Interspecific larval competition between two egg parasitoids on the refrigerated host eggs of Riptortus clavatus (Hemiptera: Alydidae)

In a previous study the refrigerated eggs of Riptortus clavatus Thunberg (Heteroptera: Alydidae) could be supplemented in the soybean field to enhance the parasitism. As a part of studies to evaluate the refrigeration of host eggs for the parasitism, host acceptance behavior and interspecific larval competition between the two parasitoids, Gryon japonicum Ashmead (Hymenoptera: Scelionidae) and Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), was compared between the multiparasitized fresh and refrigerated eggs. O. nezarae showed complete host acceptance behavior on refrigerated host eggs that were pre-parasitized by G. japonicum. And adult emergence of O. nezarae was 43 and 74% for the interval of 1 hour and 4 days between the first and second oviposition, respectively, and those were not different from fresh eggs. In G. japonicum, refrigeration did not change host acceptance behavior, but the adult emergence was reduced from 80 to 37% on the refrigerated eggs that were pre-parasitized by O. nezarae in the interval of 1 hour. Sex ratio, development time, adult longevity, and adult size of the emerged parasitoids from the refrigerated host eggs were also presented. In conclusion, the refrigeration of host eggs did not affect host acceptance behavior on pre-parasitized eggs or larval competition between G. japonicum and O. nezarae, thus may not interrupt interaction between the parasitoid populations.

Key words: Stink bug; Host discrimination; Soybean; Egg parasitoid, Inoculative release