BODY-SIZE, MALE-AGGRESSION, AND MALE MATING SUCCESS IN THE COTTONWOODBORER, PLECTRODERA SCALATOR (COLEOPTERA, CERAMBYCIDAE)

The natural history and mating system of Plectrodera scalator exhibit several unusual characteristics. Larvae and adults feed on the wood an d foliage, respectively, of the same plant, Populus deltoides. The pop ulation sex ratio, based on censuses of oviposition areas, is female-b iased. Females are significantly larger than males, yet males are inte nsely aggressive. Larger males tend to win escalated battles, which in volve grasping of antennae with mandibles, but smaller males can defea t larger males if they grasp their opponent's antenna first. Most esca lated fights involve possession of a female, but prior possession does not play a role in determining the outcome of these fights. The size- dependent fighting advantage does not translate into a mating advantag e for larger males. There is no significant difference in elytron leng th or body mass between mating and single males. Larger females are no t preferred as mates. The mating system appears to be a mixture of fem ale-defense and scramble-competition tactics. One advantage to males o f aggression may be in its effect on sperm precedence. Males appear to be able to remove previously deposited sperm from a female's reproduc tive tract.