Corn Rootworms Outwit Genetically Modified Seed

My genealogical roots deep run through many a corn field since I was born from a Nebraska-farm girl mother and an Indiana-raised father. Field corn. Popcorn. Sweet corn. You name the corn, my relatives planted it. Several decades back I even grew ornamental corn one summer to decorate Christmas wreaths. So needless to say I was riveted to a recent Wall Street Journal article about how Mother Nature is outsmarting genetically modified corn seed. (Ian Berry, “Pesticides Make a Comeback”, Wall Street Journal, May 22, 2013, p. B-1.)  

Seems that entomologists at the University of Illinois and Iowa State University found corn rootworms immune to Monsanto’s Bt (Bacillus thuringiensis) gene. That gene was originally designed to shield corn crops from this pest that feeds on leaves, tassels and silks; injures roots and can stunt or kill young shoots and plants.

The article also points out that last year America’s farmers planted 97 million acres in corn based on increasing prices and EPA approval touting reduced insecticide use that would give growers and farm workers “greater safety, protect water bodies from runoff and mitigate” harm to wildlife.

“Some of those gains are quickly being reversed,” said Michael Gray, a UI entomologist quoted in the story, who went on to say that next year over a quarter of corn farms plan to use insecticides as “cheap insurance.”

Makes senses now why sales are up for pesticide producers. To read the entire article, log on to WSJ online or review a similar story “Pesticides make a comeback against Monsanto seed” at

http://www.bignewsnetwork.com/index.php/sid/214688991/scat/3de2685784ae51b               

Frankly, I wanted to know exactly what this crawly critter chomping on corn crops looked like. During my research of “corn rootworms,” I discovered crop damage is not limited to larvae but includes the adult — two familiar beetles often found in our own backyard vegetable patch that also feeds on cucurbits, legumes and grasses — the Western striped cucumber beetle (Acalymma trivittatum) and the Western spotted cucumber beetle (Diabrotica undecimpunctata undecimpunctata). (See UC IPM Pest Management Guidelines: Corn, plus UC ANR Publication 3443.  Also UC IPM Pest Management Guidelines: Curcurbits, plus UC ANR Publication 3445.)

Photos below are of the Western striped cucumber beetle and the Western spotted cucumber beetle).  

Western striped cucumber beetle - source: UC IPM website

Western spotted cucumber beetle - source: UC IPM website

And there’s more. In fact, there’s also a banded cucumber beetle (Diabrotica balteata) and a spotted cucumber beetle (Diabrotica undecimpunctata howardi), also known as the Southern corn rootworm. In addition, there’s the Northern corn rootworm (Diabrotica barberi Smith & Lawrence), and the Western corn rootworm (Diabrotica virgifera virgifera LeConte).

When you compare the above two photos with photographs on Purdue University’s IPM website, you’ll notice that our Western spotted cucumber beetle looks identical to the Southern corn rootworm and that our Western stripped cucumber beetle appears the same or similar to the female Western corn rootworm. Plus, there’s a photo of the larvae -- the actual rootworm.  Here’s the Purdue IPM link:

http://extension.entm.purdue.edu/fieldcropsipm/insects/corn-rootworms.php

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