Eastern Tent Caterpillar Egg Hatch Under Way, Numbers Up Again

Experts report Eastern tent caterpillars are hatching in Central Kentucky in increasing numbers.

"Some tents are the size of baseballs now, so they will be easy to see," said Lee Townsend, PhD, a University of Kentucky College of Agriculture entomologist. "Caterpillars in tents out on limbs are now relocating and building large tents on branch angles on the main trunks."

According to Townsend, now is the time to check wild cherry and related trees for Eastern tent caterpillar activity to determine whether or not any management is necessary.

"Tent caterpillar populations have been gradually increasing over the past two to three years and seem to be up again this year," Townsend said. "Populations vary considerably from location to location in a county."

Entomologists anticipate full-grown larvae by the third week of April. From the end of April to the beginning of May, caterpillars will likely leave the trees where they’ve eaten the available foliage and search for additional food to complete their development.

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 the 2001-2002 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 that demonstrated 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, whose 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 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.

Holly Wiemers, MS, is communications director for UK’s Equine Initiative.

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More information on Gluck Equine Research Center and UK's Equine Initiative.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.