Five hundred and thirty two early and late term foal abortions occurred in thoroughbred horses in central Kentucky between April 28 and May 23 of 2001. Elevated, possibly toxic levels of cyanide were detected upon toxicological evaluations of 3 aborted foals and 1 mare. During this time period, high populations of Eastern Tent Caterpillars (ETC, Malocosoma americanum), were observed on many of the horse farms suffering losses. ETC larvae are known to feed on cyanogenic Black Cherry (Prunus americanum) suggesting the hypothesis that ETC may have contributed to foal loss by delivering cyanide to horses. Qualitative and quantitative cyanide assays were performed to assess this hypothesis. Cyanogenic compounds in ETC larvae were at the levels found in leaf foliage in the foregut where freshly ingested plant fragments were visible. ETC frass (feces), water containing drowned and floating ETC larvae, wandering larvae and starved larvae (6h or longer before assay) had little or no detectable cyanide or precursors. Results obtained correlate with existing literature of insects which feed on cyanogenic plant materials and indicate that ETC act to detoxify cyanide and cyanogenic precursors before allowing the leaf material to leave the insect foregut. Results indicate that ETC larvae would not efficiently deliver cyanogenic plant material to vertebrate herbivores as cyanogenic potential of larvae is approximately 10% that of plant material. Grazing horses are most likely to encounter starved or wandering larvae (as they are on the ground) and these have very low cyanogenic potential. Therefore, a direct role of ETC larvae in contributing to cyanide toxicity in horses is difficult to envision. An indirect contribution to cyanide toxicity has not been completely ruled out but would require more complex mechanisms than simple ingestion of ETC larvae or frass.
Species 1: Lepidoptera Lasiocampidae Malocosoma americanum (eastern tent caterpillar)
Keywords: horse abortions, cyanide
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA