Responses of adult Hydrellia lagarosiphon to a revised diet: implications for life cycle studies and laboratory culturing techniques

Preservation of an insect culture under laboratory conditions is essential for its study. Numerous diets have been developed for entomophagous insects undergoing screening as biological control agents in attempts to improve the nutritional quality of food provided in laboratory settings. However, less emphasis has been given to developing a more effective laboratory diet for phytophagous insects with life stages not dependant on the target species. The larvae of Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) mine the leaves of Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae). This species is currently under consideration as a biological control agent of this aquatic invasive. Rearing techniques for the adult stage of other Hydrellia species have been developed but current diets are not ideal as they result in relatively low reproduction rates. We compared alternative nutritional regimes and quantified their impact on life history attributes of H. lagarosiphon. The diets included the previously-developed yeast-sugar diet, a newly-developed insect-derived diet and a diet that combined the two. Total fecundity was significantly higher for females on an insect-derived diet compared with the traditional carbohydrate diet and the net reproductive rate (Ro) was also higher. Population doubling time (Td) was lower, decreasing by 30% compared to the traditional laboratory diet developed for Hydrellia species. Adult females fed the combination diet, including both insect and non-insect foods, laid 30% fewer eggs than those reared on an insect diet alone. Consequently, insect derived nutritional regimes could improve culturing techniques significantly and if permission to release the agent is granted, this diet may benefit mass rearing efforts potentially saving time and reducing associated costs.