The blacklegged tick, Ixodes scapularis, is prevalent throughout the northeastern and upper midwestern USA. This tick is the primary vector of Borrelia burgdorferi, the causative agent of Lyme disease, as well as Anaplasma phagocytophilum and Babesia microti, the causative agents of human granulocytic anaplasmosis and babesiosis, respectively. Ticks expend energy while host-seeking and must consume blood to advance to the next life stage. The energy required for host-seeking is derived from the tick’s lipid reserves, a valuable resource that sustains the tick until it finds the next host and can take another blood meal. This study determined how Ixodes scapularis ticks utilized lipid reserves over the course of three field seasons in the lower Hudson Valley of New York. Tick lipid reserves were determined indirectly through measurements of “physiological age” that estimate the energy a tick has based on morphometric analysis of body traits, and quantified directly through chloroform extractions of lipid from individual ticks. Physiological age ratios and lipid analyses were compared to determine which method was more accurate for estimating a tick’s physiological state.
Results/Conclusions
Field seasons in 2012 and 2013 followed winters that were warmer than average, while the field season in 2015 followed a winter that was much colder with more snow than average. The winter of 2011-2012 had just four days with at least one inch of snow on the ground, whereas the winter of 2014-2015 had a total of 60 days with at least one inch of snow on the ground. Measurements of physiological age did not correlate significantly with total tick lipid content and thus were not used in analyses. Ticks from the summers of 2012 and 2013 started the season with a mean lipid content of 2.8ug and 2.6ug, respectively, while 2015 ticks started the season with a mean lipid content of 5.8ug. Lipid content did not decrease significantly in the tick population through the summers of 2012 and 2013, while it did decrease significantly during the summer of 2015. Nymphal tick density in 2012 was the lowest the laboratory had sampled in 27 years of monitoring nymphal tick density. Based on this preliminary data, snow cover during the winter is important to help blacklegged ticks preserve their lipid resources for the following active season.