Genetic and phenotypic variation in host-seeking behavior of nymphal Ixodes scapularis ticks: implications for Lyme disease risk in the eastern United States

The blacklegged tick (Ixodes scapularis) -- which vectors the causal agents of Lyme disease, human anaplasmosis, human babesiosis, and Powassan virus -- exhibits variation in host-seeking behavior across its geographic range.  A reciprocal transplant experiment was conducted to determine whether this difference in behavior is the result of genetic differentiation, environmental influences (phenotypic plasticity), or an interaction of the two.   

Questing behavior of nymphs belonging to distinct genetic clades from the northern and southern U.S. were observed in replicated field arenas monitored simultaneously at field sites in the Northeast (Wisconsin and Rhode Island) and Southeast (Tennessee and Florida).  In May 2012, laboratory-raised uninfected nymphs representing three different genetic clades were released at each site into circular 0.5 m² experimental arenas containing wooden dowel rods emerging from leaf litter.  The experimental design consisted of four blocks of four arenas, each arena containing 50 nymphal ticks of the same genetic clade (n=8 American I, 5 Southern I, and 3 Southern II).  This design was replicated at each of the four geographic locations, with tick activity on rods recorded weekly or biweekly from May – September 2012. 

Results from preliminary observations conducted in 2011 at the Wisconsin field site demonstrate that tick activity differs between nymphal ticks of American and Southern clades, such that American clade nymphs are observed on dowels more often than are Southern clade nymphs.  Summer 2012 observations of tick questing behavior will be presented to elucidate the contribution of environmental and genetic factors to these observed differences in questing nymphs.