FTC in 2003

Surveys of forest tent caterpillar egg masses in central and northeastern Minnesota completed in this summer predict a sharp drop in next year?s caterpillars in all sampled areas except near Deer River, Hibbing, Virginia, Finland, and Gooseberry Falls State Park where populations will be high.

Besides the egg mass survey results, there are other clues that forest tent caterpillars will decline next year. First, a comparison of larval surveys in 2001 and 2002 found many more dead caterpillars, killed by diseases, hanging from branches and trunks in an increasing number of locations in 2002. Second, there was a great increase in numbers of the parasitic flies this year. Historically, they mark ?the beginning of the end?. These flies deposit living maggots on cocooning FTC. The maggots chew through the caterpillars? exoskeletons and feed on internal living tissues thus killing the caterpillar.

An early July collection of l00-plus cocoons from each of ten areas in central and northeastern Minnesota found a great increase in cocoon parasitism, as shown by the almost zero noise of fluttering moth wings in the rearing containers. This was borne out in August when the moths were counted and numbers of parasitic fly pupae, adult wasps, and disease-killed caterpillars tallied. The following table shows some of the results of this study. A similar study last year found an average of 24% of the moths emerged.

Caterpillar-to-moth success in 2002
Location Moths emerged
Hibbing 2 %
Deer River 10
Grand Rapids 9
Fr. Hennepin S Park 2
Bay Lake, Aitkin Co. 3
Floodwood 7
Two Harbors 4
Cloquet 5
NE Duluth 3
Gooseberry Falls S Park 5
Average 5

We feel that the outbreak is nearly over and there will be a sharp drop in the overall population of this forest insect in 2003. However, there will be some areas where forest tent caterpillars will survive in bothersome numbers, especially where they expanded into new areas this year and where their natural enemies (disease pathogens, parasitic flies, etc.) are minimal. Another type of situation where FTC could remain a problem is where night lights attracted egg-laying moths from surrounding areas, concentrating them on nearby trees and shrubs.