Human hosts recruit more host-seeking deer flies (Diptera: Tabanidae) while walking than sitting

Abstract

Biting flies can strongly influence the behaviour of their hosts; for example, there is evidence that some species may avoid harassment by reducing their locomotory activity. We tested the hypothesis that potential hosts can reduce their attraction to deer flies by remaining stationary – that reducing locomotory movement reduces exposure to new deer flies compared to remaining still. During early summer in central Ontario, Canada, we conducted 20-minute trials where a human host either walked or sat quietly; tabanids were captured and counted each minute using a hat outfitted with a sticky trap. During ten trials in each treatment, we captured a total of 868 deer flies, all in the genus Chrysops; the total capture while walking was nearly 5-fold greater than while sitting. During trials, the change in catch rate also differed with host activity. While the host was sitting, the mean rate of capture declined rapidly (-16% per min) to nearly zero by 20 minutes. In contrast, while the host was walking, this decline was much more gradual (-5% per minute); after 20 minutes, the catch rate remained nearly constant, at roughly half the initial rate. These results are consistent with the hypothesis.