POPULATION-DYNAMICS OF THE HOUSE-DUST MITES DERMATOPHAGOIDES-FARINAE,DERMATOPHAGOIDES-PTERONYSSINUS, AND EUROGLYPHUS-MAYNEI (ACARI, PYROGLYPHIDAE) AT SPECIFIC RELATIVE HUMIDITIES

Experiments were conducted to determine the effects of relative humidi ty on the population dynamics of single and mixed species of Dermatoph agoides farinae Hughes, D. pteronyssinus (Trouessart), and Euroglyphus maynei (Cooreman) at specific relative humidities maintained at 20 de grees C, with unlimited food. The population density of single and mix ed species (D. farinae and D. pteronyssinus) increased exponentially w hen cultured at 65, 70, and 75% RH. The mean population growth rates w ere 17.3 +/- 4.4 SD and 32.5% +/- 4.7/wk for D. farinae and D. pterony ssinus, respectively. Mean population doubling times were 2.2 +/- 0.3 and 4.2 +/- 1.3 wk for D. pteronyssinus and D. farinae, respectively. Mixed species cultures, started with equal numbers of D. farinae and D . pteronyssinus, resulted in higher percentages of D. farinae than D. pteronyssinus. In cultures started with 75% of one species and 25% of the ether, the more numerous species remained dominant and in similar ratios throughout the experiment. Both D. farinae and D. pteronyssinus population densities maintained at 85% RH declined over a 12-wk cultu re period because of mold growth. E. maynei were unable to survive at 65, 70, 75, and 85% RH, which indicated that their climatic requiremen ts were different from those of D. farinae and D. pteronyssinus. Popul ation densities of D. farinae and D. pteronyssinus cultures declined w hen held at 21-22 degrees C and relative humidities of less than or eq ual to 50%; however, at 50% RH, significant proportions of the populat ions survived for 10 wk. Half-life for desiccation of D. farinae and D . pteronyssinus at 45% RH was 11.5 and 1.2 wk, respectively, but at 50 % RH was 86.3 and 4.0 wk, respectively. The data indicated that a less than or equal to 50% RH would have to be maintained for long periods to reduce both D. farinae and D. pteronyssinus by desiccation procedur es. The results of this study show that D. farinae and D. pteronyssinu s have high reproductive potentials and population growth rates, which indicate that mite reduction procedures must be thorough or mite dens ities will return to high levels quickly following remediation if adeq uate food and suitable microclimatic conditions exist.