| Climate change is disrupting species interactions by altering the timing of phenological events such as budburst and flowering for plants and hatching for insects. Here I present a study of a tri-trophic system including eastern tent caterpillars (Malacosoma americanum); black cherry (Prunus serotina), their main oviposition host; and chalcidoid wasps, a common source of mortality for caterpillar eggs. I combined phenological and natural history observations with experimental manipulations to investigate M. americanum responses to altered temperature regimes and to assess their vulnerability to global climate change. Because this tri-trophic interaction occurs in a large portion of North America along a latitudinal gradient, I studied and compared the phenological responses of several communities from northern, central and southern localities within their home rage.;I assessed the effects of altered temperature regimes on the timing of caterpillar hatching, starvation endurance and parasitoid wasp emergence. The timing of caterpillar hatching and wasp emergence are important determinants of synchrony with food availability: foliage for the caterpillars and eggs for the wasps. The foliage of P. serotina is suitable for caterpillar consumption during a limited period, which extends from bud elongation, early in the year, to full leaf expansion, in the late spring. The length of this period differs among years according to ambient temperatures as shown in Chapter 1. Starvation endurance is an important trait because it allows for caterpillar survival when they hatch before foliage is available, and during cold periods when they are unable to perform metabolic reactions. We found that early starvation resulted in high caterpillar mortality, but those individuals that survived it did not exhibit long-term effects on pupal mass or development time. Overall, higher temperature regimes resulted in advanced phenology of both caterpillars and their parasitoids without important alterations in their relative timing. However, phenological responses differed among localities and caterpillar populations exhibited patterns consistent with local adaptation, as starvation endurance was maximized under the most familiar conditions and caterpillars under unfamiliar temperature regimes significantly delayed their hatching time. Plasticity in phenological responses was different among caterpillar populations and individuals from central localities exhibited the largest responses to artificial warming. We did not find evidence suggesting parasitoid attack patterns would change under warmer conditions.;Parasitism was a consistent source of mortality for M. americanum eggs, as most of the egg masses we collected yielded parasitoids, however, attack rates were relatively low. Parasitoid species richness and community composition varied among localities, but not according to latitude, longitude or host density. Wasp phenological patterns differed among genera and latitudes. The period between caterpillar hatching and wasp emergence was shorter in northern communities, consistent with a shorter growing season at higher latitudes. We found a hyperparasitoid species, which emerged earlier and had an emergence span four times longer than the primary parasitoids.;I conclude that warmer temperature regimes have the potential to trigger more frequent eastern tent caterpillar outbreaks by promoting increased early season survival, however this effect could be counteracted by late season asynchrony if plants develop faster than caterpillars. |
