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ARS Home » Midwest Area » Wooster, Ohio » Application Technology Research » Research » Research Project #430272

Research Project: New Strategies for Management of Invasive Ambrosia Beetles in Horticultural and Nursery Crops

Location: Application Technology Research

2017 Annual Report


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. 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.


Approach
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.


Progress Report
Research was initiated and progress was made on all Objectives (1, 2, and 3). As part of Objective 1, we conducted a second season of research comparing seasonal colonization activity of ambrosia beetles on flood-stressed trees with attacks on ethanol-baited trees and captures in ethanol-baited traps. Seasonal movement of invasive ambrosia beetles in ornamental nurseries and surrounding habitats was tracked for a second season to determine whether damaging beetles originate from within nurseries or disperse in from adjacent woodland habitats. This research demonstrated that woodlands adjacent to nurseries are the primary sources of ambrosia beetles invading those nurseries, beetle activity was related to temperature, and that beetle activity within nurseries decreases as the distance to the woodland increases. This data 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. In collaboration with researchers from São Paulo State University in Brazil, we compared two different trap designs for monitoring ambrosia beetles. Specimens are being sorted and quantified. We identified volatile compounds associated with ambrosia beetle fungal symbionts and tested their attractiveness under field conditions. Ambrosia beetles did not exhibit long range attraction to the fungal volatiles, and the fungal volatiles did not synergistically or additively enhance the attractiveness of ethanol. We characterized the morphology of olfactory sensilla found on ambrosia beetle antennae. Documenting the distribution of olfactory sensilla on the antennae will assist with electroantennogram and electrophysiological experiments aimed at evaluating attractants and repellents. As part of Objective 2, we characterized the impact of frost injury on host attractiveness and vulnerability to ambrosia beetles. Frost injury was demonstrated to induce ethanol emissions and predispose frost-intolerant trees to attack by ambrosia beetles. The influence of host tree chemistry on fungus farming and colonization success of ambrosia beetles was examined. Ethanol benefitted fungus farming and offspring production by ambrosia beetles, but inhibited growth of fungal competitors. Ambrosia beetles attacked but did not establish fungal gardens in ethanol-baited trees absent of in vivo ethanol, while fungal gardens and offspring were produced in living trees with in vivo ethanol. Since ambrosia beetles do not begin laying eggs until their fungal gardens are flourishing, this phenomenon represents a weak point in their biology that can be used for management purposes. It is therefore important to understand what factors promote and inhibit establishment of their fungal gardens. A second season of research examining colonization behavior of summer generations of ambrosia beetles was conducted. As part of Objective 3, efficacy of conventional insecticides and fungicides for preventing attacks and reducing colonization success were tested using flood-stressed trees. Insecticides, but not fungicides, reduced attacks by ambrosia beetles. Offspring production was also disrupted by selected insecticides and fungicides. 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. This research was submitted for publication in June. We conducted several experiments evaluating the attractiveness of ethanol-infused tree stems (bolts) to ambrosia beetles. Ethanol infused bolts could be an inexpensive technique for growers to monitor ambrosia beetle activity, and has great potential as an inexpensive technique for screening insecticides against ambrosia beetles. Research testing whether ethanol-injected trap trees were effective deflecting beetles away from protected trees was initiated. So far, this research indicates that traps trees are not effective for reducing attack pressure on protected trees. Experiments were conducted in Ohio and with ARS collaborators in Mississippi to determine whether ethanol-baited traps positioned along the woodland/nursery interface could intercept sufficient numbers of ambrosia beetles to reduce activity within nurseries. A “push-pull” experiment was also conducted in collaboration with researchers from Virginia and Mississippi, whereby repellents were assessed for pushing beetles away from vulnerable trees and attractants were tested for pulling beetles into annihilative traps. Results from the multi-state trials did not find an effective reduction in attacks on flood-stressed trees in the presence of attractant traps or repellent dispensers. However, increasing the attractiveness of the ethanol-baited interceptor traps could increase their effectiveness and thereby reduce attacks on the flood-stressed trees. This research is part of developing a strategy where ambrosia beetles are intercepted before they attack nursery trees, which is a potential alternative to chemical pesticides for managing ambrosia beetles in nurseries.


Accomplishments
1. Ethanol-injection induces attacks by ambrosia beetles on a variety of tree species. The ethanol-injection technique to attract ambrosia beetles to experimental trees was developed by ARS researchers in Wooster, Ohio. This technique facilitated research on pesticide efficacy, ecology and behavior of ambrosia beetles in tree crops, and has potential for use in behavior-based management strategies. However, it was tested on only three species of trees, and integrating ethanol-injection into ambrosia beetle management tactics would be more likely if it was effective on a wider variety of tree species. The current research by ARS researchers in Wooster, Ohio and their university collaborators demonstrated that ethanol-injection induced attacks on 17 species of trees in 11 families. These results should further facilitate research on damaging ambrosia beetles in tree crops, and development of behavior-based management tactics that divert beetles away from valuable crop trees.

2. Scanning electron microscopy (SEM) used to characterize sensory hairs on the antennae of two highly destructive species of ambrosia beetles. Several types of sensilla with purported olfactory functions were identified. Distributions of the olfactory sensilla were described for females and males of the two ambrosia beetle species. These results improved our understanding of olfactory hairs (i.e.sensilla) associated with two species of ambrosia beetles. Electrophysiological experiments screening beetle repellents and attractants will benefit from this improved understanding of the specific sensilla used for olfaction. Integrating repellents and attractants into a push-pull management strategy shows promise for sustainable pest management.

3. A new species of ambrosia beetle, Anisandrus maiche, has been introduced and become established in Ohio, Pennsylvania, and West Virginia. This species has been found attacking trees growing in ornamental nurseries and associated with branch dieback symptoms. ARS researchers from Wooster, Ohio, worked with microbiologists to isolate and identify a new species of fungal symbiont that associated with A. maiche, namely, Ambrosiella cleistominuta. Adults and larvae must feed on this fungal symbiont in order to properly develop and reproduce. Identifying the fungus transmitted by A. maiche will aid researchers in understanding what factors cause dieback of trees following attacks by ambrosia beetles. Hypotheses include a hypersensitive response by the tree that results in girdling, clogging of the vascular tissues by the fungal symbiont, or pathogenicity associated with opportunistic microorganisms. Identification of the fungus and its affect on trees will also assist in selecting conventional and reduced-risk fungicides for protecting or rescuing vulnerable trees.


Review Publications
Zhu, H., Rosetta, R., Reding, M.E., Zondag, R., Ranger, C.M., Canas, L., Fulcher, A., Krause, C.R., Derksen, R.C., Ozkan, E. 2017. Validation of laser-guided variable-rate sprayer for managing insects in ornamental nurseries. Transactions of the ASABE. 60(2): 337-345.
Mayers, C., Harrington, T., Ranger, C.M. 2017. First report of a sexual state in an ambrosia fungus: Ambrosiella cleistominuta sp. nov. associated with the ambrosia beetle Anisandrus maiche. Botany. 95:503-512.
Ranger, C.M., Horst, L., Barnett, J.L., Reding, M.E., Anderson, B.A., Krause, C.R. 2017. Comparative morphology and distribution of antennal sensilla on Xylosandrus germanus and Xylosandrus crassiusculus (Coleoptera: Curculionidae: Scolytinae). Annals of the Entomological Society of America. 110:172-188.
Klingeman, W.E., Bray, A.M., Oliver, J.B., Ranger, C.M., Palmquist, D.E. 2017. Trap deployments in black walnut tree canopies help inform monitoring strategies for bark and ambrosia beetles (Coleoptera: Curculionidae: Scolytinae). Environmental Entomology. https://doi:10.1093/ee/nvx133.