Trap Assays of the Walnut Twig Beetle, Pityophthorus juglandis Blackman (Coleoptera: Curculionidae: Scolytinae), Reveal an Effective Semiochemical Repellent Combination.

Thousand cankers disease (TCD), is an invasive insect-disease complex caused by the walnut twig beetle, Pityophthorus juglandis, and fungal pathogen, Geosmithia morbida. Semiochemical interruption is a viable option for protecting walnut trees from P. juglandis attack. The goal of this study was to test beetle responses to potential repellent compounds. The results of five, flight-intercept assays are reported. Assays 1-3 tested four compounds at variable release rates: (S)-(-)-verbenone, (R)-(+)-verbenone, racemic chalcogran, and racemic trans-conophthorin. Trapping results indicated that the highest release rate tested for each compound was the most effective in reducing the number of beetles caught. (S)-(-)-Verbenone was the least effective, reducing P. juglandis trap catches by 66%. (R)-(+)-Verbenone reduced the number of P. juglandis by 84%. Neither enantiomer of verbenone performed as well as chalcogran or trans-conophthorin, which both reduced the number of beetles caught by ca. 98%. Following individual assays, the most effective compounds were tested in subtractive-combination assays. Combinations of high release rates for (R)-(+)-verbenone, trans-conophthorin, and two stereoisomers of limonene (tested in a previous study) were tested in two assays. The subtractive-combination assays were inconclusive in that trap catches were similar across all treatments. All combination treatments were highly effective, achieving approximately 99% reduction in the number of beetles caught. Based on the trapping results, commercial availability, and cost of the semiochemicals tested, we conclude that a combination of (R)-(+)-limonene, trans-conophthorin, and (R)-(+)-verbenone constitutes an effective tool for reducing P. juglandis trap catches.

Management of Western North American Bark Beetles with Semiochemicals.

We summarize the status of semiochemical-based management of the major bark beetle species in western North America. The conifer forests of this region have a long history of profound impacts by phloem-feeding bark beetles, and species such as the mountain pine beetle (Dendroctonus ponderosae) and the spruce beetle (D. rufipennis) have recently undergone epic outbreaks linked to changing climate. At the same time, great strides are being made in the application of semiochemicals to the integrated pest management of bark beetles. In this review, we synthesize and interpret these recent advances in applied chemical ecology of bark beetles for scientists and land managers.

Geosmithia associated with bark beetles and woodborers in the western USA: taxonomic diversity and vector specificity.

Fungi in the genus Geosmithia (Ascomycota: Hypocreales) are frequent associates of bark beetles and woodborers that colonize hardwood and coniferous trees. One species, Geosmithia morbida, is an economically damaging invasive species. The authors surveyed the Geosmithia species of California and Colorado, USA, to (i) provide baseline data on taxonomy of Geosmithia and beetle vector specificity across the western USA; (ii) investigate the subcortical beetle fauna for alternative vectors of the invasive G. morbida; and (iii) interpret the community composition of this region within the emerging global biogeography of Geosmithia. Geosmithia was detected in 87% of 126 beetle samples obtained from 39 plant species. Twenty-nine species of Geosmithia were distinguished, of which 13 may be new species. Bark beetles from hardwoods, Cupressus, and Sequoia appear to be regular vectors, with Geosmithia present in all beetle gallery systems examined. Other subcortical insects appear to vector Geosmithia at lower frequencies. Overall, most Geosmithia have a distinct level of vector specificity (mostly high, sometimes low) enabling their separation to generalists and specialists. Plant pathogenic Geosmithia morbida was not found in association with any other beetle besides Pityophthorus juglandis. However, four additional Geosmithia species were found in P. juglandis galleries. When integrated with recent data from other continents, a global pattern of Geosmithia distribution across continents, latitudes, and vectors is emerging: of the 29 Geosmithia species found in the western USA, 12 have not been reported outside of the USA. The most frequently encountered species with the widest global distribution also had the broadest range of beetle vectors. Several Geosmithia spp. with very narrow vector ranges in Europe exhibited the similar degree of specialization in the USA. Such strong canalization in association could reflect an ancient origin of each individual association, or a recent origin and a subsequent diversification in North America.

Susceptibility of Walnut and Hickory Species to Geosmithia morbida.

Thousand cankers disease (TCD) of walnut is a result of feeding in the phloem by the walnut twig beetle (WTB), Pityophthorus juglandis, and subsequent canker formation caused by Geosmithia morbida around galleries. TCD has caused extensive morbidity and mortality to Juglans nigra in the western United States and, in 2010, was discovered in the eastern United States, where the tree is a highly valuable timber resource. WTB and G. morbida also have been found in J. regia orchards throughout major production areas in California, and the numbers of damaged trees are increasing. We tested the susceptibility of walnut and hickory species to G. morbida in greenhouse and field studies. Carya illinoinensis, C. aquatica, and C. ovata were immune. All walnut species tested, including J. ailantifolia, J. californica, J. cinerea, J. hindsii, J. major, J. mandshurica, J. microcarpa, J. nigra, and J. regia, developed cankers following inoculation with G. morbida. J. nigra was the most susceptible, whereas J. major, a native host of the WTB and, presumably, G. morbida, had smaller and more superficial cankers. Canker formation differed among maternal half-sibling families of J. nigra and J. cinerea, indicating genetic variability in resistance to G. morbida. Our inoculation studies with G. morbida have corroborated many of the field observations on susceptibility of walnut and hickory species to TCD, although the ability of the WTB to successfully attack and breed in walnut is also an important component in TCD resistance.

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.

Leptographium tereforme sp. nov. and other Ophiostomatales isolated from the root-feeding bark beetle Hylurgus ligniperda in California.

The redhaired pine bark beetle Hylurgus ligniperda (F.) is native to Europe but was discovered in Los Angeles, California, in 2003. This root-and stump-feeding beetle is a common vector of Ophiostomatales, which are potential tree pathogens or causes of blue stain of conifer sapwood. In this study Ophiostomatales were isolated on a cycloheximide-amended medium from 118 adult H. ligniperda collected from infested logs of Pinus halepensis and P. pinea at two sites in California. In total eight species of Ophiostomatales were identified and seven species that occasionally were isolated were unidentified. The most frequently isolated species were Ophiostoma ips and Grosmannia galeiforme, which were isolated respectively from 31% and 23% of the 118 beetles. The other species isolated included O. piceae (isolated from 9% of the beetles), O. querci (8%) and Leptographium tereforme sp. nov. (6%). Grosmannia huntii, L. serpens, three Sporothrix species, O. floccosum, O. stenoceras, two unidentified Hyalorhinocladiella sp. and a sterile fungus each were isolated from fewer then 5% of beetles. Most of the identified species already were known in USA and have been found in association with H. ligniperda in other countries. However the new species, L. tereforme, and G. galeiforme were recorded from USA for the first time, and this is the first report of L. serpens from western North America.

Assessment of Semiochemical Repellents for Protecting Walnut Trees From Walnut Twig Beetle (Coleoptera: Curculionidae) Attack in a Commercial Orchard Setting in California.

The walnut twig beetle, Pityophthorus juglandis Blackman, the vector of thousand cankers disease (TCD), poses a significant threat to North American walnut (Juglandaceae Juglans) trees. Despite discovery of TCD-related tree mortality over a decade ago, management options are lacking. This study represents the culmination of several years of investigating the chemical ecology of P. juglandis in hopes of developing a semiochemical repellent to disrupt the beetle's host colonization and aggregation behaviors. Numbers of P. juglandis landing on semiochemical-treated Juglans regia L. trees in a commercial walnut orchard were compared based on captures on sticky traps. Two repellent combinations were tested: R-(+)-limonene and trans-conophthorin (LimeCon), and R-(+)-limonene, trans-conophthorin, and R-(+)-verbenone (LCV). Both repellents reduced P. juglandis aggregation (captures) equally; thus, we proceeded with the LimeCon combination to reduce potential treatment cost. Subsequent trials included a 2× dose (Dual) of LimeCon. Both LimeCon and Dual significantly reduced the number of P. juglandis caught compared with the baited control, however, only for the lower of two trap positions. Beetle landings were modeled by trap distance from repellent placement on each tree. Beetle responses to the pheromone lure were surprisingly localized and did not bring the whole tree under attack. LimeCon, LCV, and Dual treatments averaged fewer than a single beetle caught for all trap distances; however, performance of the repellents beyond 150 cm is not clear due to the localized landing response of P. juglandis to pheromone lures. Further testing is required to fully analyze the zone of inhibition of the LimeCon repellent.

The Effects of Weather on the Flight of an Invasive Bark Beetle, Pityophthorus juglandis.

The walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Scolytidae), vectors the fungus Geosmithia morbida, which has been implicated in thousand cankers disease of walnut. Little is known about the flight behavior of the insect across seasons, or about the variability in its flight patterns with weekly fluctuations in weather. We sampled flying adults weekly over a 142-week period (from 29 August, 2011 to 2 June, 2014) with 12-unit black plastic multiple funnel traps baited with a male-produced aggregation pheromone in California, USA. Up to 5000 beetles were captured per trap per week, although catches in most weeks were less than 100 insects. Trap catches were regressed against terms for precipitation, solar radiation, vapor pressure, air temperature, relative humidity, wind speed, and trap catches in preceding weeks. The number of beetles captured in each of the preceding two weeks explained most variation in a current week's catch. This strong temporal autocorrelation was present in regression models developed for males, females, and both sexes pooled. These models were improved by including two environmental variables. Captures of P. juglandis increased with mean weekly air temperature and decreased with increasing mean minimum relative humidity. The percentage of variation in male, female, or total trap catch explained by the temporal variables and the two environmental variables in these multiple regression models ranged from 72% to 76%. While the flight of this invasive insect will likely be affected by site-specific factors as it spreads to new areas, the strong temporal correlation present in this system may provide a useful starting point for developing flight models for newly invaded areas.

Reproduction and Control of the Invasive Polyphagous Shot Hole Borer, Euwallacea nr. fornicatus (Coleoptera: Curculionidae: Scolytinae), in Three Species of Hardwoods: Effective Sanitation Through Felling and Chipping.

The invasive ambrosia beetle polyphagous shot hole borer is one member of the cryptic species, Euwallacea nr. fornicatus (Eichhoff), and poses a great ecological and environmental threat to ornamental and native hardwood trees and agriculturally important tree crops in southern California, United States. We monitored the emergence of polyphagous shot hole borer adults from chipped and unchipped cut logs of infested boxelder, Acer negundo L. (Sapindales: Sapindaceae), California sycamore, Platanus racemosa Nutt. (Proteales: Platanaceae), coast live oak, Quercus agrifolia Née (Fagales: Fagaceae), and red willow, Salix laevigata Bebb (Malpighiales: Salicaceae), every week for 4 to 5 mo. No polyphagous shot hole borer adults emerged from chipped or unchipped coast live oak logs, suggesting this species is not a preferred reproductive host. However, following chipping, a small number of polyphagous shot hole borer adults emerged from boxelder (up to 7 wk) and from California sycamore and red willow (both up to 9 wk). A significantly greater number of polyphagous shot hole borer adults emerged from unchipped logs of boxelder (up to 14 wk) and California sycamore and red willow (both up to 5 mo). Chipping of boxelder, California sycamore, and red willow by using common commercially available chippers reduced polyphagous shot hole borer emergence by over 97%. Emerged polyphagous shot hole borer adults were strongly female-biased, regardless of host. Chipping treatments were highly effective, but for the complete elimination of polyphagous shot hole borer from woody material, other sanitation measures such as solarization in conjunction with chipping are recommended. Environmental and ecological impact of polyphagous shot hole borer is reviewed and discussed.

Trapping Failure Leads to Discovery of Potent Semiochemical Repellent for the Walnut Twig Beetle.

The walnut twig beetle, Pityophthorus juglandis Blackman, and its associated fungal pathogen that causes thousand cankers disease, currently threaten the viability of walnut trees across much of North America. During a 2011 assessment of seasonal flight patterns of P. juglandis with yellow sticky traps baited with the male-produced aggregation pheromone component, 3-methyl-2-buten-1-ol, dramatically reduced catches were recorded when Tree Tanglefoot adhesive was used to coat the traps. In summer 2011, two trap adhesives were tested for potential repellency against P. juglandis in a field trapping bioassay. SuperQ extracts of volatiles from the most repellent adhesive were analyzed by gas chromatography-mass spectrometry, and limonene and α-pinene were identified as predominant components. In field-based, trapping experiments both enantiomers of limonene at a release rate of ~700 mg/d conferred 91-99% reduction in trap catches of P. juglandis to pheromone-baited traps. (+)- and (‒)-α-Pinene reduced trap catch by 40 and 53%, respectively, at the highest release rate tested. While a combination of R-(+)-limonene and (+)-α-pinene resulted in a 97% reduction in the number of P. juglandis caught, the combination did not consistently result in greater flight trap catch reduction than individual limonene enantiomers. The repellent effect of limonene may be valuable in the development of a semiochemical-based tool for management of P. juglandis and thousand cankers disease.

Application of semiochemicals to assess the biodiversity of subcortical insects following an ecosystem disturbance in a sub-boreal forest.

From 2000 through 2003 we used semiochemical-baited traps in northeastern Minnesota, USA, to assess changes in assemblages of subcortical forest insects after a catastrophic wind storm in 1999 and subsequent (1999-2000) fuel-reduction activities (salvage-logging and prescribed-burning). We determined the regional efficacy of fifteen semiochemical blends (pheromones and kairomones) as attractants for target and non-target subcortical insect species (Coleoptera: Anthribidae, Buprestidae, Cerambycidae, Cleridae, Cucujidae, Curculionidae, Histeridae, Nemonychidae, Salpingidae, Scolytidae, Tenebrionidae, and Hymenoptera: Siricidae). During the four summers, we trapped 86,471 subcortical insects (143 species) in baited and unbaited Lindgren funnel traps, and 500 beetles (44 species) in baited and unbaited pitfall traps. We report 23 new state collection records of subcortical insects from Minnesota. Trap catches of subcortical insects were greatest in the wind-disturbed areas 2 years after the event, and declined thereafter. Similar trends were observed for subcortical insects in the burned areas. Both wind-disturbance and burning increased the subcortical insect species richness and diversity on the landscape. The subcortical insect species compositions of the salvaged and burned forest areas differed from those of the undisturbed and wind-disturbed areas. Trap catches of subcortical insects in response to semiochemical treatments also varied with year of sampling and land-area treatment. The greatest diversity of subcortical beetle species was in traps baited with attractants for the scolytids, Dendroctonus valens [(+)-α-pinene and (−)-ß-pinene] and Dryocoetes spp. [exo-brevicomin and (−)-α-pinene], perhaps reflecting the generic nature of the baits. The most distinct species compositions were collected in response to the woodborer and Dendroctonus simplex baits, whereas the species compositions in traps with the D. valens and Dryocoetes spp. baits, and the unbaited funnel trap were the most similar. The variation in trap catch with time and across landscapes suggests that the responses of subcortical insects to semiochemicals are more complex than previously appreciated.

Efficacy of verbenone for protecting ponderosa pine stands from western pine beetle (Coleoptera: Curculionidae: Scolytinae) attack in California.

The western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae: Scolytinae), is a major cause of ponderosa pine, Pinus ponderosa Dougl. ex Laws., mortality in much of western North America. Currently, techniques for managing D. brevicomis infestations are limited. Verbenone (4,6,6-trimethylbicyclo [3.1.1] hept-3-en-2-one) is an antiaggregation pheromone of several Dendroctonus spp., including D. brevicomis, and it has been registered as a biopesticide for control of mountain pine beetle, Dendroctonus ponderosae Hopkins, and southern pine beetle, Dendroctonus frontalis Zimmermann. We evaluated the efficacy of a 5-g verbenone pouch [82%-(-); 50 mg/d] applied at 125 Ulha for protecting P. ponderosa stands (2 ha) from D. brevicomis attack over a 3-yr period. No significant differences in levels of D. brevicomis-caused tree mortality or the percentage of unsuccessfully attacked trees were found between verbenone-treated and untreated plots during each year or cumulatively over the 3-yr period. Laboratory analyses of release rates and chemical composition of volatiles emanating from verbenone pouches after field exposure found no deterioration of the active ingredient or physical malfunction of the release device. The mean release rate of pouches from all locations and exposure periods was 44.5 mg/d. In a trapping bioassay, the range of inhibition of the 5-g verbenone pouch was determined to be statistically constant 2 m from the release device. We discuss the implications of these and other results to the development of verbenone as a semiochemical-based tool for management of D. brevicomis infestations in P. ponderosa stands.

Suitability of pines and other conifers as hosts for the invasive Mediterranean pine engraver (Coleoptera: Scolytidae) in North America.

The invasive Mediterranean pine engraver, Orthotomicus erosus (Wollaston) (Coleoptera: Scolytidae), was detected in North America in 2004, and it is currently distributed in the southern Central Valley of California. It originates from the Mediterranean region, the Middle East, and Asia, and it reproduces on pines (Pinus spp.). To identify potentially vulnerable native and adventive hosts in North America, no-choice host range tests were conducted in the laboratory on 22 conifer species. The beetle reproduced on four pines from its native Eurasian range--Aleppo, Canary Island, Italian stone, and Scots pines; 11 native North American pines--eastern white, grey, jack, Jeffrey, loblolly, Monterey, ponderosa, red, Sierra lodgepole, singleleaf pinyon, and sugar pines; and four native nonpines--Douglas-fir, black and white spruce, and tamarack. Among nonpines, fewer progeny developed and they were of smaller size on Douglas-fir and tamarack, but sex ratios of progeny were nearly 1:1 on all hosts. Last, beetles did not develop on white fir, incense cedar, and coast redwood. With loblolly pine, the first new adults emerged 42 d after parental females were introduced into host logs at temperatures of 20-33 degrees C and 523.5 or 334.7 accumulated degree-days based on lower development thresholds of 13.6 or 18 degrees C, respectively.

A novel molecular toolkit for rapid detection of the pathogen and primary vector of thousand cankers disease.

Thousand Cankers Disease (TCD) of Juglans and Pterocarya (Juglandaceae) involves a fungal pathogen, Geosmithia morbida, and a primary insect vector, Pityophthorus juglandis. TCD was described originally from dying Juglans nigra trees in the western United States (USA), but it was reported subsequently from the eastern USA and northern Italy. The disease is often difficult to diagnose due to the absence of symptoms or signs on the bark surface of the host. Furthermore, disease symptoms can be confused with those caused by other biotic and abiotic agents. Thus, there is a critical need for a method for rapid detection of the pathogen and vector of TCD. Using species-specific microsatellite DNA markers, we developed a molecular protocol for the detection of G. morbida and P. juglandis. To demonstrate the utility of the method for delineating TCD quarantine zones, we tested whether geographical occurrence of symptoms and signs of TCD was correlated with molecular evidence for the presence of the cryptic TCD organisms. A total of 1600 drill cores were taken from branch sections collected from three regions (n = 40 trees for each location): California-J. hindsii (heavy disease incidence); Tennessee-J. nigra (mild disease incidence); and outside the known TCD zone (Missouri-J. nigra, no record of the disease). California samples had the highest incidence of the TCD organisms (85%, 34/40). Tennessee had intermediate incidence (42.5%, 17/40), whereas neither organism was detected in samples from Missouri. The low cost molecular protocol developed here has a high degree of sensitivity and specificity, and it significantly reduces sample-processing time, making the protocol a powerful tool for rapid detection of TCD.

Mycobiota associated with insect galleries in walnut with thousand cankers disease reveals a potential natural enemy against Geosmithia morbida.

Thousand Cankers Disease (TCD) affects Juglans and Pterocarya species. This disease poses not only a major threat to the nut and timber industries but also to native stands of walnut trees. Galleries created by Pityophthorus juglandis (vector) are colonized by the fungus Geosmithia morbida (causal agent of necrosis). It is unknown if other fungi colonizing these galleries might act antagonistically towards G. morbida. The objectives of this study were to: (1) characterize the fungal community associated with TCD-infected trees and (2) develop a pilot study addressing their potential antagonism towards G. morbida. We collected non-Geosmithia fungi from ten TCD-infected walnut trees from California and Tennessee. Four hundred and fifty-seven isolates, representing sixty-five Operational Taxonomic Units (99 % ITS similarity) were obtained. Fungal communities were found to be highly diverse. Ophiostoma dominated the communities associated with TCD-compromised trees from California, whereas Trichoderma dominated TCD-compromised trees in Tennessee. Six Trichoderma isolates showed varying levels of antagonism against three isolates of G. morbida, suggesting potential applications for the biological control of TCD. Furthermore, results from this study contribute to the growing knowledge about the observed differential disease development between the western and eastern USA and could overall impact our understanding of TCD etiology.

Cold Tolerance of Pityophthorus juglandis (Coleoptera: Scolytidae) From Northern California.

Winter survivorship of insects is determined by a combination of physiological, behavioral, and microhabitat characteristics. We characterized the cold tolerance of the walnut twig beetle, Pityophthorus juglandis Blackman, a domestic alien invasive bark beetle that vectors a phytopathogenic fungus. The beetle and fungus cause thousand cankers disease in species of Juglans and Pterocarya. The disease is spreading in the United States of America (USA) and Italy. Contact thermocouple thermometry was used to measure the supercooling points of adults and larvae and lower lethal temperatures of adults from a population from northern California. Supercooling points ranged from -12.2 °C to - 25.0 °C for adults and -13.6 °C to - 23.5 °C for larvae; lower lethal temperatures of adults ranged from -14 °C to - 23 °C. We found seasonal changes in adult supercooling points in fall, winter, and spring. The supercooling point for males was 0.5 °C colder than for females over all months and 1 °C colder in the winter than in other seasons. The cold-tolerance strategy shifted in P. juglandis adults from freeze intolerance (December 2013 and January 2014) to partial freeze tolerance (February 2014). An intermediate level of cold tolerance with a plastic response to cold partially explains survival of P. juglandis outside of its native range in the southwestern USA. In addition, we characterized the relationship between minimum air temperatures and minimum phloem temperatures in two Juglans spp. in northern California and Colorado and characterized portions of the native geographic range of eastern black walnut, J. nigra L., that may be too cold currently for this insect to persist.

Flight Capacity of the Walnut Twig Beetle (Coleoptera: Scolytidae) on a Laboratory Flight Mill.

The walnut twig beetle, Pityophthorus juglandis Blackman, and associated fungus Geosmithia morbida Kolarík, Freeland, Utley, & Tisserat constitute the insect-fungal complex that causes thousand cankers disease in walnut, Juglans spp., and wingnut, Pterocarya spp. Thousand cankers disease is responsible for the decline of Juglans species throughout the western United States and more recently, the eastern United States and northern Italy. We examined the flight capacity of P. juglandis over 24-h trials on a flight mill in the laboratory. The maximum total flight distance observed was ∼3.6 km in 24 h; however, the mean and median distances flown by beetles that initiated flight were ∼372 m and ∼158 m, respectively. Beetles flew for 34 min on average within a 24-h flight trial. Male and female flight capacities were similar, even though males were larger than females (0.64 vs. 0.57 mm pronotal width). Age postemergence had no effect on flight distance, flight time, or mean flight velocity. The propensity to fly, however, decreased with age. We integrated results of flight distance with propensity to fly as beetles aged in a Monte Carlo simulation to estimate the maximum dispersal capacity over 5 d, assuming no mortality. Only 1% of the insects would be expected to fly >2 km, whereas one-third of the insects were estimated to fly <100 m. These results suggest that nascent establishments remain relatively localized without anthropogenic transport or wind-aided dispersal, which has implications for management and sampling of this hardwood pest.

Comparative morphometric and chemical analyses of phenotypes of two invasive ambrosia beetles (Euwallacea spp.) in the United States.

The polyphagous shot hole borer (PSHB), Euwallacea sp., was first detected in 2003 in Los Angeles County, California, USA. Recently, this invasive species has become a major pest of many hardwood trees in urban and wildland forests throughout southern California. PSHB is nearly identical in morphology and life history to the tea shot hole borer (TSHB), Euwallacea fornicatus, an invasive pest of hardwoods in Florida, USA and many other parts of the world. However, molecular studies have suggested that the taxa are different species. We conducted morphometric and chemical analyses of the phenotypes of Euwallacea sp. collected in southern California (Los Angeles County) and E. fornicatus collected in Florida (Miami-Dade County). Our analyses indicated that PSHB has 3 larval instars. The third larval instar was separated from the first 2 instars by head capsule width with 0 probability of misclassification. The body length, head width, and pronotal width of PSHB adult males were significantly less than those of females. Head width and pronotal width of female PSHB were significantly less than those of female TSHB. In contrast, body length, and ratio of body length to pronotal width of female PSHB were significantly greater than those of female TSHB. However, females of these 2 species could not be separated completely by these 4 measurements because of the overlapping ranges. Cuticular hydrocarbons detected in both species were exclusively alkanes (i.e., n-alkanes, monomethylalkanes, dimethylalkanes, and trimethylalkanes). Cuticular hydrocarbon profiles of PSHB males and females were similar, but they both differed from that of TSHB females. Cuticular hydrocarbons of PSHB were predominantly internally branched dimethylalkanes with backbones of 31 and 33 carbons, whereas cuticular hydrocarbons of TSHB females were dominated by internally branched monomethylalkanes and dimethylalkanes with backbones of 28 and 29 carbons. Multiple compounds within these classes appear to be diagnostic for PSHB and TSHB, respectively.

Phylogeography of the walnut twig beetle, Pityophthorus juglandis, the vector of thousand cankers disease in North American walnut trees.

Thousand cankers disease (TCD) of walnut trees (Juglans spp.) results from aggressive feeding in the phloem by the walnut twig beetle (WTB), Pityophthorus juglandis, accompanied by inoculation of its galleries with a pathogenic fungus, Geosmithia morbida. In 1960, WTB was only known from four U.S. counties (in Arizona, California, and New Mexico), but the species has now (2014) invaded over 115 counties, representing much of the western USA, and at least six states in the eastern USA. The eastern expansion places TCD in direct proximity to highly valuable (> $500 billion) native timber stands of eastern black walnut, Juglans nigra. Using mitochondrial DNA sequences, from nearly 1100 individuals, we examined variation among 77 samples of WTB populations across its extended range in the USA, revealing high levels of polymorphism and evidence of two divergent lineages. The highest level of genetic diversity for the different lineages was found in the neighboring Madrean Sky Island and Western New Mexico regions, respectively. Despite their proximity, there was little evidence of mixing between these regions, with only a single migrant detected among 179 beetles tested. Indeed, geographic overlap of the two lineages was only common in parts of Colorado and Utah. Just two haplotypes, from the same lineage, predominated over the vast majority of the recently expanded range. Tests for Wolbachia proved negative suggesting it plays no role in "driving" the spread of particular haplotypes, or in maintaining deep levels of intraspecific divergence in WTB. Genotyping of ribosomal RNA corroborated the mitochondrial lineages, but also revealed evidence of hybridization between them. Hybridization was particularly prevalent in the sympatric areas, also apparent in all invaded areas, but absent from the most haplotype-rich area of each mitochondrial lineage. Hypotheses about the specific status of WTB, its recent expansion, and potential evolutionary origins of TCD are discussed.

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

BACKGROUND: The invasive goldspotted oak borer, Agrilus auroguttatus, is threatening the health and survival of oak trees in San Diego County, California. From two sites in the core area of the infestation, we report a 2.5 year investigation of the impact of A. auroguttatus on coast live oak, Quercus agrifolia, before and after treatment with two systemic insecticides, emamectin benzoate (EB) and imidacloprid (IC). RESULTS: None of the 446 survey trees died during the study. The crown dieback rating of most trees at both study sites remained unchanged, regardless of insecticide treatment. A higher cumulative increase in the number of A. auroguttatus emergence holes was observed on trees that were previously infested and on trees with larger diameters. Over the 2.5 year period, the new infestation rates of initially uninfested trees across the untreated and treated groups were 50% (EB) and 32% (IC), and neither EB nor IC treatment affected cumulative increases in the number of emergence holes. EB-injected trees did not have significant annual increases in the number of A. auroguttatus emergence holes at either 1.5 or 2.5 years compared with that at 0.5 years, whereas untreated trees had significant annual increases. Although IC-injected trees had a significantly greater annual increment in the number of emergence holes than untreated trees during the last year of the study, treated trees had significant reductions in annual increases in emergence holes at both 1.5 and 2.5 years compared with that at 0.5 years. Untreated trees had no significant reduction in the annual increase in emergence holes at 1.5 and 2.5 years. CONCLUSIONS: A. auroguttatus preferentially attacked previously infested and larger (diameter at breast height > 15-30 cm) oak trees, but the attacks led to very gradual changes in the health of the trees. Both EB and IC provided minor suppressive effects on A. auroguttatus emergence. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.