Customs officials inspecting a large shipment of citrus at the Port of Philadelphia in Camden recently discovered the presence of Mediterranean fruit flies, "one of the world's most destructive agricultural pests," the U.S. Department of Agriculture announced Thursday.

The discovery was made Dec. 14 during a routine examination of 105,000 crates of clementines, a popular fruit similar to tangerines, according to the U.S. Department of Homeland Security.

A DHS spokesman said that the shipment had come from Morocco and that officials of the U.S. Customs and Border Protection (CBP), an agency of DHS, quarantined all of it.

"This is an extremely important find," Kevin Donohue, acting director of the Port of Philadelphia, said in a statement. Called "medflies" for short, the species has been responsible for hundreds of millions of dollars in crop damage around the world.

Among the many crops besides citrus it can devour are apples, peaches, tomatoes, bell peppers, and melons, all important commercial crops in New Jersey and Pennsylvania. Had the flies spread to orchards and fields, the result could have been "devastating," according to Donohue.

California has spent millions of dollars to contain and eradicate medflies since 1975, including $40 million in 1981 and $60 million in 1989 to control major outbreaks.

Steve Sapp, a spokesman for the CBP's agriculture protection mission, said an inspector discovered one live larva and many dead ones during a routine sampling of the clementines before the shipper began distribution to area supermarkets before the holidays.

"Every day CBP agricultural specialists show up at the ports and do these kinds of inspections, which can be very monotonous," he said, "so we're very pleased" when such a threat is intercepted.

Adult females lay their eggs under the skins of fruit, which hatch within three days. The larvae, or maggots, feed inside the produce for five to 10 days, reducing it to pulp and rendering it inedible. They then fall to the ground and burrow, emerging as adults within as short a time as seven days.

Exporters of agricultural products to the United States must produce documentation stating that they took all necessary precautions to eliminate the threat of pest importation, according to Sapp.

The standard treatment for medflies is to chill a shipment of fruit or vegetables before exporting it, and keeping it chilled during shipping. "But this time, at least one [live larva] got through," Sapp said.

After inspection, the importer was allowed to ship these clementines to Canada, where colder temperatures effectively inhibit the spread of medflies, Sapp said.

USDA agents will review the entire sequence of the shipment, including in Morocco, where it was packed and loaded, in hope of discovering how live larvae passed through.