“In the United States, we have about 84 species of ticks and there are records of about 40 tick species biting humans, but only 10 or so are of major public-health or veterinary importance,” said Kirby C. Stafford III Ph.D., chief scientist and state entomologist at The Connecticut Agricultural Experiment Station (CAES) Center for Vector Biology & Zoonotic Diseases. He gave a presentation to PMPs at PCT’s Public Health Virtual Conference in April.
“There are at least 16 tick-associated diseases in humans in the U.S. and Lyme disease continues to be the major vector-borne disease,” said Stafford. “Lyme disease, for example, has increased steadily since 1982, when very few cases were reported to the CDC. In 2017, the number of cases reported skyrocketed to 42,743. But given that only roughly 10 percent of diagnosed cases are actually reported, the true incidence of Lyme disease in the United States is somewhere between 269,000 and 376,000 cases every year.”
The blacklegged or deer tick (Ixodes scapularis) is the major vector for Lyme disease and other pathogens. “A lot of this has to do with the geographic range of the tick. Between 1996 and 2017, the increasing geographic spread of Lyme disease cases — as well as other tick-borne diseases — appears mainly in the North and Upper Midwest.”
“Tick control is largely a homeowner problem, which relies on pest management professionals. A lot of the tools used for control aren’t necessarily available to homeowners.” Pest management professionals are the best equipped to address disease-carrying ticks, Stafford said.
FEEDING. Ticks feed by cutting into the host’s skin and inserting their mouthparts, and most secrete a cement-type substance around the mouthparts to help hold on to the host. “Ticks have to set their mouthparts, because they feed for such a long period of time,” explained Stafford. Depending on the tick species, as a general rule, it can take nymphs four days to fully engorge and adult ticks five to seven days.
Pathogens are passed from tick to host during feeding. “The pathogens for Lyme disease are actually in the mid-gut of the tick. As the tick begins to feed, the pathogens multiply and travel from the gut, through the body of the tick, into the salivary glands before the host can be infected.”
“THREE-HOST” CYCLE. Female ticks can lay huge numbers of eggs in their one and only laying cycle before they die. The blacklegged tick (a.k.a., deer tick), for example, lays 1,000 to 2,000 eggs and the lone star tick will lay anywhere from 1,000 to 8,000 eggs, but averages 3,000.
“With the exception of the soft ticks, most of these ticks are what we call ‘three-host ticks,’ which means there are three active stages: larva, nymph and adult,” Stafford said. Each stage feeds on a different host animal, drops off, and then must find a new host, except for the female, which will lay eggs and die. A few ticks, like the winter tick on moose or cattle fever ticks, are one-host ticks, in which the larvae and nymph stage remain on the host after feeding and molt to the next stage.
Larvae of the blacklegged tick feed mainly on rodents and birds, although they are not picky and will feed on any animal host. The white-footed mouse, chipmunks, shrews and a few species of birds are considered reservoir hosts — animals that carry the infection and can infect the tick. It’s here that ticks pick up Lyme disease and other pathogens.
“A diseased host animal will infect ticks,” explained Stafford. “In the wild, basically ticks infect a generation of mice and then those mice infect a new generation of ticks and so on,” said Stafford.
After larvae engorge, they drop off and become nymphs, which have to seek out a new host, which are, again, primarily rodents and birds. When nymphs drop off as adults, they’re a little more selective and will choose a medium- to large-sized host animal, ranging from dogs, cats and humans up to larger animals including white-tailed deer, its preferred host.
SEASONALITY. Each stage of tick development is seasonal. The blacklegged tick generally lays its eggs around May and the larval ticks hatch about mid-July to August — the peak month for larval tick activity. The larvae drop and molt to nymphs and survive winter under leaf litter, as well as in mouse and chipmunk burrows. The nymphs emerge the following year around mid-May through June and July — the peak month for nymph activity. After feeding, they drop off as adults, which do not hibernate. “Adult ticks can be active on warm winter days. There can also be a secondary peak in spring, which are carry-overs from fall,” said Stafford.
INTEGRATED TICK MANAGEMENT. There are a number of tick management approaches, including education to change personal protection measures, landscape modifications, as well as chemical and biological control. “Work is also being done to develop host-targeted vaccines,” said Stafford.
The first line of defense for humans — homeowners and PMPs — is to prevent tick bites with appropriate personal protection. Ticks do not fall from trees. They generally are picked up on the lower extremities, but “you’d be surprised at how fast they can move up the body,” Stafford said.
If you find you’ve been bitten by a tick, remove it as promptly as possible using a fine-tipped forceps. Simply grasp the tick as close to the skin as possible, and gently and firmly pull it out. The sooner ticks are removed the better; the risk of pathogen transmission increases as time passes. Transmission of some pathogens can begin after 24 hours, while some take as little as 15-30 minutes.
WHERE ARE TICKS HIDING? Here are a few methods for identifying the location and population density of ticks.
A tick drag or tick flag is made using white, flannel-like sheeting and is dragged along vegetation. Ticks attach to it as they would a host.
“I’ve used a tick drag in residential habitats and found that the majority of the ticks — 82 percent — were recovered within three meters of the edge of a property with stone walls, woodland edges and ornamental vegetation. This is your tick zone,” explained Stafford. “Keep in mind that the remaining 18 percent are farther away, so it’s certainly not an exclusive zone. I’ve even found them in ground cover right next to entrance steps.”
CO2 traps use dry ice to attract ticks and a sticky, tape-like material around the perimeter of the box to capture ticks. They are better used for lone star ticks, as blacklegged ticks don’t tend to move very far.
Small mammal traps are used to monitor tick abundance, as well as rates of host infection.
Landscape management and modifications can reduce the suitability of the habitat for ticks. “You’re trying to reduce the risk of exposure to ticks. This can be done through landscaping, as well as perimeter spraying,” said Stafford.
- Mow. Keep lawns mowed to reduce tick habitat.
- Remove leaf litter. Most ticks require moisture and cover for survival, such as leaf litter and ground vegetation. Ticks dehydrate fairly easily.
- Create a perimeter. Pushing back wooded areas from a yard can help reduce the number of ticks in the yard. “We did a study on using woodchip barriers along the edge of wooded areas and found we were able to reduce the number of ticks moving in to the yard by roughly half,” said Stafford.
- Move farther into the yard. “Play sets, for example, should be placed away from the tick zone on the edge of wooded areas to a more central location in the yard to minimize exposure to ticks.”
- Remove invasive plants. “High tick counts are associated with exotic, invasive forest understory, which provides an ideal microclimate for ticks, compared to native forest understory,” said Stafford. “Studies have found that reducing invasive plants — in this case Japanese barberry — reduced the number of infected, adult blacklegged ticks by more 60 percent. Similarly, the number of lone star ticks was reduced when invasive amur honeysuckle was removed.”
Spraying is the standard method for controlling ticks on most properties. “If you’re just doing a perimeter spray, you may not be getting all of the tick habitat to which residents are being exposed,” explained Stafford. “As I said, I found that 18 percent of the ticks in a yard were not around the perimeter.”
Hydraulic sprayers and backpack blowers are equally effective when applying a pyrethroid insecticide.
Chemical control is a vital control method. “The timing of the acaricide application is important. For blacklegged ticks, you’ll make the application just prior to or during the nymphal season. A second application may also be used around the beginning of July,” said Stafford. “You’ll want to make an application for adult ticks around October, when they start emerging, and possibly an application in spring if it wasn’t done the previous fall.”
Botanical 25(b) compounds are increasingly popular. There’s higher interest among consumers and some companies to use 25(b)-based products — those derived from plants. “Unfortunately, most 25(b)-based products have been found, at least among those that have been tested, to be ineffective or have limited efficacy. If they do work, they’re very volatile and require more frequent applications.” Other variables in naturally based products impacting effectiveness may include plant species, source, extraction method, essential oil composition and formulation.
HOST-TARGETED CONTROL. There’s been a lot of research on host-targeted tick control, particularly focused on white-footed mice and white-tailed deer.
White-footed mice. Targeted approaches to host-targeted tick control for white-footed mice include tick tubes, which contain permethrin-treated cotton that mice collect and use for nesting material and kills ticks.
Another is a bait box containing two non-toxic food blocks positioned so that mice and chipmunks are passively treated while eating with a low-dose of fipronil, the same active ingredient used for tick-control products for cats and dogs, and should be effective for about 30 days.
White-tailed deer. “In terms of deer-targeted tick control methods, there’s exclusion, reduction or treatment,” said Stafford.
Fencing excludes deer on the scale of acres and can reduce the number of nymphal ticks within the fence by 84 percent, adults by 74 percent and a 100 percent reduction in larvae, “because if the deer can’t get in, they’re not dropping engorged female ticks to lay eggs.” Fencing is very effective, although not practical for many people.
Reducing deer populations through controlled hunts or sharp shooters have been shown to be effective if the populations are reduced to 10-13 per square mile, but this approach may be hampered by community sentiment.
“An alternative approach is a passive deer-treatment feeding station called a ‘4-poster’,” explained Stafford. “It’s a feeding station filled with whole kernel corn and two troughs with permethrin-treated paint rollers on either side. As the deer feed, their head, neck and ears are treated with the permethrin, which is then disbursed through grooming.
“There have been a number of studies published in the Journal of Integrated Pest Management that found a 71-90 percent reduction of nymphal blacklegged ticks where 4-posters were properly deployed.”
There are many restrictions on the use of four-posters. Most states require permits, while some prohibit its use.
SUMMARY. “You’ve got to think about the epidemiological triad when trying to manage human tick bites and disease risk: pathogen, host and vector [environment]. Our approach is to interrupt the triad somewhere to break the transmission process so we can try to control the tick,” said Stafford.
“We can reduce pathogen prevalence in the host, alter the environment of the host or vector or, perhaps most difficult of all, change human host behavior or exposure to ticks.”
“There are many challenges to effective tick control or management. We’re dealing with a lot of different tick species, depending on where you are geographically, and the expanding ranges of ticks,” said Stafford.
“I think an integrated approach to tick management is going to continue to be the best way of developing the dynamics to reduce tick numbers and people’s risk of disease. We need to figure out how to define and support individual and community-wide interventions for tick control, new, safe, cost-effective prevention tools and a better understanding of how to integrate these tools in an appropriate manner to try to reduce the risk of tick-borne disease.”
The author is a Florida-based freelance writer.