The Role of Vision and Olfaction in Host Plant Recognition by the Alfalfa Weevil, Hypera postica1

Abstract

A bioassay was developed which could be used to determine what sensory modalities were involved in host finding by the alfalfa weevil, Hypera postica (Gyllenhal), or whether the orientation process was entirely random. Weevils in the bioassay chamber responded more actively (by a ratio of about 3:1) to a flat of living alfalfa than to a control flat of dead alfalfa painted green. This non-random response persisted when the direction of air flow was reversed. In fact, the only alterations which diminished the standard response were those which changed or reduced the visual stimuli reflected from the flat of living alfalfa. From this it was concluded that weevils are primarily attracted by visual properties of their host plants; olfactory cues play a subordinate role, and may be limited to the perception of a humidity gradient surrounding the plant material at very short distances.