Biology of Saperda inornata (Coleoptera: Cerambycidae) in Trembling Aspen, Populus Iremuloides1

Abstract

A biological study of S. inornata Say in trembling aspen, Populus tremuloides Michaux, was conducted in Upper Michigan and northern Wisconsin. Life-cycle information was derived from periodic collections from infested suckers and large trees, and from rearings and caged adults in the field. Continuous observations of several hours duration were made of adults in field cages to determine various aspects of their behavior. The eggs were deposited singly (usually) on the wood under a shield- or horseshoe-shaped egg niche gnawed in the outer bark by the female. There were usually 2 or 3 egg niches at 1 level on the stem. The eggs hatched in 14–15 days and the larvae mined around the stem in the outer xylem. This injury and that caused by the female during oviposition stimulated the proliferation of wound tissue, forming a globose gall at the site. Toward the end of summer the larva bored a blind tunnel inward and then upward or downward from the gall, parallel to the axis of the stem. In this central tunnel the larva overwintered and pupated in spring. Pupae were found in the field from mid-May to late June. Emergence of adults occurred from late May until early July, but mostly during the 1st 3 weeks of June. Females laid eggs in field cages from mid-June until late August, but most oviposition was over by early August. Part of the population, apparently that from eggs laid early in the oviposition period, matured after 1 summer, and emerged the following spring. The others resumed feeding in the spring, overwintered a 2nd time, and emerged the next spring, 2 years after the eggs were laid. Adults fed during the day mostly around the edges of the aspen leaves. Mating occurred from mid- to late afternoon. In the field cages there appeared to be no strong attraction of male to female or vice versa; the male apparently encountered the female more or less by chance as he walked over the twigs and foliage of the sucker. Economic loss caused by S. inornata in natural stands of aspen was negligible. However, in clonal or progeny test plantings of aspen, stunting and some top mortality caused by heavy S. inornata infestation has occurred, justifying control measures.