Density-dependent preprandial mating by deer ticks

To determine whether the prevalence of preprandial insemination in deer tic ks reflects their local abundance, we sampled adult ticks by flagging veget ation at selected sites in eastern Massachusetts in a standardized manner. Resulting female ticks were dissected to determine whether they contained e ndospermatophores, and the frequency of insemination was compared to the nu mber of questing ticks flagged at each site. The prevalence of insemination correlated closely with density of ticks. The frequency of insemination in creased linearly during the Ist 2 months during the fall. The mean daily pr obability of insemination during this period was about 1% when, on average, about 4 ticks were flagged per minute. A predictive equation was derived v ia multiple regression expressing deer tick abundance as a function of coll ection date and insemination prevalence (P < 0.05). The frequency of prepra ndial mating, thereby, was correlated with the abundance of questing deer t icks. Insemination prevalence increased predictably as the season of adult activity progressed. We conclude that a season-specific analysis of the fre quency of preprandial insemination provides a robust indicator of the abund ance of deer ticks that is unaffected by short-term fluctuations in the wea ther.