One of the most well-documented organismal responses to climate change is a change in phenology. Because insect herbivore populations are known to be strongly regulated by a diverse array of natural enemies (predators and parasitoids), it is imperative to understand how attack rates by these third trophic level members will be impacted by climate change. It is unclear whether members of different trophic levels will shift in concert or to the same degree; if not, ‘phenological mismatches’ are likely to result that could drastically impact community dynamics. We addressed the overarching question of how increasing mean temperature associated with climate change will affect the relationship between the agricultural pest Plutella xylostella and its dominant parasitoid Diadegma insulare. Caterpillars were reared in environmental chambers at three different fluctuating temperature regimes (ambient, warm +2oC, hot +4 oC) and exposed to mated female parasitoids to determine the effects of these treatments on caterpillar and parasitoid performance and phenology. Following exposure to adult parasitoids, caterpillars were reared individually until adult moth emergence, adult parasitoid emergence, or death.
Results/Conclusions
D. insulare developed significantly faster in the warm and hot treatments compared to the ambient treatment. Parasitoid development time was reduced by 21.43% in both the warm and hot treatments compared to the ambient treatment. P. xylostella also developed significantly faster in the warm and hot treatments compared to the ambient treatment. Caterpillar development time was reduced by 12.5% and 28.15% in the warm and hot treatments, respectively, compared to the ambient treatment. Significantly fewer host caterpillars were parasitized in the hot treatment compared to the ambient and warm treatments, as indicated by the number of parasitoid pupae obtained (P=.02). In addition, emergence of adult parasitoids from their puparia was reduced by 36% in the warm treatment compared to the ambient treatment, and 48% in the hot treatment compared to the ambient treatment (P=.0005). These changes in development time coupled with decreased parasitoid success at higher temperatures could cause an increase in damage to crops by herbivores in the future. These results indicate that parasitoids may become less effective biocontrol agents which has implications for both food and economic security.