SOME EFFECTS OF DESICCATION ON LOCOMOTION OF THE GRAIN BEETLE, SITOPHILUS GRANARIUS (L.) (COLEOPTERA: CURCULIONIDAE)

Abstract

Locomotion of Sitophilus granarius (L.) was studied by tracking normal and desiccated individuals at relative humidities (R.H.) of 100%, 77%, and 0%. Desiccation affected the undirected or kinetic components of locomotion, speed, or orthokinesis, and rate of directional change or klinokinesis and also the size of the turns made but the precise effect depended on both the extent of desiccation and prevailing humidity. The most obvious effect of desiccation was an increase in frequency of turning and angular velocity at 0% and 100% R.H. Directed reactions or taxes were also observed in desiccated beetles both in 0% and 100% R.H. Desiccation initially increased the general level of activity, but eventually affected locomotion by decreasing the animal's vigor. Rate of water loss during desiccation was about 13% of initial body weight per period of 24 hours and was almost identical in males and females. There was no significant difference between the sexes in the effects of desiccation on locomotion. The significance of these results is discussed in terms of orientation by individuals of the species to humidity differences in their environment.