Insects respond to temperature and moisture and their differences or gradients in grain bulks, but how small these differences can be is unknown. Response of Cryptolestes ferrugineus (Stephens) adults to 0-6 °C temperature differences in 1 m wheat (12.5% moisture content, w.b.) columns was determined in 24 h. Similarly, the moisture response of the adults was determined in 1 m grain columns with a 1 percentage point difference in the wheat moisture content (12.5 and 13.5%) at 25 °C in 24 h. Adults were highly temperature and moisture sensitive and were able to respond to the lowest temperature difference of 1 °C and moisture difference of 1 percentage point within the wheat column. The temperature preference of the adults was confirmed with the recovery of about 78% of insects from the middle warmer sections of wheat at 25 or 30 °C when there was no temperature difference at other sections of the wheat columns. Irrespective of the temperature differences, on average of about 29% of adults moved towards the warmer end with the highest recovery of 47.3% observed at the temperature difference of 6 °C. The adult recovery from high-moisture locations decreased with an increase in distance away from the point of insect introduction (0.05-0.45 m). About 14% of adults moved to the furthest location of high-moisture ends (13.5% moisture content wheat) at 0.45 m. This study provided valuable insights for the development of mathematical models to predict 3D insect movement and distribution in storage grain bins.
Keywords: bias movement wheat; insect distribution; moisture difference; temperature difference.
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