Fluctuating hydrating and dehydrating relative humidities effects on the life cycle of Dermatophagoides farinae (Acari: Pyroglyphidae)

Reducing relative humidity to <50% in homes is recommended as one means of reducing dust mite populations in the homes of those who suffer allergies to house dust mites. Because of some activities in the home (e.g., bathing, cooking, opening windows), it may not be possible to keep relative humidity constantly <50%. We determined how the fluctuating daily regimes of hydrating (75%) and dehydrating (35%) relative humidities affected the development of Dermatophagoides farinae Hughes. The life cycle was completed (egg to adults) when mites were given regimes of 24 h at 75% RH, 8 h at 75% and 16 h at 35% RH, 6 h at 75% and 18 h at 35% RH, and 4 h at 75% and 20 h at 35% RH. The time required to complete development was inversely related to the amount of moist air given daily. Development took 58.3 +/- 1.44, 64.7 +/- 1.87, and 82.4 +/- 2.39 d for 8, 6, and 4 h of moist air daily, respectively. In comparison, the life cycle was completed in 41.1 +/- 0.50 d when development occurred at a constant 75% RH. Egg incubation time was significantly longer for fluctuating ambient relative humidity compared to a continuous 75 or 35% RH. Of the emerging larvae 53.8, 72.7, 62.7, and 85.0% completed the life cycle when given 4, 6, 8, and 24 h 75% RH daily and 35% RH for the remainder of the day. This study revealed that D. farinae can complete development when given only short periods of moist air daily but the rate of development is much slower than development at a constant 75% RH. Therefore, reducing ambient relative humidity does reduce the rate of development of mite populations and the accumulation of dust mite allergen.