Bed bugs were exposed to freezing temperatures for various exposure times to determine cold tolerance and mortality estimates for multiple life stages. The mean supercooling point for all bed bug life stages ranged from -21.3 degrees C to -30.3 degrees C, with the egg stage reporting the lowest value. A probit analysis provided a lower lethal temperature (LLT99) of -31.2 degrees C when estimates from all life stages were combined, demonstrating that all stages of bed bugs are not capable of surviving temperatures below body freezing and are therefore freeze intolerant. At conditions above the LLT99, bed bug mortality depended on temperature and exposure time at temperatures above LLT99. Based on our model estimates, survival was estimated for temperatures above -12 degrees C even after 1 wk of continuous exposure. However, exposure to temperatures below -13 degrees C will result in 100% mortality in d to ensure mortality of all life stages. Unfortunately, sublethal exposure to lower temperatures did not prevent subsequent feeding behavior in surviving stages. Practical recommendations for management of potentially infested items are discussed.
The mold mite Tyrophagus putrescentiae (Shrank) is a common pest of stored food products. Until recently, commodity and facility treatments have relied on acaricides and fumigants to control this mite. However, T. putrescentiae will cause infestations in areas where acaricide or fumigant use may be restricted, prohibited, or highly impractical. Because temperature is an essential factor that limits the survival of arthropod species, extreme temperatures can be exploited as an effective method of control. Making low-temperature treatments reliable requires better temperature-time mortality estimates for different stages of this mite. This was accomplished by exposing a representative culture (eggs, nymphs, and adults) of noncold-acclimated T. putrescentiae to subfreezing temperatures to determine their supercooling points (SCPs), lower lethal temperatures (LLTs) and lethal times (LTimes) at set temperatures. The results indicate that the adult and nymphal stages of T. putrescentiae are freeze intolerant; based on 95% CIs, the adult LLT90 of -22.5 degrees C is not significantly different from the SCP of -24.2 degrees C and the nymphal LLT90 of -28.7 degrees C is not significantly different from the SCP of -26.5 degrees C. The egg stage seems to be freeze tolerant, with an LLT90 of -48.1 degrees C, significantly colder by approximately 13.5 degrees C than its SCP of -35.6 degrees C. The LTime demonstrates that 90% of all mite stages of T. putrescentiae can be controlled within commodity or packaged product by freezing to -18 degrees C for 5 h. By achieving the recommended time and temperature exposures, freezing conditions can be an effective way of controlling mites and reducing chronic infestations.
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.
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