Forestry Service Says Saskatoon Pest Tentatively Identified – for Sep. 9, 2010

In July, Canadian Forest Service staff became aware of an insect infestation occurring on wild and cultivated saskatoon berry bushes in and around the Lac La Biche area of eastern Alberta.

Based upon leaf symptoms and a photo of an unusual adult moth taken in May by amateur photographer Stan Gosche, we suspect that maple leafcutters (Paraclemensia acerifoliella) are the insects causing the damage.

This species is not normally known to be found outside of southeastern Canada on its main host sugar maple (Acer saccharum), and it has never been reported on saskatoon. However, there are historical reports of maple leafcutter in Riding Mountain National Park in Manitoba and Kaslo, B. C.

It is possible that the Alberta outbreak could be a related, unnamed species. Positive identification awaits DNA analysis and examination of next spring’s adult moths.

The damage to leaves occurs when the insect is in the form of a tiny caterpillar, about six millimetres long. The caterpillars cut small ovals of leaf, and then construct a protective case from the cut pieces. The caterpillar fastens this case to the leaf surface, lives inside it, and skeletonizes the leaf (strips away the green tissue to leave only the leaf veins).

The damage becomes apparent in mid-July, and continues until mid- August, at which point the larvae drop to the ground in their cases.

The caterpillars then turn into small dark pupae, which change into moths the following spring to repeat the cycle.

Anyone who has seen this damage on saskatoons, particularly if it’s outside the Lac La Biche area, is asked to contact Greg Pohl at 780-435-7211 or [email protected]

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