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April 18, 2003

Eastern Tent Caterpillar Update

Lee Townsend, Extension Entomologist
Department of Entomology
University of Kentucky College of Agriculture

The next 3 weeks is a critical period in terms of minimizing exposure of pregnant mares to Eastern Tent Caterpillar (ETC) larvae. The caterpillars are still aggregated on trees and are at their most vulnerable stage in terms of control. While the overall ETC population is greatly reduced compared to recent years, there are some pockets where tents are relatively abundant.

ETC larvae are present in a wide range of sizes now. Some of the earliest hatched caterpillars are over an inch long while those from eggs that were among the last to hatch are in the one-half inch range. Many smaller groups of caterpillars from individual egg masses have moved to join other colonies on the tree in larger tents near or on the trunk. These are enlarging significantly as the accumulated caterpillars grow and continue to add layers of silk.

Most caterpillars now exceed the size range in which they are most susceptible to Bt-based sprays and it is nearing the end of the optimum timing window for tree injection. Accessible nests can be destroyed or treated with a pyrethroid spray.

ETC should remain on the trees for about two weeks and will continue to feed until mature. They are unlikely to abandon their current site as long as there is enough foliage to support them and they are not ready to pupate. In previous years early movement of caterpillars occurred as they defoliated their home trees and were forced to move (about May 1). This would be about the time to check locally high populations so that control could be initiated before they disperse. In most instances this season ETC numbers are not great enough to defoliate moderate to large trees. They should remain in place and leave their trees to find pupation sites in about 2 weeks. Last year ETC cocoons were being spun about May 10.

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