Multigenerational emergence trends of Brood X Magicicada spp. across habitat types in southwestern Ohio

Abstract

Periodical cicadas (Magicicada spp.) emerge from the ground every 13- or 17-year intervals across the eastern and midwestern continental United States. Due to their long generation times, these animals are vulnerable to rapid environmental change, which has contributed to decreased densities and even extinction of different Magicicada broods. We investigated trends in population density and emergence phenology of Brood X cicadas across three reproductive events (1987, 2004, and 2021) in southwestern Ohio, comparing habitats with different levels of anthropogenic disturbance or origin: old-growth forest, rural woodlots, rural fencerows, and urban woodlots (added in 2021). Overall, we found that Magicicada cassini, M. septendecim, and M. septendecula were present in all studied sites, though the most abundant for the region was M. cassini. Our results revealed a generational decline in cicada density in old-growth forest and rural woodlots, while fencerows, often considered heavily disturbed habitats, showed a doubling in density across generations. Phenological data showed consistent protandry (earlier male emergence), with an increased offset between sexes in the 2021 emergence compared to 1987. Emergence timing also varied across habitats, with rural woodlots showing the earliest emergence and urban woodlots and fencerows (mainly composed by edge habitat) showing the latest. These findings challenge assumptions that disturbed habitats universally reduce insect populations and suggest that treed fencerows may serve as important reproductive refuges under certain conditions. However, variance and delay in female emergence may indicate changing environmental cues or phenological mismatches, potentially reducing reproductive success. To aid conservation efforts, we recommend continued and expanded monitoring of future Brood X emergences, expansion of sampling in old-growth forest sites, along with incentives to preserve and manage treed fencerows while also expanding existing tracts of forest.