In a decision hailed by environmental and development groups, the European Patent Office yesterday revoked a patent granted six years ago for an anti-fungal product derived from the neem tree, which is widely grown in India, Pakistan, and Bangladesh and has been used for centuries to make medicines, insect repellants, cosmetics, and contraceptives. The scientists and activists who challenged the patent, which had been granted to the multinational company W.R. Grace and the U.S. Department of Agriculture, said it was a perfect example of biopiracy, or corporations plundering the biological resources of the developing world and claiming ownership of applications that have been known to locals for centuries. Activists hope yesterday’s decision will set an important precedent.