Effects of Edaphic Factors on Plague Vector Fleas Parasitizing Black-Tailed Prairie Dogs

Plague is a zoonotic disease of mammals caused by the bacterium Yersinia pestis. Because plague is primarily transmitted by fleas (Siphonaptera), rates of plague transmission are expected to increase with flea abundance. Edaphic factors can influence the abundance and dispersion of fleas, suggesting that soils may play important roles in plague ecology. From June to August 2010-12, in northern New Mexico, USA, we investigated the effects of soil texture, soil moisture, and soil water-holding capacity on the abundance of adult fleas parasitizing colonial, burrowing black-tailed prairie dogs (Cynomys ludovicianus, BTPDs). We sampled BTPDs 1,741 times on 20 sampling plots distributed among 13 BTPD colonies, detecting 9,541 adult fleas on BTPDs. Fleas were most abundant on BTPDs in areas with coarse surface soils, and in areas with moderately textured subsurface soils at the average depth of BTPD nest chambers. Coarse surface soils may facilitate water percolation to BTPD nests, where the moisture could generate humid microclimates that benefit desiccation-prone fleas. Moderately textured subsurface soils, of intermediate water-holding capacity, can store water, which may increase burrow humidity. Moreover, moderately textured subsurface soils in BTPD nests may increase survival of flea larvae and pupae, facilitating their development to adulthood. That said, excessive moisture and sodden soils can favor fungi and mites, some of which are lethal to fleas. In our study, fleas were most abundant in areas with subsurface soils of intermediate moisture content. Our findings complement an accumulating number of studies, indicating that edaphic factors play important roles in flea and plague ecology.