THE ECOLOGY OF BEMBIDION-OBTUSUM (SER) (COLEOPTERA, CARABIDAE) IN WINTER-WHEAT FIELDS IN IRELAND

Bembidion obtusum (Ser.) has been found to be one of the most numerous carabid beetles occurring in winter wheat in Ireland. The species sho wed both nocturnal and diurnal activity and was found in fields from a utumn until early summer, but showed peak activity over winter when it dominated the carabid fauna. The field distribution of B. obtusum was aggregated with a mean density of 23/m2, and beetles were only found in the soil surface layer. The width of the proximal protarsal segment was used to determine the sex of live beetles, males being larger tha n females. Egg-laying by B. obtusum was recorded in the laboratory dur ing March and April. The opaque eggs were cylindrical in shape and mea sured 0.57mm X 0.34mm. The lifespan of beetles is considered to be one year. An-examination of crop contents of B. obtusum showed that signi ficantly more contained aphid remains than remains of Collembola or mi tes, but the diet varied with season.