Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 27, 1995
Publication Date: N/A
Interpretive Summary: White-tailed deer are the primary hosts for ticks that transmit agents responsible for variety of human illnesses, including Lyme disease, and are marginal, though significant, hosts for cattle fever ticks that were erdicated from the U.S., but are still abundant along the border with Mexico, and transmit the agents causing potentially fatal cattle fever illnesses in cattle. A rapid increase in deer populations in the eastern U.S. during recent years has thus resulted in more cases of tickborne diseases in humans and is also hampering efforts to maintain the cattle fever tick eradication quarantine zone in Texas along the Rio Grande River. Because of the obvious difficulties involved in working with such elusive free-ranging animals, there are currently no methods available for the control of ticks on white-tailed deer. Their importance as major hosts for ticks, however, makes it imperative that we develop control technology that is efficient, effective, and environmentally responsible. Two season of tests using ivermectin medicated corn fed to deer that were confined in nearly wild situation showed that free-living adult, nymphal, and larval ticks in the treatment pasture (21.9 hectares) were reduced by 83, 92, and 100%, respectively. This medicated bait technology is thus an important development assisting in the efforts to reduce the risk of tickborne illnesses in both medical and veterinary situations.
Whole kernel corn was treated with 10 mg ivermectin/0.45 kg corn and fed at a rate of about 0.45 kg/deer/d to white-tailed deer confined in a 21.9 ha pasture, while deer in an adjacent 16.9 ha pasture received a similar ration of untreated corn. Treatments were dispensed from February through September, 1992 and 1993, and free-living tick populations were monitored in both pastures using dry-ice traps to quantify nymphs and adults and flip-control values were calculated for all ticks collected in both pastures during 1993 showed an 83.4% reduction in adults, 92.4% reduction in nymphs, and 100.0% reduction in larval masses in the treatment vs. control pasture. Serum ivermectin concentrations in treated deer averaged 21.7 (plus/minus 3.0) and 28.3 (plus/minus 6.9) ppb during 1992 and 1993, respectively. These values compared favorably to the goal concentraion of 30.0 ppb that was anticipated under ideal conditions. This study demonstrates that a freely consumed systematically active acaricidal bait ingested by white-tailed deer under nearly wild conditions can significantly reduce the abundance of all stages of free-living lone star ticks.