113. THERMAL CONTROL OF INSECTS AND MITES W.E. Muir and P.G. Fields 13.1 CONTROL OF INSECTS WITH LOW TEMPERATURES

In Canada in most years, insect infestations have been low because of Canada's low ambient temperatures after harvest and grain cools quickly in the fall in the small bins that were common on Canadian farms. The recent trend to larger bins on Canadian farms may result in an increased insect problem because large bins stay warmer for a longer time than smaller bins (Sec. 8.6.1). Low temperatures reduce insect reproduction and survival rates. In Canada's temperate climate aeration with air at near-ambient temperatures can usually be used to control although not always eliminate insect infestations (Chap. 12). The optimal temperature for stored product insects is between 25-33°C (Table 13.1). Low temperatures reduce insect development and thus lengthen the time before populations increase to a point where they cause significant damage. The major stored-product insects in Canada cannot develop below 20°C (Sec.5.3.1). Mites in damp grain can continue developing down to 2°C (Sec. 5.5). Although no development occurs at these temperatures, insects and mites remain alive for long periods and will cause damage if the grain temperature rises. Insects exposed to cool temperatures (20-10°C) become acclimatized and their cold