California’s most troublesome tourist, a tiny, mud-coloured moth from Australia with a taste for Napa valley’s finest grapes – not to mention all other crops and the state’s fir trees – is generating panic.

Theories as to how the moth reached the Golden State abound; the most likely is that the first entered the country on a plant imported from Australia.

By the time a retired entomologist from Berkeley found one in a trap behind his house, it was too late. The invasion was under way – resulting in a $100 million (£50 million) crisis for California’s farmers and a political battle in Washington over how future invasions of exotic pests might be prevented.

As California’s farmers have found out, the Australian light brown apple moth is a very hungry creature. It might have a passion for grapes but it will happily eat anything else grown by California’s farmers. Its caterpillars will eat everything from corn and tomatoes to cherries, peaches and plums. It is able to procreate at an astonishing pace even if its life-span is shorter than the average summer holiday.

According to the California Department of Food and Agriculture, the moth poses a huge threat to the state’s $7.2 billion annual agricultural exports. “Some countries have specific regulations against this pest and many others consider it a regulated pest that would not be knowingly allowed to enter,” the department said.

“Additional measures, such as preharvest treatments and post-harvest disinfestation, would likely have to be taken to ensure that shipments to these countries are free from [the moth].”

It added that because the moth is an exotic pest – not already established in the US – other states might impose restrictions on fruits, vegetables and nursery stock, which could “severely impact the domestic marketing of California’s agricultural products”.

So far the moth – known officially as Epiphyas Postvittana, and unofficially as the light brown everything moth, due to its indiscriminate appetite – has turned up in nine of California’s counties, with state officials estimating the cost of getting rid of them at $100 million. It has previously caused havoc in Britain, Hawaii, New Zealand, and New Caledonia.

A massive operation is underway to try to eradicate the pest, prompting memories of the Mediterranean fruit fly in the early 1980s, when tons of infested fruit had to be buried. Spraying has started in Oakley and will move to Napa Valley this week. But farmers are divided over the most effective method of eradication, with chemical pesticides pitted against less effective, but less harmful, organic products.

The battle over the Australian moth has turned political. Democrats are blaming the invasion on the Bush Administration’s decision to hand over control of agricultural border inspections to the Department of Homeland Security.

A fortnight ago the House Agriculture subcommittee voted to give control of the inspection points back to federal officials. Dennis Cardoza, the subcommittee’s Democratic chairman, called the moths terrorists, adding that Homeland Security inspectors were trained to look for illegal immigrants and drugs, not moths.

Happy eater

— The Light Brown Apple Moth is native to Australia. It only appeared in the US this year

— Six to ten days after leaving the pupa, female moths lay about 300 eggs on host plants. Larvae hatch in five to thirty days

— The larvae then feed on the plants, scarring leaves and causing fruit to drop

Sources: US Department of Agriculture; South Australia Research and Development Institute

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