I noticed recently that several of the dogwoods (Cornus sp.) in our Lake Placid yard had become almost completely defoliated in the past two weeks.
Close examination revealed many caterpillar-like larvae curled up on the undersides of some of the remaining leaves. These are the larvae of the native Dogwood Sawfly (Macremphytus tarsatus). The Dogwood Sawfly is neither a moth nor a fly, but a member of the order Hymenoptera (wasps, bees, ants, and sawflies). The wasp-like adult sawfly lays eggs that hatch into larvae, the first instar of which is an almost translucent yellow. 
The second instar appears to be covered with a chalky powder.
The last instar is creamy yellow with a shiny black head and black spots along the sides.
When fully grown, the larvae cease to feed and overwinter in rotting wood in the ground. The larvae pupate in the spring and the adults emerge in the summer to mate and lay eggs on the undersides of dogwood leaves.Despite the loss of leaves, defoliated dogwood bushes don't die as the defoliation occurs so late in the growing season. However, not wanting to lose the leaves on our remaining three ornamental dogwoods, I lightly sprayed the larvae on them with an insect killing soap (organic solution of seaweed extract containing potassium salts). ;(
Very Cool! Now I have another insect to keep an eye out for!
ReplyDeleteYeh, I just saw these this week on some Panicled Dogwoods. What is the organic pesticide you used? A commercial product or one you prepared yourself? Thanks!
ReplyDeleteSawfly larvae are often mistaken for butterfly/moth caterpillars. To tell the difference, look at the prolegs (peg-like legs behind jointed legs). As seen in the last photo above, sawfly larvae have prolegs on almost every segment. Moth/butterfly caterpillars usually have at least 3 segments without prolegs. Sawfly larvae are more likely to feed in groups compared to moth/butterfly larvae.
ReplyDeleteI'm so glad to have been sent here by my blogger friend Valerie. I posted a photo of one of these today, and didn't know what it was. I hadn't made the connection between the white caterpillars on my dogwood and this last instar. Thanks so much for sharing!
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