Accelerated impregnation and maturation of the rabbit flea coincides with the spring peak litter-size of the rabbit, but its breeding performance falls off before that of the domestic host. A kairomone nestling factor, which boosts copulation, impregnation and development of fleas feeding on the newborn young, is also present in relatively feeble amounts in baby rabbit urine. This urine boosts pairing of matured (=“primed”) fleas united in tubes away from a host, but impregnation is increased only if fleas are feeding on newborn young while exposed to the urine.
Undeveloped fleas matured on the pregnant doe require a transfer to another host before they will pair, whereas fleas matured on the nestlings copulate without a transfer. A variable time-lag between transfer and copulation of fleas, dependent on the “priming” qualities of the preparatory host, suggests that a chemical intermediary is involved.
If the antennae of the females are coated with vaseline, the maturation of these fleas is delayed feeding on nestlings, but not on the prepartum doe. This delay is less marked during the spring acceleration than at other times of the year.
The breeding of a North American species of hare flea (Cediopsyllu simplex (Baker)) parasitizing Sylvilagus floridanus (Allen) is also controlled by the sex hormones of the host.