Ecological and anthropogenic factors influencing goldspotted oak borer (Agrilus auroguttatus) populations

The goldspotted oak borer (Agrilus auroguttatus: Buprestidae, Coleoptera) was first associated with tree mortality in San Diego County, California in 2008 and is believed to have been introduced via infested firewood from southeastern Arizona. The goldspotted oak borer (GSOB) larvae girdle the cambium surface, which can lead to tree mortality after several years of feeding. Approximately 21,500 coast live oak (Quercus agrifolia) trees have died due to GSOB larval feeding. We hypothesize that the change in GSOB population densities will correlate with specific biotic, abiotic, and anthropogenic factors that may predispose individual trees and forest stands to beetle injury. We measured the change in GSOB populations over a one year period by counting adult emergence holes on twenty Q. agrifolia trees at eight different locations within San Diego County.  We also rated tree crown damage on Q. agrifolia and deployed sticky traps at each location to capture adult beetles.  We measured the following biotic factors: coast live oak stand density and size class structure, phloem thickness, and woody plant species diversity. Abiotic and anthropogenic factors included slope and aspect of trees, distance of a tree to the stand’s edge, and human population density surrounding each stand.  The results from this research will hopefully reveal important relationships between ecological and anthropogenic variables and GSOB population growth that will allow land managers to prioritize eradication efforts in high risk areas as GSOB expands its range.