Q & A on 4-posters: Experts weigh in on effectiveness

With the ongoing controversy over costs and effectiveness of the 4-poster program aimed at lessening the tick population on Shelter Island, the Reporter put questions to two leading experts.A 4-poster is a  feeding stand that brushes deer with a chemical, permethrin, that kills ticks.

Dr. Daniel Gilrein, Cornell Cooperative Extension entomologist, was involved in the Cornell University-CCE study that ran for three seasons between 2008 and 2010, concluding with a final report in 2011.

Dr. Ilia Rochlin is laboratory director and an entomologist with the Suffolk County Department of Public Works Vector Control and was not directly involved with the study.
Q: Since the final report was released three years ago, is there new evidence that either supports the ongoing use of 4-posters or presents evidence to the contrary?

DG: We and others before us have demonstrated the efficacy of 4-posters for control of lone star and blacklegged deer ticks. I feel there is no question they perform as stated when deployed and maintained appropriately. There are natural fluctuations in tick populations that also must be taken into account and the devices don’t provide 100 percent control, in part, because not all deer will use them, but they can and did substantially and significantly reduce tick numbers.

IR: To determine the effectiveness of 4-posters, a tick population monitoring program should be put in place. In the absence of such a  monitoring program, the only way to measure the success is to look at the number of human cases of tick-borne disease to see whether they’ve gone down and remained suppressed relative to other similar areas nearby.

People also have to realize that there have been numerous studies on 4-posters before Cornell’s. Some of the studies were very extensive and thorough, such as the long-term USDA project in the Northeastern U.S. These multiple studies pretty much confirmed 4-posters were effective in reducing tick populations, both blacklegged and lone star, and were environmentally safe. Cornell study results were in line with those from the other studies.

Q: Some argue that permethrin pollutes groundwater.

DG: The issue of permethrin and groundwater was addressed in great detail during the study by Vincent Palmer, formerly with New York State Department of Environmental Conservation.

IR: Permethrin is highly hydrophobic, meaning it has very low water solubility. When it gets in the soil, it attaches to the soil particles and doesn’t move much until degradation. Since there is very little to no leaching of permethrin from soil, the risk of it contaminating the groundwater is very low.

Permethrin is registered as an active ingredient in over 1,400 products used in agriculture, home, garden, pet and personal protection. Permethrin used for 4-posters, likely represents a miniscule proportion of the total permethrin applied on Shelter Island in gardens, lawns, farms, for termite and structural pest control, in dog collars and personal protection against ticks and mosquitoes.

Q: Some maintain that by feeding the deer, we aren’t achieving anything to diminish the tick population, but are, instead, making the deer healthier and better able to reproduce, resulting in more deer.

IR: Whole kernel corn utilized in 4-posters has very low nutritional value for deer. It serves as an attractant and just passes through the digestive tract.

Q: Those who object to 4-posters charge that the final study wasn’t scientific because it wasn’t vetted by others not directly involved in the study.

DG: The methods, results and conclusions of the study were reviewed by others not directly involved with the work. Jim Leach at the New York State Department of Health reviewed all the residue information and protocol and he provided comments to the Town Board during one meeting as well. The New York State DEC’s Bureau of Wildlife staff also reviewed the study.

The public is also welcome to review the report and draw their own conclusions.

IR: The DEC found the study scientific enough to register 4-posters in New York for the first time despite many reservations prior and during the study. The main New York State regulatory agency thus confirmed the study’s scientific validity. We are also working on getting the results published in peer-reviewed literature. However, please note that this study was among more than a dozen that have been conducted in various locations across the United States by different agencies. These studies have been published in peer-reviewed journals.

Editor’s note: The United States Department of Agriculture conducted a seven-year study of 4-posters in five states and concluded that the devices have proven extremely effective in reducing tick numbers. A study done at the Goddard Flight Center in Greenbelt, Maryland, concluded that adult ticks were completely eliminated by the second year of the study and all stages were reduced by between 91 and 100 percent by the third year.

Q: How reliable are the tick drags in assessing the effectiveness of 4-posters in reducing the tick population?

IR: Tick flagging/dragging has been well established as a monitoring technique and is widely used by scientists in the United States, Europe and elsewhere. It is reliable when used in a consistent manner as was done in this study. Tick sampling conducted by Cornell scientists was very thorough and extensive. Reference or untreated sites were also established, so the reduction in tick populations was compared not only to the baseline, but also to the reference sites to account for annual fluctuations. The tick reduction at the 4-poster sites was significant compared to the baseline as well as to the reference sites.