New bug in town

There’s a new bug in town and it’s making a hit. It is small and easily overlooked unless you are one of the migrating birds that are currently making your way through town. 

My neighbours noted a sandpaperish texture to their car’s paint job. If you ran your hand along it, you would swear your vehicle has been over sprayed by some innocuous agent.

The windshield almost feels like it is pitted. It is almost invisible because the insect that causes it is very small. Mid-August is the time that this feeding stage makes its presence known and it carries on for a few weeks depending on temperature.

Our local white birches are looking very bleak right now. They have gone through the partial defoliation of the gypsy moth this summer. It in part might be why the “new bug” in town was not noticed as well. It comes later.

The small brown moth is easily overlooked, as it is the size of a robust mosquito. The adults lay eggs on the birch leaves. It starts its early stages of life feeding within the leaf itself. It is therefore called a leaf miner.

Around mid-August it comes out of this protective layer as it is growing and begins feeding on the topside of our birch leaves. You can see the effects now.

The trees are showing a premature browning, not the yellowing we usually get from summer drought.

This time of year the larvae are now measuring around eight millimetres. If you walk to an infected birch tree you will see the “skeletonizing” effect on the leaves.

The softer tissue has been consumed and the framework of the leaf is intact. There are small strands of silk as the caterpillars sometimes are hanging by a thread.

It is then that you can see our mystery visitor. Mystery because they peak every eight to 10 years, and in most years, they may not even be noticeable.

You can stand by an infected tree in the stillness of the evening and you will hear the tiny particulates of leaf debris and frass falling to the ground or your vehicle. Unlike tent caterpillar frass that tends to bounce of surfaces, birch miner frass seems to stick.

Like most caterpillars, there will be a pupal stag and aptly named Bucculatrix canadensisella forms a small white web-like cocoon on the underside of the birch leaves near the central rachis.

The leaf will fall as debris to the ground and over-winter there. A good control therefore is to rake the leaves and dispose of them as law permits.

Chris Blomme
Greater Sudbury