Quality assessment of Riptortus pedestris (Hemiptera: Alydidae) eggs cold-stored at different temperature and relative humidity regime

Abstract

Supplementation of host resource can be more economical method for the biological control of insect pest compared to direct release of adult parasitoids. Periodical release of non-viable cold-stored eggs of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) has been found to enhance parasitism of this pest in soybean fields. To find the optimum environmental conditions for cold storage of these host eggs, we evaluated nine different combinations of temperature (2, 6, and 10°C) and relative humidity (high 90–95%, medium 70–75%, and low 30–35%). After 30d of cold-storage, eggs were weighed and held at 26.6°C and 75% relative humidity for 8d before testing. To test the eggs’ suitability as hosts following cold storage, females of Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) were released individually onto batches of eggs, and parasitization rates and the development, emergence, sex ratio, adult longevity, and size of parasitoid progeny were examined. Eggs stored at high relative humidity showed less weight loss than those stored at low relative humidity. The number of eggs parasitized was highest (5.9/15) on eggs stored at 6°C and high relative humidity. Developmental times and adult emergence were optimal on host eggs stored at 2°C and high relative humidity. A significantly lower proportion of eggs produced male parasitoids when eggs were stored at 2 or 6°C. Adult longevity was not affected by egg storage conditions, but adult size of progeny decreased in eggs stored at 10°C. In conclusion, eggs of R. pedestris stored below 6°C and with a high relative humidity maintained the best quality for parasitization by O. nezarae.