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Evaluation of refrigerated eggs of Riptortus clavatus for the parasitization by Ooencyrtus nezarae
Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) is a gregarious egg parasitoid of Riptortus clavatus Thunberg (Hemiptera: Alydidae) and also attack three other stink bugs in soybean fields. In a previous study the refrigerated R. clavatus eggs were supplemented in soybean fields and found to enhance the parasitism by Gryon japonicum (Hymenoptera: Scelionidae), a sympatric solitary parasitoid of R. clavatus, but not by O. nezarae. Therefore, the R. clavatus eggs refrigerated for 0, 15, 30, 60 and 120 days were evaluated for the parasitization by O. nezarae in the laboratory. The number of parasitized host eggs, number of adult parasitoids emerged, immature mortality, sex ratio, development time, adult longevity, and size of the parasitoids were examined for the parasitoids exposed to or emerged from the refrigerated host eggs. All the attributes examined were not affected by the refrigeration of host eggs for up to 60 days. In addition, refrigeration did not change the reproduction capacity of the emerged adult parasitoids nor the biological attributes of their offsprings. In the evaluation of post-refrigeration period of the host eggs, O. nezarae parasitized the eggs successfully for the first 4 days after the refrigeration at 26.3ºC and 78.7% RH conditions. Since O. nezarae can parasitize the eggs of R. clavatus that were refrigerated up to 60 days, the underlying reason for the no-change in parasitism by O. nezarae in the field supplemented with refrigerated host eggs is in further investigation.
