Biology and distribution of Agrilus macer LeConte (Coleoptera: Buprestidae), a species associated with sugarberry (Celtis laevigata Willd.) mortality in the southeastern USA

Abstract

Agrilus macer is attacking sugarberry trees in the southeastern USA, a region from which few specimens have been previously collected. Despite attacking at high densities, this species appears to be a secondary pest, and there is no evidence it carries harmful fungal pathogens. Because the genus Agrilus Curtis includes significant forest pests, the association of a poorly known species, Agrilus macer LeConte, with unexplained sugarberry (Celtis laevigata Willd.) mortality in the southeastern USA is a cause for alarm. This study sought to investigate the distribution and biology of A. macer and determine whether the species is a primary cause of observed tree mortality. Through a series of studies and literature searches, we documented aspects of A. macer biology and distribution while focusing on egg-laying behavior and searching for fungal pathogens associated with oviposition sites. A. macer appears to be widely distributed throughout the southern USA, but most records are from Texas and Louisiana. Egg mass densities up to 1.2 masses per 10 cm2 (equivalent to ~ 1.9 eggs per cm2) were observed on trunks, branches, and exposed roots of dying C. laevigata trees in our study area, with an average of 16 eggs per mass. Fungi isolated from discolored sapwood around larval galleries did not cause defoliation, dieback, or mortality of sugarberry in inoculation trials. Our findings suggest that A. macer is a secondary pest on sugarberry and does not transmit harmful fungal pathogens.