Biology, ecology, and management of dogwood borer in eastern apple orchards

Abstract

AbstractThe dogwood borer, Synanthedon scitula (Harris) (Lepidoptera: Sesiidae), has the broadest host range of the clearwing moths and is considered to be an economically important pest of many ornamental, fruit, and nut trees. Since the 1980s, dogwood borer has been recognized as an increasingly important, indirect pest of apple, Malus domestica Borkh. (Rosaceae), in eastern North America, owing mainly to increased plantings of apple on size-controlling rootstocks that promote the formation of adventitious root initials (burr knots) on the rootstock and scion. Burr knots appear to be preferred oviposition sites for dogwood borer females, although infestations can also be initiated in wounds, pruning cuts, and crotches on the branches and trunk. Larval feeding in burr knots does not adversely affect the growth and vigor of apple trees, but their mining outward from burr knots into vascular tissue can ultimately cause tree decline and death. Chlorpyrifos is the most effective insecticide for controlling dogwood borer. A supplemental label in the United States permits post-bloom, trunk drench applications of chlorpyrifos specifically for control of borers in apple, with several restrictions that preclude control of infestations higher in the tree. The ongoing review of pesticide tolerances dictated by the 1996 Food Quality Protection Act of the United States of America makes the long-term availability of this chemical uncertain. Cultural practices, such as deeper planting or berming, can reduce the likelihood of infestation of new apple plantings by dogwood borer, although they do not preclude infestations from developing above the graft union. This review and discussion is based on our contention that research toward the development of alternative, behaviorally based management strategies for dogwood borer in apple and other economically important host plants is warranted. Our review and synthesis of the dogwood borer literature revealed important gaps in knowledge about basic aspects of its biology that pertain directly to the development of alternative control tactics based on behavioral manipulation. There is considerable confusion surrounding the sex pheromone of dogwood borer and conflicting results on the response of males to isomers and blends of isomers of its purported pheromone. Studies using sex attractants to monitor its phenology in apple and non-apple habitats have yielded discrepant results and conclusions. Differences in the effectiveness of commercially available pheromone lures for trapping dogwood borer have been reported and the ability of pheromone traps to accurately reflect emergence or population density remains in question. Regardless of pronounced differences in the duration and modality of the seasonal flight of dogwood borer among different geographical regions within its range, the conclusion of univoltinism across most of its range has been perpetuated, based on extremely limited developmental data collected exclusively from individuals that developed on dogwood.