Over the last couple of weeks, in southern Wisconsin at least (Dodge, Columbia, Dane Counties), conversation and questions have noted the large number of black and orange butterflies. I’ve received several calls from field crop agronomists and consultants wondering “what is this insect?” “are Red Admiral and Painted Lady common names for the same insect?”, and “will larvae of these butterflies be of economic concern in field crops?”.  

Phil Pellitteri, entomologist and insect diagnostic specialist at UW-Madison Entomology Department, has given interviews lately on this flush of …. Red Admiral butterflies. You can learn more about the butterfly activity in a recent Daily Citizen newspaper titled “Why are there so many butterflies?” http://www.wiscnews.com/bdc/news/198955 

   

Red Admiral Butterfly (Vanessa atalanta)

Photo: BugGuide.Net, Iowa State University Entomology

 

Red admiral butterflies are dark brown to black with a broad red/orange band on the hind wings and a stripe diagonally across each forewing; tips of the forewings have a pattern of white spots. Caterpillars of this butterfly feed on various plants in the nettle family (Urticaceae), such as stinging nettle. This butterfly migrates southward during winter months. There is typically one generation per year in the northern part of the U.S. Phil Pellitteri has noticed that red admiral population surges tend to occur every 8-10 years.  

Red admiral caterpillars are not an economic concern in soybeans or other field crops. They do however, closely resemble the Painted Lady butterfly (Vanessa cardui), also active this time of year.

 

Painted Lady butterfly (Vanessa cardui)

Photo: BugGuide.Net, Iowa State University Entomology

Larvae of the painted lady butterfly feed primarily on thistles in the plant family Asteraceae, (cardui is the latin name for “of thistle”), and are referred to as thistle caterpillars. Painted lady butterflies migrate from their southern climate range and eggs can be laid in soybeans as well as thistles. While usually a minor and non-economic caterpillar in soybeans, thistle caterpillars can sporadically lead to significant soybean defoliation.

 

Thistle caterpillars make webs in upper canopy soybean leaves, draw leaves together with their silk, and defoliate from inside the curled up leaf. This caterpillar is only a concern if soybean plants are small, and the caterpillar population averages about 1 insect for every other plant across the field, or if defoliation reaches 20-25 percent (Rice 2005).

 

References

 

Downing, A. 2000. "Vanessa atalanta" (On-line), Animal Diversity Web. Accessed June 27, 2007 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Vanessa_atalanta.html

 

Rice, M.E. 2005. Thistle caterpillars – mostly minor pests of soybeans. Integrated Crop Management newsletter, IC-494(15), June 20, 2005.