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If you have pregnant mares and have noticed the growth of eastern tent caterpillars on your farm, it would be wise to consider controlling the caterpillars. In a next few weeks, mature tent caterpillar larvae will move from host trees and wander about searching for a suitable site in which to pupate and eventually emerge as moths. Large larvae can move into forage vegetation, at which time they could be consumed by horses. If this occurs, pregnant mares may experience serious foaling problems.

In Kentucky, six years ago, the equine industry suffered an epidemic called "mare reproductive loss syndrome," abbreviated MRLS. It caused the deaths of fetuses in all breeds of horses and cost the industry $336 million. The losses were initially attributed to infected Kentucky 31 tall fescue. For a while, losses were attributed to poison hemlock, a toxic plant that had been growing on many of these horse farms. Today, MRLS has been linked to eastern tent caterpillars. The current thinking of researchers at the University of Kentucky is that as horses accidentally eat the caterpillars, the hairs of the caterpillars penetrate the digestive tract of the horses and cause bacterial infections. The result is death of the fetus.

Eastern tent caterpillar larvae are hairy in appearance with fuzzy covering of white hairs protruding from their black body. They have a white stripe running the length of the back and brown and yellow lines along each side. In addition, larvae will have a row of distinct oval blue spots present on each side.

The biology of this native North American insect begins with moths laying egg masses on the limbs of several tree species including wild cherry, apple, crabapple, hawthorn, maple, pear, and plum. Egg masses containing from 150 to 400 eggs are laid in a ring around branches of the host tree where they will remain until spring. In early March the eggs hatch and larvae emerge. This insect is social in nature with larvae from individual egg masses staying together to spin a silken nest in limb crotches of their host tree. Larvae grow rapidly as they feed on developing leaves during early morning, late evening, and at night. During the day they often remain in the silken nest which protects the larvae from parasites, predators, and harsh weather conditions. In 4 to 6 weeks following emergence from the egg mass, larvae will be large in size and leave the host tree in order to locate a suitable sites in which to pupate. Moths will emerge and egg masses will be laid on host trees during late summer or early fall. Eastern Tent caterpillar is best controlled on the tree as insecticides for control on forages are limited. There are several products recommended for control on the tree.

Craig Roberts
573 882-2801
and
Wayne Bailey
573 864-9905