Mortality and behaviour of two stored-product insect species during microwave irradiation

Mortality of the stored-product insects Tribolium confusum and Plodia interpunctella exposed, either intermittently or continuously, to microwave radiation (2450 MHz) was evaluated as a function of exposure time and power, as well as at different growth stages. The survival kinetic was highly quadratic (0.82 less than or equal to R(2) less than or equal to 0.99) for each of the growth stagesstudied. The target theory was used to model the dose-survival relationship. Each growth stage studied was characterized by a distinct dose-response curve. Insects were killed by overheating and the lethal medium temperature for both species was estimated at 80 degrees C for the most resilient growth stage. Intermittent exposures at 1 or 5 min intervals were generally more effective in killing insects of both species than continuous irradiation. The fraction that survived increased as the moisture content of the medium increased from 6 or 9 to 12%. The insects in the mobile state were observed to move towards the surface from inside the nutrient medium during irradiation. They also curled up and in some cases aggregation was observed. The authors did not detect any generation of 'hot spots' in the medium despite the concern of scientists involved in industrial heating of materials by microwaves. Copyright (C) 1996 Elsevier Science Ltd.