INSECT HOT TOPICS: Euonymus caterpillars

by James A. Bethke

Dan Gilrein is the extension entomologist at the Long Island Research and Extension Center, a part of Cornell University in New York, and he recently shared some photos that I found quite interesting. I think you will find it just as interesting. The photos were not taken during Halloween, and they’re not staged. The copious webbing you see in figure 1 is from the euonymus caterpillar (fig. 2), Yponomeuta cagnagella (Hüber), an invasive moth species (fig. 3) that was reported in New York in 1982 and reported sporadically in Wisconsin, Illinois and Michigan since 1989. It subsequently spread to Delaware and Maryland, and was found in Iowa in 2012. The native habitat of the euonymus caterpillar is in Europe, Asia Minor, the Middle East, Siberia and the British Isles. It is assumed that the euonymus caterpillar was introduced to North America through Ontario on seedlings of European spindle, Euonymus europaeus, imported from Holland.

Euonymus caterpillars are defoliators of the tree form of European spindle (E. europaeus), the spreading euonymus (E. kiautschovicus), the winged or burning bush euonymus (E. alatus), the Japanese euonymus (E. japonica), the wahoo euonymus (E. atropurpureus) and the winter creeper euonymus (E. fortunei). The young larvae are gregarious (feed in groups, fig. 2). It’s been observed that they usually begin feeding on the ends of branches and work their way toward the center of the plant. If not controlled early in their development, these caterpillars can quickly defoliate entire plants. Figure 1 represents a severe attack with complete defoliation, and the webbing is unsightly and can remain on the plant for a very long time. Euonymus caterpillars usually do not kill the host, but as you can imagine, death can occur with repeated defoliations.

Fig. 2. Aggregation of euonymus caterpillar larvae. Photo: John Sharpe, Town of Lewiston, NY.

If this invasive moth makes its way to California, I think it will be reported more quickly than most invasives because of the ghostly looking remnants of an infested plant. Regardless, we should be on the lookout for this moth. It could become quite a problem in the ornamental plant production industry due to its popularity as a landscape plant. Its presence in California may hinder movement of nursery plants due to regulations. In addition, the western burning bush, E. occidentalis, is a native species that could be severely impacted in the wild.

Web pages of interest with lots of interesting photos:

http://msue.anr.msu.edu/news/euonymus_caterpillars

http://learningstore.uwex.edu/assets/pdfs/A3633.pdf

http://www.ipm.iastate.edu/ipm/hortnews/2012/6-13/euonymuscaterpillar.html

http://www.gov.pe.ca/af/agweb/index.php3?number=74328

http://plantdiagnostics.umd.edu/level3.cfm?causeID=63

http://greenindustry.uwex.edu/problemdetails.cfm?problemid=50

http://www.natgeocreative.com/photography/1163764

http://msue.anr.msu.edu/news/euonymus_webworm_causing_some_damage_to_burning_bush_around_grand_rapids_mi

James A. Bethke is Farm Advisor for Nurseries and Floriculture, UC Cooperative Extension, San Diego and Riverside Counties.