Giving foreign bugs a green card

by D'Lyn Ford

Along with invading insects, New Mexico is battling an influx of nonnative weeds. Importing the weeds' natural enemies--foreign insects--may help take a bite out of unwanted plants like leafy spurge.

Over the past seven years, NMSU researchers have released brown and black Aphthona flea beetles in spurge-infested areas, including sites near Angel Fire, Cimarron and Philmont Scout Ranch.

"These scenic mountain meadows could be completely covered up if the spurge spreads,' says Dave Thompson, an entomologist with NMSU's Agricultural Experiment Station. That's exactly what has happened in Montana, Wyoming, Colorado and other states, where leafy spurge infests millions of acres. The weed spreads aggressively by seed and lateral roots, choking out native vegetation. Neither wildlife nor cattle graze on leafy spurge, which contains an irritating latex.

Flea beetles whittle spurge down to size, keeping it in check. "We're trying to use the beetles like a bio-herbicide," Thompson explains. Adult beetles feed on the top of the plant and lay their eggs at the base. Emerging larvae feed on the roots, preventing germination and regrowth.

Beneficial insects play a key role in integrated management of weeds, Thompson says. 'Forest and range lands are an ideal setting for biocontrol," he says. "With a perennial weed, the bugs always have food. These plants stay in place, as opposed to crops.'

Last year, Thompson carried coolers crawling with 700,000 beetles raised in Wyoming and North Dakota to12 infested locations. Releasing 160 beetles per square meter has reduced up to 95 percent of leafy spurge plant material.

To survive, the beetles can't completely devour the spurge. "Otherwise, they'd have a death wish," Thompson says. "But a few scattered stems left are no big deal. It's when a weed like leafy spurge gets so thick that it's a problem."

The quarter-inch beetles, like other "green card" bugs released for biological control, have been carefully studied to make sure they won't eat desirable vegetation. "In biocontrol of weeds worldwide, we have never had a released insect become a pest," Thompson notes.

Before insects are released, they are monitored in laboratory and controlled field settings at specialized research centers in other states. Thompson has worked with researchers in Wyoming and North Dakota to obtain beetles for the leafy spurge releases in New Mexico.

When construction of the Center for Sustainable Development of Arid Lands is complete in fall 2000, NMSU researchers will be able to do more biological control research. "Having a quarantine lab in the new building will allow us to test exotic insects here in Las Cruces," Thompson says.