Biological control of insect pests on oilseed rape in Europe

摘要

BIOLOGICAL CONTROL BIOLOGICAL CONTROL OF INSECT PESTS ON OILSEED RAPE IN EUROPE David V. Alford describes an EC-funded project on the bio-control of oilseed rape insect pests Introduction Oilseed rape is a major arable crop in northern Europe and is attacked by a wide range of insect pests (Alford 1999) of which the following are of greatest importance l Ceutorhynchus assimilis (cabbage seed weevil) l Ceutorhynchus napi (rape stem weevil) ndash; not present in the UK l Ceutorhynchus pallidactylus (cabbage stem weevil) l Dasineura brassicae (brassica pod midge) l Meligethes spp. especially M. aeneus (pollen beetle) l Psylliodes chrysocephala (cabbage stem flea beetle). Traditionally control of insect pests on oilseed rape has involved the use of pesticides but this has always led to potential conflict owing to the large number of beneficial insects including bees and various natural enemies of pests that visit the crop.Many workers (both within the UK and in mainland Europe) have attempted to rationalise the use of pesticides on oilseed rape by developing economic spray thresholds for the various key pests and in recent years such strategies have also been developed into decision support systems (Johnen amp; Meier 2000). Increasingly such systems are also taking account of naturally occurring enemies (e.g. Lane amp; Walters 1995). Pest control on oilseed rape therefore is becoming more a question of pest management with enhancement and exploitation of natural enemies (parasitoids predators and pathogens) becoming an important part of the overall crop protection strategy.In a recent 3-year programme of work researchers from eight European countries (Austria Denmark Finland France Germany Sweden Switzerland and the UK) collated information on the biological control of insect pests of oilseed rape under the project acronym BORIS. This work (Alford et al. 2000) has demonstrated the considerable potential of natural enemies for limiting insect pest problems on oilseed rape crops in Europe. A database giving a range of information has been established and is currently accessible via the BORIS homepage (http://www.entom. slu.se/boris/). 1 Orchard House Oakington Road Dry Drayton Cambridge CB3 8DD UK. 200 Pest ic ide Outlook ndash; Oc tober 2000 This journal is copy; The Royal Society of Chemistry 2000 Cabbage stem weevil (Ceutorhynchus pallidactylus).Photo courtesy of the author Pesticides and beneficial insects Current recommendations for the control of pests of oilseed rape in the UK are summarised by Lane amp; Gladders (2000). Available insecticides include l the carbamates carbofuran and pirimicarb l the organophosphate phosalone l a range of pyrethroids (e.g. alpha-cypermethrin cypermethrin deltamethrin lambda-cyhalothrin tau-fluvalinate and zeta-cypermethrin) Nowadays pyrethroids form the basis of chemical control strategies both within the UK and in mainland Europe. Pesticides can have unwanted side-effects on beneficial insects including parasitoids and predators and their use can conflict with the aims of biological control.However although most insecticides are known to have adverse effects when tested in the laboratory this is not necessarily the case under field conditions. If parasitoids are active in a crop at or around the time of spraying then most could be killed; spray residues on crops Pollen beetle (Meligethes spp). Photo courtesy of the author DOI 10.1039/ b008023n could also be lethal although the most frequently used insecticides (i.e. the pyrethroids) seem to have a repellent (Umoru et al. 1996). In oilseed rape crops predators are less vulnerable to pesticides as they are often protected by the crop canopy or are hiding in the soil during the time of spraying. However no crop canopy would be available in the autumn when sprays might be aimed at aphids (virus vectors) or cabbage stem flea beetle.In an advisory context it is usually emphasised that chemical insecticide treatments should be applied to oilseed rape crops only if pest damage thresholds are exceeded and this has important implications for the survival and possible enhancement of beneficial organisms. Parasitoids Most of the important insect pests of oilseed rape in northern Europe are attacked by parasitoids notably braconid wasps (family Braconidae) ichneumonid wasps (family Ichneumonidae) and chalcid wasps (superfamily Chalcoidea e.g. family Pteromalidae). Data accumulated during BORIS include reference to almost 100 species of parasitoids that attack oilseed rape pests.An indication of the potential of parasitoids in oilseed rape is shown the following examples of parasitism l brassica pod midge ndash; over 20 known species of parasitoid recorded attacking the egg or larval stages l cabbage seed weevil ndash; over 20 known species of parasitoid recorded; often in excess of 70 of larvae attacked by Trichomalus perfectus (family Pteromalidae) Europe-wide l cabbage stem flea beetle ndash; up to 61 of larvae attacked by Tersilochus tripartitus (family Ichneumonidae) in France and up to 53 in Germany l cabbage stem weevil ndash; over 50 attacked by Tersilochus spp. in France Germany Switzerland and up to 30 by T. exilis on spring rape in Sweden l pollen beetle ndash; nine recorded species of parasitoid with species of Phradis (family Ichneumonidae) and Tersilochus being most common; parasitism in excess of 80 is reported l rape stem weevil ndash; up to 95 of larvae attacked by Tersilochus spp.(family Ichneumonidae) in France and up to 81 in Austria Predators Frequent mention is made in arable cropping systems to a range of predators notably ground beetles (family Carabidae) (Kromp 1999). Rove beetles (family Staphylinidae) and various predators of aphids e.g. ladybirds (family Coccinellidae) and syrphid flies (family Syrphidae) are also of importance. Within European oilseed rape crops 25 species of ground beetle are common and of regular occurrence. Pterostichus melanarius is generally the most abundant species but in detail the relative abundance of species varies from country to country and from site to site; in Germany for example several species (e.g.Calathus cinctus and Harpalus tardus) are most BIOLOGICAL CONTROL numerous in oilseed rape growing on more sandy soils. Predators are likely to have greatest impact on aphids and on those stages of pests that at some stage in the life-cycle occur on or in the soil. The latter include fully grown larvae and pupae of pests such as brassica pod midge cabbage stem flea beetle ceutorhynchid weevils and pollen beetles. Further predation is likely to be greatest on the soil surface (for example when fully grown larvae have dropped to the ground prior to pupation) although some common predatory ground beetles e.g. Clivinia fossor and Trechus quadristriatus will often search for prey within the surface layers of the soil.Other groups of invertebrates that contribute to the overall beneficial effect of natural predation of pests in oilseed rape fields include soldier beetles (family Cantharidae); dance flies (family Hybotidae); long-legged flies (family Dolichopodidae); money spiders (family Linyphiidae) and wolf spiders (family Lycosidae). Dance flies (at up to 59 individuals mndash;2) and long-legged flies (at up to 17 adults mndash;2) are considered important predators of brassica pod midge in oilseed rape fields in Germany (Prescher amp; Buuml;chs 1996 1999) and no doubt are also of significance elsewhere in Europe. Pathogens Few studies are available to indicate the true potential of pathogens in arable cropping systems.However entomopathogenic fungi (EPFs) entomopathogenic nematodes (EPNs) bacteria viruses and protozoans all occur naturally in the field and some have been tested experimentally against oilseed rape pests as possible biological control agents. Oil-spray formulations of the EPF Metarhizium anisopliae have been used in the UK against adults of cabbage stem flea beetle cabbage seed weevil and pollen beetle (e.g. Butt et al. 1998); the potential impact of the EPF Beauveria bassiana on overwintering survival of pollen beetle adults in Finland has also been investigated (Hokkanen 1993). Although some species of EPN (including members of the well-known genera Heterorhabditis and Steinernema) are exploited commercially for control of crop pests (see Copping 1998) and also occur naturally in the field few details are available of their effect on oilseed rape pests.However in France Steinernema feltiae is reported to have halved the number of emerging new-generation rape pests (e.g. ceutorhynchid weevils and pollen beetles) and weevils in the genus Baris are regularly infested by other EPNs; Dimorphoparasitilenchus barisii for example parasitizes Baris coerulescens. Elsewhere in Europe e.g. in Sweden EPNs are reported infesting flea beetles including cabbage stem flea beetle. Bacteria and viruses are not considered of potential value within the context of European oilseed rape pest control as their hosts tend to be Lepidoptera rather than Coleoptera and Diptera.With regards protozoans certain microsporidians (e.g. Nosema meligethi the main species upon which studies have been done) have the potential to diminish pollen beetle Pest ic ide Outlook ndash; Oc tober 2000 2 0 1 BIOLOGICAL CONTROL populations by increasing winter mortality decreasing fecundity and reducing adult longevity. Nosema meligethi however appears to be restricted mainly to Eastern Europe and Finland. Future pest management strategies on oilseed rape Recent studies of the parasitoid Trichomalus perfectus in England have confirmed that this parasitoid is an important natural enemy of cabbage seed weevil. This parasitoid is also an important bio-control agent in mainland Europe. Indications are that in the 1970s this species regularly killed large numbers (often in excess of 70) of larvae on unsprayed UK oilseed rape crops.The increased incidence of spraying throughout the 1980s led to a significant decline in this natural enemy probably because the post-flowering application of the organophosphate triazophos coincided with the main flight period of the adult parasitoids. Following co-incidental changes in spray recommendations notably the withdrawal of triazophos T. perfectus appears to have become more numerous on commercial crops such that it is again an important factor in the regulation of cabbage seed weevil populations. In the presence of this parasitoid the requirement for using insecticides is greatly diminished if not almost entirely avoided as spray thresholds for cabbage seed weevil are likely to be reached on very few commercial crops; this allows farmers to have increased confidence in the viability of adopting a biocontrol strategy for this pest (Alford et al.1996). Detailed knowledge of other pest/natural enemy interactions on oilseed rape that will allow changes in current pest management practices is limited. However there is a clear need to advertise as widely as possible that natural enemies can have a significant impact on oilseed rape pests and that there are important benefits to be gained from their enhancement and exploitation in modern crop protection practices. Enhancement of natural enemies needs to involve wholefarm strategies including where appropriate the provision of suitable on-farm landscape elements to ensure the survival of key components of the system.Weed strips for example are know to enhance the beneficial effects in agroecosystems of parasitoids and predators (including those attacking oilseed rape pests such as pollen beetle) and lsquo;push-pullrsquo; strategies such as the timely mowing might usefully be developed to move populations of such antagonists from field margins into crops where they can then exert an effect on pest populations. In future it may also be feasible to attract parasitoids and predators into crops by using semiochemicals (i.e. chemicals used in interspecific or intraspecific communication). Conversely semiochemicals (and perhaps anti-feedants) might have a role in diverting pests away from commercial crops.Certainly on-farm habitat management has an important role to play in future ICM (integrated crop management) strategies. This will include the creation improvement and conservation of habitats suitable for parasitoids and predators all factors that will reduce the need for farmers to resort to the use of chemical pesticides. 202 Pest ic ide Outlook ndash; Oc tober 2000 Acknowledgements Financial support was provided by the Commission of the European Communities Agriculture and Fisheries (FAIR) specific RTD programme CT96-1314. This paper does not necessarily reflect the Commissionrsquo;s views and in no way anticipates the Commissionrsquo;s future policy in this area. References Alford D.V. (1999). A Textbook of Agricultural Entomology 1st edition. Blackwell Science Limited Oxford 314 pp. Alford D. V.; Ballanger Y.; Buuml;chi R.; Buuml;chs W.; Ekbom B.; Hansen L. H.; Hokkanen H. M. T.; Kromp. B.; Nilsson Christer; Ulber B.; Walters K. F. A.; Williams I. H.; Young J. E. B. (2000). Minimizing pesticide use and environmental impact by the development and promotion of bio-control strategies for oilseed rape pests. Final Report Project FAIR CT 96-1314 119 pp. Alford D. V.; Walters K. F. A.; Williams I. H.; Murchie A. K. (1996). A commercially viable low-cost strategy for the management of seed weevil populations on winter oilseed rape in the UK. Proceedings of the Brighton Crop Protection Conference ndash; Pests amp; Diseases 2 609ndash;614. Butt T.M.; Carreck N. L.; Ibrahim L.; Williams I. H. (1998). Honey bee mediated infection of pollen beetle (Meligethes spp.) by the insect-pathogenic fungus Metarhizium anisopliae. Biocontrol Science and Technology 8 533ndash;538. Copping L. G. (Ed.) (1998). The BioPesticide Manual. The British Crop Protection Council Farnham 333 pp. Hokkanen H. M. T. (1993). Overwintering survival and spring emergence in Meligethes aeneus effects of body weight crowding and soil treatment with Beauveria bassiana. Entomologia Experimentalis et Applicata 67 241ndash;246. Johnen A.; Meier H. (2000). A weather-based decision support system for managing oilseed rape pests. Proceedings of the BCPC Conference ndash; Pests amp; Diseases 2 793ndash;800. Kromp B. (1999). Carabid beetles in sustainable agriculture a review on pest control efficacy cultivation impacts and enhancement.Agriculture Ecosystems amp; Environment 74 187ndash;228. Lane A.; Gladders P. (2000). Pests and diseases of oilseeds brassica seed crops and field beans. In Pest and Disease Management Handbook. D. V. Alford (Ed.) Blackwell Science Limited Oxford in press. Lane A.; Walters K. F. A. (1995). Prospects for a decision support system for pest of oilseed rape in the UK. Proceedings of the 9th International Rapeseed Congress Cambridge UK pp. 1019ndash;1021. Prescher S.; Buuml;chs W. (1998). Der Einfluszlig; abgestufter Extensivierungs- maszlig;nahmen im Raps- und Erbsenanbau auf nuuml;tzliche Fliegen (Diptera Brachycera). Gesunde Pflanzen 50 213ndash;218. Prescher S.; Buuml;chs W. (1999). Fliegenzouml;nosen (Diptera Brachycera) aus abgestuft extensiv bewirtschafteten Raps- und Erbsenkulturen. Verhandlungen der Gesellschaft fuuml;r Ouml;kologie 29 265ndash;269. Umoru P. A.; Powell W.; Clark S. J. (1996) Effect of pirimicarb on the foraging behaviour of Diaeretiella rapae (Hym. Brac) on host-free and infested oilseed rape plants. Bulletin of Entomological Research 86 193ndash;210. David Alford is a Board Member of the British Crop Protection Council with particular responsibility for their programme of international conferences and symposia. Until recently he was co-ordinator of an EC-funded project on the bio-control of oilseed rape insect pests. He has published widely on crop protection issues with particular reference to insect and mite pests of European arable and horticultural crops.