Research Update: Portable Heat Chambers

It is widely recognized that bed bug control is difficult, often requiring a combination of tools and methods to achieve elimination (Potter et al. 2006, Potter et al. 2007, Wang and Cooper 2011, Bennett et al. 2015). One of the more challenging obstacles in eliminating a bed bug infestation is addressing personal items that are infested but cannot be treated with pesticides. Some items can be hot laundered in a washer or placed in a dryer, but what about infested items that cannot be laundered? This article discusses the use of portable heat chambers for disinfesting infested items that cannot be treated with traditional pesticides or laundered (or if clients are unable to launder).

Portable heat chambers use high temperature (around 50oC or 122oF) to kill bed bugs. There are many different designs, some more portable than others. Some can accommodate items as large as a piece of upholstered furniture, however, most are geared for treating small items. Bed bugs commonly infest small items like shoes, books, clothing, etc., when these items are on, or close to, the infested bed or sofa where the host spends a significant amount of time each day. Travelers and visitors sometimes also may be concerned about getting bed bugs during hotel stays or when visiting someone with a known bed bug infestation (i.e., home health care aides, housing inspectors, maintenance staff, etc.). How effective are portable heat chambers as a solution for bed bugs hiding in small items? Here we report a laboratory study evaluating the effectiveness of a portable heater.

MATERIALS AND METHODS. The product we tested, ThermalStrike Expedition, was donated from Protect-A-Bed (Chicago) (Figure 1 A, B). The instructions suggest that the treatment time required will vary based upon the amount of contents and that treatment can be terminated once the core temperature reaches 45^oC (or 113^oF) for 90 minute or reaches 50^oC. Contents within the unit may take up to eight hours to reach 50^oC.

In the first experiment, we evaluated the effectiveness of the heating unit for killing bed bugs hiding in loosely packed suitcases. In spite of the fact that most clothing can be laundered, we chose to pack suitcases with clothing for the test as the clothing is a good insulator and allows for a more rigorous test. Three heating units were tested. In each heating unit, we loosely filled the suitcase with clothing. The suitcases were 21 by 15 by 10 inches in size. We placed two Petri dishes containing live bed bugs (a field strain was used) at two central locations inside each suitcase (Table 1). Each dish contained 10 to 14 adult males, 56 to 85 adult females, 10 to 11 third- to fifth-instar nymphs, and 75 to 285 eggs (0-5 days old) and pieces of fabric cloth as harborage (Figure 1 C, D). The bed bugs were fed a week prior to the treatment. The lid of each dish has a 2.5 cm diameter opening covered with fine nylon screen for ventilation. Two control dishes containing the similar number and type of bed bugs was placed on the counter in the laboratory (22^oC) during the treatment. Two wireless HOBO data loggers (model #U23-002, Onset Computer Corporation, Bourne, Mass.) also were placed in two locations inside each suitcase and recorded temperature every five minutes. Each sensor was placed together with a Petri dish containing bed bugs. In addition, the probe of a remote digital thermometer (part of the ThermalStrike Expedition) was placed beside one of the HOBO data loggers in each suitcase to determine when to stop the heating unit. The zippers of the suitcases were closed during treatment. The suitcases were sealed in plastic bags provided by the manufacturer. One sealed suitcase was placed in each heating unit. The heating units were unplugged from the outlets when the manufacturer-provided digital thermometer reading reached 50^oC. The Petri dishes and data loggers were immediately taken out from the suitcases and cooled down with a fan. All Petri dishes were transferred into an incubator at 26^ºC, 12:12 (L:D) light cycle. The bed bug mortality was checked daily for seven days and egg hatch was observed daily for 14 days after heat treatment.

In the second experiment, we tested the effectiveness of the heating unit for killing bed bugs hiding in tightly packed suitcases using an eight-hour treatment period. The objective was to determine whether bed bugs in more densely packed materials can be killed within an eight-hour period. Two tightly packed suitcases (14 by 10 by 9 inches) were tested. Each suitcase included both clothing and a few books. A wireless HOBO data logger was placed at the center of each suitcase and recorded temperature every five minutes. Bed bugs were hidden inside the center of the suitcases using the same methods as in the first experiment. The control dish was placed on the counter in the laboratory (25^oC) during the heat treatment. The heating units were operated for eight hours. Then the Petri dishes and data loggers were immediately taken out from the suitcases and cooled down with a fan. All Petri dishes were kept in an incubator at 25^ºC, 12:12 (L:D) light cycle for 14 days. The bed bug mortality and egg hatch were observed in the same way as in the first experiment.

RESULTS. In the first experiment, it took 265-295 minutes (4.4-4.9 hours) to reach 50^oC (based on the digital thermometer). The temperature recorded by HOBO sensors at core of the suitcases were between 47-51^oC (117-124^oF) (Figure 2). The location where the three Petri dishes were placed had temperature of 48, 50, and 50^oC respectively. All bed bugs (adults, nymphs, eggs) were killed from the treatment. There was no adult or nymph mortality in the control. The mean egg hatch rate in the control was 91 percent. Mean mortality of nymphs and adults in the control was 2 percent after 7 days.

In the second experiment, the core temperature in the two suitcases reached 46 and 48^oC at 8 hours, respectively (Figure 2). All bed bug adults and nymphs were dead from the treatment. None of the adults and nymphs died in the control. On third day after treatment, both suitcases had one egg successfully hatched but nymphs died the same day. In addition, two eggs from the second suitcase attempted to hatch but nymphs failed to emerge at seven days after treatment. All 24 eggs in the control hatched after seven days. Mortality of nymphs and adults in the control was 5 percent after seven days.

DISCUSSION. Kells and Goblirsch (2011) reported that 50^oC is lethal to all bed bug development stages with an exposure time of less than one minute. The core temperature in a loosely packed suitcase reached this temperature in 295 minutes (nearly five hours). The two suitcases which were operated for 265 and 285 minutes did not reach 50^oC at the center, but none of the treated bed bugs survived the treatment. The second experiment represented the most challenging conditions for eradicating bed bugs hiding in personal belongings. Eight hours of treatment time was sufficient for eliminating bed bugs even though the core temperature never reached 50^oC.

Kells and Goblirsch (2011) found bed bug eggs were much more tolerant to heat treatment than mobile stages. The fact that two nymphs successfully emerged from eggs but died the same day and two eggs had embryo development but failed to hatch confirms that eggs are more tolerant to heat than nymphs and adults. Even though eggs were not killed immediately after heat treatment in the second experiment, they suffered a sub-lethal effect, which led to death of nymphs and failed nymphal emergence. Kells and Goblirsch (2011) estimated the lethal time to kill 99 percent of bed bug eggs was 71.5 minutes at 48oC. In our second experiment, the core temperature increased at an average of 0.06oC per minute, the same speed as that in Kells and Goblirsch (2011). The core temperature in suitcase I was 47^oC for 40 minutes and 48^oC for 20 minutes (total of 60 minutes where temperature was at least 4^oC) before the treatment ended. One egg (5 percent) hatched but the nymph died the same day. The core temperature in suitcase II was 47^oC during the last five minutes of treatment. Three eggs (12 percent) had post-treatment development but one nymph died the same day and the other two nymphs failed to emerge from the eggs. Considering that a few eggs were still able to develop after the heat treatment, it would be prudent to set 50^oC core temperature as target temperature for determining when treatment should be terminated using a ThermalStrike heating unit.

It is common that many bed bug infestations will take multiple visits to be eliminated (Cooper et al. 2015). Frequent treatment of bed linens and other personal belongings harboring bed bugs during this period is critical. A heating unit will be handy to treat these items repeatedly until all bed bugs in the residence are eliminated. When frequent laundering by clients is not possible, portable heating units (possibly provided by property management) also can be an economical alternative method. For travelers, workers and pest control professionals who frequently encounter bed bug infestations, a portable heating unit offers a convenient and safe method for eliminating bed bugs potentially hidden on clothing or personal belongs. Our study shows six to eight hours treatment time is sufficient to kill all stages of bed bugs hiding in a suitcase using ThermalStrike Expedition. The minimum time required to kill bed bugs is affected by the tightness of the materials packed in the suitcase. Loosely placing items in the heat chamber is recommended for faster kill of bed bugs.

References

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Cooper, R., C. Wang and N. Singh. 2015. Evaluation of a model community-wide bed bug management program in affordable housing. Pest Management Science 72: 45-56.

Kells, S. A. and M. J. Goblirsch. 2011. Temperature and time requirements for controlling bed bugs (Cimex lectularius) under commercial heat treatment conditions. Insects 2: 412-422.

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Potter, M. F., A. Romero, K. F. Haynes and E. Hardebeck. 2007. Killing them softly: battling bed bugs in sensitive places. Pest Control Technology 35(1): 24-32.

Wang, C. and R. Cooper. 2011. Environmentally sound bed bug management solutions. In P. Dhang [ed] Urban pest management: an environmental perspective. CABI International: 44-63.