Body size,male aggression,and male mating success in the cottonwood borer,Plectrodera scalator (Coleoptera: Cerambycidae)

The natural history and mating system ofPlectrodera scalator exhibit several unusual characteristics. Larvae and adults feed on the wood and foliage, respectively, of the same plant,Populus deltoides. The population sex ratio, based on censuses of oviposition areas, is female-biased. Females are significantly larger than males, yet males are intensely aggressive. Larger males tend to win escalated battles, which involve grasping of antennae with mandibles, but smaller males can defeat larger males if they grasp their opponent's antenna first. Most escalated 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 advantage for larger males. There is no significant difference in elytron length or body mass between mating and single males. Larger females are not preferred as mates. The mating system appears to be a mixture of female-defense and scramble-competition tactics. One advantage to males of aggression may be in its effect on sperm precedence. Males appear to be able to remove previously deposited sperm from a female's reproductive tract.