Systemic Treatment of White-tailed Deer with Ivermectin-Medicated Bait To Control Free-Living Populations of Lone Star Ticks (Acari: Ixodidae)

Abstract

Whole-kernel corn was treated with 10 mg ivermectin per 0.45 kg corn and fed at rate of approximately .45 kg/deer per day to white-tailed deer confined in the treatment pasture, whereas deer in an adjacent control pasture received a similar ration of untreated corn. Treatments were dispensed from February through September of 1992 and 1993, and free-living populations of lone star ticks. Amblyomma americanum (L.), were monitored in both pastures using dry-ice traps to quantify nymphs and adults and flip-cloths to assay the relative abundance of larval masses. Control values that were calculated for all ticks collected in both pastures during 1993 showed 83.4% fewer adults, 92.4% fewer nymphs and 100.0% fewer larval masses in the treatment versus control pasture. Serum ivermectin concentrations in treated deer averaged 21.7 and 28.3 ppb during 1992 and 1993, respectively. These values compared favorably with the goal concentration of 30.0 ppb which was anticipated under ideal conditions. This study demonstrates that a freely consumed, systemically active acaricidal bait ingested by white-tailed deer under nearly wild conditions can significantly reduce the abundance of all stages of free-living long star ticks.