The impact of food resources on predatory hoverfly Episyrphus balteatus fitness

The foraging behaviour of aphidophagous predators plays a key role in conservation biological control. However, for understanding the foraging behavior of females, most investigations have focused on the interaction between prey and host while overlooking the importance of food foraging and supply during oviposition. In Europe Episyrphus balteatus is one of the most important aphid specific predators. It depends on pollen and nectar for reproduction and longevity. However, in agroecosystem the spatial and temporal pattern of crops change consequently food resources are fluctuating, which may limit syrphids predatory performance. Thus, its important to know how they react to changing food resources. We studied the impact of resource availability on the fitness of E. balteatus. Individual mated female syrphids were released in net cages with a rape plant infested with Brevicoryne brassicae while pollen and sugar supply was manipulated to simulate limitation in food resources. As a control, pollen and sugar were provided unrestricted throughout the lifespan while the treatments included: pollen only, sugar only, withdraw of pollen from 1st to 11th day and 11th to 25th day. Deposited eggs were counted daily and foraging patterns recorded with a video observation system. Results show that syrphids contacted the food patch quite often and for longer durations before day 11. From day 11 onwards egg laying started, but food visiting frequency decreased. When syrphids could feed on pollen and sugar throughout they laid 2 fold egg numbers compared to different shortage treatments. The highest longevity occurred if pollen and sugar were available throughout being twice as long as if feeding on sugar only. These results demonstrate that pollen availability is not only essential for oviposition but also survival. Consequently, lack of pollen sources during pre-oviposition has a negative impact on egg output and longevity, both key factors for predatory efficacy of syrphids.