Thermal effects on the egg stage of four sciomyzids with reference to phenology and biocontrol potential

With the global economic cost of liver fluke estimated at US$2000 million annually, alternative sustainable control methods need to be considered. One such option is biological control using malacophagous sciomyzids (Dipt.,). The effect of a range of temperatures (14, 17, 20, 23 and 26°C) on the duration of the egg stage of Sepedon spinipes spinipes (Scopoli), Pherbina coryleti (Scopoli), Tetanocera ferruginea Fallén and Psacadina verbekei Rozkošný was assessed using thermostatically controlled waterbaths (16 h light : 8 h dark). In general, for all species, the mean and median egg incubation periods decreased as the temperature increased. Optimum growth temperatures for mass rearing purposes are highlighted for each species. The cryopreservation (-20°C) of newly oviposited eggs for the purpose of long-term storage was also assessed and possible reasons for the variability in the duration of the egg stage between the species in relation to their phenologies are discussed.