Klinokinetic and klinotactic humidity reactions of the beetles Hylobius abietis and Tenebrio molitor

Abstract

ABSTRACT. The effects of spatially uniform but temporally changing air humidity stimuli on the orientation behaviour of the large pine weevil (Hylobius abietis L.) and the flour beetle (Tenebrio molitor L.) were studied in a specially constructed vertical air flow chamber. Moist‐acclimatized but hygronegative pine weevils were exposed for 10 s to a moist air stream (c. 85% R.H.) and then for 10 s to a dry air stream (c. 50% R.H.). The Tenebrio were divided into two groups acclimatized to moist and dry air respectively. For each group the humidity during the initial 5 s in the air stream was the same as during acclimatization, and then changed to the alternative level. In Hylobius the change from moist to dry air caused a decrease in spatial displacement brought about by a decrease in walking speed and an increase in the amount of turning per unit time. In Tenebrio the change from dry to moist air caused a decrease of walking speed and a turning‐back reaction based, presumptively, on idiothetic information about the insect's previous walking direction. The average angle turned during 2 s after the humidity change was 165°. In moist‐adapted beetles the dry air stream caused an identical orthokinetic arrestment, but no klinokinetic or klinotactic reaction. Klinokinesis is redefined as a change in the circular variance of turning angles per unit time, which does not change the mean direction (or directions in cases of multimodal distributions) of the circular distribution. Accordingly, klinotaxis consists of a change in the mean directions) of the circular distribution of angular velocities. In both species the turning frequency was more constant than turning per unit distance, suggesting a temporal control in the nervous system of klinokinetic and klinotactic behaviour.