Increasing temperatures and heatwave durations negatively affect the performance of a dietary generalist

Climate variability has increased in recent decades, and this trend is
predicted to continue. Globally, there is a rise in extreme temperatures,
such as heatwaves, which are strengthening in both intensity and
frequency. As ectotherms, insects are especially affected by temperature
variation. Insects are the most speciose group of animals and important
members of most terrestrial ecosystems, providing critical ecosystem
services. Most studies of global change have investigated only a
single stressor, yet insects rarely experience one stressor at a time. Two
stressors that co-occur are heatwaves and warming temperature regimes;
thus, it is important that we study their interaction and whether diet may
help mitigate negative effects from these stressors. We used a dietary
generalist herbivore, the moth fall webworm Hyphantria
cunea (Lepidoptera; hereafter, FW), and conducted a factorial
experiment to test the separate and interactive effects of temperature
warming, heatwave duration, and host plant on FW fitness. We found
significant interactions between temperature regime, heatwave duration,
and host plant. We also found that FW follow the temperature-size rule,
but only when reared on one of the host plants, thereby supporting
previous research that diet alters insect response to changes in
temperature regime. Our results show that FW suffer reduced
fitness when exposed to high temperatures and heatwaves, with more extreme
temperatures and longer heatwaves resulting in increased negative effects
on fitness. However, some of these negative effects may be attenuated by
host plant identity, which could play an important role in how generalist
herbivores respond to increasing extreme weather events as predicted by
global change.