Knowles said that U.S. forces have found documents at an Al Qaeda training camp that showed interest in targeting farms in the United States, purposely contaminating food supplies by spreading contaminants that include foot and mouth diseases and hog cholera.

In 1986, a group calling itself the “Breeders” said it had released Mediterranean fruit flies in Southern California to protest aerial spraying of the pesticide malathion, said Carl Hafner, Fresno County agriculture commissioner. They also threatened to release the flies in the San Joaquin Valley, but apparently did not do so.

Hafner said there was evidence that the claim was not a hoax, including the discovery of unexpected life stages of the insect. The case remains unsolved.

Insects have been used as weapons in combat for decades, Hafner said, from warriors hurling hornet and wasp nests to combatants using stinging or biting insects for torture, spreading plague in infected fleas or yellow fever in infected mosquitoes.

Some of the material that Hafner presented came from a book called “Six-Legged Soldiers: Using Insects as Weapons of War” by Jeffrey A. Lockwood.

It’s well known that economic blows to agriculture can be struck by maliciously introduced insect vectors, pests that can carry viruses and bacteria throughout a crop.

Hafner said allegations of wartime use of insects for crop destruction arose during the Civil War and World War II.

As an example of the economic impacts of farm pests, Hafner cited the European grape vine moth. In March, a Fresno County quarantine triggered by the find of 11 moths was lifted, but it left producers with a cost of $11 million in treatment and compliance, Hafner said.

Hafner said the spread of pests “can open pathways for agricultural terrorists to disperse bioagents,”

She said customs and border checks help keep pests out of the fields and orchards of California, but cutbacks in funding have taken a toll. She cited the example of the loss of $84,000 in funding for inspections of beehives brought into Fresno County for pollination of almonds and other crops. Those inspections have been a key to keeping hitchhiking red imported fire ants out of the state.