Distribution, Dynamics, and Diversity of Questing Ticks in the Lower Midwest.

Abstract

We investigated the spatiotemporal patterns of medically important tick species in southcentral Indiana in 2018 and 2019. In recent decades, both Amblyomma americanum (Acari: Ixodidae) (Linnaeus) and Ixodes scapularis (Acari: Ixodidae) (Say) have been expanding their ranges into the Midwest. We report updates to the status of A. americanum, I. scapularis, and Dermacentor variabilis (Acari: Ixodidae) (Say) across 13 counties in southern and south-central Indiana. We found more northerly establishment of A. americanum and more widespread establishment of I. scapularis than previously reported in the literature. We also provide the first report of Amblyomma maculatum (Acari: Ixodidae) (Koch) in Indiana. Using negative binomial regression, we observed significant spatial variation among sampling sites in A. americanum adults and nymphs, D. variabilis adults, and I. scapularis nymphs. Further, we found higher densities of A. americanum nymphs and I. scapularis adults in more forested areas as opposed to less forested, more developed areas. We did not find significant interannual variation in tick densities for any species. More southern sites featured higher densities of A. americanum adults and nymphs, D. variabilis adults, and I. scapularis nymphs than more northern sites. Seasonally, we observed the highest peaks in tick activity in the spring and early summer, but I. scapularis adults were most common in the early spring and fall. Average adult A. americanum and adult D. variabilis densities were positively correlated at our sites. Our results reflect the northward expansion of A. americanum in the Lower Midwest, as well as the increasing geographic prevalence of I. scapularis in the region.