PI(s): Bergh, J Christopher (Project Leader)
Investigators: Leskey, Tracy (Investigator), Walgenbach, James (Investigator), Zhang, Aijun (Investigator)
Abstract: The dogwood borer, Synanthedon scitula, is becoming an increasingly important pest of apple grown on size-controlling rootstocks in eastern North America. Monitoring the dogwood borer using commercially available sex pheromone lures has produced discrepant results among published studies, due mainly to the fact that its sex pheromone had not been specifically identified. A collaborative project with USDA and NCSU scientists has led to identification of the dogwood borer sex pheromone, resulting in a tremendous increase in the number of moths captured and a significant improvement in the species specificity of the new lure. Our current efforts seek to determine whether dogwood borer populations in commercial apple orchards can be suppressed through mass trapping of males. As well, cooperators from TN, NC, VA, WV and NY are deploying the new lures in managed urban landscapes, apple orchards and woodlands in each state, to compare the seasonal flight activity and relative abundance of dogwood borer among these habitats.
Commercially available sex pheromone lures for dogwood borer (DWB) have been subopitmal in both their attractiveness to and selectivity for this pest of deciduous ornamentals and apple. Use of these lures to monitor DWB in managed urban landscapes, ornamental nurseries and apple orchards has significantly underestimated their abundance and has led to conflicting conclusions regarding its seasonal period of flight activity. Our identification and use of the correct and complete blend of DWB pheromone components has generated new information about its pest status, particularly in apple orchards, and has provided resolution to questions about its annual phenology. A comparison among native woodland habitats, managed urban landscapes and commercial apple orchards in five eastern states from New York to Tennessee showed that DWB is most and least abundant in apple orchards and native woodlands, respectively, and that the duration of its flight period becomes progressively longer from north to south.
Identification of the DWB sex pheromone also has created renewed interest in its management using behavioral manipulation techniques. Given that we have doumented a much greater capture of male moths in traps baited with the new pheromone than in those baited with virgin females, we are currently investigating the effects of mass trapping on larval populations in commecial apple orchards. Furthermore, while past attempts to manage DWB using sex pheromone based mating disruption were hindered by lack of an effective and species-specific pheromone for disrupting mating and for monitoring the effects of mating disruption treatments, use of the new pheromone blend may significantly improve the efficacy of this tactic and will certainly improve our ability to assess the outcome of such research. In addition, we have demonstrated the potent effect of a behavioral antagonist, a geometrical isomer of the main pheromone component, on the response of male DWB to its pheromone. Addition of as little as 0.5% of this isomer to the pheromone blend completely eliminates the response of males to its pheromone, and we are a developing project that seeks to disrupt mate finding using this behavioral antagonist alone.
A multi-year project evaluating the rate of infestation of new apple orchards established in Virginia and West Virginia has revealed significant differences in the susceptibility of different apple rootstocks and varieties. Further, we showed that a previously recommended cultural management tactic, soil mounding around the base of trees, has inherent horticultural problems and does not provide long-term control of DWB.
Finally, it has become apparent that the DWB is at least bivoltine, and possibly multivoltine, when development occurs on apple burr knot tissue. This finding contradicts all previous conclusions, which assumed univoltinism. We are further exploring the effects of different apple tissues on DWB larval development rates, toward an understanding of why this pest is so abundant in the apple ecosystem.
Dissemination of the results of our research via refereed publications and presentations to growers at tree fruit production meetings has led to a greatly increases awareness of the potential for DWB to impair the establishment and growth of young apple trees during their first years of life and a survey conducted in 2005 showed that apple growers have adopted more diligent scouting for and monitoring of DWB. A patent has been issued for use of the DWB pheromone and the behavioral antagonist for mating disruption and other behavioral manipulation tactics. Demonstration of the bi- or multivoltinism of DWB on apple trees grown on size-controlling rootstocks and of the prolonged duration of its annual flight period in the southern portions of its range has led to renewed interest in the longevity of chlorpyrifos treatments for its control. Previous evaluations of the duration of control afforded by this most effective product were based in New York, and recommendations for the use of chlorpyrifos are being reevaluated for more southern locations.