Oviposition Characteristics and Early Larval Mortality of Saperda inornata and Oberea schaumii1 in Michigan Aspen2

Abstract

Saperda inornata Say and Oberca schaumii LeConte are 2 species of cerambycid beetles which infest Popidus tremuloides Michx. and P. grandidentata Michx. in Michigan. Their characteristic egg-niches and damage are discussed. S. inornata makes 1 or more horseshoe- or shield-shaped egg-niches in a ring around the stem or branch of an aspen sucker. Tunneling by newly hatched larvae causes a spindle-shaped gall to form. One or 2 years is the usual life cycle. O. schaumii normally makes 1 rectangular egg-niche on the stem or top side of a side branch. The larva bores a 12.2-27.9-cm-long, linear gallery down the stem and normally emerges as adult after 3 years. S. inornata females have the potential ability to make 300 or more egg-niches, comprising about 100 galls. Most of them are made on stems 8.0-13.5 mm diameter. About 91% will have an egg and 83% of those eggs will hatch in 14 or 15 days. At least 4% of young larvae will be parasitized by Eaderus lividas Ashmead (Eulophidae) in less than 30 days. Thus, of the original 300 niches, 72% will have active larvae after 30 days. O. schaumii females may make more than 120 eggniches on branches 13.5 mm or less diameter. Of these niches, 88% will have an egg and 79% of the eggs will hatch in 14 or 15 days. After 30 days, 69% of the original 120 niches will have active larvae. No parasites of young larvae were found in O. schaumii egg-niches.