UK Home (Global Connections) College of Agriculture
Veterinary Science
Mare Reproductive Loss Syndrome Index Page

May 2, 2002

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


Eastern tent caterpillars are starting to complete their development and are beginning to leave trees in search of pupation sites (in preparation for change into the adult or moth). This natural part of their life cycle will continue over the next two weeks. The caterpillars will crawl away from the trees in which they developed and will spin silken cocoons under most any ledge or in crevices. During this time they may move several hundred feet from the trees in which they were feeding. In the case of heavily infested trees that are stripped of their leaves before the caterpillars have finished feeding, there will be dispersal to find trees on which to complete their development.

Wandering eastern tent caterpillars may accumulate on suitable trees, fence posts, and barn walls. Accumulations of these caterpillars should be destroyed to prevent pregnant mares from being exposed to them. Concentrations on fences can be brushed into buckets of soapy water.

Inspect fence row trees regularly for tents. Pole pruners or saws can be used to drop the nests, which can be bagged and discarded. This should be done during the middle of the day 10 am to 2 pm when most of the caterpillars are in or on the nest. Efforts to control eastern tent caterpillars should be directed to larvae still in trees.  In this situation, they are concentrated and treatments can be focused.  Once the caterpillars have left the trees and are dispersing the chances for successful control diminishes greatly.

Insecticides for Current Use

Synthetic pyrethroid insecticides are capable of providing quick knockdown of caterpillars.  Several products are registered for application to a wide range of sites, making them viable alternatives for eastern tent caterpillar control in many situations. None, however, is registered for application to pastures. Here are some options:

A 2-foot to 3-foot wide band of bifenthrin, cyfluthrin, or permethrin, sprayed around the trunk of infested trees may be helpful in killing caterpillars as they move down the trunks of infested trees to disperse prior to pupation.  It also may be helpful in controlling larvae leaving defoliated trees in search of more food.

Caterpillars in Pastures

Wandering larvae are active crawlers that can move long distances from the trees on which they develop.  While the carbamate insecticide carbaryl (e.g. Sevin - 14 day graze or harvest interval) is labeled for application to pastures for insect control, the potential for killing many larvae by broadcast insecticide sprays is very low.  The caterpillars are not feeding on grass so there no chance for stomach poison activity.  Contact with treated grass may not be sufficient to kill them.  In addition, caterpillars will be moving over the next 2 weeks or longer so their behavior is not synchronized enough to put all of them in an accessible location once they have abandoned the trees.

Physical Barriers

Burlap barriers can be placed as a complete band around the trunk of trees where tents cannot be reached and the burlap coated with TangleFoot spray - a very sticky material. This can be used to capture caterpillars as they crawl down the trunk to disperse. The bands must be checked regularly, accumulations of trapped caterpillars can form a bridge across which others can move. Replace and re-treat the band as needed.  Check ornamental crabs and cherry trees around paddocks and barns for tents and remove and destroy them.

Bacillus thuringiensis(Bt) sprays

During the early portion of the 2002 eastern tent caterpillar season, insecticides based upon Bacillus thuringiensis were the products of choice because there were no grazing or harvest restrictions on the labels.  Bt products must be ingested to control caterpillars, they have no contact toxicity, even when sprayed directly onto the insects.  This makes them ineffective against large caterpillars that have stopped feeding and are wandering in search of pupation sites.

Veterinary Science Home Page
UK Equine Research Foundation Home Page
College of Agriculture Home Page
UK Home Page