Contrasting effects of climate warming on hosts and parasitoids: insights from Rocky Mountain aspen leaf miners and their parasitoids.

Because temperature has pervasive effects on biological rates, climate warming may alter the outcomes of interactions between insect hosts and their parasitoids, which, for many host species, constitute the single largest source of mortality. Despite growing interest in parasitoid-host responses to climate change, there are few empirical tests of thermal tolerance differences between non-model lepidopteran hosts and their parasitoids and almost none from mountain ecosystems where warming is occurring more rapidly. We examined the thermal ecology of a host-parasitoid interaction in the Rocky Mountains using wild populations of the aspen leaf miner (Phyllocnistis populiella) and a set of previously unknown eulophid parasitoids that attack them. Host and parasitoid development rates were differentially sensitive to temperature. In addition, upper thermal limits of adult parasitoids were lower than those of host caterpillars, and in choice experiments, parasitoids reared at different temperatures showed no plasticity in preferred temperatures. However, when coupled to simulations of leaf microclimates in aspen canopies, these observations suggest, contrary to expectations, that climate warming may potentially benefit parasitoids.