Diffusivity and bias movement velocity of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) adults under different temperature and moisture differences

Understanding the movement of stored products insects is crucial to determine and predict their distribution in grain bins. The present work focuses on the determination of the diffusivity and bias movement velocity of Cryptolestes ferrugineus (Stephens) adults by using published data from our previous studies. The published data were collected under different storage conditions: different temperature differences (0 to 20 °C) and different moisture differences (1.0, 2.5, 3.0, or 5.0 percentage points (pp)) using 1 or 2 m columns for 24, 48, or 72 h movement periods. A transport equation and finite different methods were used to calculate the diffusivity and bias movement velocity of the adults. Results showed that the adult diffusivity was directly proportional to temperature difference while inversely related to moisture difference, column length, and movement period. The effect of temperature or moisture differences on diffusivity and bias movement velocity were significantly different for their synergistic or/and antagonistic interactions. Diffusivity of 1.6 × 10−3 m2/h was obtained for 5 pp moisture difference when high moisture wheat was placed at distance of 0.45 m on both sides of grain column. Similarly, for a 5 °C temperature difference, the diffusivity was 1.89 × 10−3 m2/h during 24 h in 2 m column. The bias movement velocity decreased significantly in 2 m columns compared to 1 m columns under all temperature differences in any movement periods (24, 48, or 72 h) except 20 °C temperature difference and 72 h. The synergism among the temperature and moisture was greater than their antagonistic effects during conditions of 5 °C temperature difference and 5 pp moisture difference when wet wheat was placed at 0.25 or 0.45 m. Overall, the calculated diffusivity was 3 to 3.7 × 10−3 m2/h in a heterogeneous environment. These findings are useful for three-dimensional modeling of insect movement, design and development of insect monitoring tools, and determination of sampling frequency and locations.