Eastern Tent Caterpillar Numbers Up Again

Numbers of Eastern tent caterpillars, which are linked with outbreaks of Mare Reproductive Loss Syndrome, are up for the third consecutive year.
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Numbers of Eastern tent caterpillars, which are linked with outbreaks of Mare Reproductive Loss Syndrome, are up for the third consecutive year.

April 20, 2010 -- Experts report that eastern tent caterpillar numbers are up for the third consecutive year, although populations vary from location to location.

According to Lee Townsend, University of Kentucky (UK) College of Agriculture entomologist, now is the time to check wild cherry and related trees for eastern tent caterpillar activity to determine whether management is necessary.

"The tents are easy to see now," he said. "Many of the small nests out on limbs have been abandoned because caterpillars have moved to larger tents at branch angles on the main trunks."

Entomologists anticipate full-grown larvae by the third week of April. From then through early May, caterpillars will leave the trees where they've been developing and disperse to protected sites to spin a cocoon and pupate. Once the caterpillars have reached these dispersing stages, controlling them becomes much more difficult, Townsend said.

Controlling eastern tent caterpillars is vital to area horse farms, as UK research has strongly linked the caterpillars with outbreaks of Mare Reproductive Loss Syndrome (MRLS), which can cause late-term foal losses, early-term fetal losses and weak foals.

During the 2001-2002 MRLS outbreak, an estimated 30 percent of that year's Thoroughbred foal crop was lost, and the state suffered an economic cost of approximately $336 million due to losses suffered in all breeds of horses.

UK researchers conducted epidemiological and field studies, which demonstrated that MRLS was associated with unprecedented populations of eastern tent caterpillars on Kentucky horse farms. Studies since the 2001-2002 outbreak subsequently have revealed that horses inadvertently will eat the caterpillars and the caterpillar hairs embed into the lining of the alimentary tract. Once that protective barrier is breached, normal alimentary tract bacteria may gain access to and reproduce in sites with reduced immunity, such as the fetus and placenta. Fetal death from these alimentary tract bacteria is the hallmark of MRLS.

UK entomologists recommend that unless horse farm managers have been aggressive in managing eastern tent caterpillars, or removing host trees, they should keep pregnant mares out of pastures bordered by cherry trees or other hosts for the next several weeks.