Survival and development of diamondback moth and its parasitoid Diadegma insulare under various short-term high extreme temperature regimes

One of the focal features of global climate change is the increase in magnitude and frequency of extreme temperatures.  As ectothermic organisms, insects are highly vulnerable to sudden rises in  temperature.  Laboratory studies were conducted to determine the survival and development of diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae) and its larval parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae) at various short term (2-hour) high temperature regimes.  The tolerance to thermal stress by DBM adults was found to be higher than that of D. insulare.  Survival of D. insulare adults was significantly reduced after a 2-hour exposure at a pick of 38°C with slow ramping, a sudden amplitude of 38°C, a pick of 40°C with slow ramping, a sudden 40°C, in all cases followed by one hour recovery time compared with 25°C constant.  On the other hand, survival of DBM adults was not affected by the tested extreme temperature profiles with the exception at sudden 40°C, where significantly lower proportions of DBM adults survived compared with survival at the control temperature.  There was no effect of 2-hour heat stress of up to 40°C on either parasitized or non-parasitized DBM larvae.  Mortality of D. insulare pupae was highest when they were exposed to sudden 40°C.  Larval and pupal developmental times of D. insulare were affected by temperature stresses.  Shorter larval developmental times were required when larvae were exposed to sudden 40°C three times in a week, but pupae took a longer time to adult eclosion under these conditions.  In contrast, developmental times of DBM were not affected by such extreme temperatures.  From these results we conclude that the parasitoid D. insulare is more sensitive to high stress temperatures compared to its host DBM, and the population expansion of D. insulare may be limited by climate change.

Keywords: Plutella xylostella, Diadegma insulare, extreme high temperature, development, interactions.