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Integrated Pest Management Manual

Ticks

ticks
This module is intended to serve as a source of basic information needed to implement an integrated pest management program for ticks. Any pest management plan or activity must be formulated within the framework of the management zones where it will be implemented. Full consideration must be given to threatened and endangered species, natural and cultural resources, human health and safety, and the legal mandates of the individual parks. Recommendations in this module must be evaluated and applied in relation to these broader considerations.


Ticks are external parasites on mammals, birds, reptiles, and amphibians. Both males and females feed on blood.This module describes the biology and management of five species of ticks commonly found in park settings. These ticks are all species which vector a disease, are capable of transmitting a pathogen to humans, or may in some other way affect human health. They are the Lone Star tick, Amblyomma americanum (L), American dog tick, Dermacentor variabilis (Say), Rocky Mountain wood tick, Dermacentor andersoni (Stiles), deer tick, Ixodes dammini (Spielman, Clifford, Piesman, and Corwin), and Ornithodoros spp. For each species of tick, the geographic distribution, habitat, hosts, life cycle, seasonal abundance, responses to environmental factors, and direct and indirect medical effects are described. Information concerning the removal of ticks, outbreaks of tick-borne diseases, and natural enemies are presented. Tick management approaches including methods of population monitoring, decision-making, and intervention are described. All of these tick species are attracted to carbon dioxide and generally prefer low light intensity, high relative humidity, and protection from constant breezes. Temperature and humidity are the two most important environmental factors affecting survival.



IDENTIFICATION AND BIOLOGY OF TICKS

The identification of medically important species of ticks can be done by local diagnostic facilities at universities or state agencies or with the aid of publications such as Keirans and Litwak (1989), Sonenshine (1979), and the United States Department of Health, Education and Welfare (1967), which provide keys and descriptions. Ixodes dammini was first described in 1979 and will appear as Ixodes scapularis in works prior to this date. A concise review of tick biology, management, and medical importance was provided by Goddard (1989).

Ticks are considered harmful because they transmit diseases. Like many other organisms, however, their role in the food chain serves a positive ecological function. Ticks are an essential food source for many reptiles, birds, and amphibians.


Lone Star Tick

This tick species occurs from central Texas east to the Atlantic coast and north to Iowa and New York; it has also been reported in northern Mexico. The Lone Star tick is found in wooded areas, especially where there is dense underbrush, but
it is also found in scrub, meadow margins, hedge rows, cane breaks, and marginal vegetation along rivers and streams. The immatures and adults feed on a wide variety of mammals (including humans) and ground-feeding birds.

Each female produces 3,000-8,000 eggs, which are deposited under leaf and soil litter in middle to late spring. Incubation may take 30 days or longer, depending on temperature. The newly hatched six-legged immatures, also known as larvae or seed ticks, feed for 3 to 7 days on a host. After full engorgement the larvae drop from the host into vegetation and shed their skins 9-27 days later. The eight-legged immatures that emerge are called nymphs. These attach to a second host and feed for up to 38 days; the nymphs then detach and rest for 13-46 days before they shed their skins to become adults. Adults attach to a third host, feed for 6-24 days, and detach. Oviposition occurs 7-16 days after the last blood meal. Larvae may survive for 2-9 months, and nymphs and adults for 4-15 months each (Goddard 1989); the life cycle may take up to 2 years to complete. Lone Star tick nymphs can move very quickly and may cover a person's legs or arms in less than five minutes. This is a good behavioral characteristic to note to aid in identification of this tick species.

Adults and nymphs are active from early spring through midsummer, while larvae are active mainly from late summer to early fall. Low humidities and high daytime temperatures restrict the occurrence and activity of these ticks (Goddard 1989).

Lone Star ticks transmit Tularemia to humans. Lone Star ticks infected with the agents of Rocky Mountain spotted fever and Lyme disease occur in nature, but the species does not appear to be epidemiologically important in the transmission of these diseases (see Goddard 1989).

American Dog Tick

The American dog tick is found throughout the United States except in parts of the Rocky Mountain region. It also occurs in parts of Canada and Mexico. Its habitat includes wooded areas, abandoned fields, medium height grasses and shrubs between wetlands and woods, and sunny or open areas around woods. Larvae and nymphs feed primarily on small mammals (especially rodents), while the adults feed mainly on dogs, but will readily bite humans.

The female lays 4,000-6,500 ellipsoidal eggs over a 14-32 day period and then dies. The eggs usually hatch in 36-57 days. Larvae usually engorge for 3-5 days, nymphs for 3-11 days, and adult females for 5-13 days. Unfed larvae can live up to 15 months, nymphs 20 months, and adults 30 months or longer. Mating takes place on the host (Goddard 1989, Metcalf and Flint 1962). Adults are active from mid-April to early September. Nymphs are active from June to early September and larvae from late March through July. High light intensity and low relative humidity stimulate questing behavior (Newhouse 1983).

This species is the primary vector of Rocky Mountain spotted fever in the eastern United States, and can also transmit Tularemia and cause tick paralysis.

Rocky Mountain Wood Tick

This tick is found from the western counties of Nebraska and the Black Hills of South Dakota to the Cascade and Sierra Nevada Mountains, and from northern Arizona and northern New Mexico in the United States to British Columbia, Alberta, and Saskatchewan in Canada. Their habitat is primarily fields and forested areas. This species is especially prevalent where there is brushy vegetation that encourages the small mammal hosts of immature ticks and sufficient forage to attract the large hosts of the adults. Immatures feed mainly on small mammals such as ground squirrels and chipmunks, and adults on cattle, sheep, deer, humans, and other large mammals.

Females lay about 4,000 eggs in plant debris on the soil or in crevices in construction materials, usually in masses of hundreds at a single location. Unfed larvae may live for 1-4 months, nymphs for 10 months, and adults for more than 12 months (Goddard 1989). Adults and nymphs can be found from March to mid- summer. Larvae are active throughout the summer and are associated with cool soil temperatures, shallow soil, abundant leaf litter, and high relative humidity.

This species is the primary vector of Rocky Mountain spotted fever in the Rocky Mountain states and is also known to transmit Colorado tick fever and Tularemia. It also carries tick paralysis in the United States and Canada.

Deer Tick

The deer tick is found in eastern North America including the New England, mid-Atlantic, and southeastern states, and the midwestern states of Minnesota and Wisconsin. It has also been observed in Michigan, Iowa, Illinois, and Indiana. Deer ticks prefer heavily-forested or dense brushy areas and edge vegetation, but not open areas. An exception to this occurs in upstate New York where the species is found on well-maintained lawns in residential areas. Larvae and nymphs feed primarily on small mammals (especially the white-footed mouse, other rodents, and insectivores), and also on birds, dogs, deer, and humans. Nymphs aggressively bite humans. Adults feed primarily on deer, but also attach to large mammals (foxes, raccoons, opossums, dogs) and humans.

Females lay up to 3000 eggs in soil and litter. Eggs take about 1 month to hatch. Larvae engorge for 2-3 days during the summer, detach, overwinter on the ground, and molt the following spring. Nymphs feed for 3-4 days, detach, and molt in early fall. Adult females engorge for 7-21 days, detach, oviposit the following spring, and die. The life cycle may range from 2-4 years and is regulated by host abundance and physiological mechanisms. Larvae are active from July through September, nymphs from May through August, and adults in the fall, winter, and early spring (October-May).

Distribution is associated with high humidity and mild mean winter temperatures. However, it is not restricted by winter temperatures as areas of tick activity occur in Minnesota and Wisconsin. The requirement for high humidity restricts this tick from spreading to arid areas and high mountains where desiccation is a limiting factor (Lane et al. 1991).

The deer tick is the major vector of Lyme disease in the
northeastern and midwestern United States. It is incriminated as the vector of human babesiosis in the northeastern United States.

Ornithodorus spp.

These ticks are the vector of relapsing fever, which has created serious health problems at the Grand Canyon. The relapsing-fever tick, Ornithodorus hermsi, is sand-colored before feeding, but turns grayish-blue after it feeds. The adult female is about 1/4" long.


MEDICAL EFFECTS OF TICKS

Ticks may cause paralysis in humans that is reversible when the ticks are removed. Symptoms include paralysis of the arms and legs, followed by a general paralysis which can be fatal if not reversed. The victim may recover completely within a few hours of the removal of the tick. The paralysis may be caused by a salivary toxin transmitted to humans when a tick feeds. Tick paralysis is frequently associated with the attachment of the tick at the base of the victim's skull; however, the illness occurs from attachment to other parts of the body as well. The highest incidence of tick paralysis in north America occurs near the border of British Columbia, Canada, and the northwestern United States.

The two most important tick-borne diseases in the United States are Lyme disease and Rocky Mountain spotted fever. The onset of Lyme disease is usually characterized by the development of a large, red rash which may develop a characteristic clear central area ("bulls eye"), one to two weeks after a tick bite, often in the area around the puncture. Other symptoms include joint pains, flu-like symptoms, and neurological or cardiac problems. The most characteristic symptom of Rocky Mountain spotted fever is a rash on the ankles, wrists, and forehead one to two weeks after the victim is bitten. The rash spreads to the trunk and is accompanied by fever, chills, and prostration. Both Lyme disease and Rocky Mountain spotted fever are transmitted after the tick feeds for several hours. Prompt removal of attached ticks greatly reduces the chances of infection. Both diseases are usually successfully treated with antibiotics in their initial stages. Therefore, early diagnosis is imperative. For this reason, it is recommended that the date of a tick bite be marked on a calendar. If unexplained disease symptoms occur within two to three weeks, a physician should be consulted.

The best means to prevent the transmission of tick-borne diseases and the development of tick paralysis is the prompt removal of ticks. This requires regular inspection of clothing and exposed skin for attached or unattached ticks. To remove a tick, grasp it crosswise with narrow tweezers (do not rupture the tick) as close to the point of attachment as possible. Retract or pull tick firmly in the direction of attachment; some back-and-forth wiggling may be necessary. Do not twist or rotate the tick. Do not handle ticks with bare hands because infectious agents may enter through mucous membranes or breaks in the skin. Removed ticks should be immersed in alcohol to kill them. Disinfect the bite site and wash hands thoroughly with soap and water.

The diseases listed above can be fatal. Any case of such a disease should be reported to medical authorities immediately. Frequent or multiple reports of tick-borne diseases should be reported to a National Park Service public health service representative. The representative can recommend actions to control disease outbreaks. Closing affected park areas may be advisable during such periods.

Another important tick-borne disease is endemic relapsing fever. This disease is limited to the western states and is caused by a spirochaete carried by certain ticks in the genus Ornithodorus. These ticks are found on tree squirrels (Sciurus spp.) and western chipmunks (Eutamias spp.). The disease can also be transmitted directly to the tick's offspring. These ticks usually live three to five years. Park personnel and visitors are at increased risk of contracting endemic relapsing fever when they sleep in dwellings that have become inhabited with infected squirrels or chipmunks. As with sylvatic plague, the rodents vacate the building or are killed by the humans who use the buildings. The ticks which remain behind feed on the people using the buildings. Implementation of exclusion efforts will reduce the incidence of ticks.


MONITORING AND THRESHOLDS FOR TICKS

Periodic surveys of potential or known tick habitats can reveal the presence of low-level tick infestations. This permits the application of management procedures to prevent or retard further population increase. Monitoring techniques that have proven effective (Gladney 1978) are as follows.

Examination of personnel for attached ticks. A volunteer wearing protective clothing walks through each sample site and is then inspected. Ticks attached to or walking on the collector's clothing and skin are collected in 70% ethanol for later identification and counting. Careful inspection is necessary to prevent the attachment of unnoticed ticks and possible disease transmission to the collector. Collections can be standardized in relation to time, distance, or area units covered during sampling.

Dragging/flagging. Done by dragging a white cloth over relatively open ground or "flagging" low-level vegetation (i.e., moving the cloth in a waving motion over and through vegetation) in densely brushy ground. Ticks that are questing for passing hosts cling to the cloth and can be removed for identification and counting. The "drag" consists of a 1 yd2 piece of white crib bedding or corduroy material hemmed on all edges, weighted at one end, and attached to a wooden pole at the opposite end. A rope attached to the two ends of the pole allows the device to be dragged along the ground. Alternatively, the pole can be gripped at one end so that the cloth hangs vertically downwards, and the device used to flag vegetation. Dragging or flagging success depends upon the degree of contact between the cloth and ground or vegetation surface. Useful drag techniques are described by Gladney (1978). The selection of sampling sites may have significant effects on the success of the sampling effort. Sampling sites should reflect favored tick habitats for best success. Sampling should be done under conditions that favor tick presence and activity (e.g., when vegetation is not wet and when ambient temperature is above 500 F).

Dry-ice traps. This has been proven to be the most efficient method of tick collection. It is non-destructive to host animals, does not require a human as an "attractant", and gives more reproducible results than dragging. However, the traps need to be kept in the field for several hours (preferably overnight) for best results. Dry ice is available at ice cream and beverage stores. The basic principle is to use carbon dioxide vaporizing from the dry ice to attract ticks onto a white cloth panel on which they are easily visible and can be removed periodically (if the traps are set out for a limited time under periodic monitoring), or onto a platform lined with double- sided sticky tape on which they get trapped (if the traps are set out overnight). Information on trap designs can be obtained from Garcia (1965), Gladney (1978), and Mount and Dunn (1983).

Trapping small animal hosts. Small mammals such as rodents and insectivores can be live-trapped at selected sampling sites, with traps set out in grids or line transects. Trapped animals are anesthetized and searched thoroughly for attached ticks, which are removed using fine forceps. Removed ticks can be stored in 70% ethanol pending identification and counting. The animal host is released at the site of capture after recovery from anesthesia. Gloves should be worn throughout all animal and tick handling operations. A veterinarian or qualified technician should be consulted on the proper usage of anesthetics administered to trapped animals.

Sampling sites for monitoring ticks should be selected in areas favoring ticks or are likely to receive heavy human visitation. A conscientious monitoring program is the basis of effective integrated pest management. Regular surveys should be done at all sites where ticks have been reported by park staff or visitors and at other locations that appear to be favorable tick habitats. Complete and accurate records of sampling sites and methods must be kept, so that the progress of tick populations and the effect of control measures can be gauged. After collecting the ticks, store them in rubbing alcohol or freeze in a plastic container to preserve them.


THRESHOLDS FOR TICKS

Mount (1981) proposed an arbitrary tolerance threshold of one tick/dry-ice sample, based on several years of study in recreational areas in Oklahoma. Mount and Dunn (1983) recommended that a count of 0.65 ticks per one hour of CO 2 exposure (dry-ice traps) be considered the economic threshold in lone star tick management (equivalent to one tick per visitor per day, based on the assumption that most human visitors to recreational areas will not spend more than one hour per day in tick habitats). This value may not be applicable to your particular situation and a suitable threshold level can be established by conducting regular CO2 surveys and plotting tick counts against the numbers of tick bite complaints received. This will permit the selection of a complaint threshold level for each site surveyed. Treatment should be conducted to keep tick populations below the selected threshold; a lower "action" level should be selected to trigger treatment programs. The same technique is applicable to other species of ticks as well.


NON-CHEMICAL CONTROL OF TICKS

Education

Ticks are important disease vectors in many regions of the country. Park visitors and employees need to be aware of tick species and diseases present in their area, as well as personal protection measures that should be taken by anyone who will be in tick-infested areas. Parks should use interpretive displays to inform their visitors about ways to avoid contacts with ticks.

Biological Control

Several species of ants are known to feed on ticks. Recently, releases of the parasitic wasp Hunterellus hookeri have been made on several small islands on the New England coast. This wasp attacks Ixodes dammini and has been recovered from some of the release sites (Van Driesche, personal communication).

Habitat Management

Wherever possible, visitor activities should be directed towards areas that provide unfavorable habitat for ticks. Regular inspection of the park should be performed to determine when tick management needs to be initiated. The basic principles of management include isolation of susceptible domestic animals from known tick populations and rotation of pasture or run areas to reduce tick populations.

Removal of shrubs, trees, or tall grass can be useful in situations where it is consistent with National Park Service policy regarding use of the area. Dense shrub and tree cover and tall grass provide harborage for both ticks and their animal hosts. Removal of excess brush and shrubbery and clearing the canopy trees so that 50% to 80% of a management area is exposed to direct sunlight at any time are recommended control practices for walkways, parks, and landscaped grounds (Hair and Howell 1968). Grass should be kept below 6" in height to allow the penetration of sunlight and soil ventilation. Such techniques result in higher soil temperatures, lower humidities, and lower soil moisture, all of which lead to higher tick mortality. In one study, such techniques resulted in 75% to 90% control of different tick life stages of the Lone Star tick (Mount 1981). Mowing vegetation with a bush-hog rotary mower reduced adult deer tick populations by 70% in another study (Wilson 1986).

Controlled burning of habitat may reduce tick numbers and may be feasible in a park if it is consistent with a fire management plan. For example, burning tick- infested areas on Great Island, Massachusetts, reduced deer tick populations by 38% six months after the burn (Wilson 1986). However, the long-term implications of burning are unclear. Burning typically improves deer browse in the area; thus increased deer abundance may result in the movement of ticks back into the area.

Research has shown that high deer populations can lead to increased Lone Star and deer tick populations since there will be more hosts from which a blood meal can be obtained. Reducing the deer population may be a feasible tick management strategy in locations where it is compatible with National Park Service policy. This reduction has been experimentally demonstrated in Massachusetts (Wilson et al. 1988), although the decline in tick numbers may not correspond directly to the reduction in deer population. Managing deer populations by hunting, fencing, or environmental modification should be considered seriously before tick infestations become severe and should be done within state and local guidelines. Efforts at deer management should be done in coordination with state natural resources and wildlife department personnel.

Under unusually high tick population pressure it may be necessary to treat indoor areas. The major methods of nonchemical indoor tick management include regular inspection, elimination of animal (especially rodent) harborage areas, use of food and waste-handling procedures that minimize animal entry and harborage, and animal-proofing buildings. This includes sealing all holes in foundations and walls, and screening (with heavy gauge metal screen) aboveground windows, vents, and other openings through which animals may enter. A 18" perimeter border of gravel may prevent movement of ticks from grass areas into buildings. Cracks and crevices around the base of buildings should be sealed with caulk.

Recommended practices include frequent examination of clothing (preferably by another individual) and the body (after showering), destruction of collected ticks, and wearing protective clothing (e.g. coveralls with trouser cuffs taped to shoes, high- top shoes, socks pulled over trouser cuffs, long-sleeved shirts or jackets, or mesh jackets). Clothing should be light-colored so ticks may be easily seen.

Periodic surveys of potential or known habitats can reveal the presence of low- level tick infestations, thus indicating the need for application of management practices to prevent or retard further population increase.


CHEMICAL CONTROL OF TICKS

Outdoors

Insecticides or acaricides. Several insecticides and acaricides that provide effective control of tick populations in small infested areas. At least two treatments are required for control; one in the spring for adult and nymphal stages and the other in late summer for larval stages. Surveillance is necessary to determine times of application (see Monitoring section for techniques). Low to moderate infestations can usually be controlled by one spring and one late summer treatment; heavy infestations may need two or more treatments in the spring and again in late summer and early fall. Consult your regional Integrated Pest Management coordinator to determine pesticide choice and application rates.

Aerial dispersal of acaricides requires coordination with local, state, and sometimes federal officials. Chrlorpyrifos in a 14% granular formulation applied at 7 lb/acre has been used successfully in tick control by this method (Goddard 1989). The National Park Service, however, does not currently use this method due to extensive bird kills associated with chlorpyrifos.

Vegetation management by herbicides is another tick control option. It produces the same benefits as mechanical management of vegetation; i.e., reduced harborages for animal hosts of ticks, reduced soil humidity, and increased soil temperature, all of which are detrimental to tick survival. Management of vegetation by herbicidal and mechanical methods may not always produce comparable results; Hoch et al. (1971) found that herbicidal treatment of woodlots was not as effective as mechanical vegetation clearing in reducing the population of Lone Star ticks.

Personal Protection


Ticks can be prevented from attaching to the skin or clothing by the use of repellents. Schreck et al. (1980), reported that DEET, M-1960, and permethrin provided 81%, 95%, and 89% protection, respectively, against the Lone Star tick. Mount and Snoddy (1983) showed that the application of pressurized sprays of 20% DEET to the exterior of surfaces of clothing provided 85% protection against nymphal and adult Lone Star ticks and 94% protection against adult American dog ticks. Permethrin (0.5%) gave 100% protection against both species.

However, DEET and M-1960 have a disagreeable odor and can cause skin irritations. The most effective repellent/toxicant against all tick species available at present is Permanone(0.5% permethrin), which must be used as a clothing treatment; Permanone is not intended to be sprayed directly onto the skin (Goddard 1989). Permanone remains effective for at least 1 month on unwashed clothing. All pesticide-treated clothing must be washed separately.

Indoors

Sites such as crevices, baseboards, trimming, furniture, ceilings, floors/carpets, walls behind pictures, bookshelves, and drapes should be spot-treated as needed. Crack and crevice treatments should be done with residual dusts or silica gel. This is the most effective way to use pesticides in a building. Fumigation does not work well in buildings because ticks can readily re-enter through doorways or windows.


SUMMARY

For outdoor areas, habitat reduction by mechanical removal of excess brush and overstory and regular mowing of grass 6" or less in height is recommended. Regular CO2 or drag surveys of likely tick habitats will indicate locations where treatment is required. If nonchemical measures prove ineffective, registered herbicides (for vegetation management) or acaricides (for direct kill) may be needed.

Animal-proofing park buildings through the use of exclusion techniques should eliminate indoor tick habitats and reduce the chance of future infestations.

Recommended procedures for protection of park personnel and visitors include frequent examination of the clothing and body of any person traveling through tick habitats, wearing protective clothing, and the use of clothing and/or skin-applied tick repellents.

Information should be made available to park visitors concerning known tick habitats within the park, personal protection techniques, and tick removal techniques.


REFERENCES

1. Garcia, R. 1965. Collection of Dermacentor andersoni (Stiles) with carbon dioxide and its application in studies of Colorado tick fever virus. Am. J. Trop. Med. Hyg. 14:1090-1093.

2. Ginsberg, H.S. 1992. Ecology and management of ticks and lyme disease at Fire Island National Seashore and selected eastern national parks. Scientific monograph NPS/NRSUNJ/NRSM-92/20. United States Department of the Interior, National Park Service.

3. Gladney, W.J. 1978. Ticks. pp. 102-113 In Dr. A. Bram (ed.), Surveillance and collection of arthropods of veterinary importance. U.S.D.A. Agriculture Handbook #518.

4. Goddard, 1989. Ticks and tickborne diseases affecting military personnel. United States Air Force School of Aerospace Medicine, Human Systems Division. USAFSAM-SR-89-2.

5. Hair, J.S., and D.E. Howell. 1968. Lone Star ticks: Their biology and control on Ozark recreation areas. U.S. Dept. of Commerce, Econ. Devel. Administration, Washington, D.C.

6. Hoch, AL., R.W. Barker, and J.A. Hair. 1971. Further observations on the control of Lone Star ticks through integrated control procedures. J. Med. Entomol. 8:731-734.

7. Lane, R.S, J. Piesman and W. Burgdorfer. 1991. Lyme borreliosis: relation of its causative agent to its vectors and hosts in North America and Europe. Annu. Rev. Entomol. 36: 587-609.

8. Keirans, J. E., and T. R. Litwak. 1989. Pictorial key to the adults of hard ticks, Family Ixodidae (Ixodida: Ixodoidea), east of the Mississippi river. Journal of Medical Entomology 26: 435-448.

9. Mallis, A., ed. 1982. Handbook of Pest Control, 2nd ed. Franzak and Foster, Cleveland, OH.

10. Metcalfe, C.L., and W.P. Flint, eds (revised by R.L. Metcalfe). 1962. Destructive and useful insects: their habits and control. McGraw-Hill Book Co., N.Y.

11. Mount, G.A., 1981. Control the Lone Star tick in Oklahoma parks through vegetative management. J. Econ. Entomol. 74:173-175.

12. Mount, G.A. and J.E. Dunn. 1983. Economic thresholds for lone star ticks in recreational areas based on a relationship between CO2 and human subject sampling. J. Econ. Entomol. 76:327-329.

13. Mount, G.A., and E.L. Snoddy. 1983. Pressurized spray of permethrin and Deet on clothing for personal protection against the Lone Star tick and the American dog tick (Acari: Ioxididae). J. Econ. Entomol. 76:529-531.

14. Newhouse, V.F. 1983. Variations in population density, movement, and rickettsial infection rates in a local population of Dermacentor variabilis ticks in the Piedmont of Georgia. Environ. Entomol. 12:1737-1746.

15. Schreck, C.E., E.L. Snoddy, and G.A. Mount. 1980. Permethrin and repellents as clothing impregnants for protection from the Lone Star tick. J. Econ. Entomol. 73:436-439.

16. Sonenshine, D.E. 1979. The Insects of Virginia: No. 13. Ticks of Virginia (Acari: Metastigmata). Research Division Bulletin 139. Department of Entomology, College of Agriculture and Life Sciences, Agricultural Experimental Station, Virginia Polytechnic Institute and State University, Blacksburg.

17. United States Department of Health, Education and Welfare. 1967. Pictorial keys to arthropods, reptiles, birds and mammals of public health significance. U.S. Dept. of Health, Education and Welfare, Washington, D.C.

18. Wilson, M.L. 1986. Reduced abundance of adult Ixodes dammini following destruction of vegetation. J. Econ. Entomol. 79: 693-696.

19. Wilson, M.L., S.R. Telford, J. Piesman and A. Spielman. 1988. Reduced abundance of immature Ixodes dammini following elimination of deer. J. Med. Entomol. 25: 224-228.
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