Developing semiochemical repellents for protecting Picea from Dendroctonus rufipennis (Coleoptera: Curculionidae) in Alaska and Utah, USA.

Spruce beetle, Dendroctonus rufipennis (Kirby) (Coleoptera: Curculionidae), is the most destructive pest of mature spruce (Picea) in western North America. Recent outbreaks in Alaska and other western US states highlight the need for tools to protect Picea from D. rufipennis. The primary antiaggregation pheromone of D. rufipennis (3-methylcyclohex-2-en-1-one, MCH) and various combinations of potential repellents (1-octen-3-ol, exo-brevicomin, endo-brevicomin, ipsdienol, ipsenol, limonene, and verbenone) were tested for their ability to disrupt the response of D. rufipennis to attractant-baited multiple-funnel traps. Two assays were conducted on the Kenai Peninsula, Alaska, in June and July 2021. All treatments significantly reduced the mean number of D. rufipennis caught compared to the baited control. No other significant differences were observed among treatments. Informed by these and other data, tree protection studies were established in Lutz spruce, Picea × lutzii, on the Kenai Peninsula in 2022 and in Engelmann spruce, Pi. engelmannii, in the Uinta Mountains, Utah, in 2021. All experimental trees were baited with frontalin. Repellent treatments included MCH (SPLAT MCH, ISCA Inc., Riverside, CA, USA) and at least 1 additional repellent combination. In Alaska, all treatments significantly reduced colonization (strip attacks + mass attacks) and mortality of individually treated Pi. × lutzii and all Picea within 11.3-m radius of each treated Pi. × lutzii compared to the control. In Utah, all treatments except for SPLAT MCH + octenol significantly reduced colonization compared to the control. Only SPLAT MCH + Acer kairomone blend (AKB) and SPLAT MCH + octenol reduced Pi. engelmannii mortality compared to the control. SPLAT MCH + AKB and SPLAT MCH + acetophenone and green leaf volatiles (PLUS) were the most effective across both studies. The implications of these and other results to the development of an effective semiochemical repellent for D. rufipennis are discussed.

Acetophenone and Green Leaf Volatiles Do Not Enhance the Efficacy of Verbenone for Inhibiting Attraction of Ips pini (Coleoptera: Curculionidae) to Pheromone-baited Traps in Northern Arizona.

We assessed attraction of pine engraver, Ips pini (Say) (Coleoptera: Curculionidae; Scolytinae), to pheromone-baited funnel traps treated with repellent semiochemicals in ponderosa pine, Pinus ponderosa var. scopulorum Engelm., forests in northern Arizona. Treatments included: 1) baited control (B, ipsdienol + lanierone), 2) 70 g of SPLAT Verb (a flowable, biodegradable formulation containing 10% verbenone, ISCA Technologies Inc., Riverside, CA, USA) + B, 3) 70 g of SPLAT Verb + (E)-2-hexen-1-ol+(Z)-2-hexen-1-ol + acetophenone + B, 4) 7.84-g verbenone pouch (Product #3413, Synergy Semiochemicals Corp., Delta, British Columbia, Canada) + B, and 5) 7.84-g verbenone pouch + (E)-2-hexen-1-ol+(Z)-2-hexen-1-ol + acetophenone + B. In total, 472 I. pini were collected. Trap catches were highest in baited traps and declined significantly with the addition of both formulations of verbenone. Traps treated with SPLAT Verb caught significantly fewer I. pini and male I. pini than those treated with verbenone pouches. The addition of (E)-2-hexen-1-ol+(Z)-2-hexen-1-ol + acetophenone to SPLAT Verb and the verbenone pouch had no effect on trap catch. Verbenone has potential as an effective tool for protecting P. ponderosa trees and slash from I. pini in northern Arizona, but the addition of (E)-2-hexen-1-ol+(Z)-2-hexen-1-ol + acetophenone to verbenone is unwarranted.

MCH-Based Semiochemical Repellents for Protecting Engelmann Spruce Trees From Dendroctonus rufipennis (Coleoptera: Curculionidae).

Spruce beetle, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae), is a lethal pest of spruce trees in North America. Despite decades of research, a semiochemical repellent that consistently and effectively protects spruce trees remains elusive. We evaluated the efficacy of 3-methyl-2-cyclohexen-1-one (MCH) in a proprietary, volatile compound release technology (SPLAT) alone and with two adjuvants, Acer kairomone blend (AKB) and acetophenone + green leaf volatiles (PLUS) to protect individually treated Picea engelmannii Parry ex. Engelm. (Pinales: Pinaceae), and Pi. engelmannii within 11.3-m radius of the individually treated trees from colonization and mortality attributed to D. rufipennis in western Wyoming. Ninety-one Pi. engelmannii were baited with frontalin and randomly assigned to one of seven treatments (n = 13): 3.5 g of MCH applied as SPLAT MCH (SPLAT3.5), 3.5AKB, 3.5PLUS, 7 g of MCH applied as SPLAT MCH (SPLAT7), 7AKB, 7PLUS, and baited control (bait only). All repellents except SPLAT3.5 and SPLAT7 significantly reduced colonization of individually treated Pi. engelmannii compared to the baited control. 3.5PLUS, 7AKB, and 7PLUS reduced colonization most effectively, and all repellents significantly reduced mortality of individually treated Pi. engelmannii compared to the baited control. All repellents also significantly reduced colonization and mortality of neighboring Pi. engelmannii.

Conifer bark beetles.

Fettig and Audley introduce the bark beetles-a large and diverse group of insects of which some are commonly recognized as important disturbance agents in conifer forests.

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.

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.

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.

Bark Colonization of Kiln-Dried Wood by the Walnut Twig Beetle: Effect of Wood Location and Pheromone Presence.

The walnut twig beetle (Pityophthorus juglandis Blackman) (Coleoptera: Curculionidae) is a regulated pest in the United States due to its causal role in thousand cankers disease of walnut trees, including the commercially valuable eastern black walnut (Juglans nigra L.). Several state quarantines designed to limit spread of P. juglandis regulate movement of kiln-dried walnut lumber that contains bark. Previous research demonstrated that P. juglandis will enter and re-emerge from bark of kiln-dried, J. nigra slabs subjected to extreme beetle pressure (baited with a pheromone lure and hung in infested J. nigra trees). This study evaluated P. juglandis bark colonization of both kiln-dried and fresh J. nigra slabs, varying the presence of aggregation pheromone and relative proximity to a beetle source. Wood treatment, slab location, and pheromone presence all significantly affected P. juglandis colonization, as assessed by subsequent beetle emergence. When placed on the ground directly beneath infested trees, kiln-dried slabs were not colonized, and fresh slabs were colonized only when baited with the pheromone lure (6/14 replicates). When placed in crowns of infested trees, kiln-dried slabs were colonized only when baited with pheromone (3/14 replicates), whereas fresh slabs were colonized with and without pheromone (14/14 and 1/13 replicates, respectively). Timing of emergence indicated that beetles did not reproduce in kiln-dried bark. Results suggest that the risk of kiln-dried walnut bark becoming colonized by the P. juglandis during movement of commercial wood products is very low. This information may be useful to government agencies that administer quarantines regulating the transport of walnut lumber.

Walnut Twig Beetle (Coleoptera: Curculionidae: Scolytinae) Colonization of Eastern Black Walnut Nursery Trees.

Thousand cankers disease, caused by the invasive bark beetle Pityophthorus juglandis Blackman and an associated fungal pathogen Geosmithia morbida M.Kolarík, E. Freeland, C. Utley, N. Tisserat, currently threatens the health of eastern black walnut (Juglans nigra L.) in North America. Both the beetle and pathogen have expanded beyond their native range via transport of infested walnut wood. Geosmithia morbida can develop in seedlings following inoculation, but the ability of P. juglandis to colonize young, small diameter trees has not been investigated. This study assessed the beetle's colonization behavior on J. nigra nursery trees. Beetles were caged directly onto the stems of walnut seedlings from five nursery sources representing a range of basal stem diameter classes. Seedlings were also exposed to P. juglandis in a limited choice, field-based experiment comparing pheromone-baited and unbaited stems. When beetles were caged directly onto stems, they probed and attempted to colonize seedlings across the range of diameters and across sources tested, including stems as small as 0.5 cm in diameter. In the field experiment, beetles only attempted to colonize seedlings that were baited with a pheromone lure and appeared to prefer (though not statistically significant) the larger diameter trees. Despite several successful penetrations into the phloem, there was no evidence of successful progeny development within the young trees in either experiment. Further investigation is recommended to better elucidate the risk nursery stock poses as a pathway for thousand cankers disease causal organisms.

Efficacy of two insecticides for protecting loblolly pines (Pinus taeda L.) from subcortical beetles (Coleoptera: Curculionidae and Cerambycidae).

BACKGROUND: Tests were conducted on two insecticides (carbaryl and bifenthrin) for excluding subcortical beetles (Coleoptera: Curculionidae and Cerambycidae) from loblolly pine trees (Pinus taeda L.). Two trap designs (single- and double-pane windows) and two trapping heights (1.5 and 4 m) were also evaluated for maximizing beetle catches. RESULTS: In July 2009, 15 loblolly pine trees were double girdled and were either left unsprayed or sprayed with carbaryl or bifenthrin. A total of 28 473 bark beetles were caught in window traps, including Ips avulsus Eichoff, I. grandicollis (Eichhoff), I. calligraphus (Germar) and Dendroctonus terebrans (Olivier). Both insecticides significantly reduced colonization of the trees by bark and woodboring beetles by 300-400%, with no differences in efficacy observed between the two insecticides. About 59% more I. avulsus were caught in double- than in single-pane window traps, with no differences for any other species. Traps at 4 m caught more I. avulsus and I. grandicollis (290 and 153% respectively), while traps at 1.5 m caught more D. terebrans (215%). CONCLUSIONS: Either bifenthrin or carbaryl can be used to exclude subcortical beetles from loblolly pine trees. Trapping data reflect known vertical partitioning on the bole by these insects. Double-pane traps were slightly more effective than single-pane traps in catching subcortical beetles.