Attack of the Leaf Miner (Phyllocnistis populiella)

By Janelle Eklund
It was fairly early in May and the air was filled with tiny white moths. Breathing could be a chore without channeling them into your nose. They lasted for about two weeks or so and then they seemed to disappear. Not so.
 
These adults had nestled under the leaf litter of Spruce, Balsam Poplar, and Aspen trees during the long winter months. As the Aspen and Balsam Poplar trees were just beginning to bud Leaf Miner was waking to the call of the hot month of May we had one year. They emerged in droves. The hotter and dryer it is the more they seem to like it. Populations are higher in than wetter, cooler years. Once they emerge they have a hay day feeding and mating for about two weeks. By this time the Aspen and Balsam Poplar buds have changed into beautiful lime green leaves. I love the shimmer of this welcoming greenness. But that initial burst doesn't last, particularly during years of lots of leaf miners.
 
Leaf miners then got busy laying their eggs. When populations of adults are low they lay one or two eggs per leaf. When populations are high they can lay up to seven eggs per leaf. Eggs are laid on the edge of the leaf so the adult can fold the leaf over the egg like a blanket, protecting it until the larvae hatch. At that time, like any newborn, they are hungry. They tunnel into the leaf and feed on it between the epidermal tissue. Most of it is done during the late stage of their larval growth lasting about two weeks. They are tiny white flat critters about 5 mm long. You can see how thin the leaves are so these little babies are REALLY flat. So flat that their trails are usually only seen on one side of the leaf or the other, as you can see in the pictures. A lot of the time the trails are seen on the front side of the leaf but there are also those only on the back side - or some are seen on both sides - not necessarily the same tracks. These miners of leaves go through four youth stages before they grow into an adult, all spent in the mine, mining! The adults emerge just in time to hunker down for the winter, just before the leaves start to change to their autumn dress color in late August and September, producing one generation per year.
 
If you look closely you will see that leaf miners also mine Balsam Poplar and occasionally willow. But it seems like their favorite food is Aspen. The mining produces a continuous line of switch back trails turning the leaf a silvery color. The aspens will then quake with a dull silvery shimmer. Eventually all this mining sucks all the moisture out of the leaves, turning them brown and dropping dead before their time. The trees seem to be extremely tough taking this attack year after year. But, as the attack continues every year less photosynthesis is taken in by the damaged leaves, and there is suspected reduction in tree growth, branches dying back, and top-kill.
 
We have been watching this attack for many years now in Alaska - in the year 2000 300,000 acres of trees were affected and in 2006 more than 659,000 acres were affected. In the Copper River Basin we have been watching it for many years. This is the second biggest outbreak recorded.
 
From my light to yours-
 
References: www.fs.usda.gov
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