Integrated Pest Management Manual
Although there are over 250 species of fleas described in North America (Pratt 1957), only a few are commonly encountered by humans with enough frequency to be considered pests (Ehman and Story 1982). These include the cat flea, Ctenocephalides felis (Bouche), the dog flea, C. canis (Curtis), the human flea, Pulex irritans (L), and the oriental rat flea, Xenopsylla cheopis (Rothschild). Other species, such as the rabbit flea, Cediopsylla symplex, the mouse flea, Ctenopsyllus segnis, the ground squirrel flea Diamanus montanus (Baker), and Oropsylla hirsuta, a flea that feeds on prairie dogs, may achieve pest status when their host mammals nest in or near structures or the fleas attack hunters and hikers. Some, such as the northern rat flea, ground squirrel flea, and Oropsylla hirsuta are important vectors of sylvatic plague, bubonic plague, and murine typhus.
Flea management is best done via management of the host animal's habitat. Since fleas must spend part of their life cycle on their host, the chances of encountering fleas in areas of the host's habitat where it spends most of its time (e.g., its den or nest) are much greater than in a general area, such as a field or barn in which the host may or may not be found at a given time. One author has suggested that most fleas spend more time in the host nest or burrow than on the host itself (Benton 1980). This is the emphasis that will be placed on flea management strategies in this module.
IDENTIFICATION AND BIOLOGY OF FLEAS
This document will deal with the four most commonly encountered flea species mentioned above: the cat flea, the dog flea, the human flea, and the oriental rat flea. These fleas are found throughout the United States and are most likely to be encountered in mammal and bird nests or in pet bedding. Adult fleas are ectoparasites of their hosts, but unlike many other ectoparasites they do not spend the majority of their life cycle on their host.
Females deposit eggs in groups of 1 to 18 on the host after a blood meal. Some species, such as the cat flea, can deposit up to 25 eggs per day and over 1000 in a lifetime. Eggs soon drop off or are brushed off. Due to their spherical or oval shape, they roll into cracks and crevices on the floor or in or near nests and bedding. Eggs are whitish and 1/32" in diameter. Eggs hatch in 2 to 21 days.
Larvae are approximately 1/4" when first hatched, white, and have fine hairs. They lack legs or eyes but possess biting mouthparts. Most species feed on dried blood from the host (in the form of adult flea feces) or organic debris present in cracks and crevices. They also feed on cast larval skins. Depending on the availability of food, relative humidity, and other environmental factors, larvae pass through three stages (instars) in one week to several months. Optimal temperatures for larval development are 65
The pupal stage usually lasts approximately one week. The newly emerged adult may remain in the cocoon for some time; under adverse conditions, the adult may spend up to a year in the cocoon. Emergence occurs in response to pressure applied to the cocoon or detection of host warmth, vibrations, or carbon dioxide in the host's breath.
Adult fleas are small, brownish insects flattened from side to side, without wings but with powerful jumping legs. Adults can live for several years and go without feeding for months at a time under extreme conditions. Fleas can remain in a structure long after the host mammals have been removed. Depending on the species and environmental conditions, adults can breed from two weeks to two years after emerging. Adults feed on blood, and females deposit eggs only after a blood meal. Most species remain on the host only long enough to feed. Nearly all species have host preferences but are not restricted to any one host species. This trait is responsible for the transmission of several diseases (e.g. plague or murine typhus) from one host species to another. Adults prefer warm humid places and will leave a host if it dies.
Outdoors, fleas are most abundant during humid, rainy summers and are more common outside in the southern United States than in the north. Indoors, warmth and high relative humidities are conducive to large populations. The sudden appearance of large numbers of adult fleas in mid-summer and fall ("flea seasons") is due in large part to the onset of higher humidities and temperatures which permit larval development to accelerate. Larvae may undergo arrested development in less than favorable conditions.
Medical Importance of Fleas
Flea bites vary in effect from short-lived itching welts to an overall rash to symptoms which may last over a year, depending on the sensitivity of the victim. Young children are more sensitive than older persons. Commonly, a small red spot appears where the skin has been pierced. Little swelling ensues, but the spot is accompanied by a red halo of irritated skin which usually lasts for several hours to a day.
Fleas are vectors of several diseases important to human health including plague, murine typhus, and tularemia. The oriental rat flea is the most important plague vector from rodents (primarily rats) to humans, but at least 30 other flea species can also transmit the disease, including the northern rat flea, dog flea, cat flea, and the human flea. Plague (in the sylvatic form) is endemic in the western United States among small rodents such as chipmunks, ground squirrels, and prairie dogs.
Nearly all known cases of plague in humans in the United States since 1925 have been associated with wild rodents (mostly from the Rocky Mountain states) and their fleas. The greatest threat to humans exist when domestic rats are exposed to infection from wild rodents in areas adjacent to human communities.
Murine typhus is a mild form of epidemic typhus that is usually spread by the human louse. The Norway rat population is the main reservoir of the disease. The disease is most common in the southwestern and Gulf states. The disease is commonly spread from rat to rat, and from rat to human by the oriental and northern rat fleas. It has also been transmitted by cat fleas from infected feral cats.
Fleas are also vectors of tularemia, a disease related to plague. The natural reservoirs of tularemia are cottontail rabbits in the East, and jack rabbits in the West. Most cases reported are by hunters.
Fleas can also be intermediate hosts of several species of tapeworm including species which parasitize humans, dogs, and cats.
MONITORING AND THRESHOLDS FOR FLEAS
Fleas can be monitored in several ways. The simplest is to count and collect fleas landing or crawling on an observer's lower legs for one minute. In making surveys, trousers should be tucked into white socks to prevent bites and make collecting easier (socks can be put on over shoes). Light-colored trousers are preferred to provide greater contrast and facilitate counting and collection. A variation on the above is to wrap fly paper (sticky side out) around the lower legs and count fleas adhering after a predetermined interval (Cole and Burden 1978).
Fleas may also be combed off animals for an index of animal infestation. Do this over a white surface so fleas can be easily observed (Ehmann and Storey 1982).
Pet bedding should be periodically checked for flea eggs and dried-blood feces (frass) of adult fleas. This has been described as "salt and pepper" because it looks like small flecks of black and white debris. The frass is generally cylindrical, twisted, and about 1/16" long. It is dark in color. Larvae and pupae can be found at the edge of pet bedding or animal nests.
Indoors, five or more fleas on the legs of observers in less than one minute is indicative of severe infestation.
Flea populations in animal burrows or dens can be sampled by using a flannel cloth that is run through the burrow on the end of a plumber's snake. The number of fleas on the cloth is then counted. See Barnes et al. (1972) for more detail.
NON-CHEMICAL CONTROL OF FLEAS
Several studies have indicated that fleas spend the majority of their life either on the host or in the host's bedding or nest, so flea management should focus on these. In outdoor settings, the emphasis should be on spot treatment of nests with an insecticide. Exclusion of the host animal from an area may be desirable as well, but the feasibility of this strategy will vary with the animal and the location of its nest. In the case of domestic animals, sanitation should be the focus of a flea management program. Regular cleaning of bedding and other areas where the animal spends the majority of its time should reduce flea populations to non-irritating levels.
In areas where plague is endemic (e.g. the southwestern United States), efforts should be made to keep humans and fleas (and their wildlife hosts) separate. Prairie dog towns should not be allowed to expand into campgrounds and other developed areas. Camping and other outdoor activities should be restricted during an outbreak when fleas seek other hosts. Prairie dog burrows can be dusted with insecticide. Check with Public Health Service officials if your area is affected.
In most other cases, fleas are considered pests due to the nuisance caused by their bites. In these situations, management decisions should be made on a case-by- case basis.
Fleas require warm-blooded hosts for development and for egg maturation. Elimination of suitable habitat for wild rodents and other animals near structures will often reduce flea population levels. Screened vents prevent animals from resting inside or underneath structures. Eliminating vegetation close to structures and raising woodpiles off the ground reduces rodent harborage.
Indoors, wash or vacuum all pet bedding and sleeping areas on a regular basis. Cracks and crevices should be vacuumed and sealed, especially the area between the baseboard and floor. Dispose of vacuum cleaner bags to prevent reinfestation. Pets should be washed regularly and treated with insecticides if necessary.
The ultrasonic collar is sometimes for the control of fleas on domestic animals. A recent study (Hinkel, Koehler, and Patterson, 1990) showed that ultrasound devices are ineffective.
Insect Growth Regulators
A new technology in the management of fleas is the use of insect growth regulators (IGRs). These substances are similar to chemicals produced by the flea to regulate the shedding of its skin during molting. They work by interfering with the molting process, thus preventing the immature flea from developing into an adult. This method of control is a long-term process, since it will only kill larvae as they molt. A recent study using pyriproxyfen (sold as Nylar
Fleas are preyed upon by ants and beetles that feed on larvae in the host's nest (Fox and Bayona 1968).
CHEMICAL CONTROL OF FLEAS
Insecticides are also part of a flea management program. These are applied to areas where fleas are most likely to breed, including animal bedding, cracks in floors, and baseboards. Many veterinarians also recommend the use of indoor foggers to apply pesticides to rooms where domestic animals spend the bulk of their time. Flea collars are not considered to be effective (Whiteley 1987). When insecticides are used, it should be in conjunction with sanitation (Arthur et al. 1989). One difficulty with the use of insecticides as part of a flea management program is the ability of the adult flea to remain in its cocoon as a preemerged adult. This means that the adult flea can remain in the cocoon in which it pupates until it encounters a suitable host. Insecticides have been found to be ineffective against these preemerged adults (Rust and Reierson 1989). This highlights the importance of sanitation as the key element in a flea management program.
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