The United States Department of Agriculture has developed and tested a passive topical treatment device designed to control ticks that parasitize white-tailed deer. The device consists of a bait bin that will accommodate up to 250 pounds of whole kernel corn. Feeding ports on both sides of the bin are flanked by vertical application rollers, hence the name "4-poster." Deer are treated as they rub their head, ears, and neck against acaricide-laden rollers while feeding on corn. The acaricide is dispersed to other parts of the deer by self-grooming.
Deployment of the 4-poster treated with 2% amitraz (Point-Guard®) within a fenced pasture resulted in 92% to 97% control of lone star ticks on deer that regularly used the device. In another study, 4-posters treated with 10% permethrin, deployed in a fenced facility over a 3-year period, resulted in 100% control of blacklegged ticks on deer after 2 years, 91% to 100% reduction of all stages of host-seeking ticks from sampled plots, and 70% to 95% reduction in nymphal and larval tick burdens on mice. A more comprehensive New Jersey study involving deployment of 25 4-posters treated with 2% amitraz yielded levels of control of 82.7%, 77.3%, and 94.2% for host-seeking blacklegged tick larvae, nymphs, and adults, respectively. Control of host-seeking lone star ticks peaked at 99.2%, 89.5%, and 96.9% for larvae, nymphs, and adults, respectively, during the 5-year treatment period. Tick burdens were also significantly reduced on deer from the treatment area.
Efficacy & Widespread Use
Although these studies demonstrated the effectiveness of the 4-poster technology as an alternative to habitat-targeted acaricide applications, several factors may affect its efficacy and widespread use. The availability of acorns during the fall of any given year will dramatically affect the efficacy of the 4-poster by providing an alternate and attractive food source for deer.
Another factor is host preference. Although neither blacklegged nor lone star ticks are host-specific, blacklegged ticks tend to feed on deer primarily as adults, while deer are a major host of all stages of the lone star tick. This may explain the somewhat higher levels of control of lone star ticks in the New Jersey study.
Economics is a third factor. In addition to its initial purchase price and costs for acaricide, corn, rollers, and periodic maintenance, the use of the 4-poster technology is labor-intensive. Where deer are abundant, the 4-posters may require semi-weekly visits to replace corn and recharge rollers. The United States Environmental Protection Agency has approved the registration of 10% permethrin (Y-TEX® 4-Poster™ Tickicide) for use on 4-posters. Current labeling restrictions prohibit the deployment of any 4-poster within 100 yards of a residence or other area where children might be present without adult supervision. This requirement restricts the use of 4-posters in many residential communities with small lot sizes and poses significant logistical problems in servicing the devices. Further, 4-Poster Tickicide can only be applied in New Jersey by licensed applicators.
A final impediment to the widespread use of this technology involves restrictions on feeding deer that may affect approval by some state regulatory agencies.
That being said, research has shown that a single 4-poster is able to treat the majority of deer within an area of 50 acres or more, all while introducing virtually no acaricide into the environment.
Systemic acaricides are those that when topically applied or fed to animals, move through body tissue or fluids in sufficient concentrations to stop ticks from feeding. In an island community in Maine, ivermectin-treated corn was fed to white-tailed deer. On deer that had adequate serum levels of ivermectin, adult blacklegged ticks were significantly less abundant compared to animals with low serum levels. However, no consistent differences were noted in the number of host-seeking ticks or tick burdens on small mammal hosts. Failure to reduce the number of host-seeking ticks resulted from an underestimation of the size of the deer herd and its distribution, which led to the provision of an inadequate amount of treated corn to a portion of the herd. Deer dominance at the feeding sites and seasonal availability of other food resources also affected the inadequate or inconsistent consumption of corn and, thus, ivermectin serum levels. A final concern with this strategy is the substantial withdrawal period for ivermectin before consumption of venison is permitted. Since the fall peak activity period for adult blacklegged ticks and the deer hunting season coincide, this restriction alone will limit the use of this strategy only to areas where deer are not hunted and consumed. Currently, there are no systemic acaricides registered for use in deer.