The mold mite, Tyrophagus putrescentiae, is frequently found on a wide variety of stored food products. Control measures include removal of infested product, thorough site cleaning, insecticides and fumigation. Despite these practices, re-infestation of the sites is likely as this species is very small (0.5mm) and places of refugia are abundant. This mite is susceptible to temperature and humidity, and attempts have been made to control infestations through the manipulation of environmental tolerances. However, this has proven difficult as the amount of water vapor in air varies with air temperature and means to identify lethal conditions are problematic. Further, difficulties exist with the addition of variable environmental controls which create micro-habitats promoting the survival and development of T. putrescentiae.

Employing vapor pressure deficit instead of relative humidity provides a more stable estimate of water vapor in air over varying temperatures that are typically encountered in a structure. Vapor pressure deficit is an estimate of the drying power of air that can be derived from measuring temperature and relative humidity. The objective of our study is to expose mites to a range of temperatures and VPD over time, measuring mite mortality in a bioassay format and estimating conditions that would be lethal to 50% and 99% of the population. The result is a practical approach for estimating which conditions of temperature and humidity would stress infestations and provide recommendations providing more mite-adverse conditions.