Temporal dispersal behavior of the mold mite Tryophagus putrescentiae in relation to relative humidity

The mold mite, Tyrophagus putrescentiae (Schrank), is a stored product pest of economic significance. Recent problems have occurred in bagged dog food on retail shelving. It is known that this mite will disperse in large numbers from infested food. However, there is a question whether this dispersal occurs continuously or explosively. Continuous dispersal involves gradual movement of mites from an infested food source and a slow accumulation of mites in the surrounds. Under explosive dispersal, most of the mites stay in the infested source until resources become limited and then move in large numbers over a short period of time (12-24 hours). Further, dispersal behavior of T. putrescentiae may be affected by relative humidity surrounding the infested site. To evaluate dispersal of this mite, arenas were used that contained an infested food reservoir incubated at high humidity. The area surrounding this reservoir presented mites with constant humidity treatments of 70, 42, or 32% RH; these humidity levels provide optimal, marginal or lethal conditions for mites. Mite dispersal characteristics were determined by evaluating the number of mites in the surrounding area every 24 hours for 86 days, or until explosive dispersal occurred. Upon conclusion of the experiment or when explosive dispersal occurred, mite density was evaluated. At marginal and optimal humidities, explosive dispersal was the primary dispersal mechanism detected, while no dispersal occurred when surrounds were at the lethal humidity. The results of this work have substantial impact as to how IPM measures should be conducted against this mite.