WO2018149734A1

WO2018149734A1 - A method for killing insects inside a container, such container and use thereof

Info

Publication number: WO2018149734A1
Application number: PCT/EP2018/053194
Authority: WO
Inventors: Mikkel Vestergaard Frandsen; David Kim; Tie Lan; Georgina Victoria Bingham; Lee William Cohnstaedt
Original assignee: Vestergaard Sa
Priority date: 2017-02-14
Filing date: 2018-02-08
Publication date: 2018-08-23

Abstract

A repellent source (4) is provided in the inner volume (3) of a container (1) remote from the container walls (2). Repellent (7) is released from the repellent source (4) and the insects in the inner volume (3) are repelled by the repellent (7) in a direction away from the repellent source (4). As the resulting repellent concentration is largest at the repellent source (4) and lowest at the walls (2), the insects will move to the container wall (2), where the insects are then killed by contact with insecticide (8).

Description

A method for killing insects inside a container, such container and use thereof

FIELD OF THE INVENTION

The present invention relates to a method for killing insects inside a container, for example crop storage containers, especially sacks. It also relates to such container and the use thereof.

BACKGROUND OF THE INVENTION

Crop infestation by insects and fungi is a widespread problem, especially during storage of the crop in sacks. Therefore, pesticides are sometimes used during storage, for example by directly treating grains in sacks. However, consumption of pesticides may imply a health hazard for the consumer.

Accordingly, it has become customary to treat the material of the storage sacks, thereby targeting the insects trying to enter through the sack material. For example, US patent US3859121 by Yeaden discloses impregnated textile bags for the storage and transport of food and feed, like grains, and US4966796 by Sumitomo discloses a kraft paper grain storage bag with pyrethroid for protection of grains. European patent application EP382382 by Imperial Chemical discloses impregnated woven or non- woven fabric, for example as sacks for foodstuff. Multilayer material is discussed in British patent application GB 1568936 by Heselev, disclosing packaging material for food, for example brown rice, where insecticide is incorporated in a polymer film, for example part of a laminate.

However, if the inner side of the sacks is also containing insecticide, this may diffuse into the stored crop. As pointed out in US patent US4743448, multilayer containers are better suited if the material is for human consumption, as the innermost layer can be made free from the active substance. A different approach is disclosed in international patent application WO2016/062496 by Shah and Dove and assigned to A to Z Textile Mills Ltd, where the bag is made of multiple layers. The multiple layers comprise an airtight layer, an insect barrier layer comprising an insecticide or insect repellent, and a chemical barrier layer for limiting permeation of the insecticide or insect repellent through the chemical barrier layer. The airtight layer has the effect of killing the insects by suffocation, which has the further significant effect of helping to delay the onset of resistance to the insecticide or insect repellent. As a further advantage, the low oxygen levels within the airtight bag can also prevent or slow down the growth of mold. The chemical barrier layer is ar- ranged between the inside of the storage bag and any insect barrier layers in order to protect the content from the insecticide or repellent. When an insect attempts to penetrate the storage bag, it penetrates the chemical barrier layer and comes into contact with the insecticide or insect repellent. However, as also discussed in WO2016/062496, holes in the bag material would prevent the bag from proper func- tioning.

Puncturing of sacks is very common, especially when insufficient care is taken during transport and handling. In some countries, it is even customary to use a hook for handling crop storage sacks where the hook is penetrating the sack material and creates holes of a size that promotes infestation by pests. When such hooks are used, the bag in WO2016/062496 does not function according to the purpose.

Peppers and chili have been proposed in Chinese patent application CN105775411A as insect repellent. The chili is filled into cylindrical cartridges in a rice box in order to prevent insects to enter the rice box by the odor of the chili. However, this technical solution does not give any advice with respect to insects already inside the container.

Also rodents are a severe problem for crop storage, as these rodents damage the sacks for storage when biting through the material. For this reason, a variety of substances have been proposed for protection of crops, including castor oil, capsaicin, and dena- tonium saccharide.

Due to large losses of foodstuff, there is a general interest in improved crop storage and various attempts have been tried. However, there is still a need for improvements. Therefore, it would be desirable to find technical solutions for improving crop storage, especially storage of grains.

DESCRIPTION / SUMMARY OF THE INVENTION

It is therefore an objective of the invention to provide an improvement in the art. In particular, it is an objective to provide an improved storage container for foodstuff, especially grains. This objective is achieved with a container, as well as by a method for killing insects in such container as set forth in the following. The container and method are especially useful for crop storage, for example storage of grains. A typical form of the container is a flexible bag, for example in the form of a flexible sack or a flexible large scale transport bag.

The general principle of the invention is to provide an insect repellent source in the inner volume of the container, typically remote from the container walls, for example near or at the center of the inner volume. The insect repellent causes the insects to move away from the insect repellent source and to the container wall, where the insects are exposed to insecticide. For example, the insect repellent source comprises a chemical insect repellent that is released from the insect repellent source, so that the insects in the inner volume are repelled in a direction away from the insect repellent source. The resulting repellent concentration is largest at the insect repellent source and lowest at the container walls at the largest distance from the insect repellent source, creating a repellent concentra- tion gradient which the insects will follow in their attempt to escape the repellent. At the container wall, the insects are then killed by contact with insecticide, for example by contact with insecticide on inner side of the container wall. Various embodiments of the principle are provided as explained in detail in the following. The terms "insects" is used herein for simplicity in a broad sense, covering various arthropods in connection with infection of foodstuff, especially crops, such as grain. Accordingly, the term "insect" should be understood as not limited to the Insecta class but also other arthropod classes, especially Arachnida, of which particular interest has the sub-class Acari, which contains mites. In relation to foodstuff protection, also lice are included in the term "insect". The term "insecticide" should thus also be understood in a general sense for not only killing insects but also including arcaricides.

The term "repellent" is to be understood as repelling insects, including acari and lice, but not killing them. Thus, the insects are able to stay alive and move away when exposed to the insect repellent.

The terms "inner layer" and "outer layer" are used for layers where the inner layer is closer to the inner volume of the container than the outer layer.

Although, the insect repellent source can, in principle, be provided fixed inside the container from the onset, it is, typically, positioned during filling of the container. For example, a first portion of foodstuff is filled into the inner volume of the container, for example a crop storage bag. Then, the insect repellent source is placed inside the inner volume, typically remote from the container wall, for example centrally, in the first portion of the foodstuff. Then, a second portion of foodstuff is added to the container, and the container finally closed. Often, the first portion and the second portion are about equal in volume. For example, the insect repellent source comprises a thermoplastic polymer having melt-incorporated repellent therein. The material and the repellent are selected such that the repellent is capable of migrating from inside a bulk of the polymer to the surface of the polymer from which the repellent is released. Alternatively, the insect repellent source comprises a substrate with a coating that contains the repellent. The repellent would then migrate from inside the coating to the surface of the coating and be released therefrom. As a further alternative, the insect repellent source comprises a substrate that is impregnated by the repellent, and the repellent would then migrate to the surface of the substrate and be released therefrom. Whereas, a coating is provided on the surface of the substrate, an impregnation enters the material of the substrate to a certain depth. Some types of coating on a substrate also cause impregnation of the substrate.

Impregnation is especially applicable for porous substrates. Examples of porous substrates are sponge-like polymers with open pores such that the repellent can enter the pores during the impregnation phase and later escape from the pores when used according to the purpose. Such sponge like polymers can be impregnated or coated with repellent after production. Alternatively, the porous polymers have melt incorporated therein the repellent, which is then released from bulk material to the surface inside the pores and then from the surface inside the pores out of the pores, where the latter step is potentially by evaporation or sublimation. As compared to a sheet-like insect repellent source, a similarly large surface area can be obtained by a porous substrate despite more compact overall dimensions.

For example, the insect repellent source comprises a tank, where the repellent is contained inside an inner volume of the tank, enclosed by a tank wall. For example, the repellent is present in a liquid or gel inside the inner volume, and the repellent migrates gradually from the liquid or gel, or together with the liquid or gel, through the tank wall to the surface of the tank, which is facing the inner volume of the container. The wall of the tank can be made rigid, for example made of a thermoplastic polymer, which is open for migration of the repellent through the wall of the tank to the surface of the tank. Alternatively, the insect repellent source is a flexible tank, for example made of a polymer foil material or fabric which is open for migration of the repellent from the liquid or gel through the polymer foil to the surface of the foil. Alternatively, the liquid or gel from the inner volume seeps gradually through the rigid or flexible tank wall, for example porous tank wall, of the tank to the outer surface of the tank.

In some embodiments, as an alternative or in addition to the chemical insect repellent, the insect repellent source comprises an electrical ultrasonic wave emitter configured for repellent action on insects by the emitted ultrasonic waves. Potentially, the emitted ultrasonic radiation also repels rodents, which gives an additional advantage. If the ultrasonic wave emitter is placed near or at the center of the inner volume, the insects are repelled radially away from the ultrasonic wave emitter and towards the container wall. If the ultrasonic wave emitter is placed inside the inner volume at a part of the container wall, without surrounding the inner volume, the insects are repelled from that part of the container wall towards an opposite part of the container wall on the other side relatively to a centre of the inner volume. In further embodiments, a non-living oxygen absorber is provided in the inner volume, remote from the container wall. The oxygen absorber can be iron (Fe) based or non- iron based. The oxygen absorber can also be multi- function, e.g. absorbing oxygen and releasing C02. The oxygen absorber absorbs oxygen from the vicinity of the ox- ygen absorber and creates an oxygen concentration gradient in the inner volume with the oxygen concentration increasing from the oxygen absorber towards the container wall. The oxygen concentration gradient assists in causing the insects to move to the container wall where they are killed by the insecticide. Optionally, the oxygen absorber is combined with the insect repellent source, for example into a single object or side-by- side, potentially abutting each other, or even provided in or on the same bulk object or sheet-like object. In some embodiment, the repellent is incorporated in a thermoplastic polymer and released therefrom, as explained above, and the oxygen absorber is provided on the surface of the polymer.

Optionally, the insecticidal inner layer is in contact with the foodstuff inside the container. An insect contacting the inner side of the inner layer would be exposed to the insecticide and be killed. Alternatively, the inner layer is separated from the foodstuff by a chemical barrier layer between the inner layer and the inner volume with the foodstuff. In the latter case, the insects have to penetrate the chemical barrier layer in order to contact the insecticidal inner layer. In some instances, due to the repellent gradient, the insects are driven not only to the container wall but they will also try to escape the inner volume by working their way through the container wall; during this attempt, the insects will penetrate the chemical barrier and get into contact with the insecticidal layer and get killed. The insecticidal inner layer is not necessarily penetrated, and stays intact.

In some practical embodiments, the container wall comprises also an outer layer enclosing the insecticidal inner layer, such that damage by the insect to the insecticidal inner layer does not necessarily lead to penetration of the container wall, as the outer layer would still stay intact. Such outer layer is potentially used for adding substantial stability to the container. For example, the outer layer, or several outer layers, is or are laminated to the inner layer or layers. In some embodiments, the outer layer or one of the outer layers comprises a rodent repellent in order to repel rodents from penetrating the container.

Optionally, the container wall is made from or comprises a textile, for example a wo- ven, knitted or non- woven fabric.

Optionally, also a fungicide source is provided in the container for preventing mold in the container, especially on foodstuff. For example, the fungicide is provided on an innermost layer of the container wall in order to release fungicide to the foodstuff, for example grains. Alternatively, or in addition, fungicide is provided as a separate fungicide source inside the inner volume, optionally combined with the insect repellent source. As a further alternative, repellent and fungicide are released from the same object. For example, if the insect repellent source is provided as a thermoplastic polymer with melt-incorporated repellent that is migrating to the surface, the fungicide can be incorporated as well by adding it to the molten polymer prior to extrusion or molding. In the event that the fungicide evaporates slowly, the entire inner volume of the sack can be filled with the fungicide in gas form, which is an efficient way of preventing or reducing the growth of fungi, even at a dosage of the fungicide which is so low that it is not harmful to humans.

Examples of useful materials for the container wall are thermoplastic polymers. The insecticide can be coated to the thermoplastic polymer or melt-incorporated into the polymer for long lasting efficiency. Melt incorporation is done by heating the polymer to a temperature where it melts into a liquid form, after which the active agent or agents, such as the insecticide are blended into the polymer such that the final polymer material is a blend of the polymer and the active agent. The molten mass is then extruded into a film or into monofilaments or multifilaments, which are then used for producing a fabric. The fabric can further be combined with other fabrics or films into a multilayer, for example by lamination.

The term fibre is herein used as a general term for mono-filaments and multifilaments as well as yarns in which various monofilaments and/or multifilaments are combined. Various filaments can comprise identical active agents or different active agents. The combination can be constructed such that various insecticides are released together with largely identical time-dependent release profiles and with predetermined release amounts. This is described in greater detail in the international patent application WO2010/046348 by Skovmand and in WO2009/003468 by Vestergaard Frandsen. This principle is typically chosen for combinations of insecticides with synergists and/or fugicides. Alternatively the various active agents are released with different time profiles, such that one active agent acts primarily in a first period and another active agent primarily at a later stage. For example, two fungicides or two insecticides having different time profiles can be used to exhibit different actions, such as a first evaporation phase of fast evaporation fungicide to achieve an initial killing or reduc- tion of fungi inside the stored foodstuff and then a long term slow release fungicide to prevent growth of fungi.

Also, insecticide incorporation, and optionally fungicide incorporation, and coating or impregnation can be combined in various ways. For example, the thermoplastic ex- truded fibres can have melt-incorporated therein an insecticide and be coated with a different active agents, for example a fungicide. A fungicide on the surface would act against fungi, especially, if the inner layer is an innermost layer. In some embodiments, the fungicide coating is configured for transfer of the fungicide to the crop, in particular grains, in the inner volume upon contact with the inner layer.

If an outer layer is provided outer layer, for example used as an outermost layer, it is optionally made and used for giving high stability against rupture and puncture and against animals and insects from the outside. For example, the outermost layer comprises a reinforcing material, such a textile. A net structure laminate is a useful rein- forcing material.

Optionally, the outer layer is provided with other active agents, especially rodent repellent in order to deter rodents, such as rats and mice. In some embodiments, the container wall is hermetic. This can be achieved by using polymer film with or without fabrics as part of the container wall.

In other embodiments, the container wall is non-hermetic. Optionally, the container wall is made porous, for example by using fabrics, woven, knitted or non-woven. A controlled transport of gas but not liquid through the container wall is achievable by corresponding hydrophobic impregnation.

In some embodiments, the container wall comprises a fabric layer and a film layer in combination, for example a laminate. Optionally, the film layer is water vapour permeable in order to release moisture from the inner volume.

Examples of thermoplastic polymers for the insect repellent source and/or the container wall are thermoplastic elastomers/rubber (TPE/TPR) and homopolymers and copolymers as well as blends and alloys types. Examples of thermoplastic polymers are polyethylene terephthalate (PET, polyester), ethylene vinyl acetate (EVA), ethylene butyl acrylate (EBA), poly vinyl chloride (PVC), polystyrene (PS) or polyolefms, for example polypropylene (PP) and polyethylene (PE), optionally low density polyethylene (LDPE).

Examples of repellents for the insect repellent source are oil of wintergreen, garlic, lime, citronella, black pepper, chili pepper, capsaicin & its derivatives, geraniol, catnip (napeta lactone), sandalwood, eugenol, lippia multifloria (verbena), neem, cajeput (Melaleuca Leucadendron), lemongrass (Cymbopogon Flexuosus), cedar (Cedrus De- odora), peppermint (Mentha Piperita), java citronella (Cymbopogon Winterianus), clove (Syzygium Aromaticum), geranium (Pelargonium Graveolens), rosemary (Rosmarinus Officinalis), and sesame (Sesamum Indicum).

Examples of rodent repellents are capsaicin and denatonium saccharide. Concentrations in the range of lppm and 10% are dependent on the insecticide and the desired release speed. Also possible, for example in addition to the rodent repellent, is incorporation in the container wall of powdered corn cob, optionally blended with cellulose, in order to harm rodents and prevent them from further damage to the storage container or containers.

Examples of insecticides include pyrethrin and synthetic pyrethroids, for example deltamethrin and permethrin, quinazolines, fiproles, pyroles, pyrazoles, neonico- tinoids, carbamates. Concentrations in the range of lppm and 10% are dependent on the insecticide and the desired release speed. To the insecticides can be added synergists, for example piperonyl butoxide (PBO).

An example for support particles for the repellent, insecticide and/or fungicide is nanoclay. Examples of nano-clays are attapulgite and montmorillonite. As an alternative to clay, micro-particles or nano-particles are used, for example ground natural minerals or synthetic material, including silica, alumina and silicates. Examples of support particles for active agents include also kaolin, talc, chalk, quartz, carbon black, diatomaceous earth, calcite, marble, pumice, sepiolite and dolomite. Polymer based sponge-like particles can also function as the support for repellent. The polymer can be thermoplastic or thermoset.

Examples of the container wall thickness are in the range of 0.05 mm to 1 mm. For more rigid containers, the wall thickness is optionally larger than 1 mm, for example up to 5 mm.

Examples of sizes for the insect repellent source are in the range of 1 ccm to 1000 ccm. Examples of the size of the container are in the range of 1 liter to 1000 liters.

Example of foodstuff includes cocoa, coffee, rice, beans, and grains, including maize, wheat, and barley. Additives may be incorporated into the thermoplastic polymer of the container walls, for example UV protectors, colorants, optical brighteners, fillers, reinforcement fibres, flame retardants, anti-soiling agents, further biocides, and/or fragrance.

The examples are for illustrative purpose and not limiting the invention unless defied in the patent claims.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to the drawing, where FIG. 1 illustrates a container with an insect repellent source;

FIG. 2 illustrates the container wall with a) an inner layer with insecticide, b) a middle layer of insecticide covered towards the inner volume by a barrier layer, and c) an inner layer with dispensed insecticide in the vicinity of the inner layer;

FIG. 3 illustrates examples of insect repellent sources, exemplified as a) a bulk structure, and b) a sheet structure

FIG. 4 illustrates a container with an ultrasonic wave emitter.

DETAILED DESCRIPTION / PREFERRED EMBODIMENT

FIG. 1 illustrates a closed container 1 according to the invention. The lower cylindrical features in the figure illustrates the container 1 in perspective view, and the upper circular features in the figure is a cross sectional view. The cylindrical shape is only for purpose of illustration and other forms are possible.

The exemplified container 1 comprises a container wall 2 and an inner volume 3 and is closed after filling foodstuff, for example grains, into the inner volume 3. The container wall 2 is made of a side wall 2A, a closed bottom wall 2B, and a closed top 2C, which is also closed. In the inner volume 3, there is provided an insect repellent source 4 which releases chemical insect repellent 7, for example by evaporation into the inner volume 3. By continuous but slow evaporation, a repellent gradient would exist in the inner volume such that the concentration is highest at the insect repellent source 4. In order to escape the insect repellent 7, the insects would follow the gradient of insect repellent 7 in a direction 5 towards lower concentration at the container wall 2.

This insect repellent source 4 is in the form of a rigid or flexible body, for example solid or porous, from which insect repellent is released gradually, for example by evaporation or diffusion.

The container wall 2 contains insecticide that kills the insects when in contact with the container wall or when trying to escape through the container wall or potentially when the insects are sufficiently close to the container wall to pick up insecticide that has diffused from the container wall into the inner volume in vicinity of the container wall.

For example, the container wall 2 is a single layer sheet in which the insecticide is contained, optionally melt-incorporated, such that the insecticide is gradually released by migration of the insecticide to the inner surface of the container wall. Alternatively, the inner side of the container wall is coated or impregnated with insecticide.

Optionally, also a fungicide is released from the container wall 2 to the inner volume 3 in order to prevent mold in the foodstuff. Such fungicide can also be melt- incorporated for gradual release by migration. Alternatively, the inner side of the container wall is coated or impregnated with releasable fungicide.

The single layer container wall 2, optionally, also contains a rodenticide for prevent- ing rodents to work their way through the container wall 2. For example, the outer side of the container wall 3 is coated or impregnated with rodenticide.

The container is typical a flexible bag with a container wall 2 that is a polymer foil or textile or a combination thereof. Examples include a laminate foil or a multilayer foil with numerous single foils combined into such multilayer foil, optionally with a textile included.

Various more complex build-up principles of a container wall are illustrated in FIG. 2a, 2b, and 2c.

Optionally, a non-living oxygen absorber 9 is provided in the inner volume 3, remote from the container wall 2. The oxygen absorber 9 absorbs oxygen from the vicinity of the oxygen absorber 9 and creates an oxygen concentration gradient in the inner volume with the oxygen concentration increasing from the oxygen absorber towards the container wall 2. The oxygen concentration gradient assists in causing the insects to move to the container wall 2 where they are killed by the insecticide.

FIG. 2a illustrates a first embodiment of a container wall 2 in which a multilayer structure 6 is provided having an inner insecticidal layer 6 A, facing the inner volume 3 and one or more further optional outer layers 6B directed away from the inner layer 6A. When insects are repelled by the insect repellent source 4 and move in the inner volume 3 towards the container wall 2, they will pick up insecticide from the surface 6A' of the insecticidal inner layer 6A.

FIG. 2b illustrates an alternative embodiment of a container wall 2 in which a multilayer structure 6 is provided having an insecticidal layer 6A sandwiched between one or more optional outer layers 6B directed away from the inner layer 3 and a chemical barrier layer 6C towards the inner volume 3. In this embodiment, the chemical barrier layer 6C prevents the insecticide to contact the food stuff in the inner volume 3. The insect must penetrate the barrier layer 6C in order to arrive at the insecticidal inner layer 6 A. When in contact with the insecticide, the insect dies. The insecticidal inner layer 6A is not penetrated by the insect if the killing effect is efficiently fast or otherwise prevents the insect from penetrating the insecticidal inner layer 6A. Further op- tional outer layers 6B further protects the container wall 2 from being penetrated and prevent holes. For example, the container wall 2 is provided airtight. Airtight container wall structure are discussed international patent application WO2016/062496 by Shah and Dove and assigned to A to Z Textile Mills Ltd, the examples optionally being used for the embodiment in FIG. 2b.

FIG. 2c illustrates a third embodiment, where the insecticide 8 from the insecticidal inner layer 6 A has migrated out of the insecticidal inner layer 6 A and into the inner volume. For example, the insecticide 8 is provided in a thin layer of foodstuff near the insecticidal inner layer 6A such that insects are paralyzed or killed when coming near to the insecticidal layer 6a but before they have contact with the inner surface of the insecticidal inner layer 6A. Optionally, the insecticide 8 is present as an evaporated cloud close to the insecticidal layer, such that transfer to the foodstuff is minimal, despite being outside the insecticidal inner layer 6A. Alternatively, the insecticide 8 is actually transferred to the food stuff; the latter is an option is the insecticide is not harmful to the humans or animals that consume the foodstuff.

The multilayer container wall 2 is, optionally, provided as a combination of multiple foils. Alternatively, at least some of the layers are laminated into a single layer, for example foil. In order to increase the strength of the container wall, at least one of the layers is a textile layer, optionally a net, for example woven or knitted or even produced as a non-woven fibrous sheet. The textile layer can also have the insecticide incorporated or comprise it as a coating. The various forms of the layers, foil, woven, knitted, non-woven can also be combined, for example by overlay or as a laminate.

As an example, the optional outer layers 6B contain rodenticides or rodent repellents such that damage to the container wall 2 by rodents from outside is prevented. The optional outer layers 6B may potentially also comprise further insecticide or insect repellent in order to prevent insects from outside to enter the inner volume. The insec- ticides, insect repellents, rodenticides and rodent repellents are optionally combined in a single outer layer 6B or in a multilayer structure of optional outer layers 6B.

Optionally, in the examples of FIG. 2a, b, and c, the inner insecticidal layer 6A and/or the chemical barrier layer comprise a fungicide releasable to the foodstuff in the inner volume 3.

FIG. 3a illustrates a first example of an insect repellent source 4. Is it by example illustrated as a cylindrical body but could have other shapes. Characteristic for the insect repellent source in FIG. 3a is a compact form in which the three dimensions length, height, width are within the same order of magnitude. Such structures are advantageous in that they have a relatively large volume as compared to the surface area, why such structures are useful as a long-lasting reservoir with relatively large amounts of insect repellent 7. For example, the source 4 is an insect repellent tank where the insect repellent is contained in the tank and migrates gradually through the wall of the tank into the inner volume 3 of the container. Alternatively, the insect repellent source 4 is a polymer body formed by extrusion or moulding, where the insect repellent is incorporated in the polymer, typically by blending the insect repellent into the molten polymer during production, after which the molten polymer is moulded or extruded. Alternatively, the insect repellent 7 is impregnated into the insect repellent source 4. As a further alternative, the body of the insect repellent source is porous, and the insect repellent 7 is filled into the pores or impregnated into the walls of the pores. However, porous insect repellent source 4 can also have insect repellent 7 incorporated into the porous polymer material. The large surface of the porous source 4 promotes the release of the insect repellent 7, for example by evaporation. FIG. 3b illustrates an insect repellent source 4 that has a sheet structure. Compared to the volume of the source 4, the surface area is large. An advantage of such form is a rapid release due to a large surface area. This shape is advantageous for an insect re- pellent source 4 that is coated with an insect repellent 7 coating because the large surface area can take up a large amount of such coating material. The insect repellent 7 is then released from the coating.

The specific shapes in FIG. 3a and FIG. 3b are used for illustration only, where the source 4 in FIG. 3b resembles more a two-dimensional structure as compared to the structure in FIG. 3a that is more compact and bulk-like. However, the shapes can vary from a sheet-like structure to a more bulk-geometrical structure, including but not limited to cuboids, spheres, ellipsoids, cones, torus, and rings, either alone or combined, for example into a chain. For sheet-like structures, extrusion is an advantageous production process, whereas for compact bulk structures, extrusion as well as molding is readily applicable.

Potentially, as an alternative or in addition to the chemical insect repellent 7, the insect repellent source 4 comprises an ultrasonic wave emitter configured for insect repellent action by the emitted ultrasonic waves. Potentially, the emitted ultrasonic radiation also repels rodents, which gives an additional advantage. A battery-powered ultrasonic emitter can be integrated in a bulk structure like the one shown in FIG. 3a, potentially combined with a chemical insect repellent 7. Alternatively, as illustrated in FIG. 4, the ultrasonic wave emitter 10 is provided near or at the container wall 2. The insects are repelled by the ultrasonic waves from that part 2' of the container wall 2 where the emitter 10 is provided and towards an opposite part 2" of the container wall 2.

Claims

1. A method for killing insects inside a container (1), wherein the container (1) comprises a container wall (2) enclosing an inner volume (3) of the container (1), the container wall (2) comprising an insecticide (8) configured for killing the insects upon exposure of the insects by the insecticide (8), characterized in that the method comprises providing an insect repellent source (4) in the inner volume (3), causing the insects to move away from the insect repellent source (4) and to the container wall (2), and exposing the insects to insecticide at the container wall (2). 2. A method for killing insects according to claim 1 , wherein the method comprises providing the container wall (2), filling a first portion of foodstuff into the inner volume (3) of the container (1); placing the insect repellent source (4) in the first portion of foodstuff, and adding a second portion of foodstuff to the container (1), and closing the container (1).

3. A method according to claim 1 or 2, the method comprises providing the insect repellent source (4) in the inner volume (3) remotely from the container wall (2),

4. A method according to any preceding claim, wherein the insect repellent source (4) comprises a chemical insect repellent and the method comprises releasing the chemical insect repellent (7) from the repellent source (4) and providing an insect repellent concentration gradient with decreasing insect repellent concentration from the insect repellent source (4) to the container wall (2), causing the insects to move away from the insect repellent source (4) and to the container wall (2) due to the concentration gradient.

5. A method according to claim 4, wherein the insect repellent source (4) comprises a thermoplastic polymer having melt-incorporated the insect repellent (7) therein and wherein the method comprises causing migration of the insect repellent (7) from a bulk of the polymer to the surface of the polymer; or wherein the insect repellent source (4) comprises a surface that is coated or impregnated with chemical insect repellent (7); and wherein the method comprises releasing the chemical insect repellent (7) from the surface.

6. A method according to any preceding claim, wherein the insect repellent source comprises an electrical ultrasonic wave emitter configured for insect repellent action by the emitted ultrasonic waves.

7. A method according to any preceding claim, the method comprising providing a non-living oxygen absorber in the inner volume (3) remote from the container wall (2) and causing the oxygen absorber (9) to absorb oxygen and creating an oxygen concentration gradient with the oxygen concentration increasing from the oxygen absorber (9) towards the container wall (2), the oxygen concentration gradient assisting in causing the insects to move towards the container wall (2).

8. A method according to claim 7, wherein the method comprises combining the oxygen absorber (9) with the insect repellent source (4).

9. A container for a method according to any preceding claim, wherein the container (1) comprises a container wall (2) enclosing an inner volume (3) of the container (1) for foodstuff, the container wall (2) comprising an insecticide (8) configured for killing the insects upon exposure of the insects by the insecticide (8), characterized in that the container comprises an insect repellent source (4) in the inner volume (3) remotely from the container wall (2), the insect repellent source (4) being configured for causing the insects to move away from the insect repellent source (4) and to the container wall (2). 10. A container according to claim 9, wherein the insect repellent source (4) comprises a chemical insect repellent (7) configured for releasing the chemical insect repellent (7) from the repellent source (4) and for providing an insect repellent concentration gradient with decreasing insect repellent concentration from the repellent source (4) to the container wall (2) for causing the insects to move away from the in- sect repellent source (4) and to the container wall (2) due to the concentration gradient.

11. A container according to claim 9 or 10, wherein the insect repellent source (4) comprises a thermoplastic polymer having melt-incorporated the insect repellent (7) therein; and wherein the polymer is configured for migration of the insect repellent (7) from a bulk of the polymer to the surface of the polymer and release of the insect repellent (7) therefrom. 12. A container according to claim 11, wherein at least part of the insect repellent (7) in the bulk polymer of the insect repellent source (4) is provided on support particles for migration of the insect repellent from the support particles through the bulk of the polymer to the surface of the polymer. 13. A container according to claim 12 wherein the insect repellent source (4) comprises a surface that is coated or impregnated with the insect repellent (7) and configured for release of the insect repellent (7) from the surface.

14. A container according to anyone of the claims 9-13, wherein the insect repel- lent source comprises an ultrasonic wave emitter configured for insect repellent action by the emitted ultrasonic waves.

15. A container according to anyone of the claims 9-14, wherein the container also comprises an oxygen absorber (9) remote from the container wall (2) for absorb- ing oxygen and creating an oxygen concentration gradient with increase of oxygen concentration from the oxygen absorber (9) towards the container wall (2).

16. A container according to claim 15, wherein the oxygen absorber (9) and the insect repellent source (4) are abutting each other or are combined into or onto the same object.

17. A container according to anyone of the claims 9-16, wherein the container wall (2) comprises an inner layer (6A) and an outer layer (6B), wherein the inner layer (6A) comprises an insecticide (8) and the outer layer (6B) comprises a rodent repel- lent.

18. A container according to anyone of the claims 9-17, wherein the container (1) is a flexible bag. grains.

20. Use of a method according to anyone of the claims 1-8 for killing insect dur- ing crop storage in the container.