Cat flea eggs possess a widely oval form, rounded at both ends, a slightly transparent color at the beginning, later a pearly white color, 0.5 x 0.3mm size, a smooth surface which can slightly darken later on (Karandikar and Munshi, 1950), and they are well visible to the naked eye (Fig. 6). They are laid nearly exclusively on the host by mature females and do not immediately fall from the animal after they are positioned, according to Rust and Dryden (1997). Initially the chorion of the egg is wet, which tends to prevent drop-off. But it dries rapidly and 60% of the eggs drop off within two hours of deposition (Rust, 1992). The rate at which eggs drop or are dislodged from the pelage is influenced by grooming, hair coat length, and host activity (Rust and Dryden, 1997). Within eight hours about 70% of them are dislodged from the host (Rust, 1992).
Temporal patterns of egg deposition are reported with a correlation between peak egg production and periods of the cat sleeping or resting at the middle of scotophase. Significantly fewer eggs are produced near dusk and dawn (Kern et al., 1992). Rust (1992) reported similar results of peak egg production during the last eight hours of scotophase, but no correlation between peak egg production and resting or sleeping patterns in test cats. Furthermore fleas did not change their egg production in response to different photoperiods (Metzger and Rust, 1996). Dropping off the host, flea eggs accumulate in areas where pets sleep and rest (Byron, 1987).
Egg deposition by adult females does not take place during the first 24 hours of blood feeding and is only less than half of the daily average during the second 24 hour period (Thomas et al., 1996). Further a low average fecundity was recorded during the first three days (Thomas et al., 1996). The start of the egg production is also influenced by the age of the female flea: Osbrink and Rust (1984) reported of 4-day old adult females placed on a host, beginning egg production after two days, whereas adult females younger than 24 hours require three to four days on the host before egg production starts (Osbrink and Rust, 1985). On cats, fleas reach reproductive maturity within the first week, with a peak of egg output occurring sometimes as quickly as within three days (Williams, 1983). But it may also take up to nine days for them to reach maximum egg output (Williams, 1983; Osbrink and Rust, 1984; Dryden, 1989).
Bloodfeeding as precondition for successful mating
In general, it is suggested that fleas do not mate before bloodfeeding or if they do, the mating is unsuccessful. In the cat flea, bloodfeeding is apparently necessary for both oviposition and successful mating. Mating however is not necessary for oviposition (Zakson-Aiken et al., 1996).
The number of eggs collected in different studies to gain an impression of daily production and total egg count varies greatly between hosts (Dryden, 1989; unpublished data in Rust, 1994). Rust (1994) presumes possible reasons for this to be differences in grooming which greatly affects adult survival (Dryden, 1988, 1989; Wade and Georgi, 1988) or possible differences in the host’s physiology. The reproduction in fleas is also stimulated by estrogens and corticosteroids in the peripheral circulation of the host as shown by Rothschild and Ford (1964) for the rabbit flea, possibly explaining individual variation in the extent to which a host attracts fleas (MacDonald, 1984).
Adult female fleas may produce from 11 to 46 eggs per day (Osbrink and Rust, 1984; Dryden, 1988, 1989; Hink et al., 1991). According to Hinkle (1992), fleas produce an average of 24-25 eggs per female per day on cats. Osbrink and Rust (1984) suggested that females might deposit between 300 and 500 eggs in their lifetime with an average of 158.4 eggs per female flea. Patton (1931) and Smit (1973) reported of 800 to 1000 eggs per female flea. Dryden (1989) proposes a possible production of up to 1,745 eggs during a 50 day period and well over 2,000 eggs over 113 days in unconfined fleas and cats restricted from grooming. According to him the cat flea is capable of producing 40-50 eggs per day during peak egg production, averaging 27 eggs per day over 50 days, with continued egg production for over 100 days. About 1.05-times the body weight is produced in form of eggs within 24 hours (Dryden and Gaafar 1991).
Thus, fleas are highly reproductive and work with a calculated loss as several other parasites do (Strenger, 1973). Possibly because of the inability of the immature stages, particularly the larvae, to withstand extreme changes in temperature and humidity or because of a failure of eggs to be deposited in unfavorable microhabitats, the cat flea has adapted by having a large reproductive capacity (Dryden and Rust, 1994).
Flea egg production under the influence of host and environmental conditions
Flea egg production is reported to be influenced by the source of host: fleas raised on cats produced five to nine times more eggs than those raised in an artificial system with a significant difference in the total number of eggs and the number of eggs per female (Wade and Georgi, 1988). Furthermore cat fleas have been reported to feed and survive for some time on human hosts, but no viable egg production could be recorded (Bacot, 1914; Joseph, 1976; Akin, 1984; Williams, 1986), instead of viable eggs on a variety of other hosts - calves, hamsters, rats and dogs (Williams, 1986). In contrast, Tränkle (1989) reported of reduced numbers of viable eggs produced by the cat flea when fed on human hosts. C. canis already failed to complete its life cycle on cats as no eggs laid developed to adults (Baker and Elharam, 1992).
As is the case for all the flea’s life stages the hatching of the egg is strongly influenced by environmental conditions (temperature and relative humidity (RH)). At 16°C, the number of flea eggs hatching increased with rising RH from about 70% hatch at 33% RH up to 100% hatch at 92% RH. At 27°C, nearly all eggs hatched when there was 50% RH or more. However, at 35°C the hatch only took place in moist air (75-92% RH). At the same high temperature moisture conditions below 75% RH caused desiccation. The reason for the failure of eggs to hatch in warm saturated air (i.e. 35°C) may be due to an accumulation of heat within the egg (Silverman et al., 1981). Olsen (1985) found about 70% hatch when eggs were held at 24+/-1°C and 65+/-5% RH.
The time required for hatching increases from 1.5 to 6.0 days as temperature decreases from 32 to 13°C (Silverman et al., 1981). An exposure to 3°C for one day kills 65% of the eggs. Longer exposures provide complete kill (Silverman and Rust, 1983). Eggs from C. canis hatched at 22°C and 25°C and at 50% and 75% RH (Baker and Elharam, 1992). As reported for C. felis temperature has a dominant effect on the time taken for hatching. As temperature decreased, the hatching time was observed to increase in a non-linear fashion by Baker and Elharam (1992) as well for C. canis, with RH being of greater importance for the (whole) development of C. canis than temperature.
Summary see Box 1.
BOX 1. Cat flea eggs
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