How Does Heat Kill Insects?

Heat impacts insects on several fronts each of which is detrimental to them. To begin with, heat desiccates or dehydrates them. Additionally, excessive heat disrupts the ionic balance across cell membranes; it causes injury to their DNA and to their cell’s protein synthesis machinery and denatures the enzymes resulting in metabolic injury. In other words, they get cooked.

How Much Heat is Necessary?
The lethal heat dose for drywood termites is surprisingly low; 120ºF maintained for ½ hour. Our standard dose is 130ºF maintained for one hour. To achieve this, room temperatures are typically elevated to the 150º or higher range.

If heat kills termites, why are there termites in such hot environments like attics that can exceed 120ºF? The fact of the matter is that they don’t survive in environments that exceed 120ºF. In areas such as our California Inland Valleys where temperatures during the summer are typically at or near 100ºF, the air temperature in these attics can exceed the heat tolerances of termites. In this case one of two things occurs, either they die or they migrate to another portion of the structure that is cooler during the summer. Since termites are trapped inside their gallery system young colonies have little ability to migrate and thereby escape lethal temperatures. This explains why there are fewer attic infestations in these hot areas as opposed to cooler regions such as along the coast where attic infestations are numerous. Most original infestations start in the outside perimeter of the building such as the eaves and then work their way into the interior portion of the house such as the attic. This gives the colony a safe haven from the hot attic during the summer. They simply migrate out to the eaves or down into the walls. Swarmers that emerge in the attic in these hot zones are basically doomed by the first heat wave. In cooler regions swarmers that emerge in attics find an ideal environment and therefore infestation rates in attics in cool coastal zones is much greater than attics in the inland areas.

When recommending area treatments it is important that the entire gallery system be encompassed within the area treatment otherwise the termites can and often times will move out of the treatment area to a cooler region and survive the treatment. How large of an area should you recommend for treatment to ensure that this does not happen? Lets review what is known about drywood termites that will be useful in making this determination.


Drs. Forbes and Ebeling Research Temperature Tolerances of Insects
Insects survive within a comparatively narrow temperature range and rapidly succumb when range limits are exceeded. This is the ecological basis for Heat. The surprisingly low tolerance of insects to heat is illustrated in the table below, which shows the time required for 100% mortality of four common insect pests at temperatures ranging from 115º F to 130º F. Similar data have been reported for many other insects in entomological literature references. (See Bibliography.) The range of temperature tolerances illustrated in the table below has formed the model on which Heat is based. Of particular interest is the great reduction in survival time resulting from 5º F incremental increases in temperature.
                                          

 Time required for 100% mortality of four species of insects at four temperatures (Forbes and Ebeling. 1987)

Cockroaches and ants are among the species tested that are not confined by the materials they infest. (See table above.) As accustomed temperature ranges for these insects are exceeded, they attempt to escape the heat by occupying the coolest locations available to them, such as cracks, crevices and wall voids.

Termite and flour beetles are examples of species tested that can obtain some protection from the material they infest. As temperatures rise, they move further into that medium. For example, wherever drywood termites could be found in their galleries near the surface before heat was applied, they could no longer be found there after a heat treatment. Termites seek protection from heat in their gallery system at the farthest distance from the source of heat.

The lethal dose for drywood termites is 120º F maintained for ½ hour. The recommended dose for drywood termites is 130º F maintained for 1 hour.
 

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