Left: Adult apple clearwing. Right: Larvae burrow under tree bark for almost two years, feeding on the cambium layer, before pupating. Young trees are particularly vulnerable.
Although control measures have been reasonably effective in the fight against the apple clearwing moth in British Columbia, Canada’s Similkameen Valley, the insect is proving to be alarmingly pervasive.
Following North America’s first confirmed discovery of the clearwing moth (Synanthedon myopaeformis) in B.C.’s southern interior in 2005, it has since been identified in orchards in Keremeos, Oliver, North Osoyoos, Kelowna and coastal B.C., as well as in Ontario and parts of Washington State.
The moths lay eggs in burr knots, pruning scars, grafts, and bark wounds of apple trees, then their larvae bore under the bark anywhere from below the crown area up to branches. Larvae feed on the cambium layer of trees for almost two years before pupation, and can kill young trees.
In the drier desert climate of B.C.’s southern interior, infested trees are prone to drought stress, which can contribute to tree deaths. In highly infested orchards, damage can also spread to tree canopies.
Linda Edwards, a pest management consultant whose own orchard in Cawston, B.C., is infested, said that a 2008 survey showed that in the bench area of the Similkameen Valley, where most of the orchards are located, there was 95 to 100 percent infestation by the moth.
She is convinced that the insect was introduced to the area about ten years ago from Malling 9 rootstock imported from the Netherlands, where, because of the cooler climate, the pest isn’t as prevalent.
"We didn’t have M.9 rootstock when we started replanting," she said. "We brought it in from Holland. We can even sort of figure out which nurseries probably had it."
Surveys of clearwing infestation in the Similkameen appear to confirm her suspicions.
"We surveyed every orchard from the