Humidity as a Factor Regulating Feeding and Water Balance of the House Dust Mites Dermatophagoides Farinae and D. Pteronyssinus (Acari: Pyroglyphidae)1

Feeding rates of Dermatophagoides farinae and D. pteronyssinus are significantly higher at ambient water vapor activities (av's) above the critical equilibrium activity (CEA) than below it. The quantity of water obtained with equilibrated food at av's below the CEA is insignificant when compared to that exchanged by sorption and transpiration and is not sufficient for dust mites to maintain water balance. The CEA for feeding mites is identical to that for fasting mites. Considering all possible avenues of water gain by house dust mites for maintaining water balance, their primary source of water to sustain life is that gained by passive and active sorption from ambient water vapor.