A significant area of current research is the impact of warming on food webs. However, few interactions per web are typically studied, which limits generalization and precludes evaluation of impact on consumer diet breadth and redundancy of top-down control. Here we show that experimental warming strongly decreased the success of parasitoid development across 28 Drosophila-parasitoid interactions from a tropical rainforest food web. Parasitoids responded consistently despite deep evolutionary divergence. Moreover, warming strongly narrowed the diversity of hosts that the parasitoids could utilize. Host developmental success was much less affected. In contrast, experimental cooling had only a mild effect on parasitoids and hosts. Our findings suggest that the top-down control exerted by parasitoids is likely to weaken due to warming. The range of hosts that parasitoids can use will become more limited, potentially threatening the sustainability of parasitoid populations and changing the balance between trophic levels.

Climate change is altering the relative timing of species interactions by shifting when species appear in a community and by accelerating developmental rates. However, phenological shifts may be mediated through community contexts, such as intraspecific competition and alternative resource species, which can prolong the otherwise shortened windows of availability. Using a combination of laboratory experiments and dynamic simulations, we quantified how the effects of phenological shifts in Drosophila-parasitoid interactions differed with concurrent changes in temperature, intraspecific competition, and the presence of alternative host species. We found that community context, particularly the presence of alternative host species, supported interaction persistence across a wider range of phenological shifts than pairwise interactions. Parasitism rates declined under warming, which limited the ability of community contexts to manage mismatched interactions. These results demonstrate that ongoing declines in insect diversity may exacerbate the effects of phenological shifts in ecological communities under future global warming temperatures.