Oak Borer Research Articles

Assessing the flight capabilities of the goldspotted oak borer (Coleoptera: Buprestidae) with computerized flight mills.

The goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is native to southern Arizona and is an invasive wood-boring beetle that has caused considerable mortality to native oak species in southern California. Assessing the dispersal capabilities of this woodborer may help to determine its potential environmental and economic risk within the invaded region, and possibly assist with the development of species-specific management strategies. The flight performance of A. auroguttatus adults under different age, mating, and nutritional status was assessed by tethering individuals to computerized flight mills for a 24-h trial period to collect information on total distance flown, flight times and velocities, number and duration of flight bouts, and postflight weight. The nutritional status and body size (i.e., elytron length) of A. auroguttatus adults had a significant influence on overall flight performance. Mating status and gender had no significant influence on total flight distance, duration, velocity, and flight bout time. Significant interactions between nutritional status and age were observed in the overall flight performance of A. auroguttatus, with decreased flight activity in old (approximately 6 d of age) starved individuals during a 24-h trial period. Overall, results of these flight mill assays indicate that A. auroguttatus is unable to disperse long distances across habitats that lack suitable oak hosts. This work supports the hypothesis that human-aided transportation via infested oak firewood from southern Arizona across the Sonoran desert likely caused the initial introduction, and subsequent satellite infestations of A. auroguttatus within southern California's native oak woodlands.

Densities of Agrilus auroguttatus and Other Borers in California and Arizona Oaks

We investigated within-tree population density of a new invasive species in southern California, the goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), with respect to host species and the community of other borers present. We measured emergence hole densities of A. auroguttatus and other borers on the lower stem (bole) of naïve oaks at 18 sites in southern California and on co-evolved oaks at seven sites in southeastern Arizona. We sampled recently dead oaks in an effort to quantify the community of primary and secondary borers associated with mortality—species that were likely to interact with A. auroguttatus. Red oaks (Section Lobatae) produced greater densities of A. auroguttatus than white oaks (Section Quercus). On red oaks, A. auroguttatus significantly outnumbered native borers in California (mean ± SE of 9.6 ± 0.7 versus 4.5 ± 0.6 emergence holes per 0.09 m2 of bark surface), yet this was not the case in Arizona (0.9 ± 0.2 versus 1.1 ± 0.2 emergence holes per 0.09 m2). In California, a species that is taxonomically intermediate between red and white oaks, Quercus chrysolepis (Section Protobalanus), exhibited similar A. auroguttatus emergence densities compared with a co-occurring red oak, Q. kelloggii. As an invasive species in California, A. auroguttatus may affect the community of native borers (mainly Buprestidae and Cerambycidae) that feed on the lower boles of oaks, although it remains unclear whether its impact will be positive or negative.

Population genetics of goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae): investigating the origin of an invasive pest of native oaks in California

The goldspotted oak borer, Agrilus auroguttatus Schaeffer, is an invasive woodborer in California USA that is native to oak woodlands across southern Arizona USA. Developing a classical biological control program for this pest in southern California is a high priority due to the continuing ecological and economic damage caused by this insect since its recent introduction into the area. In an attempt to determine the area of origin for this invasive beetle, analyses of the mitochondrial cytochrome oxidase and ribosomal nuclear D2 domain of the 28S gene regions were undertaken and provided insight into the phylogeographic relationship between and within populations of A. auroguttatus in Arizona and California. The area of origin for the invasive population of goldspotted oak borer in California was not determined conclusively, although our molecular data suggests the Dragoon Mountains in Cochise Co., Arizona as a possible source for the California population of A. auroguttatus. Results also confirmed that individuals collected from populations across southern Arizona and California are all A. auroguttatus, and are not part of a cryptic species complex comprised of the morphologically similar A. coxalis. Future surveys for natural enemies of A. auroguttatus will focus on the Dragoon Mountains as a potential source for co-evolved enemies for use in a classical biological control program against this invasive woodborer in southern California.

Effects of Body Size, Diet, and Mating on the Fecundity and Longevity of the Goldspotted Oak Borer (Coleoptera: Buprestidae)

Abstract The goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is an invasive wood-borer that was recently introduced into southern California from southern Arizona, and has caused the rapid mortality of thousands of native oaks. Biological control of A. auroguttatus is a management strategy of high interest, but is in its early stages, which is due, in part, to a lack of information on the basic biology and life history of this beetle. To address this shortcoming, studies were conducted in quarantine on the realized lifetime fecundity of A. auroguttatus, which was determined by comparing oviposition and larval emergence rates of females subjected to different dietary and mating treatments. Longevity and body size were also recorded for male and female adults under these treatments. Mean A. auroguttatus lifetime oviposition and larval emergence were similar in females that were continuously paired with either one or two males. Virgin females laid significantly fewer eggs and no larval emergence resulted from unfertilized eggs. The number of mates did not affect mean A. auroguttatus adult longevity, but a carbohydrate-enriched diet increased both mean longevity and lifetime oviposition by as much as 46 and 250%, respectively. There was no correlation between adult body size and lifetime oviposition, days to initial oviposition, larval emergence, and adult longevity. However, hind tibia length was marginally correlated with total oviposition period. For mass rearing A. auroguttatus eggs in the laboratory, pairing females with one male and providing adults with a continuous diet of 10% honey-water and oak foliage is recommended.

Monitoring oak-hickory forest change during an unprecedented red oak borer outbreak in the Ozark Mountains: 1990 to 2006

Upland oak-hickory forests in Arkansas, Missouri, and Oklahoma experienced oak decline in the late 1990s and early 2000s during an unprecedented outbreak of a native beetle, the red oak borer (ROB), Enaphalodes rufulus (Haldeman). Although remote sensing supports frequent monitoring of continuously changing forests, comparable in situ observations are critical for developing an understanding of past and potential ROB damage in the Ozark Mountains. We categorized forest change using a normalized difference water index (NDWI) applied to multitemporal Landsat TM and ETM+ imagery (1990, 2001, and 2006). Levels of decline or growth were categorized using simple statistical thresholds of change in the NDWI over time. Corresponding decline and growth areas were then observed in situ where tree diameter, age, crown condition, and species composition were measured within variable radius plots. Using a machine learning decision tree classifier, remote sensing-derived decline and growth was characterized in terms of in situ observation. Plots with tree quadratic mean diameter at breast height ≥21.5 cm were categorized remotely as in severe decline. Landsat TM/ETM+-based NDWI derivatives reveal forest decline and regrowth in post-ROB outbreak surveys. Historical and future Landsat-based canopy change detection should be incorporated with existing landscape-based prediction of ROB hazard.

Suitability of native and ornamental oak species in California for Agrilus auroguttatus

AbstractGoldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is a new invasive species in southern California, USA. The extent of the host range of this insect is not known, but this knowledge will have a major impact on assessment of the risks that this pest poses to oaks [Quercus spp. (Fagaceae)]. We conducted laboratory tests to determine the potential suitability of native and ornamental oak species for larvae and adults of A. auroguttatus. We infested 179 cut logs (from 163 different trees) with eggs or larvae, measured neonate survival and, after 5 months, counted feeding galleries, and noted the proportion of galleries with late instars. Initial larval survival was generally high when larvae penetrated the phloem (range: 62–98% among oak species), and low by the time larvae began to feed at the phloem/xylem interface (range: 0–25% among oak species). The majority of larvae that established a visible feeding gallery survived to the fourth instar (total of 73% for all oak species). Larval galleries were established with greater frequency in red oaks (Section Lobatae) compared with other oaks (19 vs. 7 or 4%). All red oaks tested (Q. agrifolia Née, Q. kelloggii Newberry, and Q. wislizeni A. DC.) were likely suitable hosts for larvae. Larvae were apparently able to feed on some of the other oaks (Q. chrysolepis Leibmann, Q. suber L., Q. lobata Née, and Q. douglasii Hook & Arn), although it remains unclear whether these species would be preferred hosts under natural conditions. Adult longevity and fecundity varied little by species of oak foliage fed to adults. The host range of A. auroguttatus is likely limited by suitability of oak species for the larval rather than the adult life stage. Results support published field observations that red oaks are more suitable hosts than white oaks.

Biology of the European oak borer in Michigan, United States of America, with comparisons to the native twolined chestnut borer

AbstractIn 2010–2011, we studied the European oak borer (EOB),Agrilus sulcicollisLacordaire (Coleoptera: Buprestidae), in Michigan, United States of America, and made comparisons with the native twolined chestnut borer (TLCB),Agrilus bilineatus(Weber). EOB adult flight began and peaked before TLCB. More EOB females were captured on purple and white compared with yellow and green sticky traps. More TLCB females were captured on purple, followed by yellow, green, and white, respectively. Male EOB and TLCB did not show a significant colour preference. EOB completed development primarily from areas of artificially girdled trees where the phloem had died soon after trees were girdled, while TLCB usually developed in areas of girdled trees that had some live phloem present. Both EOB and TLCB successfully attacked and emerged from girdledQuercus albaLinnaeus,Quercus roburLinnaeus, andQuercus rubraLinnaeus (Fagaceae) trees. No live EOB or TLCB were found in two ungirdled and apparently healthyQ. roburtrees that were dissected. EOB attacked and emerged fromQ. alba,Q. robur,Q. rubra, andQuercus velutinaLamarck trap logs. Differences in the pronotal groove and terminal processes can be used to distinguish EOB from TLCB larvae. Five species of parasitoids were reared from EOB and four from TLCB.

Foliar nutrients explain goldspotted oak borer,Agrilus auroguttatus, adult feeding preference among fourCalifornia oak species

AbstractAdults of the invasive goldspotted oak borer,Agrilus auroguttatusSchaeffer (Coleoptera:Buprestidae), consumed foliar weight in no‐choice feeding tests of, in descending order,California black oakQuercus kelloggiiNewb.,Engelmann oak,Quercus engelmanniiGreene, coast live oak,Quercus agrifoliaNée, and canyon live oak,Quercus chrysolepisLiebm. (Fagaceae). Furthermore, significantly more foliar area was consumed ofQ. kelloggiithan ofQ. chrysolepis. In dual‐choice feeding tests with isolated leaf disks,A. auroguttatusconsumed significantly more foliar weight and area ofQ. kelloggiirelative to the other three oak species, and more foliar weight ofQ. agrifoliathan ofQ. chrysolepis. In dual‐choice feeding tests with leaves on small branches,A. auroguttatusconsumed more foliar weight ofQ. kelloggiithan ofQ. engelmanniiandQ. agrifolia. Thus, multiple experiments suggested that adults ofA. auroguttatuspreferred the foliage ofQ. kelloggiiover that of the other three oak species, and among the other three species they did not appear to have a strong feeding preference. Factor analysis reduced the quantities of 13 foliar nutrients into two new variables (factor 1 and factor 2). Factor 1 was weighted heavily on the quantities of nitrogen, sulfur, phosphorus, potassium, zinc, and copper, whereas factor 2 was weighted heavily on the quantities of zinc, iron, and aluminum. Factor 1 varied by oak species, withQ. kelloggiihaving a higher factor 1 nutrient content than the other three species. Factor 2 response was higher inQ. kelloggii,Q. agrifolia, andQ. engelmanniithan inQ. chrysolepis. The collective effects of four macronutrients (nitrogen, sulfur, phosphorus, and potassium) and two micronutrients (zinc and copper) suggest that these might be the nutrients directing preferential feeding ofA. auroguttatusadults on the foliage ofQ. kelloggii. Leaf toughness might also play an important role in feeding preference. FemaleA. auroguttatusdid not show an ovipositional preference among the four oak species.

Occurrence, incidence and associations among fungal pathogens and Agrilus auroguttatus, and their roles in Quercus agrifolia decline in California

SummarySynchronous decline of oak (Quercus spp.) trees in woodlands has been described in Europe and eastern North America as a complex interaction of stressors that predispose, incite or contribute to tree death. This study presents a 2‐year (2010–2011) assessment of the role of pathogens in coast live oak (Quercus agrifolia) woodlands in southern California where oak mortality occurs in locations that are infested and uninfested by the goldspotted oak borer (GSOB, Agrilus auroguttatus). Cumulative coast live oak mortality was not significantly different between sites and was weakly correlated with Diplodia corticola and GSOB incidence and negatively correlated with annual relative humidity. Multiple logistic regression models explained the presence of individual fungi or GSOB at the tree level. Fisher's exact test analysis determined that the presence of D. corticola, Fusarium solani, Dothiorella iberica, Cryptosporiopsis querciphila and Diatrypella verrucaeformis were each related to origin of sample location on tree, and C. querciphila was additionally related to symptom type on the bole. Multiple linear regression models showed high correlation between environmental variables and plot‐level incidence of both GSOB and D. corticola. Disease incidence (DI) for D. corticola was highest in GSOB‐uninfested locations. Jaccard index of association (J) showed that D. corticola was negatively associated with the presence of GSOB, F. solani and C. querciphila. Results suggest that oak decline in California is an example of a complex syndrome involving strong regional differences in factors that are associated with the problem.

Agrilus auroguttatus (Coleoptera: Buprestidae) Seasonal Development within Quercus agrifolia (Fagales: Fagaceae) in Southern California

Abstract We investigated seasonal development of the goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), and physical conditions of the phloem within a preferred host species, coast live oak, Quercus agrifolia Née. We sampled infested trees on a monthly basis at two sites in southern California throughout 2011. Measurements of an exposed portion of the head capsule, the peristoma, indicated that there were four larval instars. Pupae and teneral or mature adults were found within trees from April through August. Adults were captured in flight between May and mid-October, with peak flight from July through August. Within-tree A. auroguttatus prepupal mortality did not differ between sites and increased significantly from 3 ± 3% in January to 36 ± 9% in March (mean ± SE). Prepupae were present in trees throughout most of the year, which made it difficult to determine generation time; it was likely 1 yr for the majority of individuals, and possibly longer or shorter than 1 yr for others. Seasonal A. auroguttatus development, according to within-tree development and adult trap catch, was apparently 2 mo ahead at one site, which had a greater past and current level of A. auroguttatus infestation compared with the other. There was also evidence at the more severely infested site that within-tree A. auroguttatus population densities were positively related to proportion of dying phloem tissue. This suggested that the level of current infestation affected host tree condition, or that dying tissue was more suitable for larval development.

Laboratory and field bioassays on the effects of Beauveria bassiana Vuillemin (Hypocreales: Cordycipitaceae) on red oak borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae)

An unexpected outbreak of a native longhorned beetle, the red oak borer (Enaphalodes rufulus (Haldeman)), occurred in upland oak forests of Arkansas, Missouri and Oklahoma ca. 1999–2005. Few management tools exist for reducing E. rufulus populations. Laboratory bioassays were conducted to determine susceptibility of all E. rufulus life stages to the fungal pathogen Beauveria bassiana Vuillemin. Egg, neonate, early-instar, pupal, and adult stages of E. rufulus were all susceptible to a natural isolate of B. bassiana collected from E. rufulus (ARSEF 7404) or a commercial B. bassiana product, BotaniGard®. In July 2003, 10 living, E. rufulus-infested northern red oak (Quercus rubra L.) boles were sprayed with a 2 L BotaniGard®B. bassiana suspension of 1.3×1011 viable conidia per 2m of each bole at a forested site in the Ozark National Forest, Franklin County, Arkansas. The following spring, trees were removed and sampled for E. rufulus larvae that had survived or died during the winter. Live E. rufulus larval density in untreated Q. rubra log samples was significantly greater than in treated log samples with means of 16.4±1.8 (SE) and 4.4±2.0 larvae per m2 of bark for untreated and treated logs, respectively. Application of B. bassiana spray against early-instar E. rufulus would be most effective in mid-summer of odd-numbered years to target vulnerable early E. rufulus life stages and to reduce structural damage to trees caused by E. rufulus feeding.

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

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 (< or = 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.

Identification and pathogenicity of Botryosphaeriaceae species associated with coast live oak (Quercus agrifolia) decline in southern California

Symptoms of decline have been observed on dying coast live oak (Quercus agrifolia) trees in areas throughout southern California that are both infested and uninfested by the gold-spotted oak borer (GSOB). The purpose of this study was to identify and assess the pathogenicity of several anamorph species of the Botryosphaeriaceae, including Diplodia corticola, Dothiorella iberica and Diplodia agrifolia sp. nov., that were recovered consistently from symptomatic tissues. Species were identified morphologically and by phylogenetic analyses of the complete sequence of the internal transcribed spacer (ITS) of the rDNA and partial sequences of β-tubulin and elongation factor (EF1-α) genes. Results from morphological assessments and phylogenetic analyses support the erection of a new species closely related to D. mutila, described herein as Diplodia agrifolia sp. nov. Pathogenicity of all species was verified by wound inoculation of 1 y old coast live oak seedlings under controlled conditions. Isolates of D. corticola were the most aggressive tested, and isolates of D. agrifolia were the second most aggressive. Both species caused bleeding symptoms on inoculated seedlings. Seedlings inoculated with D. corticola died within 4 wk, with the pathogen progressing up and down through the xylem in advance of living phloem and moving throughout the taproot in 70% of inoculated seedlings. Colonization and re-isolation was successful for all species. All three fungal species represent newly recorded fungal pathogens of coast live oak in California. Results from the pathogenicity test suggest that these fungi play a role in the decline of coast live oaks throughout southern California.

Partial Life Tables From Three Generations of &lt;I&gt;Enaphalodes rufulus&lt;/I&gt; (Coleoptera: Cerambycidae)

We used life table analyses to investigate age specific mortality and to better understand the population dynamics of the red oak borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae). We continually sampled populations within 177 trees at primarily two sites in the Ozark National Forest in Arkansas throughout three (2-yr) generations. The first cohort (adults emerged in 2003) was sampled during a severe population outbreak, whereas the second and third (2005 and 2007) were sampled during the population crash that followed. Generation mortality was 94% in 2003 and 99% in both 2005 and 2007. Estimates of apparent mortality indicated that the E. rufulus population crash likely occurred during or before the first overwintering period (2003-2004) of the generation that emerged as adults in 2005. We found limited evidence for density dependent mortality, which suggest that intraspecific competition after the first active feeding period was apparently not an important mortality factor during E. rufulus development. Life tables revealed that E. rufulus larvae generally experienced the greatest apparent mortality during the second summer of active feeding (80-94%) when larvae were feeding in, and moving between phloem and sapwood. The least apparent mortality was incurred during the following spring and early summer (26-67%) when late stage larvae and pupae were deepest and most protected within sapwood or heartwood tunnels. We found very little evidence for mortality from associated species. Scarring of vascular tissue in response to E. rufulus feeding occurred during early life stages and may be an important tree resistance mechanism and E. rufulus mortality factor.

Agrilus auroguttatus exit hole distributions on Quercus agrifolia boles and a sampling method to estimate their density on individual trees

AbstractIn recent decades, invasive phloem and wood borers have become important pests in North America. To aid tree sampling and survey efforts for the newly introduced goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), we examined spatial patterns of exit holes on the boles (trunks) of 58 coast live oak, Quercus agrifolia Née (Fagaceae), trees at five sites in San Diego County, southern California, United States of America. Agrilus auroguttatus exit hole densities were greater at the root collar than at mid-boles (6.1 m above ground). Dispersion patterns of exit holes on lower boles (≤1.52 m) were random for trees with low exit hole densities and aggregated for trees with high exit hole densities. The mean exit hole density measured from three randomly chosen quadrats (0.09 m2) provided a statistically reliable estimate of the true mean exit hole density on the lower bole, with &lt;25% error from the true mean. For future sampling and survey efforts in southern California oak forests and woodlands, exit hole counts within a 0.09 m2 quadrat could be made at any three locations on lower Q. agrifolia boles to accurately estimate A. auroguttatus exit hole densities at the individual tree level.

Agrilus quercicola(Fisher) (Coleoptera: Buprestidae), the Gambel Oak Borer, as a Pest ofQuercusspp.

During 2003 an unusual outbreak of the Gambel oak borer, Agrilus quercicola (Fisher), caused extensive damage to several species of oak in Denver, Araphaoe, and Douglas counties in Colorado. This followed several seasons of environmental stress that predisposed Gambel oak to the insect, but adults apparently dispersed more than 30 km during this outbreak to kill oaks a considerable distance from native Gambel oak stands. In choice tests, adults fed on foliage of Gambel oak, but not other herbaceous shrubs common in stands of Gambel oak. Yellow and neon yellow-green, but not white, sticky traps caught considerable numbers of adults. Adult flight activity began in late May, peaked in early summer, and ended in late August. A chalcid parasitoid, Phasgonophora sulcata Westwood, was noted to be an important natural enemy. No injury by this insect has been observed outside of native Gambel oak in years subsequent to the 2003 outbreak.

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

From 2009–2011, we assessed the impact of the goldspotted oak borer, Agrilus auroguttatus Schaeffer, or its sibling species, Agrilus coxalis Waterhouse, at locations in southern California (denoted infested: ICA and uninfested: UCA), southeastern Arizona (AZ), and southern Mexico (MX). Our surveys examined forest composition of oak woodlands; the degree of injury and proportion of oaks infested with either A. auroguttatus (ICA and AZ) or A. coxalis (MX); and the progression of aerially mapped oak mortality in San Diego Co. (ICA). By most measures of impact that we evaluated, the effect on oaks by the two Agrilus spp. was relatively low in their native regions, but significantly higher by A. auroguttatus at ICA sites. Larger diameter red oak species have been the preferred hosts of A. auroguttatus in AZ and ICA sites, and red oaks greater than approx. 13cm in DBH throughout California are likely at risk of injury from this invasive pest. At sites in AZ there was no evidence of infestation by A. auroguttatus on living or dead white oak species, whereas at ICA sites we recorded a minor amount of infestation by A. auroguttatus on living individuals of a white oak species (Quercus engelmannii Greene), but no mortality. In contrast, a white oak from MX sites (Quercus peduncularis) was more frequently infested by A. coxalis than were indigenous red oaks. Across all ICA sites, A. auroguttatus has infested 61% of the live larger diameter oaks and killed 13% of the oak component of the forest (vs. 4% infested and 2% dead in AZ, respectively). At survey plots near the predicted origin of the outbreak in CA, over 90% of the larger diameter red oaks have been infested. Nearly 90% of the dead oaks surveyed across all ICA sites showed evidence of previous injury symptoms from A. auroguttatus. Aerial oak mortality polygons associated with A. auroguttatus have expanded ∼50km in nine years, but our analysis confirms that the outbreak appears to still be confined to San Diego Co. The distance of oak mortality polygons from the predicted origin of the outbreak explained the most variance in a principal component analysis. The invasive population of A. auroguttatus is a significant conservation and ecological threat to the oak woodlands of California and should be managed accordingly, especially by restricting firewood movement.

First occurrence of the goldspotted oak borer parasitoid, Calosota elongata (Hymenoptera: Eupelmidae), in California

Calosota elongata Gibson (Hymenoptera: Eupelmidae) is a gregarious, ectoparasitic larval parasitoid that was described recently (Gibson 2010) in association with the goldspotted oak borer, Agrilus coxalis Waterhouse [now considered to be Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae)] in its native range in southeastern Arizona. We have discovered this parasitoid outside of its presumptive native range on 1 December 2010 near the Pine Creek Trailhead, Cleveland National Forest in San Diego Co., California, beneath the bark of coast live oak, Quercus agrifolia Nee (Fagaceae), in association with A. auroguttatus.

Electrophysiological and Behavioral Responses of the Black-Banded Oak Borer, Coroebus florentinus, to Conspecific and Host-Plant Volatiles

Aspects of the chemical ecology of the black-banded oak borer, (BBOB) Coroebus florentinus (Coleoptera: Buprestidae), were studied. Odors produced by males and females were similar, both qualitatively and quantitatively. Nonanal, decanal, and geranylacetone, identified in the headspace of both sexes, elicited strong electroantennographic responses from male antennae, but not from female antennae. In dual-choice olfactometer experiments, a blend of these three compounds was attractive to both sexes; males responded to decanal alone, while females responded to geranylacetone alone, suggesting that these compounds are responsible for activity of the blend to the respective sexes. Antennae of both sexes responded electroantennographically to the green leaf volatiles (E)-2-hexenal, (E)-2-hexenol, 1-hexanol, (Z)-3-hexenyl acetate, and n-hexyl acetate, all identified from the host plant Quercus suber. In behavioral experiments, only females were attracted to host-plant odors, and in tests with synthetic compounds, females were attracted to (E)-2-hexenol, 1-hexanol, and (Z)-3-hexenyl acetate. It is likely that these compounds play a role in foraging and/or oviposition behavior of BBOB females.

Oak decline and red oak borer outbreak: impact in upland oak-hickory forests of Arkansas, USA

Summary Oak-hickory forests in the Ozark and Ouachita Mountains of Arkansas recently experienced an episode of oak mortality in concert with an outbreak of the red oak borer (Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae)). We utilized data from the Forest Inventory and Analysis (FIA) program of the USDA Forest Service to explore changes in percent red oak (Quercus subgenus Erythrobalanus) mortality as a function of standing trees, basal area and stem density during and after the recent borer outbreak throughout the state of Arkansas. Mean red oak mortality levels in Arkansas FIA oak-hickory plots that were sampled both during and after the borer outbreak increased from 19 ± 3 to 34 ± 4 per cent of standing red oaks, resulting in significantly reduced red oak basal area and stem density in these stands. Mean size of red oaks did not change significantly during this time period, implying that all size classes experienced mortality. After red oak borer populations subsided, oak-hickory survey plots experienced increases in red oak mortality levels during a drought year (2006) and after an ice storm (2009), which suggests that these stress events, in addition to prior red oak borer infestation, could have had some influence on tree mortality.