase.
  • the p CaSpeR ⁇ Actin5C GFP ⁇ (Reichhart and Ferrandon, (1998), D. S. 81: 201-202) was digested with XbaI/Ba to remove the GFP fragment than end filled using T4 polymerase. These two fragments were then ligated.
  • the resulting clones were screened using a SmaI/EcoRV digest to select a clone of the correct orientation, placing the tTa coding region under the control of the Actin 5C promoter.
  • Stwl-tTA Stonewall-tTa Female-specific in embryos, but expressed later in both sexes.
  • tTa coding region was excised from the plasmid pUHD 15-1.no by digestion with EcoRI and PvuII. This fragment was then ligated into the vector pstwl +mCa (Clark, K A. and McKearin D. M. (1996), Development 122 (3): 937-950) digested with EcoRI/PvuII such that tTa was placed under the transcriptional control of 1.7 kb of stwl promoter genomic DNk
  • Sxl pe -tTA Sex lethal-tTA.
  • PE Early promoter
  • the tTa coding region was excised from the plasmid pUHD 15-1.neo (Gossen M. and Bujard H. (1992); PNAS, 89, 5547-51) by digestion with EcoRI/PuvII. This fragment was then ligated into the 5-1 sxl pe : bluescript (containing Sxl pe sequences (Keyes L N, et al. (1992) Cell. 6; 68(5): 933-43) digested with EcoRI and EcoRV to create sxlpe tTa bluescript.
  • a KpnI/NotI fragment containing the tTa coding region and sxlpe promoter was subcloned into the P element transformation vector pP ⁇ W8 ⁇ (Klemenz et al., (1987) Nucleic Acids Res. 15: 3947-3959) digested with KpnI/NotI to create p(sxl pe tTa).
  • Yp3-tTA Yolk protein 3-tTA Female fat body enhancer ABE) from yolk protein 3, with hsp70 minimal promoter. Expressed in female fat body in larvae and adults.
  • tRe-lacZ E. coli lacZ gene, encoding ⁇ -galactosidase. Used as reporter. Obtained from Bruno Bello (N London) As detailed in Bello et al.(1998) Development 125, 2193-2202. The heptameric repeat of the tet operator was isolated as a EcoRI/KpnI fragment from pUHC 13-3 (Gossen M. and Bujard H. (1992); PNAS, 89,5547-51) and cloned upstream of the P-lacZ fusion of the enhancer-test vector CPLZ (Wharton K A and Crews S T. (1994) Development. 120(12): 3563-9.). CPLZ contain5 the P element transposase promoter (up to —42 from cap site) and the N-terminal transposase sequence fused in-frame with lacz and the polyadenylation signal of SV40.
  • WTP-2 (white-tetO-P promoter—vector containing tRe sequences)
  • the WTP-2 vector was modified by the addition of two compliment short oligos 5′ UAS ATG+(AATTGCCACCATGGCTCATATGGAATTCAGATCTG) and 3′ UAS ATG (GGCCGCAGATCTGAATTCCATATGAGCCATGGTGGGC) into the WTP-2 MCS.
  • the oligos were allowed to anneal and ligated to WTP-2 digested with EcoRI/NotI. These oligos introduced a consensus translation stand several additional cloning sites into the WTP-2 multiple cloning site (MCS).
  • tRe-EGFP Encodes a mutant version of Green Fluorescent Protein (GFP), a jellyfish (Aequoria) gene encoding a fluorescent protein.
  • the EGFP mutant has two amino acid changes, giving a brighter, more soluble protein Used as a reporter.
  • the enhanced green fluorescent protein (EGFP, a F64L, S65T mutant derivative of GFP) coding region (Craven et al. (1998) Gene 9; 221(1): 59-68) was isolated as a NcoI/EcoRI fragment from the pP ⁇ UAS-EGFP) vector, then end filled with T4 polymerase.
  • pP ⁇ UAS-EGFP ⁇ was constructed as follows.
  • the WTP-3 vector was then digested with EcoRI and end filled with T4 polymerase and the fragments ligated together.
  • a diagnostic digest using PvuII/BamHI was then used to select a clone of the correct orientation.
  • tRe-Ras64BV32 Mutant version of Drosophila melanogaster Ras64B, involved in cell signalling. Mutant is constitutively active, making it toxic to the cell if expressed at a high enough level. Toxicity is not sex-specific.
  • the Ras 64 B V12 cDNA was cloned as an EcoRI/NotI fragment from the p ⁇ sevRas64B V12 ⁇ (Matsuo et al., (1997), Development 124(14): 2671-2680), into WTP-2 digested with EcoRI/NotI.
  • tRe-Mls- Mpu Mutant version of Drosophila melanogaster Msl-1.
  • Msl-1 is a component of the sex determination pathway that is usually expressed only in males, being repressed in females by a product of the Sex lethal gene.
  • Activity of mutant is independent of Sex lethal, making it toxic to females if expressed at a high enough level. Toxicity is therefore sex-specific.
  • the msl-1 MPU cDNA was cloned as an EcoRI fragment from M1-ECTOPIC (Chang and Kuroda, (1998) Genetics 150(2): 699-709) into the WTP-2 vector digested with EcoRI A diagnostic digest using HindIII/NotI, was then used to select a clone of the correct orientation, placing the msl-1 MPU cDNA under the control of the tRe sequences.
  • tRe-Ms-2Nopu Mutant version of Drosophila melanogaster Msl-2.
  • Msl- 2 is another component of the sex determination pathway that is usually expressed only in males, being repressed in females by a product of the Sex lethal gene. Activity of mutant is independent of Sex lethal, making it toxic to females if expressed at a high enough level. Toxicity is therefore sex-specific.
  • the msl-2 cDNA was cloned as a NotI/XbaI fragment from pM2 NOPU (Kelley et al., (1995), Cell 81; 867-877) and cloned into WTP-2 digested with NotI/XbaI.
  • [0176] Format for data the 8 numbers are the results from crosses using independent insertions of each element (to control for position effect).
  • 4 insertions of Sxl pe -tTA (A, B, C, and F) were used and two of tRE-Ras 64B V12 (B and C).
  • the order of the data are: Sxl pe -tTA (A) females with tRe Ras64B V12(B) males, ten SxlB ⁇ RasB, SxlC ⁇ RasB, SxIF ⁇ RasB, SxlA ⁇ RasC, SxIB ⁇ RasC, SxlC ⁇ RasC and finally SxlF ⁇ RasC.
  • Tetracycline conc. ⁇ g/ml Female Total Male Total 0 0, 0, 0, 0, 0, 0 50, 44, 45, 56, 40, 67 302 0.1 67, 56, 37, 23, 16, 12 211 56, 53, 50, 61, 42, 74 336 1 69, 64, 41, 13, 31, 18 236 33, 70, 39, 45, 40, 70 257 5 52, 42, 49, 19, 20, 41 223 37, 80, 41, 48, 80 291
  • Tetracycline conc. ⁇ g/ml Female Total Male Total 0 0, 0, 0, 0, 0, 0, 0, 0 38, 53, 47, 68, 38, 70, 52, 60, 481 55 0.1 54, 57, 41, 64, 40, 63, 39, 436 59, 58, 49, 73, 48, 69, 45, 47, 491 42, 36 43 1 46, 34, 35, 63, 47, 70, 64, 439 55, 40, 40, 71, 50, 72, 74, 46, 490 39, 41 42 5 52, 70, 37, 34, 35, 57, 49, 434 54, 71, 41, 42, 41, 66, 56, 55, 481 50, 50 55
  • Tetracycline conc. ⁇ g/ml Female Total Male Total 0 0, 0, 0, 0 0 0, 0, 0, 0 0 0.1 47, 56, 71, 61 235 46, 52, 53, 59 210 1 60, 46, 52, 41 199 79, 71, 68, 56 274 5 2, 51, 71, 32 156 0, 49, 62, 43 154
  • Tetracycline conc. ⁇ g/ml Female Total Male Total 0 0, 0, 0, 0, 0, 0 64, 58, 33, 66, 55, 42 318 0.1 45, 44, 72, 56, 62, 49 328 53, 54, 80, 57, 66, 58 368 1 70, 35, 61, 50, 57, 37 310 78, 36, 70, 56, 61, 42 343 5 44, 58, 58, 59, 42, 52 313 46, 68, 66, 64, 48, 55 347
  • Tetracycline conc. ⁇ g/ml Female Total Male Total 0 0, 0, 0 0 56, 47, 56 159 0.1 48, 49, 62 159 56, 68, 49 159 1 43, 45, 51 135 36, 39, 47 122 5 55, 3, 66 124 61, 5, 54 120
  • Tetracycline conc. ⁇ g/ml Female Total Male Total 0 0, 0, 0, 0, 0 0 65, 70, 61, 65, 47, 42 350 0.1 33, 54, 50, 72, 63, 50 322 42, 64, 52, 74, 67, 54 352 1 56, 56, 61, 69, 57, 43 342 59, 64, 65, 75, 64, 49 376 5 46, 51, 73, 65, 42, 39 316 44, 56, 79, 74, 52, 49 354
  • Tetracycline conc. ⁇ g/ml Female Total Male Total 0 0, 0, 2, 0, 0, 0 2 49, 58, 39, 65, 35, 51 297 0.1 36, 65, 71, 37, 59, 68 336 46, 73, 77, 46, 66, 71 379 1 42, 65, 67, 57, 35, 53 319 49, 72, 68, 59, 41, 58 347 5 55, 55, 43, 58, 36, 60 307 63, 64, 49, 63, 45, 64 348
  • Tetracycline conc. ⁇ g/ml Female Total Male Total 0 0, 0, 0, 0, 0 0 35, 35, 72, 52, 45, 37 276 0.1 34, 68, 42, 51, 33, 40 268 35, 72, 45, 56, 36, 44 248 1 41, 39, 42, 60, 70, 72 324 51, 49, 46, 61, 78, 77 362 5 70, 55, 56, 65, 43, 61 349 74, 58, 64, 73, 51, 66 386
  • reporter crosses at 25° C., females homozygous carrying an insertion of Sxlp e tTa on their X chromosome (Sxlp e tTa (A) ) were crossed to males carrying various reporter constructs.
  • single chromosome crosses ten to fifteen virgin females homozygous for the tTA construct and five to ten young males homozygous for the tRe construct were placed on food containing or lacking a tetracycline supplement. Their progeny were allowed to develop on this food.
  • Embryos were stained for IacZ using a standard histochemical method. Tetracycline conc. ⁇ g/ml LacZ positive Total LacZ negative Total 0 60, 85, 99, 60 304 78, 89, 85, 93 345 0.1 0, 0, 0, 0 0 176, 174, 178, 181 709 1 0, 0, 0, 0 0 188, 190, 181, 180 739 5 0, 0, 0, 0 0 156, 151, 159, 185 651
  • Embryos were scored for fluorescence. In the case of embryos on tetracycline-free media, these were separated, allowed to develop on tetracycline-free media and the sex of the emerging adults was scored. Tetracycline conc. ⁇ g/ml Fluorescent female male Non-Fluorescent female male 0 89, 100, 53, 55 200 0 99, 86, 46, 51 0 232 0.1 0, 0, 0, 0 — — 199, 182, 188, 153 — — 1 0, 0, 0, 0 — — 170, 135, 163, 196 — — 5 0, 0, 0, 0 — — 186, 159, 127, 200 — —
  • C(1) DX is a compound X chromosome; effectively two X chromosomes joined together.
  • the X chromosome from males crossed to C(1)DX females is therefore inherited by the sons, rather than the daughters.
  • Recombinant chromosome stocks can readily be maintained at 25° C. on epioxytetracyclie concentrations of 1 ⁇ g/ml or anhydrotetracycline concentrations of 0.1 ⁇ g/ml, showing that these non-antibiotic tetracycline analogues are effective in repressing tTA responsive gene expression.
  • the example illustrates material transmission of Tc and TC-repressible lethality using an embryo specific promoter.
  • a bnk promoter fragment of approximately 2 kb was amplified from plasmid pW + 2.8 kb bnk rescue fragment (Schejter and Wieschaus, (1993), Cell 75, 373-385) using oligonucleotide primers
  • W.T.P-2 (Bello et al., (1998), Development 125, 2193-2202) was modified by the addition of two complementary oligonucleotides
  • Flies were reared on standard yeast/cornmeal/agar food with a yeast concentration of 45-50 gl ⁇ 1 .
  • Tc-containing food was made to the same recipe with the addition of tetracycline hydrochloride (Sigma-Aldrich) solution to the appropriate final concentration.
  • a mass-reared insect strain homozygous for a dominant lethal gene or genetic system will have no progeny when mated to wild insects. In this respect the time of action of the lethal gene is irrelevant. However, for the mass-reared insects to be useful as a control agent we consider that the time of action of the dominant lethal may be highly important. A lethal phase in adulthood may kill or at least reduce the fitness of the released adults prior to mating. This would clearly be counter-productive. Many agricultural pests damage crops through the feeding of their larval stages. It would therefore be desirable to kill the progeny as early as possible, preferably as embryos. However, embryos do not feed and so will not take up a dietary repressor (tetracycline) of the lethal genetic system.
  • Insect embryos are also impermeable to most macromolecules, so exogenous tetracycline will not penetrate.
  • tetracycline ingested by a female Drosophila could pass into her eggs and hence her progeny at sufficient concentration to suppress the phenotype of a Tc-repressible gene.
  • tTa-dependent transcriptional activation is repressed by Tc.
  • tTa binds to a specific DNA sequence, the tetracycline responsive element (tRe).
  • Tc binds to tTa and this prevents the tTa protein binding to DNA.
  • Effective repression of the reporter genes was achieved by placing the parents on media containing 1 ⁇ g/ml Tc for at least two days prior to embryo collection. Seeding embryos onto media containing Tc did not appear to affect reporter gene expression.
  • NIPP1 has several advantages as a “Killer gene” in this system.
  • Flies carrying homozygous insertions of bnk-tTa or tRe-Nipp1 were crossed to each other. Flies fed on media supplemented with Tc produced viable F 1 progeny; those on media not supplemented with Tc did not (Table 2). Furthermore, F 1 survival was not affected by the presence or absence of Tc in the media on which the F 1 were raised. We have therefore constructed an efficient dominant lethal genetic system repressible by parental dietary Tc. TABLE 1 High doses of maternal Tc can suppress tTa in progeny. Tc conc.
  • a strain homozygous for second chromosome insertions of both Yp3-tTA and tRe-Ras64B V12 was tested for the effect of parental dietary Tc. 40-45 young females and 2025 young males raised at 25° C. upon food with the indicated tetracycline supplement were allowed to mate, then transferred to normal (tetracycline-free) food after 34 days. These flies were transferred to fresh vials of normal food every day for 12 days, and then removed on the 13th day. All the vials were incubated at 25° C. while the progeny developed. The total n umbers of male and female progeny emerging as adults were recorded.
  • Tc-repressible lethality using an embryo-specific promoter Tc ( ⁇ g/ml) Males Females bnk-tTa ⁇ tRe-Nipp 1Dm 0 0 0 0.1 60 58 1.0 78 82
  • This example details the construction of a vector suitable for transformation to produce an organism containing the lethal genetic system of the invention.
  • this modular vector is to allow the rapid creation of a transformation construct suitable for a given species.
  • the intention is to create a dominant repressible lethal. This is achieved by inserting a suitable promoter into this constrict, then using it to transform the target species.
  • the promoter is typically derived from the target species itself, which is probably the most direct and safest way to ensure that the promoter has the desired specificity (e.g. female-specific) in the target species. This is not, however, necessary and indeed in the example below we have used a modified actin gene promoter from the silk moth Bombyx morn, with the intention of using it in pink bollworm, a pest of cotton.
  • PiggyBac as been used successfully to transform a wide range of insects, including Diptera, Coleoptera and Lepidoptera, but it is not necessarily optimal, nor will Act5C-EGFP be the optimum transformation marker in every case.
  • the plasmid has been constructed such that the core elements of the system (tTa, tRe-Nipp1 and insulators) are flanked by unique sites for rare-cutting restriction enzymes (NozI and the SbfI-PmeI-AscI multiple cloning site) to facilitate subcloning these elements into a new transformation vector.
  • alternative insulators could be used or an additional insulator inserted 5′ of the new promoter, to protect against position effects from flanking chromatin.
  • This plasmid (pUHD5Asc) was digested with HpaI and Ba and another oligo pair inserted: tTa 3′linker+ 5′-gcggccgc ac gggccc a ctcgag cac aagctt c ggtacc ac gaattc-3′ tTa 3′linker ⁇ 5′-agct gaattc gt ggtacc g aagctt gtg ctcgag a gggcccgt gcggcgc-3′ to create pUHD15Asc3′linker#42.
  • tRe-Nipp1Dm comprises: tRe vector W.T.P-2 from Bruno Bello (Bello et al., (1998), Development 125, 2193-2202) modified by insertion of oligo pair Kozak Spe+/ ⁇ ” between.
  • piggyBac and plasmid vector are derived from p3E1.2-white (Handler et al., (1998), Proc Natl Acad Sci U S A 95, 7520-5) from A1 Handler.
  • the medfly white gene originally inserted as a NotI fragment into the HpaI site of piggybac, using linkers, was removed by digestion with NotI and recircularising.
  • a set of extraneous restriction sites vector sequences (outside piggyBac) was removed by digesting with EcoRI and SalI, end-filling and recircularising, giving p3E1 ⁇ RI-Sal.
  • This plasmid was then digested with BgUI and NotI and an oligo pair inserted to add useful restriction sites: piggy linker 2+/ ⁇ : 5′-ggcc ctcgag aga aggcct gcggccgc tgt ggcgcgcc aga gtttaaac agt cctgcagg-3′ 3′-gagctc tct tccgga cgccggcg aca ccgcgcgg tct caaatttg tca ggacgtccctag-5′ the resulting plasmid is pPB-linker2#93.
  • the Act5C-EGFP transformation marker was added by subcloning as a 4.2 kb XhoI-EcoRV fragment from Act5C-EGFP in pP ⁇ CaspeR ⁇ (Jean-Marc Reichhart) into XhoI-StuI cut pPB-linker2 to give pPB-ActSCEGFP#181.
  • the apoB insulator was added by changing the SpeI site of apoB3′MAR (Namciu et al., (1998), Mol Cell Biol 18, 2382.91) from Stephanie Namciu to ApaI using the oligo SpeI-ApaI:
  • a BmA 3 promoter fragment of approximately 190bp was amplified by PCR from pJP88 (John Peloquin) (Peloquin et al., (2000), Insect Mol Biol 9, 323-33) using Platinum Pfx polymerase (Life Technologies) and the oligos: BmA3 5′: 5′-aaavAATTCTGATAGCGTGCGCGTTAC-3′ BmA3 3′Asc-2: 5′- ggtaggcgcgcc TGGCGACCGGTGGATCCGAATG-3′
  • the minimal promoter used in combination with the tetO repeats would be a suitable plant minimal promoter.
  • this would preferably be a minimal promoter not subject to gene silencing.
  • the promoter driving tTa expression would suitably be a plant promoter, e.g. the A9 promoter for tapetum-specific expression in a system designed to eliminate pollen production in the absence of the repressor.
  • nt 1-543 derived from W.T.P.-2 (Bello et al., (1988), Development 125:2193,), of which 1-309 contains 7 repeats of the tet operator sequence (tetO), followed by 98 nt of P element transposase core promoter, from Camegie 4,-52/+51 relative to transcription start, linked by a SmaI-PstI linker (synthetic oligonucleotide, GGGCTGCAG) to the leader sequence of bsp70 from CaSpcR-hs (Thummel and Pirrotta, (1991), Dros. Inf. News. 2,) up to the EcoRI site of its polylinker.
  • SmaI-PstI linker synthetic oligonucleotide, GGGCTGCAG
  • the next section is derived from a synthetic oligonucleotide and provides a consensus Elation start and some restriction sites, followed by the coding region of Drosophila Nipp1 and 3′ UTR to polyA sequence from an unpublished cDNA in pNB40 (Brown and Kafatos, (1988), J. Mol. Biol 203:425,) up to the NotI site, which has been end-filled and cloned into an StuI site.
  • the StuI site and subsequent sequence is from W.T.P-2 and is derived from CaSpeR-hs, it is principally trailer (3′ UTR) sequence from hsp70flanked by some restriction sites.
  • Females are assumed to select mates proportionately to their abundance and fitness such that a female will choose a mate of type i with probability p i , such that:
  • n i is the number of male insects of type i and r i is the fitness of type i relative to wild type males taken to have a fitness of 1.
  • the type of insect may depend on its genotype as well as its generation—in particular, we will consider scenarios in which released flies have reduced fitness but their male progeny, regardless of genotype, have the same fitness as wild type males.
  • o i is the number of offspring surviving to the point at which density dependence acts (Maynard Smith and Slatkin 1973 Ecology 54, 384-391), and a and b are parameters. Rogers and Randolph (1984 Insect Sci. Applic. 5, 419-23) consider such a density dependent acts with an SIT program and show that the effectiveness of the SIT proms is largely determined by the natural resilience of the target insect population, characterized by the parameter b (Rogers and Randolph, 1984 Insect Sci. Applic. 5, 419-23).
  • the initial population consists equally of wild type males and wild type females. All numbers are counted relative to the initial female population, so this is 1.0 by definition and the initial wild type male population is here also 1.0. Since we are only considering populations which normally have equal numbers of males and females, the initial population of males is always 1.0 in these examples.
  • the lethal phase is not important.
  • the lethal phase must end before the developmental stage at which the insects are released, or they may lose fitness or die once the repressor has been withdrawn, e.g. following release.
  • Embryonic lethality ensures that no larvae emerge to damage crops or animals. This may not be important in the case of disease vectors such as mosquitoes, where only the adult stages transmit the disease, but is clearly critical in the case of many crop pests where it is the voracious larvae that cause the economic damage.
  • Embryo specific lethality allows the last and biggest mass-reared generation to be reared on food lacking the repressor, reducing costs and any environmental hazards associated with large quantities of Tc.
  • Embryo specific lethality (or other early lethality) can also.be combined with later sex-specific lethality, e.g. female-specific lethality.
  • sex-specific lethality e.g. female-specific lethality.
  • the genetics of such a system appear similar to that of a single-sex release of radiation-sterilised males, in that only males are reached and they have no viable progeny when mating with wild males in the natural environment.
  • the MPLS males have not been irradiated, and so do not suffer the loss of fitness and longevity consequent upon irradiation.
  • the requirement is only that that the two (or more) lethal phases do not overlap, not that one of them is specific to embryos, we could arrange that the first lethal phase is after a density-dependent mortality phase in the wild population.
  • mosquitoes in order to prevent transmission of most mosquito-borne diseases (e.g. malaria, dengue fever, yellow fever) it is only necessary to prevent the females taking heir second blood meal. Killing females as pupae, emerging adults or just following their first blood meal is would therefore be suitable.
  • the earlier non-sex-specific lethal phase only has to be earlier than this, and could therefore be as late as early adulthood, for example.
  • a first lethal phase of late larval/pupal development would be possible. Promoters suitable for all these stages are well-known—blood-meal inducible genes for killing post-blood meal. etc.
  • Using a lethal phase that first acts later than a density-dependent mortality phase in the wild population means that individuals that will later die due to the lethal effect of the RIDL system nonetheless compete for resources with their wild type conspecifics and so tend to increase the mortality of these wild type conspecifics.
  • the meiotic drive system acts to enhance the effectiveness of the RIDL system (FIG. 2).
  • Meiotic drive systems of varying effectiveness are known in a wide range of species, including Drosophila and mosquitoes.
  • each of the two homologues of a given chromosome is equally likely to be inherited, i.e. each has a 50% chance of being inherited by each individual offspring.
  • the consequence of a meiotic drive/segregation distortion system is that one chromosome is preferentially inherited.
  • meiotic drive/segregation distortion systems vary in effectiveness, we considered inheritance frequencies of 50% (i.e. no meiotic drive/segregation distortion), 60%, 70%, 80%, 90% and 100%. Higher inheritance frequencies always make the RIDL system more effective.
  • FIGS. 4 and 5 demonstrate the effects of reduced fitness on SIT and RIDL systems (with meiotic drive and multiple chromosome systems). Obviously, reduced fitness in released males decreases the effectiveness of these control systems.
  • RIDL males have twice the competitive mating fitness of SIT males. This is a very conservative estimate. Radiation reduces the competitive mating ability of the irradiated insects (by an estimated two-fold in the case of medfly) and also reduces their longevity (by an estimated 2-5 fold in the case of medfly).
  • Scenario (a) models an adult lethal phase and density-dependent mortality acting at the level of adults.
  • An adult lethal phase for RIDL might be appropriate for malaria vectors, where the females need only be killed within a week or so after their first blood meal to prevent transmission of the disease.
  • this scenario also models an earlier release and density-dependent stage, which is available for RIDL, where the release population can be released at any life cycle stage, but not for SIT where sex-separation (if used) and irradiation have to be performed prior to release, restricting the range of life cycle stages that can be released.
  • Scenario (b) is a very important and novel case. This represents a density-dependent mortality that acts before RIDL-induced mortality. In the case of mosquitoes, competition between larvae for resources is a likely stage for density-dependent effects. RIDL-induced mortality can safely be later than this, as only the adult females transmit disease. Such mortality could be achieved by using a later-acting promoter, such as that from the vitellogenin gene (for female-specific mortality) in the vector of Example 7. Tis strategy is also possible using a multi-phase 1lethal system (MPLS) in which the non-sex-specific lethal stage is later than the density dependent mortality. No equivalent strategy is available for SIT.
  • MPLS multi-phase 1lethal system
  • Scenario (c) represents release at a late life cycle stage, e.g. adults, and early RIDL-induced lethality, e.g. as embryos. Density-dependent mortality lies between these. This might represent some crop eating agricultural pests, where the larval stages do the damage and so it would be inappropriate to release these stages or to arrange for the RIDLinduced mortality to be so late that the larvae have already done some damage before they die. Unlike scenarios (a) and (b), RIDL has no especial life-cycle-derived advantage over SIT under this scenario.
  • FIGS. 6 and 7 illustrate the benefits of delaying RIDL-induced mortality until after density dependent mortality, as well as the potential further benefit of releasing insects (both males and females) prior to the density-dependent mortality. These graphs further illustrate the benefits to be gained from increased meiotic drive systems and multiple chromosome DFL systems.
  • FIGS. 6 b , 6 c , 7 b and 7 c reveal that SIT can actually lead to a higher stable population than would have been the case in the absence of the control programme. This effect has previously been noted by Rogers and Randolph (Rogers and Randolph, 1984 Insect Sci. Applic. 5, 419-23).
  • FIG. 2 Meiotic drive system. 50%, 60%, 70%, 80%, 900/o and 100% for a single locus system with no decreased fitness. The bold black line is the SIT system in each case. The RIDL system is plotted with grey lines.
  • b R 0 is 2.25 and input is 1 (relative to the initial population).
  • the population is not controlled by SIT or RIDL with 50% or 60% meiotic drive.
  • FIG. 3 Multiple unlinked loci used in RIDL system The bold black line is the SIT system in each case. The RIDL system is plotted with grey lines.
  • b R 0 is 2.25 and input is 1 (relative to the initial population).
  • the population is not controlled by SIT or RIDL with 1 or 2 loci.
  • FIG. 4 Meiotic drive system 50%, 60%, 70%, 80%, 90% and 100% for a single locus system with decreased fitness.
  • the bold black line is the SI system in each case.
  • the RIDL system is plotted with gray lines.
  • a R 0 is 1.5 and input is 0.5 (relative to the initial population).
  • the fitness of SIT and released RIDL insects is 80% of that of wild type insects. Subsequent generations are assumed to have equal fitness to wild type insects regardless of their parentage.
  • b R 0 is 1.5 and input is 1.75 (relative to the initial population).
  • the fitness of SIT is 25% of that of wild type insects, whereas released RIDL insects have 50% of the fitness of wild type insects.
  • Subsequent generations are assumed to have equal fitness to wild type insects regardless of their parentage.
  • FIG. 5 Multiple unlinked loci used in RIDL system with decreased fitness.
  • the bold black line is the SIT system in each case.
  • the RIDL system is plotted with grey lines.
  • a R 0 is 1.5 and input is 0.5 (relative to the initial population).
  • the fitness of SIT and released RIDL insects is 80% of that of wild type insects. Subsequent generations are assumed to have equalitness to wild type insects regardless of their parentage
  • the populations arc quickly brought under control with multiple loci, despite the reduced fitness.
  • b R 0 is 1.5 and input is 1.75 (relative to the initial population).
  • the fitness of SIT is 25% of that of wild type insects, whereas released RIDL insects have 50% of the fitness of wild type insects.
  • Subsequent generations are assumed to have equal fitness to wild type insects regardless of their parentage.
  • a Density dependent mortality acts before RIDL-induced mortality and acts on newly released RIDL insects.
  • SIT mains the population at a constant level of 0.8 relative to the initial population, whereas the RIDL systems quickly reduce the populations. If the population were not subject to control, we would expect the population to remain stable at the initial size.
  • b Density dependent mortality acts before Ridl induced mortality but does not act on newly released RIDL insects.
  • the population is eliminated by SIT or RIDL with 50% or 60% meiotic drive. They stabilize the population at the levels 1.2, 0.4 and 0.3, relative to the initial population, respectively.
  • the populations are quickly brought under control with greater meiotic drive levels. If the population were not subject to control, we would expect the population to remain stable at the initial size.
  • c Density dependent mortality acts after RIDL-induced mortality but does not act on newly released RIDL insects.
  • the population is eliminated by SIT or RIDL with 50%, 60% or 70% meiotic drive. They stabilize the population at the levels 1.2, 0.75, 0.7 and 0.6, relative to the initial population, respectively.
  • the populations are quickly brought under control with greater meiotic drive levels, despite the reduced fitness. If the population were not subject to control, we would expect the population to remain stable at the initial size.
  • FIG. 7 Multiple unlinked loci used in RIDL system with no decreased fitness—in a density-dependent system.
  • the bold black line is the SIT system in each case.
  • a Density dependent mortality acts before RIDL-induced mortality and acts on newly released RIDL insects.
  • SIT maintains the population at a constant level of 0.8 relative to the initial population, whereas the RIDL systems reduce the populations. If the population were not subject to control, we would expect the population to remain stable at the initial size.
  • b Density dependent mortality acts before RIDL-induced mortality but does not act on newly released RIDL insects.
  • the population is maintained at a constant level by SIT or RIDL with 1 locus. They stabilize the population at the levels 1.2 and 0.4, relative to the initial population, respectively.
  • the populations are eliminated with 2 or 3 locus systems. If the population were not subject to control, we would expect the population to remain stable at the initial size.
  • c Density dependent mortality acts after RIDL-induced mortality but does not act on newly released RIDL insects.
  • the population is maintained at a constant level by SIT or RIDL with 1, 2 or 3 loci. They stabilize the population at the levels 1.2, 0.75, 0.63 and 0.5, relative to the initial population, respectively. If the population were not subject to control, we would expect the population to remain stable at the initial size.

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