Interactive influence of temperature and relative humidity on egg parasitoids of Riptortus pedestris (Hemiptera:...

Previous studies reported that of the two egg parasitoids of Riptortus pedestris (F.) (Hemiptera: Alydidae) found in Korea, Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) appears in soybean fields much earlier than Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae). To explain this phenomenon, we evaluated the interactive influence of temperature and relative humidity (RH) on the biological attributes of these parasitoids, including adult parasitoid longevity and survival. Temperature had significant effects on all the biological attributes examined for both parasitoids, while RH only affected rates of parasitism and adult emergence. Interaction between temperature and species, but not RH and species was found to affect significantly on parasitism. G. japonicum showed higher relative increment in parasitism than O. nezarae at temperatures higher than 25 degrees C. No significant differences in progeny sex ratio were detected for either species at any temperature x humidity combination. RH had no effect on the developmental time of O. nezarae but on the developmental time of G. japonicum, which was longer at low RH. Although the biological attributes of adult parasitoids of both species showed a wide range of adaptability, but it did not explain the patterns of occurrence of these species in the field. However, G. japonicum showed greater longevity than O. nezarae at all combinations of temperature and RH and this may partially explain the seasonal pattern of occurrence of adult parasitoids in the field previously observed.