Science Services
Rediscovery of the Rosinweed moth

DNR Researcher Rich Henderson collected a few insect larvae that he noticed were causing heavy feeding damage on the prairie wildflower rosinweed (Silphium integrifolium). He reared these to adult stage, and they turned out to be a small moth. Rich passed the moths along to Les Ferge, an expert lepidopterist in Madison. Two years and a couple more experts later, the moths were identified as Tabenna silphiella, in the moth family Choreutidae.

Rich's collection and the identification process were no small achievements, as this particular species had previously been known by only eight other specimens, and no larval information had been gathered since the species was first described from specimens collected from rosinweed in northern Illinois in 1881!

Formal publication of these findings are forthcoming. Meanwhile, this page is meant to provide hobbyist and experts alike with information that will enable them to look for and identify the rosinweed moth on their own, either through feeding sign or by rearing out larvae to adults.

Collection of voucher specimens (see below) will add greatly to our knowledge of the distribution and life history of this species, but others may wish to rear out adults for the fun of it.

Typical feeding damage on rosinweed caused by the larvae of Tabenna silphiella.The earliest sets of leaves are most affected, during the months of May and June. The plant continues to grow through the attack, producing new leaves. After the larvae pupate, usually in mid June, the plant will continue to grow and produce new leaves not affected by the feeding.

Note the window-pane feeding pattern and the silken webbing that pulls the leaf edges together. Larvae live solely within this webbing as individuals or small colonies.

Photo taken by Rich Henderson, WDNR

A minute (10-12 mm) Tabenna silphiella caterpillar feeding on Rosinweed.

Photo taken by Eric Metzler, Ohio Lepidopterists Society

Photo taken by Eric Metzler, Ohio Lepidopterists Society

A silken cocoon of Tabenna silphiella. The cucoon is often built under the webbing in which the caterpillar lived. Note window-paning, black frass within the webbing, and the caterpillar at right center (hard to see).

How to rear caterpillars to adult moths

Caterpillars are not visibly active during the day and tend to stay under their webbing, so it may be difficult to see them directly. If you find rosinweed that shows signs of feeding, cut the affected stem below the sign late in the caterpillar stage, somewhere in early to mid June.

The cut stems can be treated in a number of ways, but perhaps the simplest method is to place the ends in a watering tube, or through a hole cut in in the bottom of a paper cut, and then place the stems in water. The plant material will remain fresh, and the caterpillars will continue to feed. Once the caterpillars form cocoons, it is no longer necessary to keep the stems in water. Place the cut stems in a small container such as a glass jar, assuring that air can get into the container without the moths getting out. If you wish to collect voucher specimens, place the container in a freezer once the adults emerge. This will kill the moths without damaging the wings or scales (the photographs below are from just such specimens).

Educators and hobbyists may wish to release and observe the moths in flight.

One result from this rediscovery is that the rosinweed moth is only as rare as its host plant, at least in Wisconsin. The lesson to be learned here is that if you look in the right place, and ask the right questions, real scientific discovery can be as near as your own backyard.

A top view of Tabenna silphiella.This striking species is roughly a centimeter long.

Photo taken by Eric Metzler, Ohio Lepidopterists Society.

For more information on this topic please contact:

Rich Henderson
Wisconsin DNR Research Center
Monona, WI 53716
hender@dnr.state.wi.us