Imported Currantworms are usually observed in gardens where a gardener watches a batch of the caterpillar-like larvae speedily defoliating a currant or gooseberry shrub. This unwelcome turn of events happens in June and sometimes again in July.
The adult female sawfly is about 10mm (? in.) long with a black head and thorax and yellowish abdomen. Males are a bit smaller and dark overall. They are out and about in spring just as the first currant leaves unfurl. The female uses her saw-like ovipositor to lay eggs inside the underside of the main leaf vein of a currant or gooseberry.
When the larvae are small they chew small holes in the leaves. By the time they are fully grown (about 3 weeks after hatching), these caterpillar-like larvae are about 20 mm (¾ in.) long, and are green with black spots. They chew in groups along the edges of the leaves and continue until only the mid vein of the currant leaf remains. When they have defoliated the shrub, they fall to the ground and pupate in the soil near the hapless shrub.
Sawfly larvae, which are often unpalatable to birds tend to feed conspicuously and brazenly out in the open, chewing away in an obvious manner. Caterpillars (the larvae or moths and butterflies), on the other hand, are often quite tasty to birds and feed at night or feed concealed somehow in silken nests or curled leaves. Some, like a kid who sticks his finger in the icing of a cake, tries to hide the damage by taking pieces in an inconspicuous manner.
Although Imported Currantworm larvae don’t kill the currant shrub, the shrub does not fare nearly as well or grow as it should if it had leaves to fuel photosynthesis. They don’t affect any fruit that happens to form, however.
Like many of our more vexing garden pests, Imported Currantworm is, as the name suggests a foreign species.
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Where to find Imported Currantworms in Alberta
This species does not occur in the Weaselhead/Glenmore Park area. Nora Bryan
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BRENT JOHNER
for serving as the society's PAST PRESIDENT this year