Will Eastern Tent Caterpillar Numbers Continue To Climb?

Eastern tent caterpillar (ETC) numbers have been increasing steadily over the last few years in Central Kentucky. The disastrous Mare Reproductive Loss Syndrome (MRLS) outbreak of 1999-2001 is a stark reminder of the potential threat to the equine industry posed by this insect. Studies have indicated a 9- to 12-year fluctuation cycle for ETC.  It is the time to assess the situation on horse farms, both to look for resurgence of black cherry in fencerows and nearby woodlots and to check for obviously large numbers of ETC egg masses on trees that are present.  Information on checking eastern tent caterpillar egg masses is available at http://www2.ca.uky.edu/entomology/entfacts/ef449.asp.

Primary host tree

Black cherry is the main host of ETC. This shade-intolerant species does well in fencerows, abandoned fields, and along roadsides. After the ETC role in MRLS was identified, many horse farms used the effective strategy of removing black cherry trees along vast stretches of fencerow to minimize exposure risks to pregnant mares. However, black cherry readily sprouts from the soil seed bank and regrowth can develop from untreated cut stumps. Also, birds and mammals can carry in and deposit seed from nearby sources. Consequently, there has been time for this host tree to make a comeback and for caterpillar numbers to rebound.

Tent caterpillar population dynamics

The ETC and several other tent caterpillar species have biological characteristics that result in boom-and-bust population dynamics. One important factor is the batches of several hundred eggs laid by females on twigs and small branches (Figure 1). The communal silk tents allow the caterpillars to feed and develop rapidly under the cool conditions of early spring; a time when predator abundance is low, and clusters of hairy caterpillars may provide additional protection from those predators that are present. Very small increases in survival from egg to adult can lead to significant population growth. One study showed that a survival rate from egg to adult of 0.7% or greater leads to a population increase. As tent caterpillars become more abundant, natural enemies and diseases can begin to have an impact. This usually occurs after ETC numbers reach high levels.

Figure 1. New egg mass with spumaline (the shiny, varnish-like covering). (Photo: Lee Townsend, UK)

Figure 1. New egg mass with spumaline (the shiny, varnish-like covering). (Photo: Lee Townsend, UK)

It is important to catch upswings in black cherry and ETC populations so steps can be taken to protect pregnant mares from exposure to and ingestion of these insects.  Once again, removal of trees may be an effective way to reduce potential problems.


By Lee Townsend, Extension Entomologist

Posted in Forest Trees, Landscape Trees & Shrubs