Effect of deer exclusion on the abundance of immature Ixodes scapularis (Acari: Ixodidae) parasitizing small and medium-size mammals

Effects of deer exclusion on abundance of immature Ixodes scapularis Say parasitizing small and medium-sized mammals, and the role mammals have in introducing ticks to exclosure areas, were examined at two sites in Westchester County, New York. In total, 686 mammal captures representing nine species were obtained, with white-footed mice, Peromyscus leucopus Rafinesque, composing >80% of all captures, followed by raccoons, Procyon lotor (L.); opossums, Didelphis virginiana (Kerr); and striped skunks, Mephitis mephitis Schreber. At the Near Archives site, 14% of 81 individual mice, 46% of raccoons, and 33% of opossums captured were found to cross the exclosure fence, as did 12% of 50 mice and 38% of raccoons at the Hudson Pines site. Skunks apparently did not cross the fence at either site. Mice captured exclusively outside the Near Archives exclosure hosted significantly more larvae than mice captured inside only, with fence crossers hosting an intermediate number of larvae. At Hudson Pines, numbers of larvae on fence-crossing mice and those captured solely inside the exclosure were equivalent, with tick loads on mice captured outside the exclosure significantly greater The number of larvae per raccoon did not differ significantly with capture location (inside, outside, or both sides of exclosure fence) at either site. Densities of host-seeking larvae and nymphs were significantly higher outside the exclosure than inside at Near Archives, though not at Hudson Pines. Differences in tick density inside and outside exclosures declined with each successive developmental stage so that adult density inside exclosures tended to converge with that outside at both sites. Although deer exclosures can have a significant impact on nymphal I. scapularis abundance, they may not reduce the risk of encountering infected adults. Mice, raccoons, and opossums have a role in introducing potentially infective ticks to areas where deer have been excluded, though the level of immigration of ticks into the area will likely depend on the density of ticks outside the exclosure.