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

Abstract

AbstractHost characteristics, hyperparasitism, larviposition behaviour and generation time of Sarcophaga penicillata Villeneuve a parasitoid of the conical snail, Cochlicella acuta Müller (Mollusca: Helicidae) in southern France are described. Only snails which aestivated on vegetation were found to be parasitized by S. penicillata. Sarcophaga penicillata preferred C. acuta which 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 by S. penicillata, of which 36.6% (41) failed to emerge while 34% (38) were hyperparasitized. The predominant hyperparasite was Novitzkyanus cryplogaster Bouček (Hymenoptera: Pteromalidae) which was responsible for 79% (30) of the hyperparasitism. Larvipositing S. penicillata were observed to fabricate a hole in the epiphragm of resting snails in which they deposited one larva. After larviposition, female S. penicillata remained 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 of S. penicillata when 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. penicillata enters diapause in the pupal stage within a host snail for up to 6 months. The possible utility of S. penicillata as a biological control agent of introduced conical snails is discussed.