Sex Pheromones of Noctuid Moths. XX. Short-Range Visual Orientation by Pheromone-Stimulated Males of Trichoplusia ni1,2

Abstract

Pheromone-stimulated males of the cabbage looper, Trichoplusia ni (Hubner) (Lepidoptera: Noctuidae), were observed in the laboratory for orientation and copulatory attempt behavior directed toward a pheromone source or nearby visual models positioned vertically in a cage. The models were either dried T. ni females or black paper silhouettes. When 2 models were presented simultaneously, 2 cm to the right and left of a pheromone source on a disc of filter paper, 33% of the males observed oriented to one of the models vs. 67% to the source. However, 86% of all copulatory attempts were directed toward a model vs. 14% toward the source. The models did not influence the frequency of orientation behavior of pheromone-stimulated males; they only influenced the direction of orientation. By contrast, the models influenced both the frequency and direction of copulatory attempts. All orientation and copulatory attempts were directed toward the lower apex of a model, even if that apex was the head or wing tip of a dried female. Large variations in model shape from a shape similar to a female had to be made to cause a diminution in effectiveness for directing orientation. A black paper silhouette was less effective than a normal dried female moth but was as effective as a dried female that was dyed black. Black silhouettes ½ or ¼ normal size were less effective than one of the size and shape of a female.