Using haem concentration as a metric of physiological age to infer demographic structure in natural field and forest populations of host-seeking Amblyomma americanum adults

Abstract

ABSTRACT Understanding how patterns of host-seeking behaviour differ across demographic classes in Amblyomma americanum (L.), the lone star tick, is essential in evaluating species potential as a vector of pathogens. Our objective was to characterize the relative contributions of two cryptic developmental cohorts, newly moulted and overwintered adults, to the A. americanum host-seeking population. To determine cohort identity, we used haem concentration as a metric of physiological age in ticks collected from field and forest habitats. Emergence of ticks displaying uncharacteristically high haem concentrations in late spring and early summer would indicate that newly moulted adults resume questing activity in the same season of their nymphal engorgement. Overall, haem concentration decreased significantly throughout the active season of adults from March to July of 2017 in northeast Missouri. Males displayed higher average haem concentrations than females when controlled for date of capture, but habitat-mediated differences were not significant. No subset of ticks with inflated haem concentrations was collected during the time that activization of newly moulted adults was feasible, suggesting that A. americanum adults undergo post-moulting behavioural diapause under natural conditions.