Temperature-dependent parasitism model of Trissolcus grandis Thompson (Hymenoptera: Scelionidae)

Abstract. Trissolcus grandis Thompson (Hymenoptera: Scelionidae), a native Sunn pest egg parasitoid in Iran, has the potential as a biological control agent for sunn pest, Eurygaster integriceps Puton (Het.: Scutelleridae). However, its ecological characteristics have remained unclear. Thus, this study aimed to develop a parasitism model of T. grandis with sunn pest egg as host. In order to obtain the data for the model, the longevity, survivorship and parasitism capacity of the adult female T. grandis were examined at nine constant temperatures (15, 17.5, 20, 25, 27.5, 30, 32.5, 35, and 37.5±0.5 °C), relative humidity 65 ± 5 % RH, and a photoperiod of 16:8 (L:D) h. Longevity (mean±SE) decreased as temperature increased and was the longest at 15°C (73.18±3.86 days) and the shortest at 35°C (18.98±0.48 days). A modified model of Sharp-DeMichele well described adult developmental rate (1/mean longevity) in the range of studied temperatures (r2 = 0.994) and was used to calculate the physiological age. The mean total host eggs parasitized/female (mean±SE) was greatest at 17.5°C (275.84 ± 3.21 host eggs) and lowest at 15°C (25.06 ± 3.221 host eggs). The temperature-dependent total parasitism, the age-specific cumulative parasitism rate, and the age-specific survival rate were best described by an extreme value function (r2 = 0.934), the two-parameter Weibull function (r2 = 0.967), and a sigmoid function (r2 = 0.979), respectively. I anticipate that the fitted models and parameters may be useful in developing a population model for T. grandis and lead to a better understanding of its parasitism strategy.