On Oviposition, Olfactory Conditioning and Host Selection in Rhizopertha Dominica Fab. (Insecta, Coleoptera)

Abstract

The senses used in food finding and the factors inducing oviposition in Rhizopertha dominica (Fab.), a Bostrichid beetle pest of stored grain, were investigated. The sense of smell appears to be the most important in leading the animal to an environment where food is present. Responses were obtained in an olfactometer with maize, wheat, oats and barley and with different extracts of wheat and maize. The use of the sense of sight was also investigated. Once within an environment having the odour of food the sense of touch appears to be paramount in the selection of oviposition site. The influence of size, shape and texture were investigated. But in the absence of appropriate patterns of stimuli involving both olfactory and tactile sensations, restraint from oviposition was exercised. No predilection was shown for oviposition or feeding in the food in which they were reared as larvae. Neither did the larvae especially choose for entry substances in which their parents have been reared. The animal can be made tolerant to the odour of peppermint instead of repelled by it in an olfactometer by exposing the adults to the odour of peppermint for a few weeks. The effect wears off after 10-14 days' isolation from peppermint in wheat. Olfactory receptors which appear to be located on the antennae and legs were used in both food-finding and recognition of the opposite sex. A list is given of the substances in which the animal was reared. The bearing of these results on the problem of "gestalt" in conditioning, and on changes in habit in economic insects, is discussed.