Pestic. Sci. 1998, 54, 290È299

Extended SummariesSCI Pesticides Group MeetingSemiochemicals in Integrated Crop Management:commercial prospects

T he following are extended summaries based on papers presented at the meeting “Semiochemicals in Integrated Crop Management :commercial prospectsÏ, organised by A. J. Mordue on behalf of the SCI Pesticides Group and held on 13 May 1997 at 14/15 BelgraveSquare, L ondon. T he contents are entirely the responsibility of the authors, and do not necessarily reÑect the views of the EditorialBoard of Pesticide Science.

Pest Semiochemicals in Arable Crop Protection

J. A. Pickett

Biological & Ecological Chemistry Department, IACR-Rothamsted,Harpenden, Hertfordshire, AL5 2JQ, UK

The study of chemical ecology, particularly involvingpheromones and other semiochemicals that inÑuenceinsect behaviour, promises alternative methods of pestcontrol to the exclusive use of broad-spectrum toxi-cants. However, if the potential of semiochemicals incrop protection is to be realized, a greater understand-ing of insect/insect/plant interactions and insect chemi-cal ecology generally is essential. Semiochemicals, whenemployed alone, often give ine†ective or insufficientlyrobust pest control. Use of semiochemicals shouldtherefore be combined with other approaches in inte-grated management strategies. The main components ofsuch strategies are pest monitoring (to allow accuratetiming of treatments), combined use of semiochemicals,host plant resistance and trap crops (to manipulate pestbehaviour) and selective insecticides or biological controlagents (to reduce pest populations). The objective is todraw together these approaches into a push-pull orstimulo-deterrent diversionary strategy.1 In a push-pullstrategy, the harvestable crop is protected by host-masking agents, repellents, antifeedants or ovipositiondeterrents. At the same time, aggregative semi-

Contract/grant sponsor : Biotechnology and Biological Sci-ences Research CouncilContract /grant sponsor : Ministry of Agriculture, Fisheriesand Food

ochemicals, including host plant attractants and sexpheromones, stimulate colonisation of pests on trapcrops or entry into traps where pathogens can bedeployed. Because the individual components of thepush-pull strategy are not in themselves highly efficient,they do not select for resistance as strongly as conven-tional toxicant pesticides, thereby making the approachintrinsically more sustainable.

The pea and bean weevil, Sitona lineatus L., has pro-vided a model for the initial demonstration of a simplepush-pull strategy in UK arable agriculture. In spring,adult males produce an aggregation pheromone whichattracts weevils of both sexes into pea and bean crops.Adults feed on young leaves, and larvae cause seriousdamage to root hairs and nodules. The pheromone, 4-methyl-3,5-heptanedione, which was Ðrst identiÐed atIACR-Rothamsted, is used in traps to monitor themigration of weevils from their overwintering sites andto predict their time of arrival in the crop. Such trapsshould be commercially available in the near future.Experimental Ðeld plots were treated either with thepheromone, as the “pullÏ, or with an antifeedant formu-lation of neem oil extracted from the neem tree, Azadi-rachta indica A. Juss, as the “pushÏ. Materials such asneem often do not compare favourably with conven-tional pesticides in arable agriculture. However, in thistrial, the antifeedant was sufficiently active to reduceweevil damage signiÐcantly in “pushÏ plots, while the“pullÏ plots, baited with the pheromone, had greateradult and larval damage.2 This trial demonstrated thatS. lineatus can be manipulated with semiochemicals,and that control strategies for this and other pests ofarable crops could be developed.

Highly successful Ðeld results have recently beenobtained from a programme aimed at controlling stem

2901998 Society of Chemical Industry. Pestic. Sci. 0031È613X/98/$17.50. Printed in Great Britain(

Extended Summaries : Semiochemicals in Integrated Crop Management 291

borers in subsistence cereal cultivation, initially in EastAfrica, by a push-pull intercropping strategy. The pro-gramme involves scientists from the InternationalCentre of Insect Physiology and Ecology, Kenya(ICIPE), and the Kenya Agricultural Research Institute,in collaboration with IACR-Rothamsted and employsÐeld sites near Kitale in northern Kenya and at theICIPE Mbita Point Field Station on Lake Victoria. Theprogramme is funded by the Gatsby Charitable Foun-dation as part of its strategy of Ðnancing collaborativeprojects between international research centres in Africaand advanced research centres in the UK.

Two main species of lepidopterous stem borers, onean indigenous Noctuid, Busseola fusca (Full.) and theother an introduced species of Pyralid, Chilo partellusSwinh., bore at the larval stage into the stems ofsorghum and maize, causing complete destruction of theplant or drastic reduction in yield. Six key host plantcompounds, including eugenol (4-allyl-2-methoxy-phenol), have been identiÐed by electrophysical studiesat Rothamsted and shown to be attractive in behavioralstudies in Kenya. Repellents from non-host plants, e.g.,molasses grass. Melinis minutiÑora Beauv., have beensimilarly identiÐed and include a-terpinolene. Followingthis understanding of volatile components employed bythe pests in locating suitable hosts and avoiding non-hosts, a Ðeld control programme is being developedinvolving intercropping of maize and sorghum withother species selected for behavioural activity.

Striking results have been obtained against stemborer colonisation with certain intercropping regimes ;for example, when the cereal crop was surrounded by abarrier of Napier grass, Pennisetum purpureum Schu-mach., the adults laid eggs preferentially in the latter.However, the larvae failed to develop to adulthood,although at the same time, normal levels of parasitismwere maintained.

With the non-host grass M. minutiÑora as an inter-crop, direct repulsion of the pests occurred, as was alsofound with a Desmodium species of nitrogen-Ðxinglegume. In each case, the intercrop can be used as cattlefeed, although a “training periodÏ may be necessary forthe new forage to be acceptable to cattle. This strategyÐts in well with small or medium-sized farms, i.e., up to50 ha, which have an appropriate mix of cereal andcattle production or are in communities where trade ina surplus of either crop type can easily be managed. Inaddition to the direct reduction of stem borers throughsome of the intercropping programmes, improvementsin parasitism have been observed with the intercrop ofM. minutiÑora.3 The trap crop, P. purpureum, also actsas a windbreak, preventing lodging of maize.

AcknowledgementsIACR receives grant-aided support from the Biotech-nology and Biological Sciences Research Council of theUnited Kingdom. This work was in part supported by

the United Kingdom Ministry of Agriculture, Fisheriesand Food.

References

1. Pickett, J. A., Wadhams, L. J., & Woodcock, C. M.,Developing sustainable pest control from chemical ecology.In Agriculture, Ecosystems and the Environment 64, Elsevier,The Netherlands, 1997, pp. 149È56.

2. Smart, L. E., Blight, M. M., Pickett, J. A. & Pye, B. J.,Development of Ðeld strategies incorporating semio-chemicals for the control of the pea and bean weevil, Sitonalineatus L. Crop Protection, 13 (1994) 127È35.

3. Khan, Z. R., Ampong-Nyarko, K., Chiliswa, P., Hassanali,A., Kimani, S., Lwande, W., Overholt, W. A., Pickett, J. A.,Smart, L. E., Wadhams, L. J. & Woodcock, C. M., Inter-cropping increases parasitism of pests. Nature (L ondon),388 (1997) 631È2.

Semiochemicals to Increase Parasitism inAphid Pest Control

Wilf Powell

IACR-Rothamsted, Harpenden, Herts. AL5 2JQ, UK

Parasitic wasps or parasitoids are important biologicalcontrol agents which have been used extensively in bio-logical control and integrated pest managementschemes in agriculture in many parts of the world. Someparasitoids are speciÐc natural enemies of aphids andseveral species of these are produced commercially foruse against aphid pests, principally on protected crops.A number of European species have been introducedinto other regions of the world to help to control aphidson arable crops such as legumes and cereals. Aphidparasitoids have considerable potential as biologicalcontrol agents but their efficiency is dependent upontheir presence in the right place at the right time ; theirappearance in crops should be synchronized with colo-nising pest populations early in the season. Our under-standing of parasitoid behaviour, particularly theirresponses to semiochemical cues during the host loca-tion and host recognition phases of the foragingprocess, is providing exciting opportunities for themanipulation of parasitoids in the Ðeld to enhance theirimpact on pest populations.1 However, to develop rea-listic pest control strategies involving manipulation with

Contract/grant sponsor : Ministry of Agriculture, Fisheriesand Food.Contract/grant sponsor : Home-Grown Cereals Authority.Contract/grant sponsor : Horticultural Development Council.Contract/grant sponsor : Processors and Growers ResearchAssociation.