On the Target Entomofauna of an Organic Winter Oilseed Rape Field in Estonia 100 On the target entomofauna of an organic winter oilseed rape field in Estonia TIIU TARANG 1 , EVE VEROMANN 1 , ANNE LUIK 1 , INGRID WILLIAMS 2 1 - Institute of Plant Protection, Estonian Agricultural University, Kreutzwaldi 64, EE-51014, Tartu, Estonia; e-mail: ttiiu@eau.ee, veromann@park.tartu.ee 2 - Rothamsted Research, AL5 2JQ, Harpenden, Hertfordshire, UK; e-mail: ingrid.williams@bbsrc.ac.uk. TARANG T., VEROMANN E., LUIK A., WILLIAMS I. 2004. ON THE TARGET ENTOMOFAUNA OF AN ORGANIC WINTER OILSEED RAPE FIELD IN ESTONIA. – Latv. Entomol., 41: 100-110. Abstract: In May to July 2002, potential pests (phytophagous insects specialised on cruciferous plants) and their natural enemies (hymenopterous parasitoids and carabids as predators) were studied in an organic winter oilseed rape (Brassica napus) field in Estonia using yellow and black water traps and pitfall traps. Of the potential pests – Meligethes aeneus and Ceutorhynchus assimilis were the most numerous. However, they only fed on the rape plants and did not reproduce there. Their populations were low with peaks in early June. The peaks coincided with the population peaks of parasitic wasps including Phradis morionellus, a larval parasitoid of Meligethes aeneus, and Mesopolobus morys, Stenomalina gracilis and Trichomalus perfectus, larval parasitoids of Ceutorhynchus assimilis. 41 taxa of carabids were caught. Among them, the genus Pterostichus dominated, with P. cupreus and P. melanarius being the most numerous species. The presence of natural meadow as a field margin increased the abundance of potential pests, their parasitoids and the diversity of carabid species. Key words: phytophagous cruciferous insects, parasitoids, Coleoptera, Carabidae. Introduction In Estonia, the area of oilseed rape (Brassica napus L.) is increasing rapidly and has exceeded 30, 000 ha; only 1,500 ha of this is winter-sown, however. This provides good preconditions for the population growth of potential pests, that is of the phytophagous insects specialised in cruciferous crops. The entomofauna of winter oilseed rape has not been systematically studied before in Estonia. In Europe, the most common pests of oilseed rape are pollen beetles (Meligethes aeneus Fabr., M. viridescens Fabr.), cabbage seed weevil (Ceutorhynchus assimilis Payk.), cabbage stem weevil (Ceutorhynchus pallidactylus Panz.), rape stem weevil (C. napi Gyllenhal ), brassica pod midge (Dasineura brassicae Winn.), cabbage stem flea beetle (Psylliodes chrysocephala L.) and flea beetles (Phyllotreta nemorum L., P. undulata Kutschera, P. diademata) (Free, Williams, 1978, 1979; Ekbom, Borg, 1993; Williams et al., 2002; Hansen, 2003). The management of pests on the European oilseed rape crop still relies heavily on chemical pesticides, most often applied routinely and prophylactically, often without regard to pest incidence (Williams et al, 2002). This leads to over-use of chemical pesticides which reduces the economic competitiveness of the crop and threatens biological diversity. The pesticides also kill the natural agents of biological control, which would be a natural resource of great potential benefit to the farmer and consumer (Alford et al., 1995b; Williams, Murchie, 1995). By killing natural enemies, pesticide applications must be increased further to achieve pest control (Pickett et al., 1995; Murchie et al., 1997b). The EU-funded project MASTER: MAnagement STrategies for European Rape pests (Williams et al., 2002) aims to develop economically viable and environmentally acceptable crop management strategies for winter oilseed rape which maximise biocontrol of key pests (Williams et al., 2002). This requires much greater knowledge of pest,