PS 6-77 - Identifying environmental drivers shaping the abundance patterns of sympatric blacklegged and lone star ticks in Long Island, New York

Abstract: Ixodes scapularis (the blacklegged tick), the Lyme disease vector, has a wide distribution, which partially overlaps with that of Amblyomma americanum (the lone star tick), vector of ehrlichiosis, rickettsiosis, and tularemia. Because both species share white-tailed deer as their main reproductive host, their responses to abiotic conditions have been proposed to determine their relative distributions. Regions where both ticks have been long endemic offer the opportunity to examine environmental drivers of their co-occurrence. One such area is Suffolk County, located at the east end of New York, where these two species have been abundant for around 50 years, with a high incidence of Lyme disease and other tick-borne diseases. While the blacklegged tick and the lone star tick are mostly sympatric in the county, the factors that determine spatial variation in their relative abundance have not yet been investigated. We hypothesized that abiotic factors are driving the heterogeneity in the relative abundance of these tick species and used tick surveillance data in Suffolk County to identify the main environmental drivers. We modeled the abundance of each species individually as well as the ratio of their abundance. Temperature and humidity measured on-site during surveys were used as predictors, in addition to soil texture data from SoilGrids at the surface depth. Among three soil texture categories, sand and clay content were used for GLM models. Based on GLM results, a negative effect of clay and a positive effect of relative humidity on nymphal counts were observed for both species, whereas sand content and temperature showed a varying trend between the two species. While higher sand content and higher temperature reduced the number of blacklegged ticks sampled, it increased those of lone star ticks. This corresponds to prior findings that lone star ticks are more tolerant to desiccation than blacklegged ticks. For the ratio model, clay was the only significant predictor. The increased numbers of blacklegged ticks sampled in relation to lone star ticks in soils with higher clay content indicate high water holding capacity of clay is a more relevant factor for blacklegged ticks compared to lone star ticks. Simultaneously assessing factors driving the co-occurrence of these two species would improve projected distribution models.