227 Cabbage seed weevil (Ceutorhynchus assimilis Payk.) and its parasitoids in oilseed rape crops in Estonia R. Kevväi, E. Veromann, A. Luik and M. Saarniit Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi St. 64, EE51014, Tartu, Estonia; e-mail: reelika.kevvai@emu.ee Abstract: Besides pollen beetles, the cabbage seed weevil is the second most numerous crucifer-specialist in Estonian oilseed rape crops. The occurrence of cabbage seed weevil and its hymenopterous parasitoids was studied in standard and integrated cropping systems in winter and spring oilseed rape crops in 2004–2005. Cabbage seed weevil is more synchronized with winter oilseed rape and its abundance was greater in winter than in spring. The average pod damage was 9.9% in winter and only 1.2% in the spring crop. In winter oilseed rape, the population of C. assimilis was more numerous in the integrated than in the standard cropping system. Three parasitoids of seed weevil – Trichomalus perfectus, Stenomalina gracilis, Mesopolobus morys – were caught with yellow water traps but their abundance was low. The larval parasitism rate was higher in the integrated cropping system (22.2%) than in the standard cropping system (9.7%). Trichomalus perfectus was the dominant species emerging from C. assimilis larvae. Key words: Ceutorhynchus assimilis, oilseed rape, parasitoids, insecticide, cropping system INTRODUCTION In Estonia the area of oilseed rape has rapidly increased during the last decade; it provides good preconditions for population growth of crucifer-specialist insects. Spring oilseed rape is prevailing and Meligethes aeneus (Fab.) became the most dangerous pest in this crop (Veromann et al., 2006a). But the production area of winter oilseed rape is also expanding. Cabbage seed weevil (Ceutorhynchus assimilis Payk.) is one of the major pests of oilseed rape in Europe, reducing yield of infested pods by about 18% (Alford et al., 2003; Williams, 2004). The management of the pests of oilseed rape relies on chemical pesticides. Along with the pests, insecticides also kill their natural enemies, which can substantially reduce beetle populations (Murchie et al., 1997). Ceutorhynchus assimilis is host to 34 species of parasitoids: Stenomalina gracilis (Walker), Mesopolobus morys (Walker) and Trichomalus perfectus (Walker) are most common (Williams, 2003), and capable of controlling more than 70% (Alford et al., 1995) of the seed weevil population. Therefore the conservation and enhancement of parasitoids is essential to develop alternative strategies for managing the pests (Williams, 2004). The aim of this study was to establish the occurrence of cabbage seed weevil and its parasitoids in standard and integrated cropping systems in winter and spring oilseed rape in Estonia. Agronomy Research 4(Special issue), 227–230, 2006