Ecology of Black-Legged Ticks (Ixodes scapularis) at Fort Drum Military Installation, New York

Abstract

The number of confirmed cases of Lyme disease in the United States of America has risen from 12,801 cases reported in 1997, which is the earliest year these data are available, to 23,453 confirmed cases in 2019. In the eastern United States, black-legged ticks (Ixodes scapularis) are the primary vector of Lyme disease, which is caused by the spirochete bacterium, Borrelia burgdorferi. Tick abundance tends to be highest in dense forest habitats and where wildlife diversity is low. Because wildlife species have varying levels of competency as reservoir hosts, sources of tick bloodmeals influence Lyme disease ecology. White-footed mice (Peromyscus leucopus) and eastern chipmunks (Tamias striatus) are highly competent reservoirs of Lyme disease. High mast abundance has been found to influence tick abundance as well, and there is a two-year time lag from high mast abundance to high tick abundance, as mast influences tick abundance by increasing small mammal populations. To study Lyme disease ecology, we used Fort Drum Military Installation in New York as our study area. Fort Drum had 38 cases of Lyme disease from 2004 to 2013, with a 5.7% increase in Lyme disease incidences from 2006 to 2012. Borrelia burgdorferi was identified in 18% of nymph and 48% of adult black-legged ticks on Fort Drum in 2015 and 2016. To collect black-legged ticks, we conducted tick drag surveys in 2018, 2019, and 2020 during summer and fall field seasons, where summer field seasons operated from May until August, and fall field seasons operated from August until November. In total, we completed tick drag surveys at 56 sites, with fewer sites sampled during fall field season. Tick drag surveys were conducted biweekly during summer and fall field seasons, and each summer we completed six iterations of tick drags during a 12-week period. In addition to tick drag surveys, we collected geographically referenced variables that have been correlated to tick abundance, completed habitat structure surveys and wildlife diversity camera trap surveys, and collected mast samples from Fort Drum. These data sets were used to create Negative Binomial generalized linear models. With these models, we created tick abundance maps predicting nymph and adult black-legged tick relative abundance across the Fort Drum Cantonment Area, evaluated the influence of wildlife diversity and habitat structure on nymph and adult tick relative abundance, and explored the relationship between mast and nymph tick relative abundance. Our models used to create abundance maps passed model