Proliferation of the light brown apple moth across San Mateo County in recent months has prompted state officials to put most of the Bayside in a continuous moth quarantine area, and the county is asking residents to take measures to stop the insect from spreading even further.

This week's announcement places San Mateo County cities from Millbrae to Woodside within the quarantine zone and reflects the fact that the number of male light brown apple moths in the county now stands at 286 — far fewer than in San Francisco, but still a 79 percent increase over the total detected in February.

County Department of Agriculture Commissioner Gail Raabe attributed the increase to warm spring weather, which speeds up the moth's life cycle, allowing it to reproduce more quickly. The county has no active moth-treatment program other than in Half Moon Bay and Pescadero, where pheromone-coated "twist-ties" were wrapped around tree branches in February to disrupt the moth's mating patterns.

Although the moth feeds on hundreds of different plant and tree varieties, it seems to prefer the flowers, plants and vegetables grown in greenhouses and commercial nurseries, said Raabe. That would explain why Daly City and other North County cities continue to be so widely affected by the insect. Officials suspect nurseries there imported plants containing light brown apple moth eggs from Santa Cruz. Proximity to San Francisco is also a factor.

Quarantines

have been in place in those areas for months, which means the county periodically sends biologists to 56 cut-flower and vegetable growers and 25 retail nurseries to inspect their products before they're delivered. Raabe believes that in spite of those efforts, moths now also feed on fruits and flowers in residents' backyards in San Mateo, Foster City and Woodside.

"We've detected the moth in what were previously the blank areas in the map. It no longer made sense from a regulatory point of view to have these distinct quarantines," Raabe explained.

The original quarantine zones have been in place since last April, and the county is using nearly 3,000 traps to eliminate the moths.

In an effort to contain the spread, county agriculture officials are asking residents in the quarantine zone to be very careful not to give away any flowers, plants or fruit from their backyards because they might contain unseen moth eggs. Yard waste and compost should also be kept onsite unless it is being disposed of by a licensed recycling or trash hauler.

"Not every neighborhood has the moth. You don't know you're not bringing cut flowers from your yard into an area that doesn't have them yet," cautioned Raabe. "You may think, 'Oh well, if I pick these apples or grapes to bring to someone, I'll notice there's a little green caterpillar on it.' You might, but you would have a tough time noticing if there's eggs."

The moths are likely to continue to proliferate as the state Department of Food and Agriculture ramps up its "sterile insect technique," the alternative to the aerial spraying plan denounced by many cities. The department will release the first specially bred light brown apple moths, which have been made sterile by a technology similar to an X-rayed, in the spring of 2009, with a full release in 2011.

The sterile moths will compete with normal moths for a mate. Since moths mate only once, this would disrupt the mating cycle for good.

The sterile-moth technique has been effective in battling the pink bollworm moth in the Central Valley. This pest attacks cotton crops, according to Agriculture Department spokesman Larry Lyle. It has also been used to suppress the Mediterranean fruit fly population throughout the state since the mid-1990s.

In fact, the technique has proven so effective that the department's own advisory group of international moth experts recommended it last year as the preferred method to contain the light brown apple moth.

The problem was that, at the time, everyone thought that solution would take several years to develop, according to Lyle. Biologists only recently discovered that it would be possible to produce, feed and disperse all the moths needed for this project in a shorter amount of time.

Lyle maintains that choosing the sterile insect technique had nothing to do with the hullabaloo over the aerial pheromone-spraying proposal.

"It was where the science took us, and science moves at its own pace," said Lyle. "Had we not had the breakthrough, we would have been moving forward amidst the controversy with aerial pheromone treatments."

Learn more about the light brown apple moth quarantine and treatment at http://www.co.sanmateo.ca.us//lbam.

Staff writer Julia Scott can be reached at 650-348-4340 or julia.scott@bayareanewsgroup.com.