The glass vials that Bruce McPheron pulled out of a box postmarked from Chile appeared innocent.

Inside, floating in alcohol, were samples of the Mediterranean fruit fly, an insect not much larger then a mosquito. Despite their small stature, the flies are considered one of the world's most problematic agricultural pests.

In fact, the fear of an infestation is so great that researchers in the United States are not allowed to have living specimens in their labs.

"This species attacks hundreds of food and nonfood crops," said McPheron, of the department of entomology. "It's not a trivial issue."

In December, medfly larvae were found in a shipment of clementines, a small citrus fruit similar to tangerines, from Spain, prompting the U.S. Department of Agriculture to indefinitely ban all shipments of the fruit from Spain.

"We stopped getting clementines around Christmas time," said Dan Soltis, who works in the produce section at Giant Food Store, 255 Northland Center.

The USDA contacted McPheron, who researches DNA patterns of various fruit flies at Penn State, to help track down where the flies were coming from. Contrary to their name, the Mediterranean fruit fly is not strictly found near the Mediterranean Sea.

It can be found throughout South and Central America, Africa and Southern Europe, and is able to survive in warmer climates. In the past, there have been infestations in the United States in Florida, California and Texas.

McPheron has traveled worldwide to collect samples of the fly, which he then uses to identify specific genetic markers that tell him where in the world a particular fly originated.

"The clementines came in boxes marked 'products from Spain,' " McPheron said. "That is a smoking gun."

Knowing what the DNA of a specific medfly looks like allows Animal and Plant Health Inspection Service (APHIS), a branch of the USDA, to monitor possible movement of that fly in the United States

McPheron said that nearly all of the medflies that are intercepted by the USDA at ports in the United States come to Penn State for identification. In addition to doing his own research, McPheron usually collects DNA samples from the flies and sends them to other labs for research, including labs at the University of California-Berkeley and the University of Hawaii.

According to a press release from APHIS, a team of inspectors was sent to Valencia, Spain to investigate how the medfly larvae survived in the fruit even after it was cold treated. So far, the team has not found what could have gone wrong during the exporting process.

The USDA is adamant about preventing the medfly from entering the country because as of now, the United States has no native population, and the costs if one were established would be enormous.

McPheron said estimating a specific dollar amount of damage a medfly infestation would cause is difficult. He added, however, that the host range of the medfly is large.

In addition to citrus, they will eat anything from coffee to hot peppers. In agricultural areas, there would be the risk of increased use of pesticides, something that carries large costs to society in terms of health of the community and of the environment.

Another area of concern, McPheron said, would be international trade. Right now, California is one of the biggest exporters of citrus to Asia. If medflies were found in the United States, Japan and other Asian countries, which don't have a problem with these pests, would most likely stop accepting produce from the United States.

"Estimates of the costs are in the hundreds of millions to I've heard as high as billions of dollars," McPheron said.

This is not the first time the United States has had problems with the medfly. The first infestations date back to 1928 in Florida. Since then, there have been problems with the flies in California and Texas. Historically, the outbreaks have been in urban environments.

Many times, the problem could be traced back to people bringing food into the country illegally, McPheron said. The USDA inspects all incoming produce for signs of pests.

One way to control the flies, McPheron said, would be to receive large quantities of sterilized medflies from overseas and release them in infested areas so that they will eventually die out. Other methods used in the past include fumigating affected produce or burning it.

Other countries also use McPheron's research. The samples he received from Chile, which has no established medfly population, will be used to find out where the flies are coming from.

"It's nice because you can see other people using your research," Andrea Forbes, lab manager, said about the fruit fly research conducted in the entomology lab.

McPheron said the clementine issue is winding down, but there is still no date given as to when the United States will begin importing from Spain again.

Soltis said Giant usually begins stocking clementines in late October and has them until February. When they are on sale, Soltis said, they can go through a couple hundred cases in a day.

Some Penn State students said they enjoy the small fruit.

"I like that they have hardly any seeds and are easy to peel and that they taste so good," Anne Scaduto (sophomore-psychology) said. "Easy to peel is key."