Effects of thermal stress on the biology, immune system and antioxidant enzymes of Galleria mellonella and Achroia grisella (Lepidoptera: Pyralidae), and the ectoparasitoid Bracon hebetor (Hymenoptera: Braconidae)

Temperature differences due to climate change are an effective stress factor for ectothermic insects. The thesis investigated the effects of thermal stress, applied as constant and variable heat shock, on the biology, immune system, antioxidant and phenoloxidase enzymes of the wax moths, Galleria mellonella and Achroia grisella, and the biology of the ectoparasitoid, Bracon hebetor, in the host-parasitoid relationship. G. mellonella and A. grisella exposed to constant heat shock at nine different temperatures were found to die at 40-50 °C and 34-50 °C, respectively. The mortality results showed that G. mellonella was more resistant to thermal stress than A. grisella. The optimum temperature range under constant heat shock was 30-38 °C for G. mellonella growth and 30-34 °C for A. grisella. As the exposure temperatures and application time increased, the mortality rates of last instars increased, and their life span shortened. In the immunity and enzyme activity experiments examining the time-dependent effect of temperature, total hemocyte count, mitotic index, strong-encapsulation, malondialdehyde, and phenoloxidase levels of both moths increased noticeably, especially at 34 and 40 °C. Furthermore, superoxide dismutase activity in G. mellonella and catalase activity in A. grisella were also elevated. Thus, the first pre-adult emergence mortality under constant heat shock occurred at 40 °C for G. mellonella and at 34 °C for A. grisella indicating these temperatures were developmentally and physiologically critical. The most prominent effect of thermal stress on G. mellonella-B. hebetor relationship was at 36 °C; 95% of the average 24 eggs per female reached the adult stage and adult longevity was prolonged. However, host-parasitoid relationship may also be disrupted as the larval period of the host shortens with increasing temperature in both constant and variable heat shock. Our findings emphasize that global warming may affect insects in complex and unexpected ways.