|Movement of Rhyzopertha dominica in response to temperature gradients in stored grain |
The lesser grain borer is one of the most common and damaging insect pests of stored wheat in the USA. In the autumn, the periphery of the grain bulk cools faster than the center and this allows grain insects to continue to reproduce in the center. Very little is known about the movement of the lesser grain borer in temperature gradients in stored grain. We studied the movement and temperature preference of the lesser grain borer in a 22-inch diameter cylinder with 3 inch high sides containing 44 lbs of wheat. Two temperature gradients were tested over a 24-hour period. Beetles preferred the moderate temperature region of the cylinder in the 40 to 20°C gradient, but avoided the highest temperature region. In the 24 to 20°C gradient, beetles did not move very much during the 24-hour period. When a 96-hour duration was used for the experiment, there were significantly more beetles in the warmest center region of the gradient compared to the cooler middle or outer regions.
Average Rhyzopertha dominica density in the center, middle, and outer sections of the arena after 24 and 96 h. Within a figure, bars marked with a different letter are significantly different (P < 0.05, REGW Test).
Compared to other stored grain beetles, such as the rusty grain beetle, the lesser grain borer appears to move more slowly through the grain into preferred temperature regions. It is possible that adult R. dominica may suffer higher winter mortality in grain bins compared to the rusty grain beetle because the lesser grain borer is not able to move quickly enough into the warmer regions of the grain mass as the periphery of the grain cools during the fall and winter months. This could affect the beetle's ability to overwinter in stored grain bins. (P. W. Flinn, Collaborator: D. W. Hagstrum)