Efficacy of amitraz applied to white-tailed deer by the '4-poster' topicaltreatment device in controlling free-living lone star ticks (Acari : Ixodidae)

White-tailed deer treated themselves with a commercial pour-on acaricide fo rmulation containing 2% amitraz as they fed from an ARS-patented '4-poster' topical treatment device. Whole kernel corn attracted deer to a single dev ice placed in each of two deer-fenced pastures. In the treatment pasture, t he rollers of the treatment device were charged with the acaricide, whereas the rollers of the device in the other pasture remained untreated. Deer we re allowed to use the '4-posters' during periods of tick activity beginning in early to midspring and lasting through late summer to early fall for th ree consecutive years. Pretreatment sampling of adults and nymphs with dry- ice traps and larval masses with nip cloths showed no significant differenc es in population indices between the two pastures; however, after the third year of treatment, control of nymphal and adult ticks in the treated pastu re was 91.9 and 93.7%, respectively, when compared with the untreated pastu re. Control of larval masses increased from 68.4% in year 1 to 96.4% in yea r 2, but declined to 88.0% in year 3, probably because of the presence of f eral hogs. This study demonstrated that application of amitraz to white-tai led deer through free-choice interaction with a '4-poster' device significa ntly reduced the abundance of free-living lone scar ticks in a deer-fenced experimental pasture. Moreover, the yearly pattern of incremental increases in control and the final percentage control values for all three parasitic life stages in this topical application study were similar in magnitude to that observed in a previously conducted study in which the systemic acaric ide ivermectin was used to reduce populations of free-living ticks by contr olling ticks on deer.