Apple Clear-Wing Borers Take Flight

In an effort to obtain a few good adult specimens of dogwood borer for demonstration purposes, I spent one fine morning about 10 days ago picking through the burr knots of several apple trees in the Simcoe area. My quest for dogwood borer pupae ended up being a success, and in the last few days, several male and females emerged (to be unceremonially whisked off to the freezer, pinned, and put on display). Indeed, it appears that the flight is underway in the field as well, with reports of catches in pheromone traps coming in.

The dogwood borer (DWB), Synanthedon scitula, is one of two clear-wing moths attacking apple trunks; the other is the apple bark borer (ABB), Synanthedon pyri. Adults of both species are predominantly black with yellow stripes on the abdomen and yellow legs; they resemble small wasps at first glance. The DWB has a total wingspan of 12-22 mm (females tend to be on the larger size). Wings are mostly transparent, with board black tips on the forewings. Two thin yellow markings are evident on the 2^nd and 4^th abdominal segment; these are more pronounced in the female moth (Figure 1). The anal tuft is rounded. The ABB is very similar to the DWB in terms of size and banding, but has a distinct reddish-orange spot located on the forewing, and a larger, wedge-shaped black anal tuft.

Learning to identify the adult males on pheromone traps is important, as males of several other species are attracted to the lures used for DWB. I have found one excellent guide for identification of clear-wing moths, though it may now be out of print: "A Guide to the Clearwing Borers (Sesiidae) of the North Central Unites States" (North Central Regional Publication No. 394, 1991). You can find a few nice images of several species at the Forest Pests of North America website.

Figure 1. Adult dogwood borer.

Clear-wing borers overwinter as full-grown larvae under the bark*. They pupate the following spring, with emergence beginning in late June or early July; flight may continue into August. Females lay eggs on the surface of burr knot formations. Hatching larvae bore into the burr knots, eventually moving to the cambium, and pushing out a reddish brown frass as they feed. Size-controlled rootstocks at particularly vulnerable to attack. Feeding by larvae results in a slow decline following several years of infestation.

A combination of Pounce (permethrin) plus Superior oil applied one or two times (2-3 week intervals) to the trunk area beginning at peak pheromone catch is recommended in areas prone to damage and susceptible rootstocks (M9, M26). The use of pheromone traps for monitoring adult activity is recommended. See OMAFRA Publication 360 for additional information on timing of insecticide applications.

* An excellent key for identification of the larval stages of borers (American plum borer, dogwood borer, apple bark borer, roundheaded apple tree borer, others) in apple can be found online at A Key to the Borers of Apple.

Related Links

• A Key to the Borers of Apple
• Forest Pests of North America
• OMAFRA Publication 360, Fruit Production Recommendations