Can the destruction of California’s oak woodlands be prevented? Potential for biological control of the goldspotted oak borer, Agrilus auroguttatus

Abstract

The goldspotted oak borer (GSOB), Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is an introduced and aggressive phloem/wood borer infesting native oaks in southern California. Elevated levels of oak mortality have occurred continually for the last nine years on three oak species in San Diego Co., California, USA. Biological control is being assessed as an option for longterm and widespread management of the invasive population of GSOB. Foreign exploration in the native ranges of GSOB and a related sibling species (Agrilus coxalis Waterhouse) was conducted to determine life history information, to assess the natural enemy complex, and to collect specimens for molecular analyses that could help to identify the area of origin of California's introduced population. Two species of parasitoids, Calosota elongata Gibson (Eupelmidae) and Atanycolus simplex Cresson (Braconidae), were discovered with GSOB populations in Arizona and California. No insect natural enemies were found with populations of A. coxalis in southern Mexico. However, Quercus conzatti Trel. and Quercus peduncularis Nee in Oaxaca and Chiapas, respectively, were recorded as the first known hosts of A. coxalis. A comparative analysis of our understanding of the natural enemy complexes for other pestiferous Agrilus with that of GSOB suggests that more effort should be directed at uncovering potential egg parasitoids and microbial pathogens of GSOB. Analyses of mitochondrial and nuclear ribosomal DNA (rDNA) revealed that the California population of GSOB was more similar to the Arizona population. Specimens of A. coxalis from southern Mexico were confirmed as a separate species. Additional surveys and sampling are needed across the complete native range of the GSOB species complex to develop a comprehensive inventory of parasitoid species that could be considered for use in a classical biological control program in California and to delineate the area of origin of California's population.

Forest stand composition and impacts associated with Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae) and Agrilus coxalis Waterhouse in oak woodlands

“…in declining oaks in AZ and MX, bark was removed to expose meandering larval galleries on the xylem surface or the presence of any life stage of this beetle genus (Coleman and Seybold, 2008). Phloem-or wood-boring insect injury, especially from Agrilus spp., is not well documented in these areas and this destructive sampling technique of bark removal was necessary to confirm the presence of the life stages and injury symptoms of this genus Coleman et al, 2012). Woodpecker foraging holes that expose A. auroguttatus larval galleries and/or D-shaped emergence holes on the main stem are definitive for A. auroguttatus infestation in San Diego Co., California and were required to classify an oak as infested (Brown and Eads, 1965;Swiecki and Bernhardt, 2006;.…”

“…The virulence of this new pest is still being examined, but oak mortality continues in areas that have experienced long-term exposure to this pest. Mortality of these large trees is a process that typically may occur over several years and some host resistance (e.g., formation of callus tissue) (Coleman and Seybold, 2008) and natural enemy activity (Coleman et al, 2012) have been noted in southern California that (along with nondrought periods) could perhaps moderate tree mortality in the future. Q. agrifolia is found in pure stands in the foothills and coastal areas of California and Baja California Sur, Mexico, whereas Q. kelloggii is a co-dominant species in higher elevation mixed conifer stands throughout California.…”

“…In southern Mexico, Quercus conzatti Trel. and Quercus peduncularis Nee were confirmed recently as hosts for A. coxalis (Coleman et al, 2012). Thus, in California, the invasive population of A. auroguttatus is associated with host oak species for which it had no prior co-evolutionary relationship in Arizona, and the extent of the potential short-and long-term impacts of A. auroguttatus on California's oak woodlands is unknown.…”

Buprestidae Collected as Prey by the Solitary, Ground-Nesting Philanthine Wasp Cerceris fumipennis (Hymenoptera: Crabronidae) in North Carolina

“…Buprestids are frequently intercepted at ports (Haack 2006), and species in the genus Agrilus are of particular concern. Emerald ash borer is currently the primary focus of the Cerceris biosurveillance program, but the wasp may serve as an early detection system for other invasive species recently reported in North America, including A. auroguttatus Schaeffer (goldspotted oak borer) (Coleman et al 2012), and A. sulcicollis (Lacordaire) (European oak borer) (Jendek and Grebennikov 2009). C. fumipennis was successful in detecting 17 species of Agrilus during our survey (Fig.…”

Assessing the Flight Capabilities of the Goldspotted Oak Borer (Coleoptera: Buprestidae) With Computerized Flight Mills

“…In 2009, a satellite infestation was found at Marion Bear Memorial Park in urban San Diego, CA, Ϸ32 km west of major infestation zones (Coleman et al 2012b). Another satellite infestation was discovered in fall 2012, in Idyllwild, Riverside County, CA, Ϸ70 km north of the closest known infestation (Jones et al 2013).…”