Goldspotted oak borer effects on tree health and colonization patterns at six newly-established sites

摘要

Newly-established populations of invasive wood-inhabiting insects provide an opportunity for the study of invasion dynamics and for collecting information to improve management options for these cryptic species. From 2011 to 2013, we studied the dynamics of the goldspotted oak borer Agrilus auroguttatusSchaeffer (Coleoptera: Buprestidae), a new pest of oaks in southern California, at six sites that had been colonized recently. At all sites, the percentage of coast live oaks Quercus agrifoliaNee, colonized by A. auroguttatus increased between 2011 (6-33%) and 2013 (23-40%), although beetle densities did not grow rapidly at most sites. From 2011 to 2013, there were minor changes in signs and symptoms of A. auroguttatus infestation (adult emergence holes, bark staining, and evidence of woodpecker foraging), except at one site where an outbreak occurred. At some sites, noticeable negative changes in oak crown health occurred 1year prior to positive A. auroguttatus population growth. Among sites, most of the A. auroguttatus population density (66-93%) was produced by a small number of heavily-infested trees (=brood trees). Early identification and removal of brood trees in newly-invaded areas could slow the growth of A. auroguttatus populations.