The Importance of Short and Long Time Effects of High Temperature on Insects

Temperature has the potential to alter every aspect of an organism?s biology. This is especially true when we focus on small ectotherms such as insects. Understanding the effects of temperature on insects is particularly important given that climate change scenarios predict changes in temperature across the globe. In Chapter 1 we explored the effects of heat shocks on a discrete host-parasitoid interaction, specifically asking what happens if the heat shock happened before, during or after the interaction. We found that heat shocks had a stronger negative effect when they occurred while the wasp was actively foraging. In a follow-up behavioral experiment, we observed that this result is likely caused by the heat shock quickly rendering the majority of wasps inactive. In Chapter 2 we tested how variation in temperature affects pea aphid population size and how the effect changes with average temperature. We compared the population size of pea aphids under constant and fluctuating temperature profiles across a cool temperature range (20C and 16C/24C) and a warm temperature range (28C and 24C/32C). We saw that in the cooler range, pea aphids in the constant and fluctuating temperature treatments had the same population size. However, the same was not true for the warmer temperatures. In that case, fluctuating temperature profiles produced smaller populations compared to the constant temperatures. In Chapter 3 we focused on the possible indirect effects of temperature on pea aphids mediated by the aphids? host plants. We performed five experiments where we manipulated the exposure temperature (16C, 24C, and 32C) for plants and aphids. While temperature had strong direct effects on aphids and also affected plant size, temperature had little to no indirect effects on pea aphid fecundity. While the idea of temperature change can seem straightforward, temperature effects on insects are not straightforward. Timing and variation of temperature change are important. Indirect effects though direct effects on hosts also are important. My work shows a number of approaches for investigating these different temperature effects to better understand what might happen to insects when climate changes.National Science Foundation (NSF). Grant Number 124103