Tiny wasp may be a big help in fighting citrus disease

The country’s citrus growers now have a safe ally in their battle against the dreaded dragón amarillo, the insect-born bacterial disease that ruins crops and kills trees.

Entomologists at the University of California, Riverside, have declared a tiny wasp, Tamarixia radiata, to be safe for the environment and poses no undue risk to other insects, humans or pets.

The bacterial disease is carried by the Asian citrus psyllid to which the wasp is a natural enemy. The tiny parasitic wasp lays eggs in insect nymphs, eventually killing them.

The university said that the designation came after 18 months of testing in Riverside, Calfornia. Safety testing in biological control is important as the release of natural enemies may pose some type of environmental risk, the university noted. In this instance, Tamarixia radiata were imported from the Punjab region of Pakistan, and tested for safety in quarantine for 18 months.

Our work demonstrates that Tamarixia radiata is very specific to the target it is being released to kill — the nymphs of the Asian citrus psyllid in this case,” said Mark Hoddle, the director of the Center for Invasive Species Research, whose lab performed the tests. He was quoted by the university.

Growers found the disease in northern Costa Rica in 2011. However, the infestation is much more severe in México, Florida and other locations in the Caribbean.

The study is the first one published that was designed specifically to determine the preferred host of the wasp. The results are important as the wasp already is being used for biological control in Florida, Texas, the Caribbean, Central and South America, and Mexico, said the university.

To determine the safety of Tamarixia, different species of native California psyllids were exposed to the wasp in a series of tests. The tests were designed to

give the wasp a choice between the Asian citrus psyllid and a non-target psyllid species, or there was no choice, that is, the wasp was only given access to a non-target species, one it had not evolved with. When given a choice, Tamarixia overwhelmingly attacked the Asian citrus psyllid, the researchers found, according to the university.

We have now released more than 200,000 Tamarixia radiata in Southern California at more than 350 different sites, mainly in urban areas and spanning six counties — Imperial, Los Angeles, Orange, Riverside, San Bernardino, and San Diego,” Hoddle said. “They have established and are spreading, tracking down ACP on citrus in people’s gardens and orchards.”

The Tamarixia larvae will eat the Asian citrus psyllid nymphs, killing them, and emerge as adults about 12 days later. Adult female Tamarixia also eat other Asian citrus psyllid nymphs, killing many in the process.

Much of Costa Rica’s orange crop is exported as juice, and it is a major agricultural industry. The bacteria is Candidatus Liberibacter asiaticus, which causes the citrus leaves to yellow and fall off. It also causes the fruit to be deformed and to have a sour taste. The disease turned up in Florida in 2005, causing great concern there.

The Asian citrus psyllid is Diaphorina citri.

Costa Rican agricultural experts have been sampling for the insect after a handful of trees were found to be infested in the northern zone.

The Ministerio de Agricultura y Ganadería has declared an agricultural emergency over the problem, which also is called citrus greening. The emergency allowed growers to import special bags impregnated with insecticides. There have been no mentions of importing the wasps.

The bacteria is called Huanglongbing, a Chinese name reflecting the fact that the disease was found in that country in the early part of the 20th century.

Costa Rica has spent more than $1 million in prevention, training and the creation of a lab. The cost of insecticides against the bacterial carrier is many hundreds of dollars a hectare, officials have said.

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