Gregarious development alters host utilization by the egg parasitoid Ooencyrtus fecundus (Hymenoptera: Encyrtidae)

Ooencyrtus fecundus Ferriere and Voegele (Hymenoptera: Encyrtidae) is a gregarious egg parasitoid of sunn pest Eurygaster integriceps Puton. Superparasitism enables a female to produce multiple progeny per host and thus reduces the time spent searching for hosts, but results in progressively smaller progeny as more individuals compete for limited resources within hosts. In this study, we tested whether gregarious development would affect the functional response of O. fecundus reared under laboratory condition (۲۶ ± ۲ ºC, ۵۰ ± ۱۰% RH and ۱۶: ۸ L: D h). Various host densities (۱, ۲, ۴, ۸, ۱۶ and ۳۲ eggs) were offered to females that had developed either as single, or as twins, triplets or quadruplets within host eggs. To resolve the functional responses of these females, a total exposure time of five hours was chosen, based on direct observations of handling time and the maximum daily number of host attacks/female. Functional response of the parasitoid was type III in singleton and twin parents, and type II in triplet and quadruplet ones. However, host mortality rate was ۱۰۰% in host densities ≤ ۸, suggesting density independence at lower densities as expected from a type I functional response. In such circumstances, handling time is expected to be zero, but was observed to be ۱۱.۴ to ۱۴.۳ minutes in different treatments. These results suggest that when enough time was available to find and handle all hosts, a type II functional response resembles Type I one. Searching efficiency increased and handling time decreased with body size of the parasitoid of four categories.

Keywords:

Hymenoptera , Encyrtidae , Eurygaster integriceps , searching ability , functional response