The resurgence of larch casebearer in the Great Lakes region: are natural enemies still present?

Introduced to eastern North America in the mid-19^th century, the larch casebearer, Coleophora laricella (Lepidoptera: Coleophoridae), is a small moth whose larvae inhabit a distinctive silken case. Originally native to central and northern Europe, the larch casebearer quickly established itself in North American forests by infesting native eastern larch, Larix laricina, and western larch, Larix occidentalis. It was first reported in Minnesota in the mid-20^th century. During the 1960s an exotic parasitoid wasp, Agathis pumila (Hymenoptera: Braconidae), was released as a biocontrol measure to help manage outbreaks of larch casebearer. Following the release of Ag. pumila, larch casebearer numbers in Minnesota stabilized and the biocontrol effort was deemed a success. Today, defoliation of tamarack by larch casebearer is again on the rise in Minnesota, suggesting that A. pumila as a biocontrol measure is failing. While the release of A. pumila and other parasitoids is well documented in western forests, surveys for parasitoids of larch casebearer in eastern forests are lacking. We surveyed for parasitoids of larch casebearer in June 2015 near Floodwood, MN. Here, we share results of rates of parasitism and the lowest possible unit of all emerging natural enemies as we try to determine reasons behind the resurgence of this forest defoliator.