SAN FRANCISCO -- State agricultural authorities have expanded their efforts to stop the spread of a voracious Australian moth by imposing a quarantine on the hundreds of plants the pest eats in a five-county region.

The light brown apple moth, which feeds on everything from grapes to eucalyptus trees, was spotted in the San Francisco Bay area on Feb. 27, in what officials believe was its first appearance in the continental United States.

Since then, trappers have caught more than 170 of the invasive moths.

The quarantine restricts the movement of more than 250 host plant species the moth eats in a 182-square mile region in portions of Alameda, Contra Costa, San Francisco, Marin and Santa Clara counties.

"It's a very generous host list because the moth eats anything that's green," California Department of Food and Agriculture spokesman Jay Van Rein said Friday. "We've trapped less than 200 of these things, so it's not apparent yet how heavy the infestation is."

The tiny moths usually spread not through flight, but by laying their eggs on the leaves of trees or nursery plants, or traveling hidden inside fruit or greenwaste.

The quarantine is effective immediately for residential and community groups and commercial nurseries and gardens. To prevent the moth's further spread, its host plants and their clippings cannot be shipped until inspectors deem they are moth-free, Van Rein said.

A group of scientists from Australia, New Zealand and Hawaii assembled by the U.S. Department of Agriculture is assessing the threat in California, officials said.