The Life Table and Parasitism Rate of <i>Diadegma insulare</i> (Hymenoptera: Ichneumonidae) Reared on Larvae of <i>Plutella xylostella</i> (Lepidoptera: Plutellidae), with Special Reference to the Variable Sex Ratio of the Offspring and Comparison of Jackknife and Bootstrap Techniques

Abstract

Abstract The life table and parasitism rate of Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae), a larval parasitoid of the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae), were studied at 25 ± 1°C, 65 ± 10% RH, and a photoperiod of 16:8 (L: D) h. The data were analyzed based on the age-stage, two-sex life table theory. Because the sex ratio of offspring varies with the age of the female parent, we used only female offspring to calculate the intrinsic rate of increase (r), finite rate of increase (λ), net reproductive rate (R0), and mean generation time (T) by using the jackknife technique, the values of which were 0.18407 d-1, 1.2021 d-1, 17.94 offspring, and 15.69 d, respectively. We also calculated these parameters by using bootstrap technique. They were not significantly different from those estimated by using the jackknife technique. We included both male and female offspring in the calculation of the parasitism rate. The net parasitism rate (C0) was 42.63 aphids. Moreover, population projection showed differences between simulated population based on total offspring and female offspring. Because both the offspring sex ratio and the parasitism rate depend on female age, it is necessary to use the age-stage, two-sex life table for a correct analysis. Frequency of the net reproductive rate estimated by using bootstrap technique fit normal distribution well, whereas frequency data estimated by using jackknife technique failed the normality test. We suggest that the jackknife technique should not be used for the estimation of population parameters.