The signs held by the protesters ranged from the straightforward ("stop biotech") to the witty ("resistance is fertile") to the political ("money for food, not corporation") to the amusing ("genetically modified frosted freaks") and even the profane ("buck fiotech").

Alyson C. Ewald, who came to Boston from Vermont for the conference, said she participated in the counter-demonstration because of her concern about the side effects of biotechnology.

"Like with nuclear power, it is dangerous to go with new technologies without considering the irreversible results," she said. "We have enough food to feed the whole world. It only depends on money and access to power. We need compassion and understanding, not new technology."

Protesters worried that genetic alterations in one species can affect neighboring plants and animals, like monarch butterflies they claim have been damaged by pollen from genetically modified corn.

"That's why so many people are dressed as butterflies," Ewald said.

But biotech advocates presented research to dismiss those claims.

C. S. Prakash, a participant in the conference, claimed in the Telegram and Gazette that field studies show the butterflies' exposure is too minimal to cause harm.