Effects of prey species and its density on larval performance of two species of hoverfly larvae, Episyrphus balteatus de Geer and Eupeodes corollae Fabricius (Diptera: Syrphidae)

Functional response and effects of prey species, Acyrfosiphon pisum (Harris) and Aphis craccivora Koch, and its density on larval performance such as survival rate and development time in addition to adult weight gain of the two predatory hoverflies, Episyrphus balteatus de Geer and Eupeodes corollae Fabricius, were examined in the laboratory. Our study revealed that prey density positively influences larval performance and the adult weight of the two hoverfly species. However, the effects of prey species on survival rate and development time differed: A. pisum was better food for E. balteatus, while the larval performance of E. corollae was enhanced by A. craccivora. In addition, the effect of prey density differed with development stage, since voracity increased with larval development. Both hoverfly species tended to eat a larger number of preys with lower quality, which in turn resulted in lower performance. The functional response differed between species involved and among development stages. During the third-instar stage, both species showed linear relationships as a functional response, while Holling's Type II response was observed during the young instar phase. E. balteatus tended to have linear relationships than E. corollae, and this would be caused by the larger size of E. balteatus, which in turn consumed more aphids than did E. corollae. This study suggests that the differences in the effects of prey species and its density on the larval performance of the two hoverflies, are attributable to the differences in the range of food habit and body size.