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We conducted studies using a commercial freezer maintained at −17.8 °C to determine the time needed to kill Tribolium castaneum eggs in a pallet of flour. Each bag weighed 22.7 kg, and there were 5 bags in each of 10 layers. The dimensions of the pallet were 109-cm wide by 132-cm long by 123-cm tall, and the weight of the stacked pallet was approximately 1152 kg. We conducted tests for nine internal goal temperatures of −12, −10, −8, −6, −4, −2, 0, 4 and 8 °C. Internal temperatures in the most central location of the flour pallet reached: −11.0, −9.4, −6.9, −5.0, −3.5, −1.6, −0.1, 3.3, and 5.6 °C and were achieved after 11.0, 9.1, 8.9, 7.2, 6.7, 5.8, 5.5, 5.2, and 4.2 days, respectively. For treatments where the goal temperature for the center bag ranged from −12 to 4 °C, egg mortality was 100% in bags located in both the periphery and in the center of the pallet. When the temperature goal for the center bag was 8 °C, 7 ± 2.5% of the eggs survived in bags located near the center of the pallet. Our data showed that temperatures that follow the dynamic temperature curve that takes place over 24.2 days (cool down and warm up for the 0 °C temperature goal) resulted in 100% mortality of T. castaneum eggs. The reason for the difference in mortality for a static compared to a dynamic temperature treatment may be due to the fact that the dynamic temperature treatment occurs over a much longer duration. The fact that the treatment only required 5.5 days in the freezer before it could be shipped makes it a practical method to disinfest pallets of flour, especially because the bags do not need to be removed from the pallet and no chemicals are used. |
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