Effects of temperature acclimation and age on movement of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) adults in response to temperature gradients

Adult Cryptolestes ferrugineus (Stephens) were reared at 30 °C or acclimated to 15, 25, or 35 °C for different periods (2 days or 1, 2, or 5 weeks). Populations 1 day old, 1, 5, 10, or 20 weeks old, or of mixed age were held in 10 cm × 10 cm × 100 cm wheat columns (14.5% ± 0.2% moisture content) with a temperature gradient (10 °C/m, 25–35 °C) or a constant temperature (25 or 30 °C) for 1, 6, or 12 days; movement and distribution were then determined. Acclimation to 25 °C for a short time (less than 2 days) did not influence adults' response to temperature in the wheat column. Adults acclimated to 15 and 35 °C responded differently to temperature in the wheat column, preferring temperatures above 30 and 35 °C, respectively. Increasing the duration of the acclimation to 15 or 35 °C resulted in higher aggregation. Acclimation temperature might be more important than exposure time for influencing insect behaviour. During their movement in the wheat columns, adults were also acclimated to the tested temperatures, and they did not always stay in a warmer area if the "cold" area was warmer than 25 °C. Adults that were 1 day old had a lower response (i.e., less movement) to temperature gradients than the older insects. Among the older insects, the response to temperature gradients did not decrease with increasing age, even at 20 weeks.