This fly has an all-black body with distinct white or yellow legs depending on its growth stage. These flies can reproduce without a mate and their short life cycle allows for multiple generations per year. The larvae hatch from eggs and look like little green caterpillars, and it is at this stage that all the damage is done. The larvae produce the zig-zag pattern on the leaves and the later stage larvae can consume the entire leaf itself. They are seen almost exclusively on elm trees however the flying adults may travel up to 90 km from their birth tree.
Its native range is in Asia but it was introduced into Europe around 2003 and continues to be a pest there. The fly was first observed in Canada in the region of Quebec in 2020, and its means of getting here have yet to be determined.
This fly has the potential to impact our native elm trees, if this species spreads and impacts trees to the degree that the emerald ash borer did there will be a serious issue. However, the sawfly does not impact the trees in the same manner as the borer so this claim may not be 100% accurate. They are also invasive in Europe and have been known to completely defoliate trees.
It was originally detected in Quebec but sightings have been popping up from Ottawa to Brockville. So it is evident that this species is moving fast.
Impacts & Control
The larvae stage sawflies eat the elm leaves in a zig-zag pattern, which can lead to defoliation and leave the tree in a weakened state. The potential combination of the sawfly with dutch elm disease is a serious potential threat.
There is little being done in Canada right now but we are in the stages of detection. We are urgently trying to determine how this species got to Canada and we are trying to determine its current range. In Europe where the species is also invasive the use of pesticides is a yearly effort but we have yet to approve or deem this level of control necessary in Canada.