If You Can't Beat 'Em, Heat 'Em

June 1, 1997

This study of U.S. Army food facilities at Fort Knox shows that thermal control provides dramatic long-term reduction of cockroach populations.

The U.S. Army maintains many food service facilities which typically serve 200 to 700 soldiers three meals a day, seven days a week. Many are operating in buildings constructed during the middle part of this century, and control of German cockroaches (Blattella germanica) has been a constant challenge in some of them.

Direct-fired, propane heater injecting heat into kitchen area. These heaters have been used for the last 14 buildings treated.

One installation in particular, Fort Knox, Ky., was unable to control cockroaches in about a dozen of its 50 food service facilities. Four strains were collected and tested for resistance using the glass jar tarsal contact method (Rust et. al., 1993). These strains were the most resistant of 45 strains collected Army-wide from 1989 to 1992, and were resistant to almost all of the residual adulticides. Behavioral resistance to a microencapsulated organophosphate was also found using the choice box method (Rust et. al., 1993).

Due to the resistance levels and cockroach infestation history, it was decided that an alternative to conventional control methods was needed. Heat has proven to be an effective technique for killing the various life stages of stored product pests (Shepard, 1984) and termites (Forbes and Ebeling, 1987). Heat is also being used by a few pest control companies to control cockroaches. Isothermics Inc., a training and marketing agency, licenses the patented use of sublethal temperatures (110oF) and boric acid to control cockroaches (Quarles, 1994 and 1995). Topp Construction Services Inc. produces chambers for thermal control of cockroaches in equipment such as watercoolers.

THE PROCESS. A brief description of our treatment methods are outlined below. Those interested in conducting this process should request a copy of U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM) Technical Guide No. 208, Procedures for Thermal Control of Cockroaches in Army Food Service Facilities. This 65-page quide provides detailed instructions, safety precautions, equipment specifics, and a checklist for on-site use. The guide may be requested from USACHPPM, Attn: Entomological Sciences Program/TG208, APG MD 21010-5422; or may be accessed via the Center’s Web site at http://chppm-www.apgea.army.mil/ento/tg208.

Forbes and Ebeling (1987) reported that cockroaches were killed by exposure to 120oF for 27 minutes; however, no reference was made to the eggs. We found that at 115oF for 45 minutes or 120oF for 30 minutes, all adults and nymphs were killed and no nymphs emerged from ootheca. Therefore, we selected 115oF for 45 minutes as our target temperature and time.

The 20 facilities treated have mostly been one-story structures with concrete subflooring and concrete block walls. They ranged in size from 5,000 to 10,000 square feet. To prepare the facility, all refrigerated and non-refrigerated perishables were removed from the areas being treated (e.g. meats, salads, spices, fruits, vegetables, and bread), since the electrical equipment was turned off to keep the motors and wiring from overheating. However, large walk-in freezers and refrigerators were kept operating if their compressors were located out of the area being treated. Also removed were heat sensitive items such as wax candles, chocolates, flammable liquids, aerosol containers, and compressed gas cylinders (such as those used at soda fountains). As a precaution, large-screen televisions, computers, and computer diskettes were removed. The gas supply to the building was also turned off.

All facilities had a chemical fire-suppression system for the gas range hoods, with the fusible elements designed to activate at 260oF, so activation of this system was not a concern. However, the pressurized canisters associated with these systems were typically rated to withstand temperatures of only 120oF. If these were not removed, they were wrapped with a 2-inch-thick insulating foam and their temperatures monitored during the process to insure that the rated temperature was not exceeded. A fire suppression specialist was always consulted since some compressed gas cylinders have no safety release valve and must be removed.

When sprinkler systems were present, the water supply was shut off, in case of an accidental discharge, and the sprinkler heads were insulated with a ceramic fiber blanket. The exhaust hoods of gas ranges and other venting ducts were sealed by covering the exit vents with plastic sheeting to prevent a chimney effect and excessive heat loss. In addition, the heating/air conditioning system was shut off.

No attempt was made to heat the wall voids or crawlspace. Therefore, it was critical that all holes in the walls and floor were sealed thoroughly to prevent safe harborages and escape routes for cockroaches. Floor drains can harbor cockroaches, so they were flushed with hot water and the metal screening caps were wrapped with aluminum foil to prevent cockroaches from entering.

The day prior to the heat treatment, Gentrol EC, an insect growth regulator containing 65.7% hydroprene, was applied as a spot, and crack and crevice application. Gentrol is chemically stable to 140oF and complements this process well. Temperature-sensing thermocouple wires connected to a data recorder were used to monitor temperatures. Ceiling temperatures were sampled, since that area was generally the hottest, and we did not want to exceed 150oF. Other sites sampled were in the lowest available equipment harborages, since these were the most difficult areas to heat.

Some areas were either not heated or were slow to heat. To prevent cockroaches from escaping to these areas, escape barriers were made by placing double-sided sticky tape (Mr. Sticky) across the floor and a couple feet up the doorjambs. In those facilities where the ceramic floor tile was not firmly cemented to the concrete floor, the heat can cause air to expand underneath the tiles and lift or crack them. To minimize this problem, the floor was sounded with a rubber mallet to identify loose sections and 1/8-inch holes were drilled through the grout between the tiles to vent the air as it heated.

Since undertaking this precaution, only two small (less than 150 square feet each) areas of tile have been damaged in the last 13 facilities treated.

All refrigerator doors were kept closed during the heating process to prevent damage to the plastic door seals. We have found that older models of a few freezer-refrigerators with door panels pressure-fitted together (as opposed to being welded together) and insulated with foam may become distorted due to foam expansion caused by heat. Freezers or refrigerators with this type of construction were removed from the areas being heated.

Direct-fired propane heaters have been used for the last 14 buildings treated. These heaters (see photograph) were easily handled, safe to operate, and required only seven amps of electricity. Air heated to 175oF or less was delivered through 18-inch-diameter flexible ducts at approximately 19 miles per hour, which produced good mixing and air circulation within the facility. The heaters are not designed to operate in high temperatures, so they were placed outside the heated area. One heater was used for each 6,000 to 8,000 cubic feet of space. Typically, after two hours of heating a facility, cockroaches began exiting equipment and common harborage areas and congregated in the cooler parts of the room. When cockroach congregations were observed they were vacuumed with the backpack-style li’l Hummer vacuum cleaner, equipped with a HEPA filter and a high-temperature, high-limit shutoff switch.

Following the initial vacuuming, the heating ducts were systematically shifted every 30 to 45 minutes to ensure that all areas of the facility reached the target temperature. Prior to each duct movement, all clusters of cockroaches were vacuumed. When cockroaches were no longer observed in significant numbers, heating was ceased, and a final inspection and vacuuming was conducted.

Once heating and vacuuming ceased, generally within 4 to 6 hours, a residual adulticide mixed with Gentrol was applied in accordance with label directions. The residual adulticide used was either cyfluthrin, chlorpyrifos, or propetamphos. In no instance was an adulticide used after thermal treatments that had not been used in the months and years prior to thermal control. The same is true for Gentrol. Therefore, the dramatic population reductions cannot be attributed to pesticide applications. Bait stations were placed and maintained in the receiving area to minimize reinfestation.

To prevent heat injuries everyone drank plenty of water and/or juice, and limited their time within the heated facility to 20 minutes per hour. In our trials, we have had no heat-related injuries.

Cockroach populations were monitored with 12 to 18 sticky traps placed at floor level during monthly sanitation inspections. A biased sampling plan was employed by placing traps in areas of suspected cockroach infestation. Based on this sampling plan, a trap index of two or more cockroaches per trap per night was established as the threshold that triggered a thorough pesticide application including the use of residuals, dust, and baits. If the trap index was less than two, then dust and/or baits were applied in selected areas at the surveyor’s discretion. All pesticide applications, both before and after heat application, were performed by the installation’s pest control team using its standard operating procedures.

THE RESULTS. Detailed results are presented for three representative buildings in Figures 1 through 3. These figures graph the number of cockroaches per trap per night and show when the pesticide applications were made before and after thermal control. A full arrow indicates a complete pesticide application using a residual insecticide and possibly dust, baits and an insect growth regulator. A half arrow indicates that only baits and/or dust were used. Also, data for each facility are displayed indicating the difference in the quantity of insecticide applied for equal periods of time pre- and post-thermal control.

In Building 2377, the trap index the night before and the night after thermal control was 44 and 35 cockroaches per trap, respectively. It was not uncommon to find relatively high trap indices immediately following a thermal treatment since the cockroaches have been displaced from their normal harborages down to the floor where the traps were located. By two weeks post-treatment, the cockroach population dropped below a trap index of two and remained at this level for all but one of the 18 months since the thermal control. Since thermal control treatment, only one application of residual insecticide was made, as opposed to 14 applications during the 18 months prior to thermal treatment. This represents a 20-gallon reduction of insecticide spray. During this period, 12 to 24 bait stations were placed in the facility on seven separate occasions.

In Building 6542, the trap index reached 4.1 three months after thermal treatment. This was the only facility where an insect growth regulator was not used in conjunction with thermal control. Following the application of a residual insecticide and insect growth regulator three and four months after thermal control, the trap index decreased and has remained below 1.0 for all of 1995, with a few applications of boric acid dust, 12 to 24 bait stations, and one application of an insect growth regulator in December 1995. Despite these pesticide applications, there was still a 75% reduction in residual insecticide spray and a 32% reduction in insecticide dust and labor hours.

In Building 2373 (Figure 3), the trap index the morning after thermal control was more than five times higher than the day before. However, within two weeks the trap index dropped to 0.5, and within two months to 0.1; it has remained below that level for the last 14 months. In fact, no cockroaches have been observed or trapped in this facility within the last six months. In the 16 months since thermal control, only one prophylactic application of an insect growth regulator, four prophylactic applications of dust, and the placement of 12 to 30 bait stations have been made.

While some cockroaches remain in these facilities, we have been able to drastically reduce their numbers and eliminate the yearly population peaks that occurred in late summer and early fall.

Once holes in the walls and floor are sealed, the equipment is the only remaining harborage. Almost all food service equipment is stainless steel, which conducts heat very effectively; therefore, the cockroaches either remain in the harborage and die from heat or they escape to the floor where they can be vacuumed up or come in contact with the insect control chemicals. Without heat, many of these harborages may have gone undetected or been difficult or impossible to treat with pesticides. As discussed by DeMark (1994), cockroaches spend about half of each nymphal stage within the harborage and are safe from insecticide applications not directed into the harborage. Heat forces those nymphs out of the harborage. Thus, all segments of the population are affected in a single thermal treatment.

To determine the level of customer satisfaction with this treatment, questionnaires were distributed to 10 treated food service facilities. When asked whether the method should be offered to other facilities that request it, 95% responded “yes.” Based on the survey results and our contacts with food service personnel, we believe that there is a high degree of interest in thermal control among the Army food service community.

THE COST. We have analyzed the cost of conducting thermal control in a 10,000-square-foot facility in which 7,500 square feet were heated. This area is actually about four times the size of a typical fast food restaurant. Food service personnel spent about 40 hours preparing the facility for thermal control and bringing it back into operation. A total of 55 hours were spent caulking, turning off and back on the mechanical systems, and constructing a plastic wall between the serving and dining area, which was unheated. The thermal team spent 120 hours. This was longer than usual since the facility had to be heated in two phases due to its configuration. Approximately $700 of propane and miscellaneous supplies were used. While this is an expensive clean-out, we believe it is a good value. Unprecedented levels of control were achieved, and when the labor (including fringe benefits) and material cost are amortized over the number of meals served in a year, the cost is only about three quarters of a cent per meal.

Even though thermal control treatments as currently configured require considerable planning, a relatively high initial capital investment, considerable labor, and may damage small areas of the floor tile, this technique does provide dramatic long-term reduction of difficult-to-control, insecticide-resistant German cockroach populations. In our survey of and discussions with Army food service personnel, we have found a high degree of interest in and satisfaction with this methodology. We believe that with additional experience it can be streamlined, simplified, and made more cost-effective.

The authors, By Brian C. Zeichner, Alfred L. Hoch and Donald F. Wood, Jr., are with the U.S. Army Center for Health Promotion & Preventive Medicine, Aberdeen Proving Ground, Md. Gentrol is a registered trademark of Sandoz Agro Inc. Mr. Sticky is a registered trademark of Lo-Tox Products International and Lil’ Hummer is a registered trademark of Miracle Maufacturing Corporation. Safe-Heat Thermal Pest Eradication Equipment is manufactured by Topp Construction Services, Media, Pa.

The opinions and assertions contained in this article are the views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. Use of trademarked names does not imply endorsement by the U.S. Army but is intended only to assist in the identification of a specific product.

ACKNOWLEDGMENTS. This project was partially funded by the U.S. Army Environmental Center as part of its effort to reduce pesticide use by the Army. This work was also supported in part by appointments to the Postgraduate Internship Program at the USACHPPM administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and USACHPPM. Many individuals have contributed to the development of this methodology, making the field trials possible, as well as the collecting and recording of trap data. In particular, the authors would like to acknowledge Bob Ruddell, Chad Riccelli, Al Freeland, Bill Grimes, Michael Cecil, Don Reynolds, Paul Prather, Leon Alvey, and Robert Badger of Fort Knox; Dan Topp and John Murray of Topp Construction Services Inc., for training and consultation on the use of the heaters; Kristina Hutchison, who participated in the field trials and data analysis, and Joyce Kopatch, for preparing the graphs, of USACHPPM; and John Willard, Directorate of Resource Management, U.S. Army Garrison, Aberdeen Proving Ground, for providing the cost analysis.


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