Movement and distribution of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) adults in response to moisture in wheat filled in different lengths of columns

Abstract

Major abiotic factors like the temperature and moisture and their differences or gradients significantly influence the insect movement and their distribution in grain bulks. The temperature response of adult Cryptolestes ferrugineus (Stephens) in stored wheat has been analyzed well in literature. However, the adult responses to nonlinear moisture differences or gradients are not yet studied in detail. The present work focused on determining the sensitivity of adults to moisture differences in grain bulks. The moisture response of the adults was determined in 1 and 2 m grain columns with 3 or 5 percentage points difference in wheat moisture content (12% and 15 or 17%) at 25 °C in different movement periods (12, 24, or 48 h). Adults could readily detect moist wheat in 24 h with positive hygrotactic response. More than 88% of adults remained in the high moisture wheat when introduced in the moist wheat. Adults demonstrated strong capability to respond to moist wheat irrespective of 3 or 5 percentage points of moisture differences. The adults tended to move away from dry wheat (12%) in search of high moisture wheat. The moisture response of the adults was significantly influenced by the movement distance and was effective until 0.25 m. Movement period significantly influenced adult recovery from the high moisture grain when movement distance was less than 0.5 m. There were many aggregations near and in the moist wheat, showing a uniform biased movement under bidirectional conditions in 1 and 2 m grain columns.