Comparative studies on the effect of temperature on lifetables of Rastrococcus invadens Williams (Homoptera :Pseudococcidae) and Gyranusoidea tebygi Noyes(Hymenoptera: Encrytidae)

Laboratory studies of Rastrococcus invadens (host insect) and Gyranusoidea tebygi (parasitoid) were carried out at five constant temperatures of 20, 25, 30, 33, and 35°C. Mango plant, Mangifera indica, was used as the host plant for R. invadens. A cohort of 20 larvipositing females was used at each temperature for both R. invadens and G. tebygi. The number of offsprings produced by each female and mortality within the cohort were recorded daily until all the members of the cohort had died. From these, fecundity and survival rate were calculated and used to construct the life tables of the two insects. The developmental period for R. invadens and G. tebygi increased with decrease in temperature from 20 to 33°C. At 35°C, the development of the male mealybugs was prevented beyond second instar, and females beyond first instar. The lower developmental temperatures for male and female R. invadens were 18.0 and 18.7°C, respectively, while those for G. tebygi were 8.5 and 9.8°C, respectively. Longevity and reproductive periods were inversely related to temperature for both insects. The optimum temperature for both insects was 30°C. This was the temperature at which intrinsic rate of increase, total progeny, and net reproductive rate attained maximum values for R. invadens and G. tebygi. A comparison of the host-parasite relationship of R. invadens and G. tebygi showed that theparasitoid G. tebygi had a superior net reproductive rate, RO, at higher temperature. At temperatures between 20 and 33°C, G. tebygi had a higher intrinsic rate of increase than its host, R. invadens. It issuggested that G. tebygi can persist and increaseinnumber over its host, and should be able to effectively control R. invadens at all the temperatures studied.