[Alternative Treatments] The Heat Is On

The use of temperature extremes for insect control is an effective and environmentally sensitive approach that relies on rapidly changing the temperature of the target insects before they can adjust. This tactic is considered a low hazard to people and the environment. What is a heat treatment? How do you perform a heat treatment? This article will provide some background information on this topic and 10 tips for performing a proper heat treatment (HT).
However, one should not ignore the insect control benefits of cooler temperatures. Low temperatures, usually those below 50°F, will eventually stop an insect population. Since there is no reproduction, the population remains static, eventually dying out. Since most insects prefer temperatures in the 75°F to 90°F range, cooler temperatures may repel insects. Colder temperatures may be utilized for insect control but one should do it the proper way. Since an insect’s body fluids act like anti-freeze, they will die below a certain temperature. This is known as the critical transition temperature (CTT) which also applies to high temperatures. The key is not to allow insects to acclimate to the lower temperatures. Cold temperature extremes for insect mortality should be quick. A cold temperature “rule of thumb” is to maintain an insect temperature of less than 10°F for a minimum of seven days.
The use of hot temperatures has been a feasible treatment for stored product insect control in various food-processing facilities since the early 1900s. Current attitudes toward pesticides along with subsequent restrictions (e.g., FQPA) have provided a challenge to controlling stored product insects inside buildings. Some historical structural, mechanical and electrical (computerized automation) concerns make it important to clarify HT parameters; HTs that are effective for insect control and will not damage structural, mechanical and/or electrical materials. Research at Kansas State University (KSU) has shown that all life stages of the red flour beetle, Tribolium castaneum, do not survive 122°F for two hours. A HT’s duration will depend upon ambient conditions, application technique and building/equipment design. For example, a 125°F  to 130°F temperature on both sides of a 6-inch concrete floor may require 16 to 20 hours to reach the same temperature in the middle. An empty metal bin might require four to eight hours to reach the 125°F to 130°F temperature. The target zone for HTs is 125°F 135°F. The time will depend upon variables such as the heat source, amount of air movement, amount of heat loss, and equipment or structure (heat penetration). However, when the temperature reaches 122°F for two hours or longer (where the insect is), the mission has been accomplished. Note that the term heat sterilization refers to a temperature higher than 160°F. Although these higher temperatures will kill insects rapidly, it may damage some equipment and is generally reserved for microbial elimination.
A specific temperature and time for insect mortality will depend upon the type of insect and its “genetic” heat tolerance. Common stored product insects such as the red flour beetle, Tribolium castaneum, may require a different heat parameter than other beetles such as a goliath beetle, Goliath orientalis. Some other insects such as German cockroaches, spider beetles and filth flies have revealed some lower lethal temperatures. Any specific temperature for mortality will vary depending upon the stage of the insect’s life cycle. Research at KSU has demonstrated the early larvae stages are the most difficult to kill with heat. It is important to identify the insect species and know its heat-related characteristics (if known) before establishing the heat parameter. An exposure inside an incubator with caged insects provides an indication of that particular species’ response to a higher temperature. Here are 10 tips for performing a heat treatment.

1 Provide Sufficient Heat: This seems
 simple enough but requires doing your homework. A lack of heat energy takes more time and may not get the job done. Using too much heat may increase costs and sometimes makes it difficult to maintain the desired temperature. Examine the specific area and/or adjacent areas to heat treat and identify the sequence of heat up (outside and around insects first).

2 Provide Spot Heat Treatments:  Why
 heat-treat 3 million cubic feet when a pest problem only exists in 3,000 cubic feet? “Spot” heat-ups within a building during operation are effective. Large structural HTs can be done best with propane/gas fired heaters. Electric and/or steam heaters are usually best for smaller treatment areas.

3 Provide Adequate Preparation: Plan-
 ning and preparation prevents a pitiful performance. Utilize a preparation checklist in your plan to identify and prevent the unexpected (for example, a sprinkler head release). Develop a “who will do what and when” action plan. Ask suppliers to provide information on their materials or equipment when exposed to a 125oF to 135oF environment.
4 Perform a Residual Insecticide
 Application: Apply a residual insecticide into cracks and crevices along the outside perimeter of the heated area to control insects that will likely try to escape.

5 Control the Heat Source: Depending
 upon the job, a temperature of 125oF to 135o F is usually sufficient. Experience has demonstrated that 140oF is the maximum temperature to do the job itself (roasting the bugs) while minimizing damage to equipment and structures. Numerous air movers have stopped operating when the temperature is higher than 140oF.

6 Provide a Uniform Distribution of
 the Heat: Develop an overall air movement plan where larger air circulators and smaller fans are positioned to eliminate cool zones. A reserve supply of air circulators and fans should be ready for action. However, do not overlook the power supply necessary to energize the air movers. You can utilize multiple power outlets with numerous extension cords to spread out the amp loads.
7 Provide for Temperature Moni-
 toring: Remote ongoing monitoring with instant feedback is the best method. Predetermine locations for temperature measurements to include areas that are hard to reach. Utilize a high performance laser thermometer (good for less than 10 minutes at a time) for regular monitoring on a “buddy” system and for infrequent cool zone challenges. You must get the hot air to the insect, wherever the insect is, and verify that the temperature is a lethal one.

8 Provide Efficacy Monitoring: Use 
    the target insect pest, if possible, placed in traps that are positioned strategically throughout the heat-treat zone. Use multiple life stages of the test insect; especially early instar larvae, as part of the post heat treat efficacy report.

9 Utilize IPM: Combine heat with
 other pest management solutions to enhance the overall effectiveness of the treatment. Use exclusion for a tighter structure, preventing insect re-entry. Use sanitation for removal of food and shelter, preventing insects from insulating themselves. Remove ingredients, package supplies and products from the heat zone to prevent any product damage.

    Conduct a Post-Heat Treatment 10 Evaluation: Evaluating the performance of the HT while fresh in the team’s mind will improve the efficacy, effectiveness and economics of future heat treatments.

heat Pest treatment Q&A. Now let’s take a look at some commonly asked  questions about heat treatments:

1. Does a heat treatment have to be done over a holiday weekend?
Answer: Traditionally, HTs were done over long weekends and on holidays. The rationale was the plant was down anyway, so with employees out, it could be heat-treated. Newer thoughts on HT in food plants are being developed that are not tied to weekends or holidays. Smaller areas of the plant with active insects can be heat-treated while the facility remains in operation.

2. We’ve always used a fumigant to kill the bugs in our mill. Why would HT be better?
Answer:  If you are trying to decide between HT and using a fumigant, it is not really a matter of one method being better than another. There are many considerations, such as the costs for heat versus the costs for sealing a plant and releasing a fumigant, safety issues, etc. Both treatments have their advantages and disadvanages. The key is to select the proper treatment for the job.

3. Do we really have to clean up everything for a heat treatment?
Answer: YES! Experience has shown that insects can find residues of finished product that can provide enough insulation from the effects of the heat that enable them to survive. If prescribed temperatures are not maintained from the ceiling down to the floor and temperature gradients are allowed to exist, it can conceivably be 10 or more degrees lower at the floor where insect pests crawl. Add to that a way to insulate themselves and they will survive. Clean-up is the cornerstone for any successful HT.

4. How does HT kill insects?
Answer: The application of heated air on insects has a very detrimental effect because insects will come down to the temperatures of their surroundings. Because of their inability to cool themselves quickly enough or find air that is cooler, they quickly desiccate (dry out) and die.

5. Why are checklists necessary?
Answer: The simple answer is because we as humans cannot remember everything. There are many activities taking place at the same time during preparation for heat treatment, and many people involved in those activities, so it is imperative to follow a checklist. A checklist will be a work in progress and should be updated to reflect new equipment and/or renovations.

6. How do we make sure we don’t have runaway temperatures during a heat treatment?
Answer: Equipment and the employees operating heat-producing equipment must carefully and consistently monitor, check and document the activities and operations of unit heaters in order to stay within the prescribed heat treatment formula. Some heaters’ thermostats can be set at the upper temperature limit such as 140oF.
7. Do we have to seal our building like we do for fumigation?
Answer: No. Once you close up a building that is reasonably tight (shut the doors and windows) and you continue to generate superheated air, the amount of heated air that remains in the area being treated (even if you lose some of the hot air) should be adequate to do the job required. Some hot air escaping here and there can be good for efficacy such as the windowsills or around exhausts where insects may be hiding.

8. What if my plant is not set up for a HT, can we still do it?
Answer: A HT survey needs to be made that can determine the feasibility of using heated air to kill and control insects before ever agreeing to do a HT in any food plant. Engineering studies need to be made and the results studied by knowledgeable experts to determine what thermal stresses, if any, could be created. Heat providers are a good place to start.

9. We have steam boilers in our plant; can we use that for heat treatment?
Answer: Yes. Throughout the 20th century, this was the primary source of HTs first, because it was already available, and second, there were unit heaters that could push the heat into the far reaches of the plant with no extra effort. Utilizing air movers to move the hot air to the insect, wherever that insect is, can supplement the in-place unit heaters.

10. What are “cool spots” and “hot spots” when talking about heat treatments?
Answer: These are relative terms that refer to specific areas in heat-treated rooms that are already in the range for the prescribed temperature of around 130oF. If there is not sufficient airflow in a corner or behind a piece of equipment, the temperature required to kill insects may not be reached, and those insects may survive. If there is a thermostat malfunction and the unit continues to increase in temperature above the prescribed 130oF, then a hotter-than-necessary area may cause damage to nearby equipment or to the building.

11. What is meant by “thermally shocking” a building or equipment?
Answer: When a building or equipment is subjected to HT temperatures too fast, and the result is damaged buildings, equipment, connections and electrical. Expansion joints will gradually widen, floor-wall junctures may separate slightly and connection sealing may be stressed. The physics of applying superheated air will cause objects, or materials to expand.

12. We did a heat treatment in our mill and did not get a good clean-up.  Will the heat treatment be just as effective?
Answer: You will have to wait and see, but not likely. Think in terms of the four stages in the life cycle of most stored product insects. You may have killed the adults that were exposed, but what about the larvae that were buried (insulated) within the unclean material left in an area? Insects will migrate to these type of areas sheltering themselves from the heat.

13. After a heat treatment, an employee was moving a slip-sheeted pallet of product left in a heated area and found live flour beetles on the floor under the pallet. How did this happen?
Answer: The natural instinct of insects is to avoid or escape from those conditions that cause them discomfort. If we as humans provide them that condition, they will surely find it. It may be thought impossible to squeeze under a slip-sheeted pallet of product. With deviations that occur in most floors, insects will usually protect themselves from the effects of the heat.

14. Why do I need to remove food products from a heated area?
Answer: A few reasons exist. One, these products will act as a shelter source that insects will migrate toward, actually increasing the level of contamination. Two, these products act as a “heat sink,” using more hot air to do the job. And three, the performance characteristic of the food will likely change when exposed to these temperatures and time. Wheat does not mill as well. Flour does not bake as well and we know what happens to chocolate.

15. Is there a temperature difference inside closed equipment during a HT?
Answer:  A slight difference of a few degrees below the room temperature does exist. In addition there is a cool-down delay affect where the inside temperature is a few degrees higher.

16. Will new technology that we see today improve HT in the future?
Answer:  Yes. Today’s technology will make HTs easier to conduct. Picture remote temperature monitoring that will quickly identify cool zones. In addition, the reporting of the entire HT process will be more accurate and more timely, with virtually instant information feedback.

17. Why is heat treatment becoming more popular today?
Answer: It seems that the phase-out of methyl bromide is acting as an awareness catalyst for heat treatments.  The industry emphasis of IPM is also helping to improve awareness and the benefits for heat treatments. Heat treatments have always been effective, and it seems we are bringing an old insect control tactic back to the future with current technology.

The author, owner of Quality Centered Consulting (www.qualitycenteredconsulting.com), can be reached at odosland@giemedia.com.