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Large aspen tortrix

Aerial surveys followed by ground checking revealed that the large aspen tortrix was present near Duluth this past spring. Defoliation of aspen, as well as, pupal cases of the tortrix were found in T51N-R13W and in T50N - R14&15 W.

Early in the spring, tiny larvae of the large aspen tortrix mine buds of aspens before they open, causing holes in the leaves still enclosed inside the buds. As the leaves expand, the tortrix feeds on the leaves, rolling, folding and tying them together for shelter. The larvae are dark green to black and about 3/4 of an inch long when fully developed. About mid-June they pupate in leaves they have tied together. Adult moths emerge about two weeks later, to mate and lay eggs.

The large aspen tortrix populations sometimes develop into large outbreaks, just like the forest tent caterpillar, consuming aspen leaves on millions of acres. The last large outbreak of tortrix in Minnesota lasted from 1969 to 1973. Since then, pockets of tortrix defoliation have been found, like this year, but they quickly declined and did not develop into large outbreaks. Time will tell what happens with these populations.

Aspen webworm

In late August, the aspen webworm, Tetralopha aplastella, was found on a few aspen east of Ely. Each two to three-inch diameter web consisted of several leaves tied together with silk. Inside each web was a 3/4 to 1 inch long yellowish-brown caterpillar with a darker brown head, thoracic shield and broad subdorsal stripes. In several webs there were remnants of the cocoon of the forest tent caterpillar, indicating that the webworm took advantage of this feeding site without having to create its own shelter.

Before the leaves fall in September or October, the caterpillars drop to the ground on strands of silk, spin a cocoon in the duff and overwinter as prepupae. Next June they will change into powdery gray moths. Eggs are laid on leaves partly rolled by other insects. The literature indicates that this forest pest occurs across the continent, and it feeds on many hardwoods. In a l985 publication, "Insects of Eastern Forest" it was known as the maple webworm. This forest insect rarely reaches population numbers that sufficient foliage is eaten to damage trees, although the webbed leaves may make ornamental trees unsightly.