SAN FRANCISCO — A moth with a devastating appetite for grapes is causing worries in California's San Joaquin Valley, the country's top grape growing region. The European grapevine moth, unknown to this country until late last year, has found its way to the region's heart of Fresno County, where grapes are a $725 million-a-year industry and the valley's top crop. Three moths were discovered in traps in separate locations in Fresno County over the last week, and local, state and federal agriculture officials have started an aggressive campaign to stop the invader from multiplying.