Beetle May Have Role in Leafy Spurge Battle

Leafy spurge, an invasive noxious weed that is a major problem in North Dakota and other northern plains states, is considered a prime candidate for biological control methods because it tends to infest rangeland and other noncultivated areas where chemical control is not economically feasible. Biological agents used in the fight against spurge range from tiny flea beetles to sheep and goats.

North Dakota State University researchers are working with a small beetle native to Italy that may occupy a niche in the arsenal of anti-spurge agents.

According to Denise Olson, an assistant professor in NDSU’s Department of Entomology, Oberea erythrocephla, commonly known as the longhorn beetle, could play a valuable role in biocontrol of leafy spurge, even though its impact is less dramatic than that of the more familiar Aphthona flea beetles.

The longhorn beetle larvae feed on spurge stems rather than on roots like the Aphthona larvae. It takes longer to reduce spurge stands, and the Oberea alone probably never would reduce a large infestation, Olson says. The Oberea also reproduce more slowly, with females producing about 60 eggs compared to 100 to 300 per female flea beetle.

She says the Oberea may prove valuable in areas where the flea beetles have not been successful. The flea beetles are most successful where leafy spurge forms fine root hairs very near the soil surface. In areas where climate or soil types make the spurge plants send down deep taproots, the flea beetle larvae don’t feed as well.

Oberea feeding habits are different. The longhorn beetle females first girdle the spurge plant stem, draining the latex, which is toxic to the larvae. They then drill holes in the stem above the girdling point and deposit eggs. The larvae burrow down the stem into the root crown, damaging the spurge plant.

Olson is working with TEAM Leafy Spurge, a USDA-funded program that involves the four-state region of North and South Dakota, Montana and Wyoming. The NDSU researchers have established Oberea sites near Medora, N.D., Camp Crook, S.D., Ekalaka, Mont., and Sundance, Wyo. There is also a colony of beetles established near Kindred, N.D. Oberea have been collected from this colony to establish the western sites plus a research site near Kindred and one near Towner, N.D.

The Oberea beetles were first released at the research sites last year, with 800 adults per site. Another 200 beetles were released at each site this year. The researchers are looking for signs of egg depositing and larvae feeding on spurge stems, and are taking spurge stem counts to determine if any reduction is occurring.

After the first year, says Olson, they have observed egg depositing and girdling of stems. Stem counts indicate that the spurge stands have been reduced, though the reduction may not be obvious.

Olson believes the best role of the longhorn beetle may be as a complement to other control methods, keeping stands of leafy spurge at low levels after they have been reduced by other means.

There is considerable interest in the longhorn beetles in areas where leafy spurge is bad and the flea beetles have not been effective, Olson says. "We wish we could give them something that will perform like the flea beetles, but we just don’t have it right now," she says. "We’re trying to see where the longhorn beetle fits in, where its role is going to be."

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Source: Denise Olson, (701) 231-6292
Editor: Gary Moran, (701) 231-7865