Insect life history traits exhibit remarkable phenotypic plasticity in response to environmental conditions. This plasticity allows individuals to synchronize their life cycle with seasonal change and cope with unfavorable conditions. We followed an experimental approach to compare the effects of temperature and host quality on the performance of herbivores growing under a long, constant photoperiod (typical of mid-summer conditions) vs a decreasing photoperiod (simulating the end of the growing season).
Results/Conclusions
Exposure to a decreasing photoperiod advanced pupation time of larvae growing at low temperatures and delayed it on larvae growing at high temperatures. This resulted in a drastic reversal of the temperature-size rule (larger size at lower temperatures), even for individuals feeding on a high-quality host. While decreasing photoperiod was the main cue triggering diapause induction, feeding on a low-quality host at low temperatures also induced diapause in larvae growing at a constant photoperiod. Conversely, exposure to high temperatures while feeding on a high- quality host overruled the diapause-inducing effect of decreasing photoperiod in a fraction of studied individuals. These results indicate that moderate heatwaves at the end of the growing season may enhance winter survival, while intense heatwaves may also result in interrupted generations.