To counteract water loss due to excretion, cuticular transpiration and respiration, various groups of arthropods have developed mechanisms for active uptake of water vapor from unsaturated air. Active water uptake has been demonstrated in the larval and pre-pupal stages of rat fleas (Xenopsylla) and in the adults of hen fleas (Ceratophyllus). In this study, active uptake was examined in the larval, pre-pupal, pupal and adult stages of the cat flea, Ctenocephalides felis. To determine active uptake capabilities, pre-desiccated fleas were massed, placed at relative humidities ranging from 44% to 93%, and massed again after 24 hours. The lowest relative humidity where no mass change occurred indicated that water loss was equal to water gain and was designated the critical equilibrium humidity. The critical equilibrium humidity for the larval stage was found to be below 59% relative humidity. Some individuals of the pre-pupal and adult stages also demonstrated active uptake. The site of active water uptake was also explored in this study. As demonstrated in Xenopsylla, it appears that active uptake in Ctenocephalides felis occurs through a specialized portion of the gut tube known as the rectal sac. Active water uptake is necessary to prevent desiccation and ensure proper development.
Species 1: Siphonaptera Pulicidae Ctenocephalides felis (cat flea)
Keywords: active water uptake
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