WO2006046067A1

WO2006046067A1 - Biological control of insect pests

Info

Publication number: WO2006046067A1
Application number: PCT/GB2005/004184
Authority: WO
Inventors: David William Hartley; Alan Roy Davies
Original assignee: International Pheromone Systems Limited
Priority date: 2004-10-29
Filing date: 2005-10-28
Publication date: 2006-05-04
Also published as: GB2419531A; GB0424074D0

Abstract

A method of controlling insect pests in commercial crops such as orchards comprises the steps of: arranging a pathogen source (34) proximate to a lure (22); attracting the insect pests to the lure so that they acquire and carry pathogen from the source; and allowing the pathogen-carrying insects to move away from the lure into the population of the insect pests in the orchard, whereby the pathogen is transferred to that population. Traps (10, 100) and sources (28, 128) for containing and dispensing a live pathogen (34), used in carrying out the method, are described. The lure may comprise a semiochemical such as a pheromone. The method is effective against codling moth (Cydia pomonella) infestation. The pathogen may be a fungus such as Beauveria bassiana, Metarhizium anisopliae or Paecilomyces fumosoroseus.

Description

BIOLOGICAL CONTROL OF INSECT PESTS

Invention Background

This invention relates to a method for the biological control of insect pests in commercial crops, by assisted establishment of epizootics so as to destroy the pest populations. The invention particularly concerns traps and pathogenic material dispensers for controlling insect populations. For simplicity, the invention is discussed below in relation to arboreal agriculture and in particular in methods for controlling codling moth damage in apple and pear crops. However, the invention is of more general applicability.

Arboreal agriculture, such as commercial fruit growing in orchards, is an important economic activity and growers are concerned to minimise crop damage by controlling insect pests. Currently insecticides are widely used for this purpose. The estimated market value of insect control products for top fruit in Europe and the Middle East in 2004 is 70 million Euros, the market value for fruit and nut insecticides in the 25 EU countiies being 5.7 million Euros.

Use of insecticides to control insect pests has led to concerns over damage to human health through pesticide residues, as well as concerns over more widespread ecological damage. It is well known that insecticides, if used inappropriately, may affect "non-target" organisms, may persist in the environment and may become concentrated in the food chain. For ecological as well as economic reasons, growers are therefore being encouraged to reduce their pesticide inputs and target them more precisely on pest species by adopting integrated pest management techniques. One such technique is to use insect traps, baited with the appropriate synthetic pheromone lure, to monitor insect numbers so as to be able to time the application of insecticides for maximum effect. Pheromone lures are also used for insect population control by mating disruption. Certain insecticides, such as organophosphates, judged to be particularly harmful to the environment, have recently been withdrawn from the EU market. There is thus a need for alternative insect pest control strategies.

The codling moth (Cydia pomonella) is an orchard pest found throughout apple and pear production areas worldwide. The moth lays its eggs on fruit and the moth larvae will bore into the core of the apple or pear with the resultant feeding damage leaving the fruit unsaleable. During any season several generations may be produced, depending on climatic conditions. Pheromone traps have been used to monitor moth numbers so that insecticide spraying can be timed to coincide with egg hatch. However, with this technique destruction of the insects is still entirely dependent on the application of insecticides.

Other researchers have successfully developed bioinsecticides - biological agents such as viruses and fungi - used to kill insect pests. Bioinsecticides also have their drawbacks. They are relatively expensive and, though selected to be particularly harmful to a target range of organisms, may nevertheless exhibit a fairly broad spectrum of activity so that they still destroy beneficial or harmless species as well as the target pests. To be effective in reaching the target population in lethal dosages over a short timescale, bioinsecticides may have to be applied to the crop in undesirably large quantities, adding to the environmental risks. Their efficacy may also be affected by climatic factors such as temperature and humidity and their lethal effects may be relatively short-lived, so that repeated applications are often necessary. They may also be too specific to target entire pest complexes in a given crop.

Investigations have been conducted into the control of diamondback moth infestation using a combination of a semiochemical and a pathogen (J. K. Pell et aL, A Pheromone Trap for Dispersal of the Pathogen Zoophthora radicans Brefeld. (Zygomycetes: Entomophthorales) amongst Populations of the Diamondback Moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae): Biocontrol Science and Technology (1993) 3, 315-320; Michael J. Furlong et al, Field and laboratory evaluation of a sex pheromone trap for the autodissemination of the fungal entomopathogen Zoophthora radicans (Entomophthorales) by the diamondback moth Plutella xylostella (Lepidoptera: Yponomeutidae): Bulletin of Entomological Research (1995) 85, 331-337. The diamondback moth is a severe pest of brassica crops. The control technique uses a pheromone lure to attract male moths to a source of fungal pathogen. The males become infected and are then allowed to return to the environment so that they vector the pathogen to the rest of the moth population. Research has been carried out using other semiochemicals and pathogens for other pest targets (see Chapter III-3 of "Field Manual of Techniques in Invertebrate Pathology", edited by LA. Lacey and H.K. Kaya, published 2000 by Kluwer Academic Publishers, the Netherlands). To date, however, such techniques have not found commercial application for controlling pests in arboreal crops. The present inventors have developed and tested traps and pathogen dispensers for use in pest population control methods using a combination of a pheromone and a pathogen.

Summary of the Invention In a first aspect, the invention provides a trap for use in controlling insect pests, as defined in claim 1. In one embodiment, the trap comprises a pathogen source and a lure attractive to the insects, and an outer surface providing an alighting point for flying insect pests attracted by the lure, the trap directing the insects onto the pathogen source and allowing the insects to return to the environment. In another aspect, the invention provides a trap for use in controlling insect pests, as defined in claim 11. With such a trap, the insects may fly around the lure, passing into and out of the pheromone plume, with the pathogen source positioned such that the insects brush or knock against it or pass through a pathogen shower emanating from it, so as thus to become inoculated with pathogen in flight.

The trap may comprise a housing having one or more entry apertures through which a semiochemical is emitted from the lure and through which the attracted insect pests enter the housing. In one embodiment, a downwardly inclined, preferably funnel-shaped surface leads the insects away from the entry aperture(s) towards the pathogen source situated within the housing. The funnel may for example be shaped as an inverted cone or pyramid. The housing preferably comprises one or more apertures through which the insects exit the trap structure after having habituated to the semiochemical and passed through or across the pathogen source.

Alternatively the trap may comprise spaced upper and lower plates between which the lure and pathogen source are positioned. The spacing between the plates defines generally open sides of a structure through which the attracted insect pests can enter and leave. The lure is preferably positioned above the pathogen source towards the centre of the plates. Preferably the upper plate has a larger diameter so as to overhang the lower plate. The upper plate shields the lower plate, lure and pathogen source and the lower plate accommodates the pathogen source and helps direct the flying insects onto it.

In a further aspect, the invention provides a pathogen source for use in an assisted autodissemination pest trap, as defined in claim 16. The pathogen source may comprise an open-topped container for pathogen in powder form. The powder may be covered by porous material such as gauze, or may be impregnated into a porous pad, to prevent overloading of the insect pests with the pathogen.

The primary source of pathogen close to the lure need not be large in quantity, but can be sufficiently concentrated so that a substantial and sufficient proportion of insects attracted to the lure become pathogen carriers. The carrier insects thus act as an effective means of transporting the pathogen to the general population of pest insects in the crop (autodissemination). The pathogen is transmitted from carriers to infect hitherto non-carriers by the normal encounters between individuals in the orchard population, for example during foraging or mating. This may include encounters between different stages in the insect lifecycle (permutations of egg, larva, pupa, and adult in the case of the codling moth and other Lepidoptera). The transmission mechanism may vary from one pathogen to another, the infectious agents for example being transferred by contact or air currents; by being eaten or by ingestion during respiration; in body fluids, in moisture; or combinations of such mechanisms. The rate of transfer and the rate of infection by the pathogen within the crop pest population can be high enough to establish an epizootic and so destroy the majority or a substantial proportion of the insect pest population, whereby insect damage to the crop is reduced or substantially eliminated.

The lure may be effective to attract a particular insect pest or a defined set of insect pests. For example, its active ingredient may comprise a semiochemical attractive to a group of insect pests or a particular insect pest. Precise attraction of a single pest species can be achieved using a sex pheromone. The lure may be non-chemical, such as a light source used to attract nocturnal insects. Particular wavelengths may be used to attract particular species groups.

The pathogen may be selected to be effective against a range of pest species. In that case a lure can be used which is attractive to a narrower set of insect pests (e.g. a complex of pest species associated with a particular crop) or a single insect pest species. In this way the insect pest control method can be tuned to a particular pest species or a relatively precise set of pests, minimising its effects on beneficial or other non-target species. Although the pathogen can be chosen to be effective against a fairly broad range of insect pests, the lure will ensure that the primary source of infection acts solely upon a target species or set of species attracted to it. The carrier individuals will return to their habitat, often preferentially to that part of the habitat actually populated by other insects of their species, so the opportunities for non-target organisms in other habitats to become infected with the pathogen are small. The epizootic is thus substantially confined to the target species or set of species governed by the lure, despite the broader efficacy of the pathogen. On the other hand both the lure and the pathogen can be targeted to a particular species or small group of species so that the control method is doubly tuned or filtered so as to target the selected species set very precisely, with no significant effects on other species, such as other species sharing the same habitat.

Advantageously the pathogen comprises a fungus or similar organism whose reproductive cycle includes the production of infective units (for fungi these are spores) thereby increasing the chances of infecting other target individuals. The pathogen may comprise a fungus selected from the group Beauveria bassiana, Metarhizium anisopliae and Paecilomyces fumosoroseus. The pathogen may be provided in the form of (dry) fungal spores, although other formulations are possible for suitable retention to form the primary source until they are picked up by the target insects attracted by the lure. The pathogen may likewise be suitably formulated to aid its acquisition by or inoculation of the target insects.

The lure preferably comprises a pheromone specifically attractive to the target pest species (for example codling moth). The pheromone formulation and/or lure construction preferably provides for slow release and hence a sufficiently long field life to provide effective crop protection with minimal field maintenance.

The lure and pathogen are arranged in a trap structure (autoinoculator) which provides an alighting point for flying insect pests attracted b}' the lure and which directs the insects onto the pathogen source.

The trap structure preferably retains the insects in contact with the pathogen source for a sufficient period to acquire an effective amount of pathogen. The trap structure advantageously protects the pathogen source against the weather and wind dispersal and provides improved conditions (temperature, humidity, UV shielding, etc.) for preservation of the pathogen and inoculation of the insects with the pathogen or acquisition of the pathogen by the insects.

The control method preferably comprises distributing a plurality of the lures and associated pathogen sources throughout the crop, so that the insect pests carry and distribute pathogen to their habitat throughout the crop. Where the pest is codling moth, the lures are preferably spaced at intervals of less than 40m, more preferably 20m or less. Each lure and associated pathogen source is advantageously positioned at a height where the lures operate efficiently to attract the target insects - in the case of codling moth, preferably in the upper half, more preferably the upper third, of the orchard canopy.

Further preferred features of the invention are in the dependent claims. Illustrative embodiments of the invention, showing further preferred features and advantages, including examples of some trap configurations and pathogen source¹ consteuctions, are described below with reference to the drawings.

Brief description of the Drawings Figure 1 is a somewhat diagrammatic section through a first insect trap embodying the invention and Figure 2 is a somewhat diagrammatic section through a second such trap.

The trap shown in Figure 1 is a modified form of the "castellated" insect monitoring trap available from Oecos Limited, UK (www.oecos.co.uk). The modified trap 10 comprises an opaque lid 12 having a depending castellated skirt 14. The castellations define entrance apertures 16 for insect pests such as the codling moth. A snap-in basket 18 with apertures 19 and a removable cap 20 is fixed in a centre hole in the lid 12. A rubber septum 22 impregnated with a synthetic pheromone or other semiochemical attractive to the insect pest whose population is to be controlled is placed in the basket 19. The septum 22 is porous so as to slowly release the pheromone over a period of several weeks. Alternatively, a porous polyethylene vial can be used to contain and controllably release the semiochemical. Such septa and vials are known for use in forming pheromone-releasing lures for insect monitoring traps, and are commercially available.

As shown in Figure 1 , the septum 22 is held approximately level with the apertures 16 so that cross currents of air can carry the pheromone into the environment and attract the insect pests to the entrance apertures 16. The trap 10 further comprises a translucent body portion or bucket 24 fitted to the bottom of the skirt 14. An opaque funnel-shaped baffle 26 is positioned between the skirt 14 and the upper rim of the bucket 24. It has been found that the downwardly inclined upper surface of the baffle 26 encourages codling moths, alighting on the outer surface of the trap and attracted through the apertures 16, to crawl through the apertures and venture further into the trap, rather than just exiting through the apertures 16 again, once they have become habituated to the pheromone.

In the case of the codling moth, the main constituent of the natural pheromone is (E₅E) — 8,10 - dodecadienol. It has been found that rubber septa or polyethylene vials loaded with 1 - 4 mg of this compound are effective to attract male codling moths for a period of more than three weeks. The pheromone release rate is approximately proportional to loading. Besides depletion through evaporation, active pheromone is also lost through isomerisation of the conjugated diene from the E₅E to the Z₅E , E₅Z and Z₅Z isomeric forms. Experimental results suggest that this is a greater problem in the rubber septa than in the polyethylene vials.

However over the course of a three week test period there were no significant differences in the effectiveness of the two different kinds of lure in attracting male codling moths.

The lower open end of the baffle 26 is disposed above an upwardly open dish-like container 28 for the pathogen. Insects leaving the trap 10 therefore pass downwardly through the baffle 26, through the pathogen container 28 and between the lower rim of the baffle 26 and the upper rim of the container 28, before leaving the bucket 24 trough exit slots 30. The container 28 is supported from the base of the bucket 24 on a pedestal 32. The pathogen 34 is placed in the container 28, in a form which will be picked up by insects passing through the container 28 as they leave the trap 10. For example dry fungal spores in loose powder form can be used. The insects will usually spend some time confined within the trap 10 before finding the exit slots 30, so that there is a good chance that they will pick up the pathogen 34 as desired. For example, codling moths tend to fly around aggressively within the trap and may pass multiple times up and down through the funnel, between the head space surrounding the lure-containing basket 18 and the pathogen container 28. There are thus multiple chances for the insect to acquire an effective dose of the pathogen. The pathogen container 28 may have a porous cover 38 supported by the pathogen powder so as to control the amount of pathogen picked up by each visiting insect and prevent overloading. The cover remains supported at the surface of the heap as powder is used up. The porosity of the cover is sufficient to allow pathogen particles to pass through and be picked up by insects crawling across or otherwise coming into contact with the cover. In this way, the insect can receive a controlled dusting of the pathogen powder. The porosity of the cover may be selected to control the pathogen dose received. At the same time, the cover prevents the insects from "drowning" in the loose powder. The cover may be for example a porous fabric or fine plastics gauze. Alternatively, particles of the pathogen can be impregnated into a porous or reticulated substrate such as an open celled foam or fibrous pad. In the case of insects that habitually crawl across steeply inclined, near vertical or even inverted surfaces, the porous cover or pad may be provided as a lower side wall or bottom wall of the container. Pathogen particles may then fall out of the container under gravity, when disturbed by an insect. Yet alternatively, the pathogen may be supplied as a liquid formulation, again with dosage optionally controlled by a porous cover or pad. For transportation and storage, the cover or pad may be protected behind a tear-off or otherwise removable seal. The seal may be, for example, a metal or plastics foil (not shown) e.g. ultrasonically welded to the rim of the container 28. Additionally or alternatively, the seal may comprise any suitable removable lid. Similar arrangements can be used to seal covers or pads exposable in the lower side wall or bottom of the container. Thus, the pathogen may be supplied to the end user pre-packaged in the container 28.

The trap 10 protects the pathogen 28 from the sun (e.g. UV light and excessive drying), from the weather and from wind dispersal. If a given pathogen is more effective in particular ambient conditions, the interior of the trap can be adapted accordingly. For example if a high humidity is required, a means for keeping the trap interior moist can be provided, such as by an absorbent wad or paper, connected to a wick and a water reservoir.

AU three fungi mentioned above are effective as the pathogen and can be cultured by known methods to obtain spores in dry powder form. Beauveria bassiana is commercially available as a technical powder from Emerald BioAgriculture Corporation (www.emeraldbio.com). A spray formulation sold under the registered trade mark BOTANIGARJD is approved in several countries for use as an insecticide. Other potentially suitable pathogens, with details of their formulation, commercial sources and target pest organisms, are listed in "The BioPesticide Manual: a world compendium" edited by L. G. Copping, 2^nd edition published 2001 by the British Crop Protection Council (BCPC), Alton, Hampshire, U.K.; ISBN 1 901396 29 0. This manual also contains information on various semiochemicals. Selecting pathogens from target pests can produce strains suitable for use on different local pest populations in different climates. For example, the applicants have isolated and cultured different strains of B. bassiana from codling moths in English and Spanish apple and pear orchards.

Figure 2 shows a simplified form of trap developed by the applicants, which proved effective in contaminating codling moths with fluorescent marker powder in wind tunnel tests and in field trials. As shown in Figure 2, the trap 100 comprises upper 112 and lower 114 slightly dished circular plates, held spaced from one another by pillars 116. The pillars 116 are fonned in two halves, each half respectively moulded with the upper and lower plates 1 12, 114 and snap-engageable with the other half to hold the plates together. A central hole in the upper plate 112 accommodates a basket 18 and lure 22 similar to those in Figure 1. A container 128 for pathogen 34 is supported at the centre of the lower plate 114, below the basket 18. The pathogen may again be a powder, optionally with a porous cover or retaining pad and seal as described above. Insects attracted by the lure 22 will fly between the upper and lower plates 112, 114 and will come into contact with the pathogen 34 in the container 128 as they fly around the lure 22, passing into and out of the pheromone plume in an attempt to locate its source. The insects may thus brush or knock against the pathogen source and become inoculated with pathogen. The exposed surface of the pathogen 34 within the container 128 is sufficiently large to ensure adequate contact with the flying insects as they pass into and out of the trap 100. Alternatively, the pathogen infectious units can be actively discharged from the source e.g. as a shower or spray, through which the insects pass. Pathogen sources, e.g. an actively sporulating fungus, in this case can be located on the upper 112 and/or the lower 114 plate. An actively discharging pathogen source can also be used in the trap shown in Figure 1. The insects can pass freely into and out of the trap 100 through the peripheral gap defined between the spaced plates 112, 114. The extended upper plate 112 shields the lure 22 and pathogen 34 from the sun and weather, although perhaps to a lesser extent than the more enclosed arrangement of Figure 1. On the other hand the trap 100 of Figure 2 allows more unrestricted access to the pathogen source by the target insects.

In use e.g. to control codling moth populations, the traps are positioned at regular intervals throughout the orchard. The spacing between adjacent traps should preferably ensure that target insects can be attracted to one or another of the traps from substantially anywhere in the orchard or other crop. For example when using (E,E) - 8,10 - dodecadienol lures for codling moth, the trap spacing should not exceed 40m and preferably should not exceed 20m. The traps are positioned (e.g. suspended from lugs 36, Figures 1 and 2) at a suitable height to attract the insects concerned. In the case of codling moths, the traps are positioned in the upper half, preferably the upper third, of the orchard canopy. Trap positioning may also take into account other factors, such as prevailing wind direction (the lures being placed upwind of the pest population).

The traps described are effective in attracting the target insect pest to the lure, allowing it to acquire the pathogen and allowing the pathogen-contaminated pest to return to its habitat. The word "trap" as used in this specification is to be understood in this context, and not as requiring insects to be captured and permanently retained. The traps and pathogen source can be modified within the scope of the claims, e.g. to suit the physical characteristics and behaviour of different insect pests.

Claims

1. A trap (10) for use in controlling insect pests, the trap comprising a pathogen source (28, 32, 34) and a lure (22) attractive to the insects, the trap directing the insects onto the pathogen source and allowing the insects to return to the environment, the trap comprising a housing (12, 24) having one or more entry apertures (16) through which a semiochemical is emitted from the lure and through which the attracted insect pests enter the housing, characterised in that a downwardly inclined surface (26) leads the insects away from the entry aperture(s) towards the pathogen source situated within the housing.

2. A trap as defined in claim 1 comprising an outer surface (12, 24) that provides an alighting point for flying insect pests attracted by the lure (22).

3. A trap as defined in claims 1 or 2, in which the downwardly inclined surface (26) is funnel-shaped.

4. A top as defined in claim 3, in which a plurality of the entrance apertures (16) are distributed circumferentially adjacent to an upper rim of the funnel-shaped surface (26).

5. A trap as defined in claims 3 or 4, in which a lower exit aperture from the funnel- shaped surface (26) is disposed above the pathogen source (28, 32, 34).

6. A trap as defined in any preceding claim in which the lure (22) is supported substantially level with the entry aperture(s) (16), whereby a crossflow of air causes a plume of the semiochemical to be emitted from the entiy aperture(s).

7. A trap as defined in claim 6, in which the lure (22) is suspended from a roof (12) of the trap.

8. A trap as defined in claim 7, in which the lure (22) is removably insertable through an aperture formed in the roof (12) of the trap.

9. A trap as defined in any of claims 1 - 8, in which the housing (12, 24) comprises one or more apertures (30) through which the insects exit the trap structure after having habituated to the semio chemical and passed through or across the pathogen source (28, 32, 34).

10. A trap as defined in claim 9, in which the pathogen source (28, 32, 34) is supported in the housing (12, 24) between the entry and exit apertures (16, 30).

11. A trap (100) for use in controlling insect pests, the trap comprising a pathogen source (128, 34), a lure (22) attractive to the insects, and spaced upper and lower plates (112, 114) between which the lure and pathogen source are positioned, characterised in that the spacing between the plates defines generally open sides of a structure through which the attracted insect pests can enter and leave.

12. A trap as defined in claim 11, in which the lure (22) is positioned above the pathogen source (128, 34) towards the centre of the plates (112, 114).

13. A trap as defined in claim 11 or 12, in which the upper plate (112) is larger than and overhangs the lower plate (1 14).

14. A trap as defined in claim 11, 12 or 13, in which the upper and lower plates (112, 114) are connected by spacer pillars (116).

15. A trap as defined in claim 14, in which the pillars (116) comprise snap-engageable joints.

16. A pathogen source for use in an assisted autodissemination pest trap, the source comprising a container (28, 128) for living pathogen (34), characterised in that the dosage of the pathogen picked up by pests encountering the source is controlled by a porous cover (36) or pad.

17. A pathogen source as defined in claim 16, in which the pathogen (34) is impregnated into the porous pad.

18. A pathogen source as defined in claim 17, in which the porous pad is fibrous or comprises an open celled foam material.

19. A pathogen source as defined in claim 16, in which the porous cover (36) comprises a porous fabric or gauze.

20. A pathogen source as defined in claim 16 or 19, in which the cover (36) is supported on a heap of loose pathogen (34).

21. A pathogen source as defined in claim 16 or 19, in which the cover is provided in the container (28) base or lower side walls.

22. A pathogen source as defined in any of claims 16 — 21, in which the cover or pad is protected behind a removable seal.