The Impact of Food Resources on Fitness of Episyrphus Balteatus

Abstract

Syrphids effectiveness as predators of aphids depends on the supply and quality of pollen and nectar. Pollen is required for reproduction and nectar for survival. Most investigations have focused on the interaction between prey and the predator while overlooking the importance of food foraging and supply during the different physiological phases. It is important to know how pollen and nectar supply affects the overall fitness of hoverflies. We investigated the impact of resource availability on the fitness of E. balteatus. Individual mated female syrphids were released in net cages with rape plant infested with Brevicoryne brassicae. Pollen and sugar supply was manipulated to simulate limitation in food resources. As a control, pollen and sugar were provided throughout the lifespan while the treatments included: pollen only, sugar only, withdraw of pollen during pre-oviposition and oviposition period. Oviposited eggs were counted daily and foraging patterns recorded with a video observation system. Feeding on pollen and sugar throughoutresulted in a 2 fold the number of eggs compared to different shortage treatments. Lack of pollen during pre-oviposition and feeding on sugar only lead to a complete lack of egg laying. The highest longevity occurred if pollen and sugar were available throughout being twice as long as if feeding on sugar only.Feeding on pollen alone resulted in same longevity as when feeding pollen and sugar throughout. Syrphids contacted the food patch containing pollen quite often and for longer durations during the pre-oviposition period. The number of visits and durations then decreased during oviposition period.  These results demonstrate that pollen availability is not only essential for oviposition but also enhanced survival.Consequently, lack of pollen sources during pre-oviposition has a negative impact on egg output and longevity.