Cabbage Family Carnage

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Filed under Outdoor Notes

November 11, 2011

Just before the recent snowstorm, I noticed that something was eating the mustard greens in my garden. I wasn’t too concerned; I figured the snowstorm would get rid of the little mustard-munching miscreants.

Mustard Greens

Mustard greens should look something like this.

Wrong again. In a week that included a foot of snow, two frosts, and one hard freeze, the mustard bed was devastated.

Damage from Purple-backed Cabbage Worm

Mustard should not look like this

Purple-backed Cabbage Worm (Evergestis pallidata)

The culprit.

The culprit was a little spiky-looking caterpillar. I assumed it was some kind of Pierid butterfly—a White or a Sulphur of some type. Several Pierids will eat anything in the cabbage family (Brassicaceae), which includes mustard.[1]

I took a couple of pictures, assuming that it would be easy to identify.

It wasn’t.

Now, until fairly recently, identifying caterpillars was almost impossible for all but the specialist with access to an extensive library. That all changed in 2005 with the publication of David L. Wagner’s Caterpillars of Eastern North America. Wagner’s book describes over 700 species; it is a tour de force, and it has never let me down—until now.[2] The culprit was not in Wagner, but all the Pierids for our region were. This caterpillar was not a Pierid.

So I got on the internet and yelled for help, and Curtis Lehman, the Pennsylvania Regional Coordinator for Butterflies and Moths of North America, was kind enough to make the ID: Evergestis pallidata—the Purple-backed Cabbageworm.[3]

Identification in hand, I went online and found a wealth of information…in German and Finnish and Swedish and French. Apparently it is a rather common little critter in Europe (in England the adult moth is known as the Chequered Straw). I could not tell whether or not it was a native to Europe and North America or an invasive.

It is apparently not all that well known in the States.

I have never seen the adult—that I know of. It is not a particularly striking moth (this link will take you to the Moth Photographers Group page for the species).

Knowing that it was devastating vegetable crop, I figured that the extension agency would have some information. But the Penn State Agricultural Extension does not list the Purple-backed Cabbageworm as a pest.

Moving north, I learned that, in Connecticut, the Purple-backed Cabbageworm “sometimes feeds on leaves, webbing them together, or bores into the stem and roots. There are 2-3 generations per year and the late generation is most damaging. This insect is rare, however, and control is not usually necessary. “[4]

Certainly this qualifies as a late generation, and it surely was most damaging, but the insect is not rare enough for my taste—which runs toward mustard greens sautéed with onions and a little bacon—without caterpillar bits.[5]

Control is looking like a real good idea.

Continuing north, I found a site from Newfoundland that partially answered the question of origins:

“This is a decidedly northern species…found throughout most of Canada except for British Columbia, and as far south as Virginia and Kentucky in the eastern United States, and northern Arizona in the West. It is likely of European origin, but has been in North America at least since 1869. It is recorded as a pest principally in Canada’s Maritime Provinces.”[6]

So it “likely” came from Europe, which is where it was first described, in 1767, by a German parson named Johann Siegfried Hufnagel, who was living in what is now Poland. Parson Hufnagel is one of those marvelous amateur folks who, in the early days of scientific classification (Linnaeus was still alive), contributed his lasting little bit to the body of knowledge. In a two-year furor scribende, he published thirteen separate papers in the Berlinisches Magazin, one of the earliest natural history journals. To this day, he  still credited with the description of more than 80 species.

Not bad for a country preacher.

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[1] This used to be Cruciferae. I don’t know why they changed it; I’m sure they had a reason.

[2] Wagner’s book describes over 700 species. However, there are more than 12000 species of moths—and hence moth caterpillars—in North America. Throw in another 700 and some butterfly caterpillars, and while you’re at it, toss in several dozen sawflies—whose larvae look a lot like caterpillars. Obviously, no field guide can show them all.

[3] Because there is not enough confusion between common names, which change from place to place and language to language, and Latin names, which change at the caprice of science, lepidopterists have adopted yet another system for categorizing moths: the Hodges Number, which is based on an out-of-date checklist published in 1983. For those interested, Evergestis pallidata is Hodges number 4897.

[4] Connecticut Agricultural Experiment Station. Cabbage (Brassica), http://www.ct.gov/caes/cwp/view.asp?a=2823&q=377594 (accessed November 10, 2011).

[5] According to my cook, greens are easy. First, wash the greens (remove the caterpillars). Sautee some onions and bacon until lightly brown, pour in some chicken broth and steam the greens until tender. If I missed anything, it’s not her fault.

[6] Florence Grovida Gardening. Vegetable Pests, http://www.grovida.com/vegetable-pests/purplebacked-cabbageworm-evergestis-pallidata-hufnagel-lepidoptera-pyralidae.html (accessed November 10, 2011).

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