Location: Application Technology Research2013 Annual Report
1a. Objectives (from AD-416):
#1: Develop improved techniques for managing scarabs and ambrosia beetles in nurseries by determining the biology and ecology of exotic scarabs and ambrosia beetles in relation to the nursery ecosystem, the response of nursery crops to root herbivory by exotic scarabs and potential relationship to attacks by ambrosia beetles, and by examining interactions between exotic ambrosia beetles and the nursery ecosystem including factors leading to attacks on nursery trees by ambrosia beetles, especially as it relates to abiotic and biotic stress. #2: Evaluate sustainable, environmentally-friendly alternatives to conventional insecticides, including reduced-risk chemicals, microbial products, and botanical extracts for control of ambrosia beetles and scarabs. #3: Develop new application methods and strategies for ambrosia beetle and scarab control and to prevent their distribution to uninfested parts of the United States and abroad.
1b. Approach (from AD-416):
The development and survival of Anomala orientalis (oriental beetle, OB) larvae will be evaluated on a variety of woody ornamental species. The relationship between constitutive and induced defensive compounds in the roots, along with total carbon and nitrogen levels, and development and survival of OB will be determined. OB larvae have caused considerable damage to trees and shrubs in ornamental nurseries and in production of small fruits such as blueberries and cranberries. Despite the damage this species causes in woody nursery and small fruit crops, there has been very little research evaluating trees and shrubs as hosts for OB. Species and varieties of trees and shrubs that are poor or marginal hosts would either not need protection from OB or acceptable levels of protection might be achieved by lower rates of insecticides. Data will be analyzed each season and adjustments will be made to experimental design if necessary. If we identify species that are especially good or poor hosts for OB, we will conduct additional testing on varieties within those species and closely related species to see if their quality as hosts is similar (good or poor). This information will be used to identify suites of characteristics (chemical compounds, nutritional, etc.) that make a woody plant a viable host for larval OB. This data could then be used by plant breeders to develop varieties resistant to OB.
3. Progress Report:
In 2013, we continued research projects on interactions of oriental beetle larvae (invasive scarab) and ornamental nursery crops as hosts; growth-response of nursery trees to root-herbivory by scarab larvae; monitoring ambrosia beetles with ethanol-baited traps and ethanol-injected trap trees; modeling the relationship between ambrosia beetle activity and temperature; optimizing an odor-based trap-tree tactic for inducing attacks on trees by ambrosia beetles; evaluating synergism between ethanol in injected trees and volatiles emitted from those trees; identifying host-derived volatile cues used by Xylosandrus germanus to locate hosts; determining the influence of water-stress on tree attractiveness and susceptibility to ambrosia beetles; screening for compounds that act in synergism with ethanol for attracting ambrosia beetles; characterizing the spatial distribution of trees attacked by ambrosia beetles within ornamental nurseries. We also started research on dispersal of ambrosia beetles into nurseries. The previous activities are primarily related to Objective-1 of the project plan (Develop improved techniques for managing scarabs and ambrosia beetles in nurseries by determining the biology and ecology of exotic scarabs and ambrosia beetles in relation to the nursery ecosystem, the response of nursery crops to root herbivory by exotic scarabs and potential relationship to attacks by ambrosia beetles, and by examining interactions between exotic ambrosia beetles and the nursery ecosystem including factors leading to attacks on nursery trees by ambrosia beetles, especially as it relates to abiotic and biotic stress.) with some relative to Objective-3 (Develop new application methods and strategies for ambrosia beetle and scarab control and to prevent their distribution to uninfested parts of the United States and abroad). Research was also conducted on evaluating verbenone as a repellent to ambrosia beetles in the field; testing insecticides and entomopathogens for control of ambrosia beetles; and determining residual activity of insecticides for controlling exotic ambrosia beetles. Those projects are related to Objectives-2 (Evaluate sustainable, environmentally-friendly alternatives to conventional insecticides, including reduced-risk chemicals, microbial products, and botanical extracts for control of ambrosia beetles and scarabs) and -3 of the project plan.
1. Modeling the relationship between activity of the ambrosia beetle Xylosandrus germanus (a species of ambrosia beetle) and temperature. The exotic ambrosia beetle Xylosandrus germanus is one of the most problematic ambrosia beetles in ornamental nurseries in the Northeastern, Midwestern, Atlantic, and Southeastern states. Because these beetles are so small and difficult to detect, it is difficult for growers to synchronize their protective sprays with beetle activity. Sprays applied too early are wasted, while excessive damage can occur when sprays are applied too late. ARS scientists at Wooster, OH developed a model for predicting emergence of the ambrosia beetle Xylosandrus germanus based on the bloom sequence of ornamental plants, and a model based on daily maximum temperatures wherein an extended weather forecast can be used to predict beetle activity. This model can be used by growers to determine whether they need to spray or can wait. This will enable growers to be more efficient controlling ambrosia beetles, which will save them money by not applying unnecessary insecticide sprays. Furthermore, knowledge of such a relationship will lead researchers to investigate similar models for other damaging ambrosia beetles to develop more efficient programs within their management.
2. Significance of physiological stress on host preference by a non-native ambrosia beetle. The process by which Xylosandrus germanus chooses which trees to attack in ornamental nurseries has been poorly understood. ARS scientists at Wooster, OH demonstrated that despite a host range >200 species, X. germanus preferentially attacks living, but weakened trees. Beetles use a sophisticated olfactory mechanism to efficiently pinpoint the source of trees emitting ethanol, which is produced by trees in response to stress-induced injury. Results from controlled experiments support anecdotal observations from ornamental nurseries that flood-stress induces the emission of ethanol by trees and thereby predisposes them to attack. When given a choice, beetles selectively attack trees intolerant of flooding, but do not attack trees tolerant of flooding. Beetles also do not attack neighboring trees that are not flooded or emitting ethanol. These results are helping growers to understand the relationship between tree stress and attacks by ambrosia beetles. Growers were initially under the impression that attacks occurred on “apparently healthy” trees, but through our research efforts, growers are beginning to recognize that X. germanus preferentially attacks unhealthy trees while neighboring healthy trees are not attacked. Growers are realizing that trees can look apparently healthy or visually healthy, but instead be “inapparently stressed” and inconspicuously emit ethanol and other volatile attractants in response to acute and chronic stress. Growers are identifying risk factors and making efforts to minimize stress-induced injury to reduce the likelihood of environmental factors predisposing trees to attack.
3. Reducing attacks by ambrosia beetles on trees using verbenone. Olfaction plays an important role during host selection by ambrosia beetles. Verbenone is an antiaggregation pheromone produced by bark beetles that reduces their attacks on trees. Few studies have examined the influence of verbenone on ambrosia beetles and none have examined the influence of verbenone on X. germanus. We examined the extent to which verbenone interrupted the attraction of ambrosia beetles. Field studies demonstrated verbenone reduced attraction by a variety of ambrosia beetles to ethanol-baited traps. A verbenone dispenser attached to ethanol-injected trap trees deployed also reduced ambrosia beetle attacks compared to trap trees without a verbenone dispenser. Our research efforts also documented a direct relationship between distance from a verbenone dispenser and ambrosia beetle attacks on trap trees in Ohio, but was inconsistent in Tennessee and Virginia. However, while attacks occurred on trap trees regardless of their proximity to a verbenone dispenser, the higher density of attacks per tree occurred on trap trees farthest away from the verbenone source in Ohio and Tennessee. These results indicated that verbenone alone could be somewhat useful for discouraging ambrosia beetle attacks on individual trees or on a small spatial scale.
Persad, A., Siefer, J., Kirby, S., Montan, R., Rocha, O., Reding, M.E., Ranger, C.M. 2013. Effect of emerald ash borer on structure and material properties of ash trees. Arboriculture and Urban Forestry. 39:11-16.