Cooperative Extension San Joaquin County
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Cooperative Extension San Joaquin County

Posts Tagged: Asian citrus psyllid

Continued vigilance needed in the fight against Asian citrus psyllid

Asian citrus psyllid is established in some urban Tulare County communities.
Two Asian citrus pysllids (ACP) were found in a trap near Exeter in November, just 10 miles away from the UC Lindcove Research and Extension Center. That brings to 29 the number of locations in the central San Joaquin Valley, from Bakersfield to Dinuba, where Asian citrus psyllids have been trapped.

Perhaps still more unsettling is the fact that reproducing populations of ACP have been found in urban areas in Tulare County, confirming that the pest is established in a county where farmers produce citrus valued at more than $1 billion annually.

“The psyllid is here, it's established, but still at low levels,” said Beth Grafton-Cardwell, director of the Lindcove REC and UC Cooperative Extension citrus entomology specialist. “We need to be very aggressive and treat it and eliminate populations as best we can.”

Asian citrus psyllids are a serious concern for California citrus producers because they spread Huanglongbing (HLB) disease. The disease causes tree decline, production of small, bitter fruit and eventually tree death. There is no cure once a tree is infected.

Around the world, once ACP arrives, HLB soon follows. Such was the case in Florida. ACP was first found in 1998, the disease followed in 2005, and by 2008 it had spread throughout the state.

“They allowed the psyllid and the disease to spread on nursery plants,” Grafton-Cardwell said. “Here, it's a different situation. We are taking many measures to reduce psyllid populations and limit their spread around the state in order to buy researchers time to find long-term solutions for HLB disease."

To date, only one HLB-infected tree has been found in California, a multi-grafted backyard tree in Hacienda Heights. It was quickly removed and destroyed. Other trees may be infected, but not yet detected. It will take a tree with HLB about a year to show visual symptoms of the disease. One goal of UC research is to identify a way to detect HLB more rapidly.

For example, scientists at UC Davis are refining a mobile chemical sensor that can detect diseased citrus trees by sniffing their volatile organic compounds. Another team of scientists is looking for changes in citrus trees' metabolism when infected with HLB.

Citrus growers can help by regularly monitoring their trees for signs of ACP and, when treating for other pests, use insecticides that are known to be effective against ACP. A chart of effective pesticides is on the interactive Asian Citrus Psyllid Distribution and Management website.

The website also contains information for residents who have citrus trees in their landscapes. Photos of the adult and juvenile insects, the distinctive waxy tubules left behind when they feed, and citrus leaves from and HLB-infected tree can aid in determining whether home trees are infested.

An initiative to manage endemic and invasive pests and diseases is part of the UC Division of Agriculture and Natural Resources Strategic Vision 2025.

Posted on Tuesday, November 25, 2014 at 8:12 AM

Invasive meltdown

Ants can be a huge nuisance in and outside our homes, particularly if you have food lying around. But now, it turns out, they’re unwelcome, too, on citrus trees.  

A year ago, UC Riverside entomologists released Tamarixia, a parasitoid wasp and natural enemy of the Asian citrus psyllid (ACP) imported from Pakistan, into a biocontrol grove in Riverside, Calif. Tamarixia can serve as an excellent biocontrol agent against ACP, a citrus pest first detected in 2008 in Southern California that is capable of spreading citrus greening disease, or Huanglongbing

Tamarixia radiata parasitizing an Asian citrus psyllid nymph in Bell Gardens, Los Angeles County. (Photo: Mark Hoddle, UCR)
Tamarixia’s success starts with a female laying an egg on the underbelly of an ACP nymph. When the egg hatches, the parasitoid larva will scrape away the nymph’s belly, carving out a hole to push through to enter the nymph’s body. Feeding on the contents, the larva eventually excavates the entire nymph, leaving only a shell or husk of the nymph behind.

Female Tamarixia can kill psyllids also by “host-feeding.” They use their ovipositors as daggers to stab psyllid nymphs numerous times until the nymphs start to bleed. As bodily fluids ooze out of the nymph, Tamarixia sucks up this rich protein needed for developing more eggs. 

An excellent way then to control ACP populations! Yes, but only until the ants come marching in. Argentine ants are threatening to disrupt the biocontrol of ACP by battling it out with Tamarixia on citrus branches. While not quite a Vader-Skywalker lightsaber duel on a precarious walkway, an “invasive meltdown” begins when the ants gang up to protect the nymphs.

“ACP nymphs produce a white, sugary waste product called honeydew, a good carbohydrate source for the ants,” explains Mark Hoddle, the director of the Center for Invasive Species Research at UC Riverside, whose research team has released Tamarixia into several Southern California citrus groves. “The ants, therefore, will protect the nymphs from Tamarixia.  We have seen ants chase female Tamarixia off the psyllids, and even catch and eat them!”

Argentine ants tending an infestation of Asian citrus psyllid nymphs. Ants may hamper biological control of ACP by Tamarixia. (Photo: Mark Hoddle, UCR)
Hoddle’s lab is now collecting ACP nymph honeydew to analyze it for sugars so that feeding trials can be conducted on the ants. The research could help the lab produce more effective ant-baits that when left on citrus trees would help decrease the ant population and then reduce, too, the attacks on Tamarixia.

“If you kill off the ants, Tamarixia can play the role of the biocontrol agent it was cast to do on citrus trees,” Hoddle says. “We’re seeing that the ants are impacting Tamarixia in two ways: they are preventing Tamarixia’s establishment in some areas; and, where Tamarixia is already established, the ants are not allowing these parasitoids to reach their full biocontrol potential.”

Posted on Thursday, December 13, 2012 at 8:33 AM

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