I recently received a report from Dennis Epplin, crop systems educator in Mt. Vernon, about blister beetles stripping some corn plants, including the silks, in a cornfield in Jefferson County. He had been finding intense, localized infestations of blister beetles in alfalfa and soybeans earlier this summer, but the infestation he encountered in corn was the most severe. Although the infestation was not economic (from a whole-field perspective), the injury was devastating in small areas of the field. And to prove his point, Dennis sent three good photographs of clusters of the striped blister beetle feeding on corn leaves and corn silks.
Striped blister beetles feeding on corn leaves (photograph courtesy of Dennis Epplin, Mt. Vernon, IL).
Striped blister beetles feeding on corn silks (photograph courtesy of Dennis Epplin, Mt. Vernon, IL).
Corn silks clipped off by striped blister beetles (photograph courtesy of Dennis Epplin, Mt. Vernon, IL).
Although most of us have probably seen clusters of blister beetles feeding in alfalfa or soybeans, Dennis's observation of these pests in corn is a first for me. Their clipping of fresh silks resembles injury caused by Japanese beetle or corn rootworm adults; the injury they cause by feeding on leaves resembles injury caused by many other defoliators in corn, including armyworms and grasshoppers.
The striped blister beetle is about 1/2 inch long, with prominent orange and black stripes. Other characteristics shared by several species of blister beetles are a broad head; narrow "neck" (prothorax); long, slender legs; and long, pliable wing covers that cover most of the abdomen. As alfalfa producers know, blister beetles produce cantharadin, a toxin that causes painful blisters when it contacts mammalian tissues. Cantharadin can be especially toxic to horses that feed on hay infested with blister beetles. In addition, blister beetles have been implicated as possible vectors of bean pod mottle virus in soybeans.
On a good note, blister beetle larvae are predators of grasshopper eggs, destroying as many as 24% of the eggs in an area. Because of this, blister beetles usually are more prevalent during a year when grasshoppers are common and during the following year. In addition, blister beetle adults also are known to feed on pigweed.
We consider blister beetles to be more beneficial than pestiferous (although their presence in alfalfa hay is a notable exception). Therefore, it's best not to overreact to their presence, even though injury to the plants can be quite severe in areas of the field where the beetles congregate.-- Kevin Steffey