AdultsOnce the flea emerges from the cocoon, it will not undergo any further molts, and the only size increase occurs due to swelling of the abdomen after feeding (Dryden 1989a). To identify the different species of Ctenocephalides spp. the outer appearance of the imagines can be used (see also ‘General Morphology’). Key distinguishing features of the two most important species of pets, the cat and the dog flea, have been documented by Soulsby (1982): C. felis: Both pronotal and genal combs are present; length of head is generally greater than twice the width; first two spines of the genal comb are approximately equal in length. The tibia of all 6 legs is armed with 4 to 5 teeth (see Fig. 2). C. canis: Both pronotal and genal combs are present; length of head is not twice as wide; first spine of genal comb is noticeably shorter than the second spine. The tibia of all 6 legs is armed with 7 to 8 teeth (see Fig. 2).
Fig. 2: Morphological differentiation of the cat flea (C.felis) and the dog flea (C.canis) original size upper right: 3.0 mm A variety of stimuli help seeking a hostAfter emerging from the cocoon, the flea almost immediately begins seeking a host (Dryden 1993) searching for a blood meal (Dryden 1989a). A variety of stimuli attract newly emerged fleas. Visual and thermal factors have been found to be primarily responsible for attraction and orientation to the host (Osbrink and Rust 1985b). Combinations of different stimuli including tactile stimuli, CO2, air currents and light together with the adult’s age stimulate locomotion and modify the adult’s responsiveness, at the same time limiting environmental interference while locating the host (Osbrink and Rust 1985b). Stimuli that failed to elicit an observable response were substrate vibrations, cat odor, sounds, changes in light intensity, and the passage of shadows (Osbrink and Rust 1985b). Visual stimuli have shown to be attractive to the cat flea, but even in their absence, fleas were attracted by heat with air currents (created by a warmed moving target), as well as CO2 increased flea activity (also reported by Benton and Lee 1965), quantifiable only in the absence of visual stimuli (Osbrink and Rust 1985b). Fleas possess specialized, powerful legs for jumping onto a host, and according to Osbrink and Rust (1985b) their jump seems to be directed but not precise, responding to the amount of stimulus and not to the pattern. Thirty-four centimeters have been recorded in jumping (Dryden 1996). An increase of the size of the visual stimulus increases the response of the stimulus, thus a potential host is the more attractive to the flea the larger its size is (Osbrink and Rust 1985b). Osbrink and Rust (1985b) could not observe any visual orientation under red light or an increase in attractiveness by increasing the complexity of patterns on the target, so that acute form vision does not occur in the cat flea (Rothschild and Clay 1952; Osbrink and Rust 1985b). Additional stimulation in form of air movements were necessary to evoke a directed jump onto a stationary heated target, which was simply causing attraction and orientation in the cat flea (Osbrink and Rust 1985b). Adult cat fleas display positive phototaxis and negative geotaxis in both the unfed and engorged state (Dryden 1988). By that the newly emerged cat flea residing in the carpet will move on top of the carpet canopy where it will be able to jump onto a passing host (Dryden 1989a), enhancing the success in host acquisition (Dryden and Rust 1994). The cat flea has proved to be most sensitive to light with wavelengths between 510 and 550 nm (green light) and insensitive to wavelengths between 650 and 700 nm (Crum et al. 1974; Pickens et al. 1987). The flea’s responsiveness to certain wavelengths of light explains observations that adult fleas congregate around vents to crawl spaces, entrances to dog houses, and window sills (Dryden and Rust 1994). Their responsiveness to light can be used to capture fleas in light traps (Dryden and Rust 1994). Unfed flea can survive several days without a blood mealThe activity of cat fleas peaks at dusk (Koehler et al. 1989; Bossard 1997), which coincides with cat activity (Kern et al. 1992). Newly emerged, unfed cat flea can survive several days before taking a blood meal. In cool, dry air, 10% of newly emerged cat fleas survived for 20 days, while in moisture saturated air, 62% survived for 62 days (Silverman and Rust 1985). At 24°C and 78% RH, 95% died within 15 days (Dryden 1988), and under ambient room conditions averaging 22.5°C and 60% RH, 95% died within 12.3 days (Dryden 1989a). No life cycle stage (egg, larva, pupa or adult) can survive for ten days at 3°C or five days at -1°C (Silverman and Rust 1983). Survival rates of fed imagines without any given environmental conditions were stated as 234 days (Bacot 1914), 58 days (Soulsby 1968) and 11.8 days (Osbrink and Rust 1984). At temperatures of 5-15°C and 70-90% RH C. canis imagines were observed to survive seven days and C. felis adults an average of ten days. Derived from investigations with different environmental conditions, the survival time of unfed adult fleas increases with increasing humidity and sinking temperature and varies between 0.5 days at 35°C/2% RH and 40 days at 16°C/100% RH (Silverman et al. 1981b). Longevity of unfed adult cat fleas increases significantly in saturated air at 16°C compared to combinations of lower RH’s and higher temperatures (Silverman et al. 1981b) (see Table 4). Table 4. Effect of temperature and humidity on the longevity of unfed adult female cat fleas (C. felis) (average number of days for 90% mortality)
For C. canis, adults were maintained at 8-10°C in saturated air for up to 58 days (Bacot 1914). Low RH associated with subfreezing temperatures are likely to preclude adult cat flea survival off the host (Silverman et al. 1981b). During the warmer months of the year, it is doubtful that adult fleas can live for more than a week in the absence of a host or a suitable microclimate that is relatively cool and moist (Silverman et al. 1981b). The only function of an adult: reproducingOnce on a host, the cat flea begins feeding within seconds and mating occurs on the host in the first eight to 24 hours, with most females having mated by 34 hours (Akin 1984; Dryden 1990) (see also ‘Eggs’). Female cat fleas seem to have multiple matings, for young as well as fully mature and gravid females have been observed in the act of mating (Akin 1984). Furthermore it has been observed that the spermatheca (sperm holding organ) acquires progressively more sperm over the first 24 hours (Akin 1984). Multiple mating of one female with several males and sperm precedence which means that sperm deposited by the last male is the first used for fertilization, is often combined with protogony (i.e. females tend to develop before males) in insect species (Thornhill and Alcock 1983). Although most insect species exhibit protandry (males tend to emerge before females), cat fleas belong to a much smaller group that exhibits protogony (Thornhill and Alcock 1983). The multiple mating (Akin 1984) and the protogony may speak for possible sperm precedence in cat fleas (Dryden and Smith 1994). After the first blood meal, the flea must continue to feed and reproduce in order to keep its metabolism in balance (Baker 1985). The adult flea is the perfect example of a parasite that must live on its host in order to survive. As an adult, its only function is to reproduce and it must feed constantly in order to do so (Baker 1985). According to Zakson-Aiken et al. (1996) bloodfeeding is apparently necessary for oviposition as well as for successful mating. Males require feeding before the epithelial plug is unblocked in their testes (Akin 1984). (see also ‘Eggs’ and ‘Larvae’) For blood intake, the suctorial mouth parts, well adapted to piercing and sucking from the skin are used. The host’s epidermis is penetrated by the flea’s maxillae. A tube, the epipharynx, enters the capillary vessels and draws up blood while saliva from the maxillae is deposited in the surrounding tissue (Lavoipierre and Hamachi 1961) (Fig. 10).
Thus minimal damage to the skin is caused (Lavoipierre and Hamachi 1961). The saliva of the cat flea contains a substance that may soften and spread dermal tissue, assisting in the penetration of the dermis by the proboscis (Feingold and Benjamini 1961). It further contains an anticoagulant, helping in the uptake of blood (Deoras and Prasad 1967). The flea requires a period of between two and ten minutes to engorge (Rothschild 1975). The amount of blood consumed by a female cat flea is an average of 13.6μl (+/-2.7μl) per day, which is equivalent to 15.15-times the body weight (Dryden and Gaafar 1991). Female fleas increase their body weight by 40% during an one hour stay on a host while male fleas only show an addition of 3%. Within 48 hours the fleas reach their maximum weight. In females an addition of 140% (here 1.08 mg) respectively in males of 19% (here 0.43 mg) could be recorded (Schelhaas and Larson 1989). Male fleas feed less frequently than females. Females were observed attached and feeding in one site for more than three hours, whereas males were rarely attached for periods longer than 10 to 20 minutes as reported for the bird flea (Ceratophyllus idius) (Schelhaas and Larson 1989). Unpublished laboratory observations by Pospischil (2001, personal communication) stated the maximum time of feeding of C. felis to be 5-10 minutes and of Archaeopsylla erinacei, the hedgehog flea, 20 minutes. Males do not only feed less than females, they are also more active on the host (Dryden 1990). Once cat fleas feed on a host for a few days and initiate reproduction, they apparently reach a point at which they become dependent on a constant source of blood (Dryden 1993). By now the cat flea is thought to be a permanent parasite of its host. Dryden (1989b) found 85% of female and 58% of male cat fleas to be still present after 50 days on cats which have been restricted in their normal grooming activity (by declawing, fitting with an Elizabethan collar and housing in specially designed metabolic cages). Others report only a recovery of 22% of the fleas after 22 days on a cat (Hudson and Prince 1958). A permanent association of the cat flea with its host has already been described by Elbel (1951) and Deoras and Prasad (1967). Fleas leaving the host will either be dead or will die within four days (Dryden 1989a). Cat fleas which have fed for five days on a host and then been removed and held at approximately 24°C and 78% RH, died within 48 hours (males) respectively 96 hours (females) (Dryden 1988). When fed only for twelve hours and then removed from the host, 5% were still alive at 14 days (Dryden 1993) so that once a few days are spent on a host a permanent and vital relationship seems to be established. Maximum longevity of cat fleas has not completely been demonstrated, but survival on hosts which have been restricted in grooming activity has been reported for at least 133 days (58% of all the female fleas were recovered) (Dryden 1989b). Cat fleas housed in screen-covered microcells were reported to have an average on-host longevity of 7.2 days for males and 11.2 days for females (Osbrink and Rust 1984). C. canis has been reported to live for up to two years when fed on dogs (Harwood and James 1979). An important role in the survival and longevity of fleas on the host is played by the grooming behavior of flea-infested animals (Hudson and Prince 1958; Osbrink and Rust 1984; Wade and Georgi 1988). Cats spend a considerable part of each day grooming themselves and have been shown to remove up to 50% of their flea parasite load within one week (Wade and Georgi 1988). Some pets may tolerate a small to moderate number of fleas, others groom themselves almost constantly, thereby ingesting and dislodging many of the fleas (Dryden 1993). Osbrink and Rust (1985a) reported of 70% of feline hosts having only relatively few (<7) fleas. Any cat flea dislodged from the host through grooming activity must return to the host or acquire another within a couple of days or the flea will die (Dryden 1993). But there is also some form of interhost movement by the adult flea (Rust 1994), of importance also for epidemiology (see chapter ‘Flea Epidemiology’). Infrequent, short term contact between infested and uninfested hosts is insignificant for the movement of adult cat fleas (Blagburn and Hendrix 1989). But nevertheless movements between hosts of 2-15% of the cat fleas infesting a host are possible (Rust 1994). Significantly more female cat fleas have been observed to remain on the host (Rust 1994). Movement occurs between hosts whether the hosts are permitted to live together or not. Movement by adult cat fleas between hosts occurs at a low rate and the likelihood of establishing new infestations by adult fleas transferring from one host to another exists, but does not seem to be as important as primary larval breeding sites (Rust 1994). Transference can also occur when cats and other hosts are killed and consumed as it is supposed for cat flea infestations of coyote, fox, and other carnivores (Rust 1994), and known to occur in weasels (Mustela sp.) (Marshall 1981). Summary see Box 5.
References
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