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A major pest of Atlantic forests is the spruce budworm caterpillar which outbreaks every 35 years and causes large scale tree mortality. Historically, budworm management has largely ignored other species in the food web. Broadening the focus could reduce budworm outbreaks while balancing the multiple demands on our forests. However, the food web surrounding budworm including other caterpillar species that are attacked by budworm parasitoids has been relatively undersampled and under-researched. Therefore, we tested two hypotheses: the alternating hardwood-softwood parasitoids hypothesis where parasitoids attack other caterpillars on hardwoods when budworm are rare and attack budworm on balsam fir or other softwoods when budworm are plentiful, and the mixed stands natural enemies hypothesis where stands with a mixture of softwood and hardwood trees harbour greater abundances and diversity of budworm parasitoids. We tested these hypotheses using stable isotope analysis of budworm parasitoids and through community analyses of parasitoids sampled along a hardwood gradient. We found indications that parasitoids do attack caterpillars on hardwoods and budworm on balsam fir, but found mixed results for the natural enemies hypothesis. Our study highlights the importance for budworm management of understanding the dynamics of the food web surrounding budworm.

Environmental stress from abiotic conditions imposes physiological limits on communities. Stressful conditions can act as environmental filters on the individuals present in an assemblage or taxa available to colonize a given habitat. This can reduce a community’s diversity and make its composition more phylogenetically clustered. I tested this prediction using rove beetles (Staphylinidae, Coleoptera) collected across an elevation gradient in northwestern Costa Rica. Using DNA barcodes and phylogenetic estimates of community structure, I found high species turnover across elevation, and that staphylinid diversity (measured both through barcodes and phylogenetically) increased linearly with elevation. This diversity was negatively related to surface area and temperature, and positively with precipitation. I suggest that historical biogeography, rather than contemporary environmental stress alone, has produced these diversity patterns.