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New Mexico State University

New Mexico State University

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Drought Increases Populations of 'Hit-and-Run' Beetles

LAS CRUCES - When Carol Sutherland began hearing unusual reports of mysterious gaps appearing in New Mexico farmer's fields this spring, something snapped. The entomologist with New Mexico State University's Cooperative Extension Service immediately thought of click beetles.



Just as many of New Mexico's crops were beginning to germinate, last winter's dry weather showed up as a jump in the number of click beetle larvae. Sometimes called wireworms, the larvae bore into the plant's delicate tissues. (05/24/2002) (Courtesy Photo by H. Leroy Brooks)

Just as many crops were beginning to germinate this growing season, last winter's dry weather showed up as a jump in the number of click beetle larvae, sometimes called wireworms, as well as another troublesome member of the beetle family, the false wireworm.

"Sometimes the cause of the damage can be very difficult to find because it happens fast - boom - and the beetle larvae moves on," Sutherland said. "It's kind of hit-and-run in a way because the plant just appears to dry up and die. Finding bite marks on the stem or roots is difficult, and catching the larvae in the act is rare."

The beetle larvae feed at soil level or just below, boring into the plant's delicate tissues. "Just a few bites into these seedlings and they're toast," Sutherland said. The beetles invade chile, corn, cotton and alfalfa, along with wheat, other small grain crops and vegetables that were planted early this spring or last fall, she said.

They lay their eggs near these succulent plants. When the larvae hatch, they graze on available plant roots. Some have life cycles in which they spend more than a year in this damaging larvae stage.

New Mexico's continuing drought favors the beetle grubs. In dry conditions they search for food and moisture, and the most numerous plants out there may be crops. However, the beetles also live in desert environments and some range grasses.

"Some spend their entire life cycle away from cultivated agriculture in adjacent rangeland," Sutherland said. "Others are commonly seen wandering around vegetation in valley areas, including irrigated crops."

They get the name click beetle because of their ability to snap their thorax when placed on their backs or held between the fingers. Adults are reddish-brown to dark brown, trim, slender, hard-shelled beetles about a third to a half inch long. They're often seen flying into lights at night during the summer months.

Wireworm eggs are seldom seen because they are deposited in the soil. A female beetle lays several hundred tiny, pearly white, eggs in the soil. The grubs normally encountered while digging around on damaged plants are from a quarter- to three-quarters of an inch long, yellowish-brown, cylindrical, slender and very firm to the touch. False wireworm larvae look very much like click beetle larvae, but aren't as firm.

After the larvae take a bite of seedling plants, there's not a lot anyone can do to help the tiny plants survive, Sutherland cautioned. Preparation and planning for potential damage go a long way in controlling these insects, she said. Prevention of wireworm damage requires appropriate insecticidal treatments before or at planting time.