Andrew D. Graves

Population structure of Geosmithia morbida , the causal agent of thousand cankers disease of walnut trees in the United States

The ascomycete Geosmithia morbida and the walnut twig beetle Pityophthorus juglandis are associated with thousand cankers disease of Juglans (walnut) and Pterocarya (wingnut). The disease was first reported in the western United States (USA) on several Juglans species, but has been found more recently in the eastern USA in the native range of the highly susceptible Juglans nigra. We performed a comprehensive population genetic study of 209 G. morbida isolates collected from Juglans and Pterocarya from 17 geographic regions distributed across 12 U.S. states. The study was based on sequence typing of 27 single nucleotide polymorphisms from three genomic regions and genotyping with ten microsatellite primer pairs. Using multilocus sequence-typing data, 197 G. morbida isolates were placed into one of 57 haplotypes. In some instances, multiple haplotypes were recovered from isolates collected on the same tree. Twenty-four of the haplotypes (42%) were recovered from more than one isolate; the two most frequently occurring haplotypes (H02 and H03) represented 36% of all isolates. These two haplotypes were abundant in California, but were not recovered from Arizona or New Mexico. G. morbida population structure was best explained by four genetically distinct groups that clustered into three geographic regions. Most of the haplotypes isolated from the native range of J. major (Arizona and New Mexico) were found in those states only or present in distinct genetic clusters. There was no evidence of sexual reproduction or genetic recombination in any population. The scattered distribution of the genetic clusters indicated that G. morbida was likely disseminated to different regions at several times and from several sources. The large number of haplotypes observed and the genetic complexity of G. morbida indicate that it evolved in association with at least one Juglans spp. and the walnut twig beetle long before the first reports of the disease.

Sanitation Options for Managing Oak Wood Infested with the Invasive Goldspotted Oak Borer (Coleoptera: Buprestidae) in Southern California

ABSTRACT Movement of invasive wood-boring insects in wood products presents a threat to forest health and a management challenge for public and private land managers. The goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is a new pest in San Diego and Riverside Cos., CA, believed to have been introduced on firewood. This beetle has caused elevated levels of oak mortality since 2002. From 2009–2011, we tested several sanitation methods, applicable to large and small land parcels, to reduce or prevent goldspotted oak borer emergence from infested oak wood. In most experiments, emergence of goldspotted oak borer adults from the positive controls demonstrated that the beetle could complete development in firewood-sized pieces of cut oak wood. In 2009, adult emergence from sun-exposed oak wood began and peaked 2- to 4-wks earlier at a low elevation site than at a high elevation site (late May to late June). However, there were no significant effects of elevation or host species on the emergence response of goldspotted oak borer by solarization treatment in this study. Solarization of infested wood with thick (6 mil) and thin (1 mil) plastic tarpaulins (tarps) did not significantly reduce emergence of adults despite recordings of greater mean and maximum daily temperatures in both tarped treatments and greater relative humidity in the thick-tarped treatment (all compared with nontarped controls). Grinding wood with a 3″-minus screen (≤7.6 cm) significantly reduced goldspotted oak borer emergence compared with control treatments, and this was the best method for reducing adult emergence among those tested. In a separate grinding study, no adults emerged when wood was ground to 9″-minus (22.9 cm), 2″-minus (5.1 cm), or 1″-minus (2.5 cm) screen sizes, but a low level of adult emergence from the positive controls limited any inferences from this experiment. Debarking cut wood pieces eliminated goldspotted oak borer emergence from the wood fraction, but adults emerged from the shaved bark and phloem.

Developing Monitoring Techniques for the Invasive Goldspotted Oak Borer (Coleoptera: Buprestidae) in California

ABSTRACT The goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is an invasive species that has colonized oak woodlands in southern California. To better define its seasonal flight activity, assist with forest and integrated pest management activities, and define the current distribution in California, an effective monitoring technique for A. auroguttatus is necessary. We assessed the efficacy of two colors of flight-intercept prism traps, the placement of these traps at three heights, and several commercially available lures [Manuka oil, Phoebe oil, and a green leaf volatile, (3Z)-hexenol] for monitoring the flight of adult A. auroguttatus. Landing rates and the densities of D-shaped emergence holes of A. auroguttatus adults were assessed on the lower stems of coast live oak, Quercus agrifolia Née, of varying size and crown health classes. Purple flight-intercept prism traps placed at heights of 3 m and 4.5 m caught significantly more female A. auroguttatus than green prism traps. In one experiment, males also responded at a significantly higher level to purple than to green prism traps placed at 3 m height. The addition of commercially available lures significantly enhanced male, but not female, A. auroguttatus trap catch when compared with unbaited control traps. There were no differences among male flight responses to the three lures. A. auroguttatus landing rates and emergence hole densities were significantly greater on the largest-diameter trees (>76.2 cm diameter at breast height) and on trees with severe crown thinning or complete crown collapse. The annual increment in emergence hole densities was also significantly greater on trees with severe crown thinning or complete crown collapse. In three trapping studies over multiple years in southern California, the adult flight period began as early as mid-May, peaked in mid-June to early July, and ended in early- to mid-September. To demonstrate the efficacy of the detection method for A. auroguttatus (unbaited purple traps at 3 m height), a delimitation survey conducted from 2009 to 2012 confirmed that the species was only present in San Diego Co., but that the distribution was expanding northward.

Invasive Bark and Ambrosia Beetles in California Mediterranean Forest Ecosystems

This chapter discusses the native ranges, histories of introduction, recent research efforts, and the potential impacts of some of 22 species of invasive scolytids in California’s Mediterranean forest ecosystems. The diversity of native and ornamental tree species, the varied climatic zones, and the widespread importation of nursery stock and packaged cargo have made California a fertile location for the introduction and establishment of bark and ambrosia beetles. Eight of the twenty two taxa are ambrosia beetles; four are spermophagous (e.g., Coccotrypes and Dactylotrypes sp.); six are hardwood bark beetles (Hypothenemus eruditus, Scolytus sp., Phloeotribus liminaris, and Pityophthorus juglandis); and four are coniferophagous bark beetles (Hylurgus ligniperda, Ips calligraphus, Orthotomicus erosus, and Phloeosinus armatus). Five of the species have probable native ranges elsewhere in North America (indigenous exotic species), whereas nearly all of the remaining species have likely origins in Eurasia with at least four of those with clear roots in true Mediterranean ecosystems. Several appear to be from Africa. Many of the species were first detected in heavily urbanized southern California. Detailed overviews are provided for an ensemble of species that have had or could potentially have the most impact on California forest or orchard resources (H. ligniperda, O. erosus, P. juglandis, Scolytus multistriatus, S. rugulosus, S. schevyrewi, and Xyleborinus saxeseni). Another potentially damaging species, the polyphagous shot hole borer, Euwallacea nr. fornicatus, is treated elsewhere (Chap. 26). The introductions of these taxa range from species that may have invaded over 100–150 years ago (e.g., Hypothenemus eruditus, S. rugulosus, or X. saxeseni) to 10–15 years ago (10 of the 22 species have been detected since 2000). Dactylotrypes longicollis (a spermophage); Euwallacea nr. fornicatus; and Hylurgus ligniperda represent new generic records for California. Trends and conditions that favor future invasions by other members of this group of insects and a California watch list are presented.

3-Methylcyclohex-2-en-1-one for area and individual tree protection against spruce beetle (Coleoptera: Curculionidae: Scolytinae) attack in the southern Rocky Mountains

Abstract We tested 3-methylcyclohex-2-en-1-one (MCH) and an Acer kairomone blend (AKB) as repellent semiochemicals for area and single tree protection to prevent spruce beetle (Dendroctonus rufipennis Kirby) attacks at locations in Utah and New Mexico. In the area protection study, we compared host infestation rates of MCH applications at three densities (20, 40, and 80 g MCH ha–1) against a control treatment over 0.64 ha plots centered within ∼1.25 ha treatment blocks. All treatments included two baited funnel traps within the plot to assure spruce beetle pressure. Following beetle attack, plots were surveyed for new spruce beetle attacks and to quantify stand characteristics. The probability of more severe spruce beetle attacks was significantly reduced, by ∼50%, in each of the MCH area treatments compared with the control treatment but there was no significant treatment difference among the MCH deployment densities. For the single tree protection study, we compared attack rates of MCH, Acer kairomone blend (AKB), and MCH plus AKB on spruce beetle-baited trees against bait-only trees. Each treatment was applied over a range of host diameters to test for host size effects. Seventy-five percent of control trees were mass-attacked, about one-third of MCH- and AKB-alone spruce was mass-attacked, and no MCH plus AKB spruce were mass-attacked. These results suggest that MCH alone is a marginal area and single tree protectant against spruce beetle but that deployment with other repellents can significantly increase treatment efficacy.

Efficacy of Systemic Insecticides for Control of the Invasive Goldspotted Oak Borer (Coleoptera: Buprestidae) in California

Abstract From 2009 to 2013, we tested four systemic insecticide formulations and five application methods against the invasive goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), in California. The insecticides were evaluated in three experiments: 1) 2009 remedial applications of emamectin benzoate (stem-injection) and imidacloprid (stem-injection and soil-injection); 2) 2009–2012 emamectin benzoate and imidacloprid initially applied at different times during the dormant season with varying injection technologies; and 3) 2013 dinotefuran applied to several tree diameter size classes. Adult leaf-feeding bioassays were used to assess the impact of systemic treatments against A. auroguttatus, whereas enzyme-linked immunosorbent assays determined the quantity of the active ingredient of insecticide residues in foliage. Imidacloprid (experiment 1) persisted at elevated levels in foliage of coast live oak, Quercus agrifolia Née, for 1.5 yr following stem injections. Stem injections of emamectin benzoate (experiment 2) sometimes significantly decreased survival in adults fed foliage from treated Q. agrifolia, and both the emamectin benzoate and imidacloprid treatments reduced adult feeding in some trials. Imidacloprid residues in Q. agrifolia and California black oak, Quercus kelloggii Newb., foliage remained at elevated levels (>10 µg/g) ∼2 yr postapplication. In 2013 (experiment 3), dinotefuran residues were highest in foliage collections 2 wk postapplication and greatest in smaller diameter oaks, but insecticide treatment had no effect on survival or frass production by adults fed foliage from treated trees. Systemic injections of emamectin benzoate and imidacloprid applied during the dormant season to uninfested or lightly infested oaks can reduce adult A. auroguttatus survival and maturation feeding.