Orientation of Papilio demoleus larvae in relation to size, distance, and combination pattern of visual stimuli

Abstract The responses of P. demoleus larvae to vertical rectangular sheets of Citrus leaves increased with the horizontal and vertical visual angles subtended by the sheets presented on one side only. The leaf-sheets differing in size but subtending identical visual angles at different distances elicited an equal larval response. Even when presented a choice between two leaf-sheets subtending identical visual angles at two different distances, the larvae showed an equal response to both. Thus, the larval orientation was determined by the visual angles subtended by the leaf-sheets rather than their linear dimensions and distances. The larval responses could be related with the horizontal and visual angles of the leaf-sheets by a regression equation. The leaf-sheets with irregular or wavy margins also elicited the same larval response as the equivalent leaf-rectangles with straight margins. The orientation of larvae to two leaf-sheets, offered together as a choice on two sides, showed varying degrees of deviations from the responses to the same sheets presented singly. The larval responses to the leaf-sheets offered together could be quantitatively related to their responses to the sheets offered singly by two regression equations.