Maple petiole borer has been reported in northeastern Illinois. The larva of this sawfly eats through the peti-ole of maple leaves 1/4 to 1/2 inch from the lamina. The ground becomes littered with leaves with short, ragged petiole stumps. The main part of the petiole stays on the tree for a time before dropping. Home-owners get excited and upset about the number of leaves on the ground, but it is a small percent of those remaining on the tree. This insect is not a health threat or even an aesthetic threat to the tree. Control is not needed, which is good because little can be done.
Eggs are laid in the spring into the petiole near its base, where it joins the twig. The egg hatches into a grublike larva that tunnels up the petiole, eating the insides. Near the leaf blade, the larva eats most of the way through the petiole, causing the petiole to weaken, turn brown and then black in that area. Wind may cause the petiole to break in the weakened area, causing the leaves to fall. The sawfly larva stays in the part attached to the twig. A few days later, the petiole drops; the larva leaves it, tunnels into the soil to pupate, and emerges the next spring. There is one generation per year.