Effects of temperature and prey availability on the malacophagous larval stage of Sepedon spinipes (Scopoli) (Diptera: Sciomyzidae): potential biocontrol for gastropod vectors of parasitic diseases.

摘要

Sciomyzids (Diptera) are unique amongst insects in that they are almost exclusively malacophagous and hence have potential to be used as biological control agents of gastropod vectors of parasitic diseases. However, information on optimum growth conditions for mass rearing is lacking for most species. In this study, we used two feeding regimes (limited and excess snails) at constant temperatures (14, 17, 20, 23 and 26 degrees C) to determine the effects of temperature and food availability on duration of and predation during the larval stage of Sepedon spinipes with the aim of identifying optimum conditions for mass culturing. The data suggest that rearing the larvae at 23 degrees C with excess snail prey is optimal. Median larval duration was significantly shorter (albeit circa 1 day) under excess rather than limited feeding, suggesting that some type of larval compensatory mechanism operates when prey is limiting. We propose that larvae of S. spinipes respond facultatively to prey availability and may feed saprophagously when food is in short supply. The longevity of fed (one snail) and unfed neonates was also assessed outdoors and at 14-26 degrees C to determine the optimal physiological state of pre-release larvae. Median survival period of unfed neonates tended to decrease with increasing temperature but survival doubled at 20, 23 and 26 degrees C when one snail was provided. Since first instars can only successfully attack a narrow prey size range, neonates of S. spinipes should be fed one snail prior to release as it will increase the time larvae have to locate such prey.