Response of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) adults to small temperature (0-6 °C) and moisture (1%) differences in wheat.

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.