Use of vapor pressure deficit to predict humidity and temperature effects on the mortality of mold mites, Tyrophagus putrescentiae

Abstract

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 degrees 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 LT(50) and LT(90) estimates. These mortality estimates were then regressed on their associated VPD and the resulting regressions (LT(50) and LT(90)) were significant at P < 0.0001, and provided acceptable R(2) values >or=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.

Effects of Japanese Barberry (Ranunculales: Berberidaceae) Removal and Resulting Microclimatic Changes on Ixodes scapularis (Acari: Ixodidae) Abundances in Connecticut, USA

“…Calculating VPD includes both temperature and RH values and returns the "drying power" of air based on these values (Eaton and Kells 2009). Bertrand et al (1996) found that blacklegged tick survival was lower in habitats with low RH and high VPD.…”

Susceptibility to Mortality in Weather Extremes

“…Water-vapor pressure (wvp) is the water content of a mixture of water vapor and other constituents of air; water vapor pressure (hPa) is computed as 41,42 : $$\mathrm{normalW}\mathrm{normalV}\mathrm{normalP}={6.1078}^{*}{10}^{false({7.5}^{*}\mathrm{normalT}\mathrm{normald}false)/false(237.7+\mathrm{normalT}\mathrm{normald}false)}$$ Water vapor pressure is lowest during winter and highest during summer.…”

Mite species inhabiting commercial bumblebee (Bombus terrestris) nests in Polish greenhouses

“…The simplest way to control mite presence is to decrease humidity, as many species are not able to complete development at a relative humidity lower than 60% (Sánchez-Ramos et al 2007; Eaton and Kells 2009). On the other hand, favorable developmental conditions for several mite species undoubtedly occur in greenhouses, from which we obtained nests after exploitation.…”