The mold mite, Tyrophagus putrescentiae (Shrank), frequently infests a variety of stored food products in ideal, but rather limited conditions. Major factors limiting survival of this mite are the temperature and humidity imposed on T. putrescentiae as it develops within and disperses among sites. However, since relative humidity is dependent upon air temperature, determining survivability in a habitat can be difficult in the presence of structural temperature variations. Vapor pressure deficit (VPD) provides a method of combining both relative humidity and temperature into a single number that can be used to determine conditions detrimental to mite survival. This study utilized a bioassay format to measure mortality of T. putrescentiae when exposed to a range of seven temperatures (5-35°C), 10 relative humidities (0-100% RH), 17 exposure times (0.5-240 h), with and without food. With these combinations of temperature and RH, mortality curves (mortality versus time) that displayed a sigmoidal relationship were used to calculate LT50 and LT90 estimates. These mortality estimates were then regressed on their associated VPD and the resulting regressions (LT50 and LT 90) were significant at P < 0.0001, and provided acceptable R 2 values ≥0.83, regardless of whether food was present or not. At room temperature, threshold of VPD for T. putrescentiae development was below 8.2 mbar, this estimate being initially calculated from published values. For mites exposed to drier conditions, above 8.2 mbar, survival time was curtailed dependant on the magnitude of VPD. As the VPD exceeded 12 mbar, mites experienced substantial (>90%) mortality within 58 (33, 101) h; and further increasing VPD decreased the time of exposure to achieve mortality. This study demonstrates that making subtle changes in humidity or temperature to reach a target VPD may provide control of mite outbreaks and reduce areas inhabitable for T. putrescentiae.
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Acknowledgments This work was funded by a grant from Nestle Purina PetCare, with additional support from the University of Minnesota Agriculture Experiment Station (MN-019) and the Minnesota Pest Management Association. Critical review of this manuscript by R.D. Moon, A.J. Walter, J. Olson, and M. Goblirsch is greatly appreciated. The authors acknowledge and value the additional input provided by this Journal’s anonymous reviewers.
- Logistic regression
- Nutritional status
- Relative humidity
- Stored products pest
- Tyrophagus communis