Species’ phenologies are changing at differing rates across taxonomic levels in response to climatic changes, thereby potentially affecting the temporal overlap of interacting species. Shifts in the phenological synchronization between insect herbivores and their host plants could have consequences for individual survival, fitness and population viability for the insect herbivore. Here, we experimentally manipulated spring temperature around families of the western tent caterpillar (Malacosoma pluviale californicum) and buds of its host plant, red alder (Alnus rubra) in the field. The primary objectives of this study were to test whether the phenologies of the two species changed in the same direction and magnitude in response to warming and to test the effects of warming and any shift in synchronization on insect performance. We attached egg masses to the branches of alder trees at two locations on the University of British Columbia’s (Canada) campus. Aerated clear polyethylene bags were attached around the egg masses on the tips of the branches and acted as our ‘greenhouses’.
Results/Conclusions
While warming led to significant shifts in phenological synchronization, these shifts did not translate into significant differences in insect development time or final weight between treatments. Warming advanced the timing of larval emergence but not budbreak leading to a range in mismatch from -20 to +10 days, with larvae emerging before and after the appearance of leaves. Development was fastest and final weight was greatest when larvae emerged just after leaf emergence. Our results suggest that warmer springs in the future could shift the timing of the tent caterpillar life cycle, with both larvae emerging and adults ovipositing earlier in the season, without any consequences for fecundity. Shifts in phenological synchronization could potentially modify the tent caterpillar’s population dynamics and lead to outbreaks in areas that are historically outbreak-free.