Effects of heat shock: before, during, and after a parasitoid attack on pea aphid

In host-parasitoid systems altered abiotic factors can affect both species directly, while also affecting how they interact with each other. If the abiotic effect and species interaction have discrete events as opposed to be continuously occurring, it may be the timing of an abiotic change compared to the species interactions may also be important.

This study investigates the role of timing in relation to how heat shocks (short-term large increases in temperature) affect a host-parasitoid system. Using a controlled environment, we tested how the timing of a heat shock (increase temperature from 26C to 38C for 4 hours) affects parasitism of a parasitoid wasp (Aphidius ervi) attacking its host, the pea aphid (Acyrthosiphon pisum). We tested three time treatments: 1) heat shock before the wasp lays eggs, 2) heat shock while the wasp is foraging, and 3) heat shock after the wasp has attacked hosts. Our response variable is the successful production of wasps in the pupal stage (mummies).

Our results showed that the heat shock had the largest effect while wasps were actively foraging; a heat shock during this time resulted in very few new wasps. In the other treatments mummy production was only slightly lower than controls without heat shocks.

These results show the potential importance of timing when considering the effects of heat shocks and climate change on host-parasitoid interactions. This may add another factor that should be taken into account and enhance efforts to predict the effects of abiotic factors through time.