EVALUATION OF FREEZING TO CONTROL WOOD-DESTROYING INSECTS (ISOPTERA, COLEOPTERA)

Structural insect pests may be killed by exposure to freezing temperat ures. The critical thermal minimum (CTmin) is the threshold low temper ature at which an insect succumbs from momentary exposure to temperatu res decreasing at 1 degrees C/min. The CTmin was -21.3 degrees C for t he western drywood termite, Incisitermes minor (Hagen); -17.2 degrees C for workers of Incisitermes snyderi (Light); and -13.9 degrees C for workers of the Formosan subterranean termite, Coptotermes formosanus Shiraki. The CTmin for the southern lyctus beetle, Lyctus planicollis LeConte, was -35.6 degrees C for eggs, -26.2 degrees C for small larva e, -30.0 degrees C for medium larvae, and -24.3 degrees C for large la rvae. The effectiveness of liquid nitrogen (N-2) to chill wall voids b elow the CTmin values for these structural pests was tested in a mock up wall. The time to the CTmin was affected by the rate at which liqui d N-2 was released into the void and the vertical location of the rele ase point. Fiberglass insulation in the wall affected the pattern of c ooling by deflecting the liquid N-2 around the insulation. Plumbing an d electrical fixtures in the wall were not damaged by liquid N-2, even though they were exposed to temperatures as low as -50 degrees C. How ever, liquid N-2 cracked vinyl floor tiles adjacent to the wall. The o xygen level in confined spaces where liquid N-2 was released rapidly d ropped below 19.5%, the minimum acceptable level for worker safety. Co nsequently, fans probably should be used to circulate fresh air into t he areas where liquid N-2 is used, and electronic monitoring should be done to ensure safe oxygen level. Because insects survive if they are not exposed to at least their CTmin, it is important to monitor accur ately the internal temperature of target wood with thermocouples to en sure that the CTmin has been reached where the insect actually occurs. To achieve an effective low temperature throughout a structure, virtu ally every void would need to be treated. Otherwise, it is unlikely th at isolated pockets of termites could survive by escaping exposure to the CTmin. Proper placement of thermocouples could be extremely import ant.