Biology of Oberea schaumii (Coleoptera: Cerambycidae) in Trembling Aspen, Populus tremuloides1

Abstract

The biology of Oberea schaumii LeConte in trembling aspen, Populus tremuloides Michaux, was studied in Upper Michigan and northern Wisconsin. The life cycle was determined through periodic collections of the insects from suckers and large trees, and from field rearings. Various aspects of adult behavior were learned from extended observations of adults in field cages. Eggs were usually laid on stems and twigs 5–15 mm diameter and 1–6 years old. They were deposited singly (usually) in elongate, rectangular egg niches gnawed in the bark by the female. Egg niches occurred on all aspects of vertical stems but only on the upper sides of leaning stems or side branches. The egg hatched in 14–15 days and the larva bored into the wood and then downward from the egg niche, parallel to the axis of the twig or stem. The larva widened and lengthened this tunnel throughout its development, ejecting borings to the outside through 3 ejection ports. When completed, the gallery averaged 17 cm long and 4 mm diameter. Most (77.5%) individuals required 3 yrs to complete development. Eggs were laid from late June to early August and the larvae fed for 3 summers, overwintering in the gallery. Pupation occurred from mid-May to early June of the 4th calendar year, and adults emerged during the last 3 weeks of June, 3 years after eggs were laid. Five percent emerged in 2 years and 17.5% emerged 4 years after eggs were laid. Adults fed during the day along the midribs on the under sides of leaves and on the outer bark of new shoots and older twigs. Mating was observed during the day; males and females mated more than once even on the same day. Economic loss caused by O. schaumii in natural stands was negligible.