Mechanical Disturbance and Light as factors influencing the Pullulation of Calandra granaria Linn

Abstract

Summary The phenomenon of pullulation of weevils in grain masses has heen examined under several controlled conditions and the results subjected to statistical analysis. The conditions employed were (i) absence of light and mechanical disturbance, (ii) light stimulation and mechanical disturbance applied together, (iii) light alone, and (iv) mechanical disturbance alone, 1 Without the application of a stimulus weevils move through the grain, the males accumulating in the surface layers in numbers greater than can be accounted for by an even distribution through the grain. Females, on the other hand, accumulate in smaller numbers in the surface layers and, therefore, may be said to show some avoidance of these regions. 2 When stimulated, either by light alone or by mechanical disturbance alone, or by both these means together, the movements of both sexes are greatly increased and are significantly in excess of those observed during quiescence. 3 Generally it is found that females need the application of some stimulus to evoke activity of an order similar to that shown by males. The greater initial pullulation of males in quiescence is not increased by stimulation in the same degree as is shown by females. 4 Females are particularly responsive to light stimulation and exhibit a response from light stimulation alone approximately equal to that resulting from both mechanical and light stimulation when appued together. Their response to mechanical stimulation alone is definite, though less in extent, than that arising from light. Males, on the other hand, show that the effects of the two stimuli are approximately additive, the effect of light alone, and of mechanical disturbance alone being together about equal to the effects of these two stimuli when applied together. 5 There is some evidence that females tend to respond to a longer succession of repeated stimuli than do males. 6 It is suggested that some of these differences between the sexes may have resulted from the complete segregation of the sexes imposed in these experiments, and that had experiments been conducted on mixed sexes the differences in male and female activity might not have been so marked.