Large-Scale Monitoring of Insecticide Susceptibility in Cat Fleas, Ctenocephalides Felis

The cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae) is the most important ectoparasite of domestic cats and dogs worldwide. Infestations can lead to skin inflammation and cause flea allergy dermatitis, and fleas are also capable of transmitting several other parasites and diseases between animals and, indirectly, to humans. Fleas have a homometabolous life-cycle consisting of egg, larval, pupal and adult life-stages. The life-cycle takes between 18 and 70 days depending largely on climatic conditions. Eggs are laid in an animal's pelage and usually fall off the host prior to hatching. Eggs hatch after 2–3 days at room temperature and the larvae inhabit carpets, animal bedding, or small crevices in the household environment, feeding primarily on faecal blood droplets produced by adult fleas. The egg and larval stages are extremely susceptible to desiccation and require a relative humidity greater than 50% for development. After three moults, the larva spins a cocoon and metamorphoses into an adult. Adult fleas can remain in cocoons for weeks until host-related cues such as vibrations or an increase in CO₂ concentration stimulates emergence. Once emerged, adults will die within 10 days if they do not successfully find a host. Prior to 1995, successful flea control usually involved a combination of strategies. These included host-targeted and environmental insecticides and mechanical means of reducing or eliminating flea stages from the pet's environment. Mechanical methods included washing of pet bedding, vacuuming of carpets, furniture cushions, rugs or other substrata.

Because the outdoor development of flea life stages was limited to protected areas, clearing of yards helped to eliminate environments conducive to visits by urban wildlife and stray and feral pets. Treatment of indoor and outdoor environments with pesticides requires an understanding of what to use and where use them. For this reason, pet owners often consulted with veterinarians or knowledgeable and licensed pest control specialists to optimize treatments. With the advent of on-animal therapies, the paradigm regarding flea control has changed dramatically. As long as all pets with a home can be treated, the need to treat the indoor and outdoor environments has been reduced considerably. As with many other cases of pest management, the sustainability of flea control strategies is threatened by the evolution of pesticide resistance. However, work to document resistance is compounded by the fact that many reports of poor control are attributable to reduced mortality caused by substrates, climatic factors and deficiencies in the way that treatments are applied. There is nonetheless no doubt that strategies employed in the past using carbamates, organophosphates, pyrethroids and pyrethrins have led to confirmed cases of resistance. Biotic factors such as reproductive potential and operational factors such as the persistence of chemicals and repeated use of the same active ingredient are likely to have been contributing factors.