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

Biological attributes of parasitoids are influenced by physical factors such as temperature and humidity. Our previous studies found that Gryon japonicum (Ashmead) and Ooencyrtus nezarae Ishii, egg parasitoids of Riptortus pedestris (Fabricius), have different occurrence pattern. The current study was carried out in laboratory to understand the interactive effect of temperature and relative humidity on the occurrence pattern of the parasitoids. Twenty 4-5 day old mated females G. japonicum and O. nezarae were released individually on eggs of R. pedestris at combinations of three temperatures (20, 25, and 30°C) and three relative humidities (high, medium and low) for five consecutive days. Temperature had significant effect on all the biological attributes of both parasitoids. The highest number of eggs was parasitized at 30°C and low RH by both the parasitoids. Significant interaction of species and temperature was found in parasitism. Relative increment in parasitism by G. japonicum was higher than O. nezarae at 30°C whereas at 20°C the increment was not significant between the species. Both the temperature and RH may not have affected host quality assessment by the parasitoids as no significance in sex ratio of the progeny was detected. Temperature had significant effect on the development time of both species. Effect of RH on the development time of O. nezarae was also not found while development time of G. japonicum became longer in low RH. The relationship between occurrence pattern and response to environment conditions of the parasitoids was discussed.