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8 : The cat flea: applied biology

Search for a host by the adult

Adult Ctenocephalidesfelis rely on visual and thermal stimuli to fmd their host²⁹. Certain factors such as age of the flea and the level of CO2 modify their ability. Ctenocephalidesfelis is morę sensitive to light rays of wavelengths between 510 and 550 nm (green light) than to light of wavelengths between 650 and 700 nm ³⁰’³¹. A yellow-green filter of 515 nm wavelength is twice as attractive to adult Ctenocephalidesfelis than white light³¹. The responsiveness of fleas to light rays explains why fleas are found in large numbers in passage ways, at the entrance to dog kennels, and by doors and Windows. This response to light is the reason behind the use of light traps to capture fleas.

Although Ctenocephalidesfelis orientate themselves and move spontaneously towards a light source, this tropism is notably increased when the light source stops suddenly and temporarily. In one report, an intermittent light trap allowed collection, within 20 hours, of 77% and 57% of fleas released at 4.1 and 8.5 metres respectively from the trap³¹. The short interruption of light produced by the trap could be mimicking the shape of a host moving around, the trigger for the jumping reflex. In addition to visual stimuli, thermal stimuli are extremely important in acąuiring a host²⁹. In a given area, adult fleas make elear distinctions between heated targets and those maintained at ambient temperaturę.

Positive phototropism and also negative geotropism, improve the chances of success in host acąuisition. Newly emerged fleas move towards the surface of carpets, rugs or vegetation where they are morę likely to encounter a host.

They can survive for several days before taking a blood meal. Their survival is strongly correlated to ambient temperaturę and humidity. In air with saturated humidity, 62% of adult Ctenocephalides felis can survive for 62 days, whereas, in a cold and dry environment, only 10% of fleas survive for 20 days²¹. At 22.5°C and 60% RH, only 5% of Ctenocephalides felis survive for 12 days⁸.

Alternatiye hosts

The reappearance of fleas, several weeks or many months after apparent eradication of an infestation is a problem regularly encountered by owners who treat their infested animals. The prolonged survival of pre-emerged adults and the lack of penetration of insecticides into carpets may explain many of the reinfestations that occur within several weeks to months after the treatment. Nevertheless, other explanations are necessary to account for the annual reappearance of infestations in temperate climates. Although certain species of flea pass their winter months as pupae or adults off their host, no stage of Ctenocephalides felis can survive for 10 days at 3°C or for 5 days at -1°C.

Annual recurrence may be connected with the large variety of hosts of Ctenocephalides felis. This flea can be harboured by many wild mammals: coyote, fox, polecat, various rodents, coypu, opossum and ferret⁵. These altemative hosts, some of which live in close proximity to man and his pet animals, can be permanent sources of re-infestation. Elimination of certain wild mammal species in urban areas may reduce the number of repeated infestations of Ctenocephalides felis.

Conclusions

The eggs and larvae of the cat flea cannot survive major climatic variations, particularly in temperaturę and humidity. Hence, areas suitable for the development of Ctenocephalides felis are generally limited. In most households, only a smali proportion of eggs develop into adults. Flea populations survive due to a high reproductive capacity, the large rangę of hosts available and because of the strong association between the flea, the host and its resting areas. A large percentage of immature stages can survive, if temperaturę, relative humidity and larval food reserves are optimal. In these conditions, an explosion in flea populations can be observed to the detriment of man and his pet animals.

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