2013 Annual Report
Collaborative research was conducted with ARS scientists into: (1) optimizing trapping strategies for ambrosia beetles, (2) determining the influence of water stress on tree attractiveness and susceptibility to ambrosia beetles, and (3) screening insecticides and repellents against ambrosia beetles. The following is a summary of research highlights from the five year project.
The granulate ambrosia beetle (Xylosandrus crassiusculus) is the dominant species attacking nursery stock in Virginia and collected in ethanol-based monitoring tools.
Ambrosia beetle traps only captured adults when daily maximum temperatures exceeded 70 oF.
Ethanol-injected container-grown and field-grown trees located within nursery blocks are effective at trapping the granulate ambrosia beetle in large numbers.
As in Ohio, a positive correlation was demonstrated between the concentration of ethanol injected into individual trees and ambrosia beetle attacks.
As in Ohio and Tennessee, injecting various tree species with ethanol resulted in abundant ambrosia beetle attacks, but there was not a significant influence of host on the number of attacks. Emission of ethanol is believed to be the key factor.
Ethanol-injected trap trees positioned in between nursery stock and adjacent woodlots effectively intercepted ambrosia beetles and diverted attacks away from valuable nursery stock. Neighboring non-injected trees were not attacked. While effective in capturing beetles before they reached the nursery stock, the trap tree strategy may be impractical for growers to easily adopt and implement.
As an alternative to trap trees, bolts with ethanol infused into a drilled cavity were found to be effective for capturing beetles. Ongoing studies are determining if such traps can intercept enough beetles to divert attacks away from valuable trees within commercial nursery blocks.
Ethanol-soaked tree bolts were highly effective for detecting and monitoring ambrosia beetles, and potentially useful for deflecting beetles away from valuable nursery stock. Tree bolts soaked in denatured ethanol were as attractive to ambrosia beetles as lab-grade ethanol.
Towards developing a push-pull strategy, on-going research is being conducted into the ability of verbenone, a bark beetle anti-aggregation pheromone, to repel or push ambrosia beetles away from valuable nursery stock.
Similar to Ohio, field studies in Virginia from 2011 found ambrosia beetle attacks decreased with decreasing proximity to a verbenone emitter.
As in Ohio, North Carolina, and South Carolina, flood-stress predisposed nursery trees to attack by ambrosia beetles. Neighboring healthy control trees were not attacked. Additional experiments demonstrated the ability of flood-stress to induce ethanol production by trees and thereby predispose them to attack by ambrosia beetles. Tissue samples sent to ARS confirmed elevated amounts of ethanol in flood-stressed trees compared to healthy trees.
As in Ohio, drought-stressed trees were less attractive than flood-stressed trees to ambrosia beetles, which is believed to be due to differences in moisture content.
Flood-stressed trees were less attractive to ambrosia beetles than ethanol-injected trees (if recently injected). Thus, trap trees or an equivalent strategy could be used to deflect beetles away from valuable nursery stock that might be emitting low levels of ethanol.
Japanese snowbell (Styrax japonica) subjected to heavy root pruning at a commercial nursery were subsequently attacked by ambrosia beetles.
Insecticide efficacy trials determined that permethrin-based insecticides were the best option for managing ambrosia beetles, but insecticide applications did not always protect physiologically-stressed trees from attack.
This research relates to the following objectives of the parent project: (1) to reduce, through knowledge generated by research, crop losses and damage caused by insect pests of ornamental nursery crops, turf, and other horticultural crops; (2) to develop alternative management strategies for pest control that will reduce dependence upon traditional uses of insecticides, and lessen impact on groundwater.