Equine Initiative
Bulletin from the Livestock Disease Diagnostic Center, May 13, 2009:
"The Livestock Disease Diagnostic Center at the University of Kentucky has recently completed two necropsy cases with findings consistent with and suggestive of Mare Reproductive Loss Syndrome. One case was a late-term fetus. The other was an early fetal loss. We see a couple cases like this every year and they are considered endemic--i.e. not a reason for major concern. This is the height of the Eastern Tent Caterpillar season. We recommend that you refresh your clients' awareness on the importance of keeping pregnant mares away from areas where the caterpillars are found."
March 25 News Release:
Eastern tent caterpillar egg hatch underway, numbers trending up
LEXINGTON, Ky. (March 25, 2009) - Experts report that eastern tent caterpillars have begun hatching in central Kentucky and that their population numbers are trending up.
"Populations of the eastern tent caterpillar have increased noticeably over the past three years," said Lee Townsend, University of Kentucky College of Agriculture entomologist. "While infestations of the magnitude seen during the 2001-2002 Mare Reproductive Loss Syndrome (MRLS) outbreak are not anticipated, it is clear that eastern tent caterpillar populations are on the upswing and could be heavier than normal in some areas. Assessments and management decisions can be made in a few weeks as the silvery baseball-sized tents start to show up on branches."
According to Townsend, egg hatch is following a historically normal pattern so far this year in central Kentucky. While daily temperatures will determine the development rate of the caterpillars, there is no way to predict areas where caterpillar numbers will be higher or lower. Entomologists will be closely monitoring caterpillar development over the next two to three weeks.
"Eastern tent caterpillars are early spring insects and can cope with the erratic weather patterns that can occur in March and April. Development, including egg hatch, occurs when the temperature is above 37 degrees Fahrenheit. At 50 degrees, it takes about a month for all eggs to hatch. Warmer conditions will promote hatch over a shorter period of time and give a more uniform population," he said.
According to entomologists, small caterpillars will soon be moving to feed on the leaves that have begun appearing in trees and will build tents at branch and limb forks. The caterpillars will then begin moving from branches to large limb angles within the trunk. Entomologists anticipate full-grown larvae by the third week of April. By the end of April to the beginning of May, caterpillars are likely to be dispersing from trees. A few weeks later, the caterpillars will leave the trees where they've eaten the available foliage and search for food to complete their development.
Once the caterpillars have reached these dispersing stages, controlling them becomes much more difficult, Townsend said. If needed, control should target caterpillars while they are gathered together in the trees.
However Townsend cautions against spaying too early.
"Poor early control in previous research has resulted in a recommendation against very early sprays against small caterpillars," he said.
Controlling eastern tent caterpillars is vital to area horse farms, as UK research has strongly linked the caterpillars with outbreaks of 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.
Epidemiological and field studies conducted by UK researchers demonstrated that MRLS was associated with unprecedented populations of eastern tent caterpillars on horse farms in Kentucky. Studies since the 2001-2002 outbreak have subsequently revealed that horses will inadvertently eat the caterpillars and that 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.