Influence of the Intrastand Position of Black Locust Trees on Attack Rate of the Locust Borer (Coleoptera: Cerambycidae)

Abstract

The attack rate of locust borers, Megacyllene robiniae (Forster), was studied in relation to intrastand position in 15 native black locust ( Robinia pseudoacacia L.) stands in western Maryland during 1987-1988. Each stand was divided into the following intrastand positions: mixed forest, forest-clone edge, clonal growth, clone-open edge, and open growth. Borer attack rate was lowest in mixed-forest black locust and increased as stands extended from the forest edge into adjacent open areas as clonal growth and growing in the open. Tree size decreased and tree vigor increased from mixed forest to open growth. However, borer attack rates increased from mixed forest to open growth within all classes of diameter at breast height and among trees with high vigor. Symptoms of previous borer attacks were positively correlated with current attack rates within all intrastand positions. We found no significant intrastand differences in borer survivorship from the spring larval stage to adult emergence. Intrastand differences in attack rate may have been caused by factors affecting oviposition or survival of the egg and fall-winter larval stages. Evidence of an inverse relationship between borer attack rate and tree vigor existed only in the mixed-forest intrastand position.