Courtship Behavior of the Oriental Fruit Moth (Grapholitha molesta)1: Experimental Analysis and Consideration of the Role of Sexual Selection in the Evolution of Courtship Pheromones in the Lepidoptera 2

Abstract

The courtship behavior of Grapholitha molesta (Busck) (Oriental fruit moth) males, as analyzed by means of conditional probability matrix techniques, consists of a relatively stereotyped sequence of behaviors culminating in an elaborate hairpencil display directed toward and performed 1 or 2 cm from the female. The display is comprised of multiple rhythmic extrusions and retractions of the white hairpencil organs and claspers at the end of the abdomen, accompanied by corresponding 45 and 90 cm/sec “puffs” of wind generated by the vibrating wings and directed toward the female. The stimuli contained in the display, primarily chemical and anemo-tactile (wind movement), attract the female, who walks to the hairpencils, where contact with the end of the abdomen causes the female to cease walking. The tactile stimulus from the female causes the male to turn quickly and attempt copulation. The female again walks forward, with the wing nearest the male raised, and copulation follows. The visual stimulus of the calling female acts in conjunction with female-emitted pheromone components to release the sequence of male courtship behavior. Visual feedback from the attracted female moving toward the male causes the form of the display to be altered, making the 1st extrusion longer. Successful courtship sequences last ca. 1.5 sec. The male hairpencils and courtship behavior of this species are hypothesized to have evolved primarily by means of sexual selection involving “female choice ”, in which a female preference and preferred male trait become linked as a result of the mating advantage conferred upon male offspring of discriminating females. Male courtship pheromones of other Lepidoptera and “coyness” in females also may have evolved by this mechanism. The hairpencil display is viewed as a form of clasper extension behavior that has become “ritualized” through the process of sexual selection.