Cascading Effects of Brood X: Changing Trophic Dynamics due to the Periodical Cicada Emergence

In the spring of 2021, the eastern United States experienced a remarkable biological phenomenon, the emergence of billions of 17-year periodical cicadas (Magicicada spp.). The resource pulse created by this dramatic increase in insect biomass alters trophic cascades with potentially drastic and lasting consequences on terrestrial food webs, including those in deciduous oak forests. While resource pulses are an important ecological perturbation, the duration and magnitude of their effects are poorly documented. The objectives of this study are to determine how the periodical cicada emergence affects bird predation on oak-feeding caterpillars and oak-feeding herbivore population diversity and abundance. Using plasticine caterpillars to determine how the cicada emergence changed the intensity of bird predation on caterpillars, we found that bird predation on clay caterpillars decreased while arthropod predation on clay caterpillars increased during the cicada emergence. Furthermore, oak-feeding herbivore abundance increased after the cicada emergence, likely due to an ecological release of predation on oak-feeding herbivores after birds shifted to foraging for cicadas, a more plentiful and accessible food source. Climate change, landscape simplification, and introduction of non-native pests are all contributing to increasingly large and economically devastating insect outbreaks. Our results suggest that these insect outbreaks can satiate local birds, allowing for the ecological release of predation on local caterpillars and the potential for increased herbivory on plants.