An organic farm in northeastern Lancaster County is the first confirmed presence in the Western Hemisphere of a tiny but destructive pest known as the onion leafminer.

The owner of the commercial farm reported 100 percent loss of leeks, onions and chives and told investigating officials the pest had been present for several years.

That has local growers worried and both state and federal agriculture officials have sprung into action to find out how widespread and what kind of a potential threat the leafminer poses to onions, leeks, chives and shallots.

Native to Poland and Germany, the pest has spread in the last decade or so to Europe, Asia, Turkey and parts of Russia and Turkmenistan.

In Great Britain, where the leafminer, also known as the allium leafminer, showed up in 2003, it is on the Royal Horticultural Society’s list of top 10 garden pests.

The pest was discovered in Lancaster County around Christmas. Already, a quickly launched survey by plant inspectors for the state Department of Agriculture has discovered the pest also in Chester, Dauphin, Delaware, Lehigh and Delaware counties.

“The first report came in as a 100 percent crop loss. That’s something we always have to take seriously,” said Sven Spichiger, an entomologist with the Department of Agriculture.

“First we have to figure out how widespread it is.”

Spichiger said it was “entirely possible” that backyard gardeners in the area could lose their onion sets this season.

The leafminer harms plants both by the adults depositing eggs in leaf tissue, by the feeding of pupa and by the holes inviting bacterial and fungal infections.

An alert recently issued by Penn State Extension says available literature “suggests organic production and market garden productions systems tend to be most at risk.” Organic  growers are loathe to use pesticides.

Tim Elkner, a Lancaster-based Penn State Extension specialist in horticulture, said he’s hoping that if the pest has been around Lancaster County for several years without reports of damage until now, that the the leafminer won’t pose a serious threat to local growers.

He said local farmers growing a local variety of onion known as sweet onion have planted more than 100 acres and there have been signs that the pest was present but not causing widespread damage.

“I’m becoming a little more optimistic,” Elkner said.

He’s also hoping that pesticides may prove effective in combating the bug. In Europe, growers have successfully deployed covers over crops to keep leafminers out.

But when Shelby Fleischer, a Penn State professor of entomology, was asked just how much of a pest the leafminer will become,  he replied, “We really don’t know yet. I don’t think it can be good news.”

The state agriculture department will soon have recommendations for growers and the latest information on the leafminer threat on its website.