Multiple effects of temperature, photoperiod and food quality on the performance of a pine sawfly

Many entomologists strive to understand what consequences climate change will have on insect performance. Such understanding is important, not least, when trying to predict the future impact of pest insects. In this study, it was reported how the multiple effects of temperature, photoperiod, and food quality affected the survival, development, and the final weight of the European pine sawfly (Neodiprion sertifer Geoffr.), an herbivorous outbreak species in boreal pine (Pinus spp.) forests. Sawfly larvae were reared in two different temperatures (15 and 20 degrees C) and under two different light regimes (20 and 18 h light). The larvae were fed pine needles either low or high in diterpene content. A 5 degrees C higher temperature did not affect the survival of the larvae, but reduced the development time by 3741%. The final weight was reduced by 22% in the warmer temperature, but only in combination with a short day length. A high content of diterpenes in the needles reduced the susceptibility to the virus by 31%, but did not otherwise affect the performance of the larvae. This study shows that the larval development could be shortened in a warmer climate and thereby decreasing the risk of predation. This per se may increase the risk for insect outbreaks, but the interactive effects of warmer temperatures with other abiotic and biotic factors such as day length and food quality (indicated in this study), and potential better performance of natural enemies and pathogens, illustrate the possibility for complex outcomes in a climate change perspective.