Annual fluctuations of mites and fungi in Danish house-dust: an example.

For one year dust was sampled monthly from a single mattress. Until August mite counts were at background levels. In September and October there was a burst in the counts for the house-dust mite, Dermatophagoides farinae and for the house mite, Glycyphagus domesticus. Their occurrence might be interpreted as a response to large densities of an unidentified yeast in September. This yeast appeared when the indoor absolute humidity exceeded 9 g H2O/kg dry air. The mite Tarsonemus rakowiensis reached its maximum in October, and might be a possible house-dust mite predator, although the evidence is far from conclusive. An aliquot of ten grams of mattress dust sampled from a mite-free location on top of the mattress hardly became infested, although the environmental conditions were ideal. Obviously, the mattress dust from the dry room was not optimal for either the yeast or the mites.