A programme of self‐steered turns as a humidity response in Tenebrio, and the problem of categorizing spatial manoeuvres

Abstract

ABSTRACT. Dry‐acclimatized mealworm beetles, Tenebrio molitor L. (Coleoptera: Tenebrionidae), were exposed to a rapid change from dry to moist air in an arena with vertical air flow providing spatially uniform humidity, thus precluding orientation along humidity gradients. Subsequent angles of turn were significantly clustered around 90d̀ and 180d̀, and took the beetles back into the region from which they had come. The possibility of geomagnetic orientation was ruled out experimentally and in the apparent absence of other external directional cues it is concluded that the turn sequences were idiothetically controlled and pre‐programmed. This and other cases of ‘longitudinal’ klinotaxis are discussed in the wider context of kineses and taxes and the currently‐questioned value of these categories.