Dietary behaviour of Sepedon (Parasepedon) ruficeps and Sepedon (Sepedomyia) nasuta (Diptera: Sciomyzidae) and the distribution of their snail prey in Benin (West Africa)

Abstract

Sciomyzidae (Diptera) larvae live as predators and/or parasitoids of snails. They have potential economic importance as biological control agents against gastropods that are vectors of parasitic diseases. In the present study, the use of Sepedon larvae in schistosomiasis control was evaluated by studying the influence of environmental parameters on snail distribution and the impact of prey duration and availability on the survival of Sepedon (P) ruficeps and Sepedon (S) nasuta larvae. The predatory capacity of the larvae was also evaluated by determining the influence of snail consumption on the longevity of the different larval stages. The study was carried out from August 2014 to July 2015 in three locations. A total of 3,448 specimens were collected, showing high diversity and abundance, with a significant difference (df = 2, c2 = 582.97; P < 0.05) among locations. The snail distribution was influenced by environmental variables (total hardness, electric conductivity, Ca 2+ , O 2 , Mg 2+ ). The predator/prey interaction between Sciomyzidae species and snails was examined. No difference in the mean duration of immature stages and a mean predation capacity of the two flies ( P = 0.50) vs. ( P = 0.31) respectively for Sepedon (P) ruficeps and Sepedon (S) nasuta . The consumption varied considerably depending on the ratio of predator (larva) to prey (snail) size and the larval stage. Both these Sciomyzidae consume healthy or parasitized snails by schistosome larvae indiscriminately. They appear to be equivalent agents for biological control of freshwater snails which are intermediate hosts, involved in the transmission of human schistosomiasis or veterinary distomatosis.