Scientists injected 2,200 corn stalks with a microbe effective against the destructive European corn borer Thursday in the first approved outdoor test of a genetically engineered ``plant vaccine.'' Environmental groups did not oppose the tests, which were approved by the U.S. Environmental Protection Agency and the Department of Agriculture. The tests of the Cxc-Bt at the federal experimental station here are the first approved of a genetically altered ``plant vaccine,'' said Peter Carlson, chief scientist of Crop Genetics International, which developed the biological pesticide. Cxc-Bt was also injected into an acre of corn owned by Crop Genetics on Maryland's Eastern Shore, a company spokesman said. Only one other genetically engineered crop protector, Frostban, a frost-inhibiting microbe, has been approved for field testing by the EPA. ``I think the result could be reduced use of chemicals for crop protection,'' Carlson said. He said that would be ``good for farming, good for the environment and good for the food supply.'' The corn borer, a moth larva introduced to the United States in 1908, is one of agriculture's most destructive pests, attacking about 200 plant species, Crop Genetics said. It costs American farmers $400 million a year, according to the U.S. Agriculture Department. The Audubon Society and Environmental Defense Fund took a wait-and-see attitude. The important question is whether testing and regulation will be adequate because Cxc-Bt is just the beginning of a rush of perhaps hundreds of similiar products, said Maureen Hinkle, the society's director of agriculture policy. Carlson said the main purpose of the test is to determine whether the pesticide will spread from plant to plant, an undesireable effect. The microbe works by attacking the alkaline stomach of corn borers, giving them ulcers. It doesn't affect humans, according to researchers. In previous laboratory experiments, the microbe killed the borers in petrie dishes and sickened them when tested in a greenhouse, the company said. Jeremy Rifkin, president of the Washington-based Foundation on Economic Trends, said the pesticide hasn't been shown to work in greenhouse tests and has lowered corn yields during some tests.