Location: Application Technology Research2018 Annual Report
Objective 1. Develop improved techniques for monitoring invasive ambrosia beetles in nurseries based on new knowledge of behavior, movement, and flight activity across different habitats. Sub-Objective 1a: Assess the seasonal activity of attacks using flood-stressed trees, ethanol-baited trees, and ethanol-baited traps. Sub-Objective 1b: Characterize abundance, diversity, distribution, and seasonal movement of Xylosandrus species within nurseries and surrounding habitats; determine the primary sources of ambrosia beetles invading nurseries with emphasis on Xylosandrus species. Objective 2. Characterize the role of tree health on the host-selection and host-preference behavior of ambrosia beetles in ornamental nurseries. Sub-Objective 2a: Compare the capacity of drought-stress and flood-stress to predispose trees to attack. Sub-Objective 2b: Assess the impact of frost injury on predisposing trees to attack. Sub-Objective 2c: Compare the colonization success of ambrosia beetles on stressed vs. healthy hosts. Sub-Objective 2d: Determine the susceptibility and tolerance of trees to colonization by ambrosia beetles during spring and summer; determine colonization behavior and activity of summer generations of X. germanus. Sub-Objective 2e: Characterize and identify time-course volatile emissions from living, but weakened trees used by ambrosia beetles during host-selection. Objective 3. Develop improved technology for applying or improving the efficacy of chemicals to effectively manage ambrosia beetles and evaluate alternatives to conventional insecticides for managing ambrosia beetles in nurseries. Sub-objective 3a: Assess the ability of insecticides to reduce attacks and disrupt colonization of stressed trees by ambrosia beetles. Sub-Objective 3b: Test efficacy of a variable rate, sensor-guided spray system for applying ambrosia beetle controls to nursery trees. Sub-Objective 3c: Evaluate capacity of ethanol-injected trees to reduce attack pressure on vulnerable trees and improve efficacy of insecticide treatments. Sub-Objective 3d: Optimize an ethanol-based interception tactic for invasive ambrosia beetles. Sub-Objective 3e: Integrate repellents and attractants for deflecting beetles away from vulnerable trees and intercepting them with trapping tactics as part of a push-pull management strategy.
Objective 1a: The seasonal activity of ambrosia beetle attacks needs to be characterized to develop non-chemical interception strategies against ambrosia beetles. Seasonal activity of attacks will be characterized on flood-stressed trap trees and ethanol-baited trees, and compared against ethanol-baited traps. Objective 1b: The local sources of ambrosia beetles colonizing nursery trees are uncertain. Resident populations within nurseries are unlikely because growers apply insecticides to prevent colonization, and remove infested trees when colonization is detected. Habitats, especially wooded areas, surrounding nurseries are potential sources of beetles infesting nurseries. Objective 2a: The capacity of drought stress to predispose trees to attack will initially be assessed using species with varying degrees of drought intolerance. Objective 2b: Preliminary studies indicated that low temperature stress predisposes trees to attack by ambrosia beetles. Experiments under controlled conditions will be used to characterize the capacity of frost injury to predispose trees to attack, which will help growers identify vulnerable species and make more informed management decisions. Objective 2c: The ability of X. germanus to colonize stressed vs. healthy hosts will be compared. Flooding, which predisposes trees to attack by X. germanus, will be used as the stress factor. Objective 2d: Seasonal vulnerability of trees to attacks by ambrosia beetles will be examined. Trees in early stages of post-dormancy development and summer trees (full canopies) will be compared. Objective 2e: Ethanol is currently the most important compound known for ambrosia beetle host location, but other compounds emitted from physiologically-stressed trees may also play a role in signaling host vulnerability and suitability. Flooding will be used to stress trees and make them attractive to ambrosia beetles. The time-course emission of volatiles will be collected from flood-stressed and healthy trees to identify compounds attractive to ambrosia beetles. Objective 3a: Trunk applications of conventional and botanical insecticides will on trees stressed by flooding. In addition, trees will be injected with different concentrations of ethanol to determine whether the stress level influences efficacy of insecticides protecting trees from attacks by ambrosia beetles. Objective 3b: A prototype variable sensor guided sprayer will be tested as a delivery system for trunk applied insecticides to protect trees from ambrosia beetle attacks. Objective 3c: Ethanol-injected trees will be tested as trap trees to reduce attack pressure on nursery trees and enhance efficacy of protective trunk sprays. Objective 3d: Ethanol-baited traps and ethanol-injected trees will be tested as interception devices to reduce colonization of nursery trees by ambrosia beetles. Objective 3e: A push-pull management strategy will be pursued by combining the use of repellents with the strategic placement of highly attractive traps or trap trees in between nurseries and neighboring woodlots.
Research was initiated and progress was made on all objectives. Objective 1. Develop improved techniques for monitoring invasive ambrosia beetles in nurseries based on new knowledge of behavior, movement, and flight activity across different habitats. Data from the previous two years of research on seasonal movement of ambrosia beetles was used to develop models for predicting the seasonal timing of beetles moving into nurseries that growers can use to synchronize their protective treatments with beetle activity. Knowledge gained from this research was also used to develop experiments testing an interception strategy for managing ambrosia beetles in tree crops as part of Objective 3 (below). In collaboration with researchers from São Paulo State University in Brazil, ARS researchers in Wooster compared different trap and lure designs for monitoring ambrosia beetles. An optimal trap and lure design was identified as part of these studies. In collaboration with researchers from the Slovak Academy of Sciences, we compared the attractiveness of absolute vs. denatured ethanol for monitoring ambrosia beetles. Experiments were also conducted to compare the behavioral responses of ambrosia beetles to absolute vs. denatured ethanol. Electroantennogram experiments were conducted to compare the antennal responses of ambrosia beetles to absolute vs. denatured ethanol. Denatured ethanol was determined to be an inexpensive and effective alternative to absolute ethanol. In collaboration with researchers from Purdue University and Tennessee State University, we compared the attraction of ambrosia beetles to volatiles identified from a fungal symbiont. Electroantennogram experiments also characterized their antennal responses to the volatile compounds. One of the fungal volatiles increased attraction of ambrosia beetles to ethanol and could improve trapping efforts. Objective 2. Characterize the role of tree health on the host-selection and host-preference behavior of ambrosia beetles in ornamental nurseries. We compared the vertical distribution of attacks on freeze-stressed vs. flood-stressed trees. These experiments were conducted in collaboration with researchers from Virginia Tech. Attacks on flood-stressed trees mainly occurred around the base of the stem, while attacks on freeze-stressed trees were distributed along the upper stem and branch tissues. The difference in vertical distributions of attacks will assist growers, arborists, and researchers in determining the abiotic stressor that predisposed trees to attack, thereby helping to reduce the risk of attacks in the future. The correlation between attacks and ethanol emissions from flood-stressed trees were assessed. A simple and portable ethanol sampling device was also tested. The ethanol sampling device will aid arborists and growers in rapidly identify trees at risk of attack by ambrosia beetles. Research examining the relationship between the duration of tree stress and colonization success of ambrosia beetles was initiated. Trees were flood-stressed for varying lengths of time and colonization success of attacking ambrosia beetles was determined. Objective 3. Develop improved technology for applying or improving the efficacy of chemicals to effectively manage ambrosia beetles and evaluate alternatives to conventional insecticides for managing ambrosia beetles in nurseries. We tested the influence of tree attractiveness on efficacy of insecticides for a second year. Trees were injected with three different concentrations of ethanol to establish low, moderate and high levels of attractiveness to ambrosia beetles. We were successful at establishing different levels of attractiveness in trees, and showed that as attractiveness of trees increases efficacy of insecticides against ambrosia beetles decreases. Ethanol infused bolts were used to test insecticide treated netting to prevent entry of ambrosia beetles into trees in collaboration with research by ARS scientists in Mississippi. Insecticide treated netting was also tested on flood-stressed trees as part of the collaboration with researchers in Mississippi. If effective, insecticide treated netting could be wrapped around the trunks of trees, which would significantly reduce drift of insecticides from the conventional trunk sprays. We conducted second year of research testing an interception strategy where ethanol-baited traps positioned along the woodland/nursery interface could intercept sufficient numbers of ambrosia beetles to reduce activity within nurseries. While the interception traps captured thousands of beetles during the spring season, numbers of beetles within nurseries were not reduced. Insecticide impregnated fabric was tested for protecting the stems of flood-stressed trees from attack by ambrosia beetles. This research was conducted in Virginia and Ohio as a collaboration with researchers from Virginia Tech and ARS. The insecticide-treated netting was effective under field conditions for reducing attacks. This project has been merged with 5082-21000-017-00D and so 5082-22000-014-00D will terminate this year, FY 18. Project Summary: During this project, ARS researchers demonstrated the primary sources of ambrosia beetles infesting nurseries are woodlands adjacent to ornamental nurseries. Improved trap and lure designs were identified for monitoring ambrosia beetle activity. ARS researchers established that monitoring and interception tactics should focus on the nursery-woodland interface. Growers should therefore avoid planting tree species vulnerable to attack along the edges of their nurseries. Seasonal activity of a recently introduced species of ambrosia beetle (Anisandrus maiche) was also established. ARS researchers determined that A. maiche exhibits peak activity after other destructive ambrosia beetles, thereby increasing the length of time during spring and summer months that trees are at risk of attack by ambrosia beetles. ARS researchers established that freeze-stress, in addition to flood-stress, predispose trees to attack by ambrosia beetles. In contrast, drought-stress was not found to induce attacks. ARS researchers demonstrated that healthy trees are not at risk for attack by opportunistic Xylosandrus species ambrosia beetles. A portable sampling device was identified by ARS researchers that rapidly detects the emission of ethanol from living but weakened trees. These results will help growers and arborists to adjust production practices to minimize the risk of attacks. ARS researchers also determined that ambrosia beetles specifically attack trees emitting ethanol because the presence of ethanol in the host tree tissues benefits the growth of their fungal symbiont and suppresses the growth of fungal garden competitors. Understanding the factors that influence the establishment of ambrosia beetle fungal gardens will aid ARS researchers in developing novel management tactics to disrupt ambrosia beetle colonization success. ARS researchers established that the efficacy of protective treatments of insecticides declines as trees become more attractive due to the emission of ethanol. ARS researchers also determined the residual efficacy of the primary insecticides used by growers to protect trees from ambrosia beetle attack. Results from this project also demonstrated that certain insecticides, but not fungicides, reduce the colonization success of ambrosia beetles and reduce the need for culling attacked trees. While insecticide applications reduce ambrosia beetle attacks, they do not completely prevent attacks from occurring. ARS researchers established that maintaining tree health is the most important management tool for minimizing the risk of attacks by ambrosia beetles. A ‘push-pull’ management strategy was developed that integrates repellents and attractants for pushing beetles away from vulnerable trees while simultaneously pulling beetles into annihilative traps. In particular, an interception strategy was developed to intercept ambrosia beetles before entering ornamental nurseries.
1. Influence of tree attraction on efficacy of insecticides against ambrosia beetles. Field observations suggest efficacy of insecticides against ambrosia beetles declines as attack pressure increases. However, this phenomenon was not tested previously. The current research by ARS researchers In Wooster, Ohio demonstrated that efficacy of protective treatments of insecticides decreases as the level of tree attraction to ambrosia beetles increases. This research further emphasizes the importance of maintaining tree health to reduce attack pressure by ambrosia beetles on trees.
2. Stress-induced ethanol within trees benefits fungus farming by ambrosia beetles. Exotic ambrosia beetles are destructive wood-boring pests of trees growing in tree nurseries and orchards. Adult ambrosia beetles transmit their symbiotic fungus and secondary microorganisms into trees, which results in branch dieback and tree death. Ethanol is emitted from physiologically stressed trees, and ambrosia beetles are strongly attracted to trees emitting this compound. ARS researchers in Wooster, Ohio demonstrated ambrosia beetles specifically attack tree tissues containing ethanol, a known antimicrobial agent, because it benefits the growth of their fungal symbiont gardens within host tree tissues. Simultaneously, the presence of ethanol in host tree tissues suppresses the growth of microorganisms that compete with their fungal symbiont. Since ambrosia beetles do not begin laying eggs until the fungal gardens are flourishing, it is critical to understand what factors promote and inhibit the establishment of the fungal gardens. These results will help researchers to develop novel management tactics that disrupt the establishment of ambrosia beetle fungal gardens and thereby prevent host tree colonization.
3. Media moisture levels are critical for minimizing risk of ambrosia beetle attacks. Exotic ambrosia beetles are destructive wood-boring pests of trees growing in tree nurseries and orchards. Ambrosia beetles attack trees emitting ethanol due to physiological stress, including poor drainage/overwatering/flood-stress. ARS in Wooster, Ohio and university researchers have collaboratively demonstrated that maintaining adequate moisture levels substantially decreases the risk of ambrosia beetle attacks. While insecticide applications reduce Xylosandrus species ambrosia beetle attacks on flood-stressed trees, healthy trees absent of ethanol emissions are not at risk for attack. Managing moisture levels at or below 50% and maximizing tree health provides protection against Xylosandrus species ambrosia beetles without the need to preventive insecticide treatments. These results will help growers of ornamental and horticultural trees to minimize the risk of ambrosia beetle attacks and reduce insecticide usage.
Reding, M.E., Ranger, C.M. 2017. Residue age and tree attractiveness influence efficacy of insecticide treatments against ambrosia beetles (Coleoptera: Curculionidae). Journal of Economic Entomology. 111:269-276.
Oliver, J., Ranger, C.M., Reding, M.E., Youssef, N., Moyseenko, J. 2017. Single and combination insecticides evaluated as regulatory immersion treatments to eliminate third-instar Japanese beetle (Coleoptera: Scarabaeidae) from small diameter field-grown and containerized nursery plants. Journal of Entomological Science. 52:274-287.
Addesso, K., Baysal-Gurel, F., Oliver, J., Ranger, C.M., O'Neal, P. 2018. Interaction of a preventative fungicide treatment and root rot pathogen on ambrosia beetle attacks during a simulated flood event. Insects. 9:1-11. doi:10.3390/insects9030083.
Ranger, C.M., Biedermann, P., Phuntumart, V., Benz, Y.P., Beligala, G.U., Ghosh, S., Palmquist, D.E., Mueller, R., Barnett, J.L., Schultz, P., Reding, M.E. 2018. Inordinate fondness for alcohol benefits fungus-farming by ambrosia beetles. Proceedings of the National Academy of Sciences. 115:4447-4452.
Anderson, A., Ranger, C.M., Frank, S. 2017. Interaction of insecticide and media moisture on ambrosia beetle (Coleoptera: Curculionidae) attacks on ornamental trees. Environmental Entomology. 46:1390-1396.