The eggs are laid separately or in small series of two to six, generally in the litter of the host or the dust of the dwellings.1 A female flea deposits several hundred eggs during her life: 200 to 300 eggs for Xenopsylla cheopis, 800 for Ctenoce-phalides felis and several thousand for Tunga penetrans. Eggs will hatch after one or two weeks according to the species, temperature and humidity. Each of

Figure 1.14 Adult male Oropsylla montana flea (Photo courtesy of CDC/DVBID, BZB, Entomology and Ecology Activity, Vector Ecology & Control Laboratory, Fort Collins, CO/John Montenieri).

the three larval stages lasts approximately two to six days. The larvae have a negative phototropism and are very hygrophilic. They are active and feed on a variety of organic debris, the remnants of digested blood produced by adults, small arthropods present in the nest and even dead adult fleas. The larval lifespan is 10-21 days. The pupa is motionless living inside a cocoon and does not feed; this stage lasts one to two weeks. The adult leaves the cocoon and shortly afterwards, the male and female copulate and seek a host for the first blood meal. Both sexes are hematophagous. The saliva of fleas is irritating and certain people have a particular sensitivity, bites can result in sleep loss, nervous disorders, etc. Secondary infections can also occur when bites are scratched. A blood meal occurs every two to four days for species living in burrows, and every day (or more) for those species living on their host. The flea quickly leaves the host if death occurs and will rapidly seek out another host. This behaviour is of great epidemiologic importance in the propagation of diseases. The longevity of the adults is about ten months, although this varies according to species and conditions. The optimum range of temperature and humidity is generally narrow: 22 °C to 24 °C and greater than 80% humidity for X. cheopis. Three models of behaviour have been identified: (1) the species which live permanently on their host like the "fur fleas'', e.g. X. cheopis, P. irritans (human flea), and jump from one host to another; (2) the ''nest fleas'' which live in the nest and visit the host to take their blood meals, and have only a weak aptitude for jumping; and (3) the sedentary species which live fixed by their oral parts on the host, like Echidnophaga gallinacea on poultry or Spilopsyllus cuniculi on rabbits, or embedded in their host like Tunga penetrans.

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