The role lipids play in blacklegged tick (Ixodes scapularis) longevity

Background/Question/Methods

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 agents of human granulocytic anaplasmosis and babesiosis, respectively.  Ticks expend energy while questing for hosts and will consume blood once during each of their three life stages.  The energy required for questing 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.  The purpose of this study was to determine how Ixodes scapularis ticks utilize lipid reserves under controlled laboratory conditions and compare their lipid usage with ticks under field conditions.  The known-age, laboratory-reared ticks in this study were pathogen-free.  Wild caught ticks were collected in southeastern New York State.  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 and mass determination.  Physiological age ratios and lipid analyses will allow for better understanding of the temporal pattern of the blacklegged tick’s active season.

Results/Conclusions

Laboratory reared, pathogen-free Ixodes scapularis nymphs lost lipid mass steadily over the 38 weeks of the study.  The physiological age ratio steadily decreased as well, suggesting that it may be possible to predict the amount of lipid a tick has from its physiological age.  Statistical differences were not found in the raw lipid masses of native ticks collected in 2012 and 2013.  However, both summer 2012 and 2013 nymphal ticks appeared to start the active season with depressed lipid levels when compared to the laboratory-reared ticks.  Possible explanations for these depressed lipid levels will be discussed.  There was an increase in the physiological age ratio and lipid reserves late in the season in both 2012 and 2013, suggesting the presence of newly molted, host-seeking, nymphal, blacklegged ticks.  These results suggest that the population dynamics of the blacklegged tick are more complex than currently understood.