Three-dimensional movement and distribution of <i>Tribolium castaneum</i> (Coleoptera: Tenebrionidae) and <i>Cryptolestes ferrugineus</i> (Coleoptera: Laemophloeidae) in stored wheat at different temperatures and at different times

Understanding the movement and distribution patterns of insects is crucial for developing effective stored grain management protocols. This research investigates 3-dimensional movement and distribution of Tribolium castaneum (Herbst) and Cryptolestes ferrugineus (Stephens) separately at different temperatures (5, 10, 20, and 30°C) and for different movement periods (1, 2, 3, and 24 h) in stored wheat with a uniform moisture content of 14.5% (wet basis). The experiments were conducted in a wooden container with internal dimensions of 0.7 × 0.7 × 0.7 m. The wheat was filled into 343 mesh cubes (referred to as cubes), each measuring 0.1 × 0.1 × 0.1 m, arranged in 7 layers after being loaded into the container. One hundred insects were introduced into the center cube (the center of the container) at the start of each experiment. After the desired movement period, the cubes were removed in less than 45 min from the wooden container. The wheat in each cube was wrapped in labeled plastic bags, sieved, and the insects were recovered and counted. Results indicated that both species exhibited movement speeds > 7.2 m/d in vertical and horizontal directions at higher temperatures (20 and 30°C). At lower temperatures (5 and 10°C), their vertical speed was higher than their horizontal speed. Tribolium castaneum ceased movement at 5°C, whereas ~13% of C. ferrugineus adults continued to move at this temperature. The drift effect and geotaxis influenced the movement and distribution of both species in the vertical direction, while their horizontal movement followed a diffusion pattern.