Effect of the host embryogenesis on efficiency of Trissolcus vassilievi

Egg parasitoids are the most important natural enemies of sunn pest, Eurygaster integriceps (Hem.: Scutelleridae). Knowledge on ecological requirements of natural enemies has essential role in success of applied biological control programs. One issue in this context is the effect of host embryogenesis upon performance of those wasps that developed within host eggs. This issue was studied by exposing new laid eggs (control), as well as one, two, three, four and five day old eggs to Trissolcus vassilievi. Two parasitoid populations were used in this study obtained from Tabriz and Varamin. Five day old eggs were rejected by the parasitoid except in six cases, all of which were allocated to male progeny. No significant difference was observed in the number of parasitized eggs between the two populations, but difference among host ages was significant. There was no significant difference in parasitism rate of wasps in ≤ 2 day old eggs, nevertheless significant decrease was observed in three and four day old eggs. Adult emergence rate, sex ratio (female%) and fecundity were influenced by host age. Fecundity significantly decreased by increasing host age over one day and a maximum 50% difference was recorded between control and four day old eggs. Those wasps that were developed in developed stages of host eggs were capable to partially compensate their initial lag in first week of the reproductive life. As a conclusion, host embryogenesis has little impact on the parasitoid fitness before two days, while more effects were observed in older eggs.