The impacts of extreme and fluctuating temperatures on trait-mediated indirect aphid–parasitoid interactions


Jordan A. Bannerman, Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada. E-mail:


1. Global climate change models predict an increase in the frequency and magnitude of extreme temperature events. These temperature events, heatwaves for example, will impact a wide range of physiological and behavioural processes, particularly in ectotherms, and may therefore influence interactions between species.

2. Anti-predator responses may be more costly under more severe temperature regimes and therefore trait-mediated disturbance could lead to high mortality or reduced reproduction under extreme and fluctuating temperature regimes.

3. We examined the impacts of extreme and fluctuating temperatures on trait-mediated indirect interactions in an aphid–parasitoid community.

4. In treatments that isolated the effects of trait-mediated disturbance from the effects of foraging parasitoids we found that an increase in both the amplitude and frequency of peak temperatures reduced aphid numbers and provided evidence that the cost of trait-mediated disturbance could increase under frequent periods of high temperature. Aphid dispersal also increased with more frequent periods of high temperature.

5. In treatments where female wasps were allowed to freely forage (direct + trait-mediated effects), there was no evidence that extreme and fluctuating temperatures influenced the wasp's foraging ability. Exposure to extreme fluctuating temperatures did not influence the offspring production of exposed wasps or the position of the mummies within the plots.