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

Abstract

1 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. 2 From 2011 to 2013, we studied the dynamics of the goldspotted oak borer Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), a new pest of oaks in southern California, at six sites that had been colonized recently. 3 At all sites, the percentage of coast live oaks Quercus agrifolia Née, colonized by A.auroguttatus increased between 2011 (6-33%) and 2013 (23-40%), although beetle densities did not grow rapidly at most sites. 4 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 1 year prior to positive A. auroguttatus population growth. 5 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.

Acute Oak Decline and Agrilus biguttatus: The Co-Occurrence of Stem Bleeding and D-Shaped Emergence Holes in Great Britain

“…Certainly, the degree of success A. biguttatus can have in the final stages of decline can be dramatic, as highlighted by the emergence of 102 beetles in an eight-week period from a heavily declined tree (that died in the following year). A similar pattern can be seen with Agrilus auroguttatus Schaeffer, where a small number of symptomatic trees produce the majority of emerging adults [58].…”

Impact of the goldspotted oak borer, Agrilus auroguttatus, on the health of coast live oak before and after treatment with two systemic insecticides

“…Because many insects prefer to colonize weakened or previously infested trees rather than healthy trees, we examined the effect of previous infestation levels on subsequent infestation by A. auroguttatus and on the rate of decline of the oaks. We also measured infestation levels as they related to trunk diameter to confirm observations by our group that had suggested that larger diameter trees were more likely to be colonized by A. auroguttatus . We selected two study sites in the core area of the zone of infestation in San Diego County, California (Fig.…”

“…C). At newly infested sites on the periphery of the zone of infestation, Q. agrifolia in the 11–20 cm diameter class were rarely infested, whereas greater proportions of Q. agrifolia in the larger diameter classes were infested and, in particular, brood trees were observed in the larger diameter classes (>41 cm DBH) . At both Deerhorn Valley and Japatul Valley, the greatest cumulative increase in emergence holes was observed on trees with an intermediate DBH (between 20 and 41 cm) (Figs A and B).…”

“…Currently, the primary approach available for managing A. auroguttatus involves preventing infestation of healthy trees by limiting movement of and destroying insects in infested wood through procedures such as debarking, tarping or grinding . Trees targeted for removal and sanitation are the so‐called ‘brood’ trees, which appear to concentrate a large proportion of local populations in newly infested areas . In addition to these sanitation measures, biological control has been considered as a potential management technique .…”

Native and introduced range surveys for egg parasitoids ofAgrilus auroguttatus, an invasive pest of native oaks in California

“…At each site, 10 trees infested with larval A. auroguttatus were selected for deployment of A. auroguttatus sentinel eggs to survey for potential natural enemies targeting this life stage in the native and invaded ranges. Previously infested trees were selected because they appear to be more attractive to A. auroguttatus adults Haavik, Flint, Coleman, Venette, & Seybold, 2014). Trees were considered infested if symptoms described in Hishinuma et al (2011) such as larval galleries and exit holes were present.…”