As a pest management professional, you may have heard stories similar to these: a homeowner describing microscopic white bugs seen walking across a computer keyboard, opaque specks peppering the wall of a kitchen pantry, or a grocery store manager commenting that employees are repeatedly sweeping up an unidentifiable brown dust that keeps accumulating under the shelf of a particular packaged product. If any of these scenarios sound familiar, mold mites may be to blame.
Mites are not insects, but small arthropods that are closely related to ticks. The mold mite, Tyrophagus putrescentiae, is a widely distributed species of mite that is commonly found in soil, homes and buildings. Adult mold mites are very small, measuring only about 0.3mm in length. Because of their minute size, a few individuals here or there go virtually unnoticed. But, when the right conditions are met, these mites can proliferate quickly, and large populations can wreak havoc in a home pantry or on a retail grocery shelf by destroying food products and commodities, rendering them unfit for consumption.
The common name “mold mite” would seem to infer that this mite’s diet consists only of mold or moldy foods. While it has been documented to feed on fungi, molds and yeast, Tyrophagus putrescentiae is also known to infest a wide range of stored products, particularly those with a high fat and protein content. The Latin genus Tyrophagus translates to “cheese eater,” but dried meat, pet food, ground grain and seeds are also highly susceptible to mold mite infestation, even if they are free of mold contamination.
Adult female mold mites may lay up to 488 eggs during their lifetime. The life cycle of a mold mite consists of the egg, 1 larval stage, 2 nymphal stages and adult. The larval stage has only 6 legs, while the nymphal stages and adults have 8 legs. Under ideal conditions (68°F and >65% RH), the development from egg to adult can be completed in 1-3 weeks, and a population of mold mites can double in as little as 2-4 days.
One sign of a severe infestation is the presence of a gray or brown dust on or adjacent to a food product. This dust, referred to as biomass, is composed of live and dead mites of all life stages, shed skins, fecal material and food particles. If you scoop some of this biomass up, and look closely, you may see the surface of the dust moving. Under a magnifying lens, the movement is even more dramatic. The presence of this dust indicates that there is a severe infestation nearby and probably smaller populations in adjacent areas.
Another sign signifying a severe infestation is the sudden appearance of many individual mites migrating across a surface. Mold mites will undergo a rapid dispersal when conditions become unfavorable; either from overcrowding, food reduction, or a sudden change in environmental conditions. This mass migration indicates that not only is there contaminated foodstuff nearby, but that it is so overpopulated that mites are dispersing in search of a new food source.
Once the potential source of the infestation is located, closer inspection may need to be undertaken. Mold mites are very small and almost clear in appearance, making them difficult to see with the naked eye. A flashlight and a hand lens are useful tools for these kinds of inspections. These mites do not always feed in the surface of the foods they are infesting. Cutting open kernels of dry pet food, digging into the center of a bag of grain or slicing into a sample of cured meat may expose a mold mite population that would have otherwise gone undetected.
The first step in treating a mold mite infestation is the identification and removal of all contaminated food sources. Doing this will eliminate the source of the majority of the mites. The next step is to reduce the potential for any reinfestation by eliminating the mites that are living in the immediate area. Keeping the area clean, including cracks and crevices, removes places to hide and potential food sources for mold mites that may be coming in from peripheral sources. In addition, lowering the ambient temperature and humidity of the space creates an area unfit for mold mite development.