Periodical release of non-viable refrigerated eggs of Riptortus pedestris (Fabricius) has been found to enhance field parasitism level in soybean fields. However, optimum refrigeration conditions required for the eggs in order to preserve its quality to ensure effective level of parasitism for a longer period has been rarely reported. We assessed optimum environment condition for refrigeration of the eggs using three different temperatures (2, 6, and 10℃) and relative humidities (RH) (high, medium and low). Eggs of R. pedestris were refrigerated at nine combinations of temperature and relative humidity for 30 consecutive days. Those eggs were taken out and after 8 days, mated female Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) were individually exposed to the eggs, and their development, emergence, and sex ratio were examined. Number of eggs parasitized was highest (5.9) on eggs stored at 6℃ and high RH. Significantly higher male proportion was recorded in the eggs stored at 10℃. However, RH had no effect on the sex ratio. For both male and female, development time was the least on host eggs stored at 2℃ and high RH. Adult emergence was recorded highest from the eggs stored at 2℃ followed by 6℃ and at high RH. In conclusion, eggs refrigerated below 6℃ at high RH condition maintained better quality of R. pedestris eggs for the parasitization by O. nezarae.

Gryon japonicum (Ashmead), an egg parasitoid of Riptortus clavatus (Thunberg) is an economically important pest of various crops. As a conservational biological control, non-viable refrigerated eggs of R. clavatus were released to enhance parasitism by the parasitoid in soybean field. Since fenitrothion is an insecticide broadly used against R. clavatus, we investigated the effect of fenitrothion on the parasitization of refrigerated host eggs by G. japonicum. The acute toxicity of fenitrothion was compared with seven pesticides by topical application, exposure to residue, and oral ingestion. Fenitrothion, spinosad, cyfluthrin, carbosulfan and thiamithoxam caused 100% mortality within 24 hours by topical application. Fenitrothion was also highly toxic to G. japonicum when ingested orally. In sublethal effects of fenitrothion on G. japonicum in refrigerated and fresh host eggs, adult emergence of G. japonicum decreased by 12% and 34%, respectively, compared to control when the fenitrothion was applied on 8th day after parasitization. Parasitism on refrigerated eggs after a day of fenitrothion spray was higher as compared to the fresh eggs. However, parasitism on both refrigerated and fresh eggs significantly reduced when the parasitoids were provided with the fenitrothion sprayed eggs after an hour. In conclusion, there is no negative effect of fenitrothion on the parasitization by G. japonicum.

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.