Early tent caterpillar hatch prompts reminders about MRLS

An abnormally warm KY spring is creating favorable conditions for these pests while prompting reminders about MRLS.

Eastern tent caterpillars (ETCs) have begun to hatch ahead of schedule in Kentucky, according to a news release posted March 6 by the University of Kentucky College of Agriculture, Food and Environment on its website. Entomologists from the college say that the abnormally warm spring has created favorable conditions for an early annual hatch.

Source: University of Kentucky College of Agriculture, Food and Environment website
Steve Patton, UK Agricultural Communications

“The Eastern tent caterpillar is one of our early riser pests,” says Jonathan Larson, UK assistant extension entomology professor. “Usually, we have a couple more weeks of waiting in Central Kentucky before we reach egg hatch. However, with the strangely warm winter, we are way ahead of schedule … western counties are even further ahead, with some counties between 120 and 140 growing degree days already.”

Connection to MRLS

This could be a concern wherever there are both ETCs and broodmares in foal because of the connection to Mare Reproductive Loss Syndrome. Consumption of large numbers of the caterpillars by pregnant mares caused staggering foal losses in 1999-2001, hitting Kentucky’s Thoroughbred nurseries particularly hard.

According to the news release, “MRLS may cause early- and late-term foal losses or weak foals. UK researchers conducted studies revealing horses will inadvertently eat the caterpillars in pastures and feedstuffs. The caterpillars’ hairs, specifically the hair cuticles, can embed into the lining of the horse’s 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.

Mare management tips

“When mature, the 2- to 2.5-inch long, hairy caterpillars may wander from their host trees to seek protected areas to spin their cocoons or additional food if their natal tree becomes defoliated,” the release continues. “At such times, they may crawl along fence lines and into pastures. If practical, farm managers should move pregnant mares away from areas with abundant wild cherry trees to minimize caterpillar exposure. The greatest threat is when the mature caterpillars leave trees and wander to find places to pupate and transform to the moth stage.”

The ETC prefers to feed on cherry, crabapple, maple and apple trees, among others. The caterpillars receive their name from the silken tents they build in branch rooks and crotches to protect their nest from predators and parasitoids. ETC populations fluctuate from year to year depending on the climate, predators or pathogens.

“While we haven’t seen levels of caterpillars reach the extremes we saw during [the 1999-2001 MRLS outbreak], we do like to let people know when they have started their activity each year so that concerned horse owners can start to monitor for webs on their property,” Larson says.




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