Mating behavior ofXylotrechus pyrrhoderus Bates (Coleoptera: Cerambycidae). VI mating system

Observations made in an outdoor cage showed that most pairings of the grape borerXylotrechus pyrrhoderus Bates were formed via inflight orientation of females towards pheromone-releasing males. The male sex pheromone induced orientation behavior in flying females, as well as walking approaches and prolonged lingering periods near the pheromone source in alighting females. When an approaching female failed to elicit any response in a male (e.g., when the male was copulating), she touched and sometimes mounted him. This behavior stimulated the males and often resulted in successful copulation. The male usually inseminated the second female, and the male's fitness increased when the second mating occurred more than 5 min after the start of the firt mating. These results suggest that male-like behavior in females (i.e., approaching and mounting behavior) has biological significance. The grape borer sometimes forms pairs via incidental encounters of the sexes. This is the same as the prevailing mating system of cerambycids. It is suggested that the male sex pheromonemediated mating system of the grape borer developed from the prevailing system of cerambycid groups.