Male size, mating success, and breeding habitat partitioning in the whitespotted sawyer Monochamus scutellatus (Say) (Coleoptera: Cerambycidae).

The whitespotted swayer Monochamus scutellatus (Say) (Coleoptera: Cerambycidae) breeds in recently killed conifers in northeastern North America, especially white pine Pinus strobus L. We cut down 4 white pines in Pocahontas County, West Virginia, in June 1981, in order to study the behavior of sawyers attracted to the trees. Far greater numbers of both male and female sawyers were attracted to the largest of the trees cut. At all trees, females preferred the parts of the tree of greater circumference. These preferences may be related to greater larval survival in large-circumference regions. Male and female numbers at breeding site peaked at about 1200-1500 h EST; at this time, males generally outnumbered females by about 2:1. We placed males in 3 size classes: L (>2.0 cm), M (≦2.0 cm, ≧1.8 cm), and S (<1.8 cm). At the largest of our 4 trees, L males disproportionately frequented the portion of the trunk preferred by females. L males were far more successful than M and S males in mating and in agonistic encounters with other males. L males were thus apparently able to exclude smaller males from the preferred region to some extent.