PREY PREFERENCE AND EGG-PRODUCTION OF THE CARABID BEETLE AGONUM-DORSALE

In order to elucidate whether the aphid Rhopalosiphum padi is low qual ity food for the carabid beetle Agonum dorsale, as it has previously b een found to be for cereal spiders, we performed a series of experimen ts using fruit flies Drasophila melanogaster as a standard alternative prey ('control prey'): 1) Prey preference, 2) Aphid consumption for s atiated and starved beetles, 3) Egg production on different diets and 4) Preference experiments with fruit flies coated with a taste of diff erent prey types. Other alternative prey types used were earthworms an d sciarid midges, all potential prey in the field. A. dorsale has a lo w preference for aphids compared to fruit flies. Apparently there is a n upper limit to the consumption of aphids independent of hunger and m uch below the beetles' total food demand. Egg production on a pure die t of aphids is lower than on a pure diet of fruit flies; it is extreme ly low on a pure diet of earthworms; the highest fecundity is found on a mixed diet. As fruit flies coated with a taste of aphids or sciarid midges are less prefered than flies covered with a taste of fruit fli es there may be a chemical factor, acting through taste, involved in d etermining prey preference.