FRESNO, Calif — Dozens of foreign insects and plant diseases slipped undetected into the United States in the years after 9/11, when authorities were so focused on preventing another attack that they overlooked a pest explosion that threatened the quality of the nation's food supply.

At the time, hundreds of agricultural scientists responsible for stopping invasive species at the border were reassigned to anti-terrorism duties in the newly formed Homeland Security Department — a move that scientists say cost billions of dollars in crop damage and eradication efforts from California vineyards to Florida citrus groves.

The consequences come home to consumers in the form of higher grocery prices, substandard produce and the risk of environmental damage from chemicals needed to combat the pests.

An Associated Press analysis of inspection records found that border-protection officials were so engrossed in stopping terrorists that they all but ignored the country's exposure to destructive new insects and infections — a quietly growing menace that has been attacking fruits and vegetables and even prized forests ever since.

"Whether they know it or not, every person in the country is affected by this, whether by the quality or cost of their food, the pesticide residue on food or not being able to enjoy the outdoors because beetles are killing off the trees," said Mark Hoddle, an entomologist specializing in invasive species at the University of California, Riverside.

Homeland Security officials acknowledge making mistakes and say they are now working to step up agricultural inspections at border checkpoints, airports and seaports.

While not as dire as terrorism, the threat is considerable and hard to contain.

Many invasive species are carried into the US by people who are either unaware of the laws or are purposely trying to skirt quarantine regulations. The hardest to stop are fruits, vegetables and spices carried by international travelers or shipped by mail. If tainted with insects or infections, they could carry contagions capable of devastating crops.

Plants and cut flowers can harbor larvae, as can bags of bulk commodities such as rice. Beetles have been found hitchhiking on the bottom of tiles from Italy, and boring insects have burrowed into the wooden pallets commonly used in cargo shipments.

Invasive species have been sneaking into North America since Europeans arrived on the continent, and many got established long before 9/11. But the abrupt shift in focus that followed the attacks caused a steep decline in agricultural inspections that allowed more pests to invade American farms and forests.

Using the Freedom of Information Act, the AP obtained data on border inspections covering the period from 2001 to 2010. The analysis showed that the number of inspections, along with the number of foreign species that were stopped, fell dramatically in the years after the Homeland Security Department was formed.

Over much of the same period, the number of crop-threatening pests that got into the U.S spiked, from eight in 1999 to at least 30 last year.

The bugs targeted some of the nation's most productive agricultural regions, particularly California and Florida, with their warm year-round climates that make it easy for foreign species to survive the journey and reproduce in their new home.

A look at the damage:

— No fewer than 19 Mediterranean fruit fly infestations took hold in California, and the European grapevine moth triggered spraying and quarantines across wine country.

— The Asian citrus psyllid, which can carry a disease that has decimated Florida orange groves, crossed the border from Mexico, threatening California's $1.8 billion citrus industry.

— New Zealand's light brown apple moth also emerged in California, prompting the government in 2008 to bombard the Monterey Bay area with 1,600 pounds of pesticides. The spraying drew complaints that it caused respiratory problems and killed birds. Officials spent $110 million to eradicate the moth, but it didn't work.

— The sweet orange scab, a fungal disease that infects citrus, appeared in Florida, Texas, Louisiana and Mississippi, which all imposed quarantines.

— Chili thrips, rice cutworms and the plant disease gladiolus rust also got into Florida, which saw a 27 percent increase in new pests and pathogens between 2003 and 2007.

— The erythrina gall wasp decimated Hawaii's wiliwili trees, which bear seeds used to make leis.

— Forests from Minnesota to the Northeast were also affected by beetles such as the emerald ash borer, many of which arrived in Chinese shipping pallets because regulations weren't enforced.

In all, the number of pest cases intercepted at US ports of entry fell from more than 81,200 in 2002 to fewer than 58,500 in 2006, before creeping back up in 2007, when the farm industry and members of Congress began complaining.

Once the pests get established, costs can quickly spiral out of control. The most widely quoted economic analysis, conducted in 2004 by Cornell University, puts the total annual cost of all invasive species in the US at $120 billion. Much of that burden is borne by consumers in the form of higher food costs and by taxpayers who pay for government eradication programs.

For instance, if the destructive infection known as citrus canker were to become established in California, which produces most of the nation's fresh oranges, consumers would pay up to $130 million more a year for the fruit, according to an ongoing study by scientists at the University of California at Davis.

"It's all about early detection, and it wasn't their priority at the time," said A.G. Kawamura, secretary of the California Department of Food and Agriculture from 2003 through 2010, who was sharply criticized for the spraying in Monterey Bay.

And it's not just humans who pay the cost. Wildlife and beneficial insects die when fields are sprayed.

The problems began when the Homeland Security Department absorbed inspectors who worked for the Department of Agriculture. The move put plant and insect scientists alongside gun-toting agents from Customs and Border Protection and resulted in a bitter culture clash.

Agriculture supervisors were replaced in the chain of command by officials unfamiliar with crop science. Hundreds of inspectors resigned, retired or transferred to other agencies. Some of the inspectors who remained on the job lost their offices and desks and were forced to work out of the trunks of their cars.

It took authorities years "to learn there's an important mission there," said Joe Cavey, head of pest identification for a USDA inspection service. "Yeah, maybe a radioactive bomb is more important, but you have to do both things."

At the time of the merger, at least 339 of 1,800 inspector positions were vacant. By 2008, vacancies had increased to 500, or more than a quarter of the original workforce.

The effect of the exodus was profound. One East Coast port director told a congressional investigator that she was left without a single agriculture inspector. An airport technician in Bangor, Maine, said there wasn't one within 50 miles for two years.

One agriculture inspector who defied authority was demoted, despite being credited with saving California's citrus industry from the potentially devastating effects of canker.

While working at an international mail center outside San Francisco, the inspector found a package destined for Ventura labeled "books and chocolates." Inside were 350 citrus cuttings from Japan that were infested with canker, which has killed more than 2 million trees across Florida but does not exist in California.

He showed it to a supervisor, who, according to the Congressional Record, replied: "Look, we are here to protect the country from acts of terrorism. What do you expect me to do?"

The inspector sidestepped the supervisor and called the USDA. The resulting investigation ended with arrests and the incineration of 4,000 potentially infected trees that had been growing at an unregistered nursery in a prime citrus region.

But within a month, the whistleblower was demoted to search through the dirty laundry of passengers returning from foreign trips.

Government officials now acknowledge the problems and say they began taking corrective steps after Sen. Dianne Feinstein of California threatened in 2008 to propose a bill that would move inspectors back to the USDA and increase their numbers.

"That was a huge moment for everybody," said Kevin Harriger, Custom and Border Protection's acting executive director of agriculture programs. "We took it on the chin and said, 'You're right. We heard you. We've been remiss in several key areas.'"

Critics in Congress say serious damage has already been done. Sen. Daniel Akaka, a Hawaii Democrat and member of the Senate Committee on Homeland Security, said the improvements aren't happening fast enough. He's asked the Government Accountability Office to reopen an investigation.

"When change like this happens, you hope people get it right the first time," said Rep. Dennis Cardoza, a California Democrat who also investigated the problems. "But if they don't, it's not them who pay the price. It's society that does."