Effect of a botanical acaricide on Ixodes scapularis (Acari: Ixodidae) and nontarget arthropods.

We tested the effectiveness of the rosemary oil-based insecticide, Eco-Exempt IC2, to control all stages of Ixodes scapularis (Say) in southern Maine. We selected plots in oak-pine forest where I. scapularis is endemic and recorded the abundance of ticks and nontarget arthropods before and after applications of IC2, bifenthrin (a synthetic pyrethroid), and water (reference treatment). Licensed applicators applied high-pressure spray treatments during the summer nymphal and fall adult seasonal peaks. Both acaricides sprayed during the summer nymphal season reduced nymphal I. scapularis/hour to zero. IC2 was as effective as bifenthrin in controlling nymphs through the rest of the nymphal season and also controlled adult ticks 9 mo postspray compared with 16 mo for bifenthrin, and both acaricides reduced larvae through 14 mo postspray. Both acaricides sprayed during the fall adult season reduced adult I. scapularis/hour to zero; IC2 controlled adult ticks 6 mo postspray compared with 1 yr for bifenthrin. Both fall-applied acaricides controlled nymphs 9 mo postspray and reduced larvae up to 10 mo postspray. Impacts on some nontarget arthropods was assessed. Colleoptera, Hymenoptera, and Collembola declined 1 wk postspray in acaricide-treated plots, and in IC2 plots all numbers rebounded by 20 d postspray. For bees and other flower-visiting insects there were no detectable reductions in nests produced, number emerged from nests, or number of foraging visits to flowering plants in IC2 or bifenthrin plots. IC2 was phytotoxic to the leafy portions of select understory plants that appeared to recover by the next growing season.