Biowarfare. Bacteria can kill larvae of the Colorado potato beetle.

Bugs to Battle Beetles

ORLANDO, FLORIDA--Scientists have found new weapons in the battle against the Colorado potato beetle, a pest whose appetite costs American farmers some $100 million a year in lost crops and control measures. Three species of bacteria can kill the beetles, the researchers reported here on 21 May at the annual meeting of the American Society for Microbiology. The finding could lead to new organic pesticides, or even transgenic potatoes that resist the beetles.

Bacteria are rarely used to thwart insects, but there is one well-known--and wildly successful--example: Bacillus thuringiensis, a bug whose toxin, Bt, is applied widely in pest control. The gene for Bt has also been cloned and built into corn, soy, and other crops. These insect-resistant varieties require less pesticide. But the Colorado potato beetle, which likes to munch on potato, eggplant, and tomato plants, is developing resistance against Bt, as it has to many chemical pesticides in the past. "If anything can be considered a superbug, it is the Colorado potato beetle," says entomologist Glenn Holbrook of Pennsylvania State University, University Park.

Looking for alternatives, Phyllis Martin and Teddi Shropshire of the U.S. Department of Agriculture's research center in Beltsville, Maryland, mixed high concentrations of different microbes into pellets of an artificial beetle diet, which they fed to beetle larvae. One of the microbes, Serratia marcescens, was known to hurt insects; the strain the researchers used came from a diseased termite colony. It killed about 45% of the beetle larvae in 5 days. But a bacterium isolated from forest soil, called Chromobacterium violaceum, was even more effective, killing 90% of the larvae in 3 days. The champion was a light-emitting bug, Photorhabdus luminescens, that was 100% lethal.

The finding may lead to new control methods, Holbrook says, although he notes that the high doses of bacteria used in the trial would be difficult to apply to crops. But there are other strategies, Holbrook says, such as spraying the bacterial toxins themselves--if they can be identified--or building their genes into plants.

Related sites

To find the presentation abstract, search here for "Colorado" in the presentation title and "Martin" as the presenter
More about the Colorado potato beetle, from the University of Vermont
USDA's Beltsville Agricultural Research Center