Host distribution, larviposition behaviour and generation time ofSarcophaga penicillata(Diptera: Sarcophagidae), a parasitoid of conical snails

Abstract

AbstractHost characteristics, hyperparasitism, larviposition behaviour and generation time ofSarcophaga penicillataVilleneuve a parasitoid of the conical snail,Cochlicella acutaMüller (Mollusca: Helicidae) in southern France are described. Only snails which aestivated on vegetation were found to be parasitized byS. penicillata. Sarcophaga penicillatapreferredC. acutawhich were both significantly higher off the ground and larger in size than the population averages. Of the 2768 snails collected at the study site, 4% (112) were parasitized byS. penicillata, of which 36.6% (41) failed to emerge while 34% (38) were hyperparasitized. The predominant hyperparasite wasNovitzkyanus cryplogasterBouček (Hymenoptera: Pteromalidae) which was responsible for 79% (30) of the hyperparasitism. LarvipositingS. penicillatawere observed to fabricate a hole in the epiphragm of resting snails in which they deposited one larva. After larviposition, femaleS. penicillataremained with the freshly parasitized snail a mean time ± SE of 25.2 ± 10.3 min. It is suggested that this may be an adaptive response to avoid superparasitism. The mean generation time ofS. penicillatawhen reared in the laboratory was 18 days, indicating that more than six generations are possible during summer in the south of France. During winter,S. penicillataenters diapause in the pupal stage within a host snail for up to 6 months. The possible utility ofS. penicillataas a biological control agent of introduced conical snails is discussed.