Synergistic and antagonistic effects of temperature and moisture differences on movement and distribution of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) adults in horizontal columns of wheat.

The distribution of insects in stored grain bulks is significantly influenced by temperature and moisture, or their gradients or differences. This study examined the movement and distribution of Cryptolestes ferrugineus (Stephens) adults under different combinations of temperature (5 or 10°C) and moisture differences (2.5 or 5 percentage point difference) in horizontal 1 m wheat columns in 24 h. Adults showed a nonoriented distribution in dry or damp wheat (less than 15% moisture content), while the distribution was partially biased in wet wheat (17.5% moisture content) due to slightly increased temperature or spoilage of the wet wheat in 1 replicate. Adults showed a positive response to warm and damp or wet wheat. Under any levels of temperature (5 or 10°C) and moisture differences (2.5 or 5 percentage points) in 24 h, about 75% of adults were recovered from moist wheat where insects were introduced. Adults equally preferred both moist cool grain and dry warm grain located at ± 0.25 m. However, the preference for dry warm grain was stronger than moist cool grain when the movement distance was 0.45 m. The sensing ability of adults and their preferences were not only determined by movement distance but also by the magnitude of temperature and moisture differences. Thus, the findings of the present study will help in better understanding adult response to realistic temperature and moisture distributions that commonly occur in storage structures and to develop stored grain ecosystems mathematical models.