Citrus greening disease has infected six citrus trees on the Yucatan peninsula, spread by an infestation of a plant-sucking, aphid-like insect. There's a virtual insect highway across the width of Mexico, and once the disease-carrying Asian citrus psyllid hops on, California is in trouble, said Beth Grafton-Cardwell, a University of California, Riverside entomologist and director of the Lindcove Research and Extension Center. Mexico 'is infested with the bug and they will gradually move the disease across the country,' Grafton-Cardwell said. 'This disease is a citrus grower's worst nightmare.' Farmers agree. 'This is an existential threat. It would put us out of business,' said Jim Churchill, a Pixie tangerine grower in Ojai, Calif. Although the disease doesn't affect humans, it's lethal to citrus trees. It ruins the taste of fruit and juice before killing the plants, experts said, and there is no known way to rid a region of the pathogen once it's struck. The disease has killed tens of thousands of acres of trees in Florida and threatens to put that state out of the orange juice business, according Florida's Department of Citrus. Since its discovery in Florida in 2005, the disease has spread to every citrus-growing county in the state, contributing to the death of about 5 percent of its trees every year. It has wiped out much of the citrus industries in China, India, Saudi Arabia and Egypt and has ravaged parts of Brazil. How long California's citrus industry has before it too is afflicted by the disease is anybody's guess, Grafton-Cardwell said. Also called Huanglongbing or HLB, the disease could take years to reach the state or far sooner if someone helps it along by bringing an infected plant across the border. California's citrus industry already is on high alert. Small colonies of psyllids from Tijuana have established themselves in San Diego and Imperial counties. But none of the psyllids trapped in the those colonies turned out to be carriers of Huanglongbing disease. It was a lucky break, said Ted Batkin, president of the Citrus Research Board in Visalia, Calif. What inspectors fear is the kind of citrus Armageddon that occurred in Florida, where officials surmised an uninfected psyllid fed on a diseased plant and flew to nearby citrus trees, spreading the disease. Other psyllids fed on the newly infected plants, distributing the pathogen throughout Florida. An alternate source of infection could come from a psyllid carrying the disease hitchhiking in from overseas and starting the disease here. California had a close call last month. Only the smart work of Chelsea, a Labrador retriever that sniffs out contraband plant material, kept diseased psyllids from escaping into some of the state's prime citrus growing areas. While working with agricultural inspectors at a FedEx depot in Fresno, Calif., Chelsea pointed to a duffel bag that had arrived from India. A plastic bag of curry leaves inside the duffel contained one dead adult psyllid and nine live juvenile insects, or nymphs. Tests subsequently found that nymphs were infected with Huanglongbing. (Begin optional trim) 'The nymphs were put in alcohol and sent to the state lab in Sacramento for testing. We burned the curry leaves in case we didn't get all the bugs,' said Tye Hafner, Fresno's deputy agricultural commissioner. Hafner said the duffel bag belonged to a woman from India who was visiting her daughter in Fresno. The woman's luggage was lost in transit. The airline found the duffel and was delivering it to the woman at her daughter's home via FedEx when it was intercepted by Chelsea and the inspectors. California caught a lucky break when the traveler became separated from her luggage, Hafner said. The curry leaves might have escaped detection in customs. 'Something like this wouldn't show up on an X-ray machine,' Hafner said. (End optional trim) 'We are fairly confident that we intercepted the disease before it was released into the environment,' Hafner said. Although California farmers have been able to vanquish various species of fruit flies and phylloxxera, an insect that once ravaged the state's vineyards, the methods used to control previous threats are largely ineffective in stopping the psyllid. The insects are asexual and don't need to find a mate, so just one infected insect can by itself create whole colonies of disease carriers. There are no effective parasites or predators to use against the psyllid population. And growing and releasing sterile psyllids -- a successful way to control fruit flies -- will have no effect because of the bug's ability to reproduce asexually. Between various state, industry and federal efforts, about $50 million is earmarked for citrus greening research and containment efforts, officials estimate. Much of the research focuses on developing a disease-resistant tree. Grafton-Cardwell says there's been some progress, but such a tree is still probably years off. That's why California officials are so focused on setting traps and rooting out any psyllid populations. 'We need to buy time for the scientists,' Grafton-Cardwell said. And for farmers. 'I lie awake at night worrying about this,' said Churchill, the Ojai tangerine farmer. 'We have found the disease now in Fresno, and we have the vector, or insect, that carries it already in the state. We are just lucky they haven't found each other.' 