Flea control: Does the environment really matter? (Proceedings)

Fleas have been around a very long time having evolved from their ancestors about 125-150 million years ago. There are approximately 2500 species and subspecies of fleas worldwide, 94% of which parasitize mammmals and the other 6% parasitic on birds. Fleas undergo a complex cycle of development beginning with the egg. Female fleas are prolific egg producers with some producing an average of 25 eggs/day. Eggs are, generally, laid on the host. They are sticky and may adhere briefly to the fur, but, eventually fall off into the environment. Here, they develop and the first-stage larvae hatch. They feed on organic matter present in the environment. For many fleas, the food of choice is the fecal pellet voided during feeding by the adult. The flea larvae grow, molt twice, and then enter the pupal stage. During this stage, adult fleas develop, which eventually emerge from the pupae. Emergence may be stimulated by mechanical compression and vibrational stimuli (potential host present!). Body warmth, air movements, substrate vibrations, sudden changes in light intensity and CO2 are important stimuli used by fleas for finding a host. Once the host is located, fleas begin to feed, mating occurs and egg production begins.

Within the US, Ctenocephalides felis is reported to be the most common flea infesting dogs and cats. Although true, there are regional differences in flea species present; thus, C. felis may not be endemic in an area although this does not mean the flea will not be present. Ctenocephalides felis eggs, generally, hatch in about 5 days, depending on temperature and relative humidity (RH). Fifty percent of eggs hatch at 95 F and 70% RH in 1.5 days. At 55 F and 70% RH, 50% of eggs will hatch in 6 days. Larvae are susceptible to heat and desiccation and cannot survive below 50% RH (neither can eggs or adults). At 78% RH and 75 F, the larvae become pupae in about 11 days. The pupal stage is the most environmentally resistant stage surviving RH as low as 2 % RH at 60-80F. However, pupae, along with the other stages, cannot survive cold temperatures. All stages only survive about 10 days at 37 F and 5 days at 33 F. Adults develop and emerge from the pupae in about 5 days at 80% RH and 80 F. However, pre-emergent adults can remain in the pupae for as long as 174 days when conditions dictate. In general, cooler, drier climates result in longer life cycles with adults emerging over a longer period of time while warmer, more humid climates support a shorter flea life cycle. Under ideal conditions, the generation time for C. felis is about 1 month, but can be as short as 20 days. Given the short generation time and the prolific egg production, it evident why flea populations can build up in a short amount of time.

Because as much as 95% of a flea population at any given time is thought to be in the environment, and these stages are usually inaccessible to on-animal agents, control of fleas on the animal does not necessarily mean the flea population has been controlled. Successful control usually involves a combination of strategies that target both the host and the environment. Numerous safe and effective adulticidal products are available for on-host flea control. Many of these incorporate insect growth regulators or insect development inhibitors which inhibits egg hatching. However, only those eggs produced by a female flea which has ingested these products will be prevented from hatching. Some products work so quickly that fleas are killed before viable eggs can be produced. However, eggs already in the environment can continue to develop and hatch, giving the unknowing pet owner the impression that the flea control product is not working. Simultaneously with the on-animal control should be environmental control. Simple, mechanical means of environmental control include washing of pet bedding and other materials in areas frequented by the animal. Vacuuming of carpets, furniture, and other areas at risk is an effective means of reducing environmental flea populations. Vacuum's with a "beater bar" are preferred as they will reach deeper into the carpet and furniture fabric. The vibration will stimulate adult fleas to emerge, which are then vacuumed away. Brushes will also scarify pupal surfaces, resulting in the inability to regulate water and dessication. Vacuuming is not an effective means of removing larvae because they coil around carpet fibers. However, vacuuming will remove flea feces, helping to eliminate the larval food source. Steam-cleaning can kill adults, larvae and some eggs. However, the vibrations will stimulate the remaining eggs to hatch, so a thorough vacuuming may also be necessary. Numerous insecticides are available for the treatment of both the indoor and outdoor environment. However, consultation with a licensed pest control specialist is recommended for such applications.