ACP Spread in Bakersfield Area, Ingenious Research Proceeds

Ingenious Research Effort to Fight ACP Spread with Natural Predators

 

By Joanne Lui, Associate Editor

 

beth_grafton-cardwell
Beth Grafton-Cardwell, Cooperative Extension specialist, University of California, Riverside Department of Entomology

As we have reported in-depth before on California Ag Today, the Asian Citrus Psyllid (ACP) is a tiny, mottled brown insect that poses an ever-increasing threat to the state’s robust citrus industry, as well as to residential citrus trees. The pest can spread a bacterium known as Huanglongbing (HLP) that is fatal to citrus trees. The disease has nearly shut down Florida’s citrus industry.

Beth Grafton-Cardwell, cooperative extension specialist in integrated pest management, UC Riverside Department of Entomology, explained the significance of the recent ACP spread to Bakersfield. “That is really problematic because it’s mostly in the urban areas. It’s very difficult to find, to control and to stop that spread. It’s going to move out from that region into the local citrus orchards, and so there are lots of meetings and discussions right now to mobilize growers to get treatments to help protect their citrus orchards against the psyllid.”

#CitrusMatters
#CitrusMatters

To contain the ACP problem, Grafton-Cardwell stated, “There are traps everywhere, but the traps are not terribly efficient. So, we really need to carefully examine groves and flush [new leaf growth] for the nymph form,” she said.

According to Agriculture and Natural Resources, University of California’s Statewide Integrated Pest Management Program:

Adults typically live one to two months. Females lay tiny yellow-orange almond-shaped eggs in the folds of the newly developing “feather flush” leaves of citrus. Each female can lay several hundred eggs during her lifespan.

ACP UC IPM
ACP (Source: ACP UC IPM)

The eggs hatch into nymphs that are wingless, flattened, yellow or orange to brownish, and 1/100 to 1/14 inch long. Nymphs molt four times, increasing in size with each nymphal stage (instar), before maturing into adult psyllids. The nymphs can feed only on soft, young leaf tissue and are found on immature leaves and stems of flush growth on citrus.

Save Our CitrusThe nymphs remove sap from plant tissue when they feed and excrete a large quantity of sugary liquid (honeydew). Each nymph also produces a waxy tubule from its rear end to help clear the sugary waste product away from its body. The tubule’s shape—a curly tube with a bulb at the end—is unique to the Asian citrus psyllid and can be used to identify the insect.

Grafton-Cardwell and other experts are concerned because once the ACP becomes established in urban areas, it is difficult to eradicate. “It starts spreading into the commercial citrus, and we’re off and running,” she commented.

bayer-save-our-citrusIn a ingenious effort to control the spread of the psyllid, trained teams of entomologists have imported Tamarixia radiata, a tiny wasp that naturally preys on ACP, from Pakistan to research and release in California. A cooperative effort of the University of California Riverside, Citrus Research Board, United States Department of Agriculture and California Department of Food and Agriculture, researchers are also exploring the effectiveness of another beneficial insect called Diaphorencyrtus aligarhensis to assist Tamarixia with control of the Asian citrus psyllid. To see where Tamarixia and Diaphorencyrtus have been released, visit this University of California’s website map at, “Distribution of ACP, HLB and Parasites in California,” and turn on the parasite layers.
Grafton-Cardwell said, “They’re going to inundate that area,” with natural ACP predators, “so hopefully that will push back a little bit.”

Breaking News: Cal Poly Opens New Greenhouse and Insect Rearing Facility

New Greenhouse Facility Opens to Save Citrus from Psyllids that Vector HLB

Facility to Rear Tamarixia Radiata, Natural ACP Predator

By Patrick Cavanaugh, Farm News Director

 

Scores of citrus industry leaders, citrus growers, scientists and CDFA officials attended the ribbon cutting event TODAY at the opening of a new greenhouse on the Cal Poly Pomona campus to rear Tamarixia radiata, a tiny parasitic wasp imported from Pakistan because it is an Asian Citrus Psyllid (ACP) nymph predator. ACP, in turn, is a serious nonnative citrus pest that can vector Huanglongbing (HLB)—a deadly citrus disease also known as Citrus Greening—that has devastated the powerhouse citrus Screenshot 2016-07-25 12.24.41.png

industry in Florida, threatens to ruin additional citrus economies, and is the biggest threat the California citrus industry has ever faced.

According to the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA-APHIS), infected citrus trees “produce fruits that are green, misshapen and bitter, unsuitable for sale as fresh fruit or for juice. Most infected trees die within a few years.” ACPs have been detected in Alabama, American Samoa, Arizona, California, Florida, Georgia, Guam, Hawaii, Louisiana, Mississippi, Northern Mariana Islands, Puerto Rico, South Carolina, Texas and the U.S. Virgin Islands. Of those locations, the HLB disease has been detected in California, Florida, Georgia, Louisiana, Puerto Rico, South Carolina, Texas and the U.S. Virgin Islands.

ENTER:  Tamarixia radiata

Use of the ACP predator, Tamarixia radiata as a biological control for ACP was discovered by Mark Hoddle, biological control specialist and principal investigator, UC Riverside ( UCR), Department of Entomology. The first release of Tamarixia was in December 2011 after USDA-APHIS cleared the natural enemy for release from the Quarantine Facility at UCR.

Mark Hoddle UC Riverside Department of Entomology
Mark Hoddle UC Riverside Department of Entomology

“Tamarixia can kill ACP nymphs in two different ways,” explained Nick Hill, a Tulare County citrus producer and Citrus Pest & Disease Prevention Program (CPDPC) chair.  “The first is parasitism. In this instance, a female parasitoid lays an egg underneath a fourth or fifth instar—the larger and final developmental stage of the ACP nymph before becoming an adult—nymphs that are most preferred by Tamarixia for parasitism. When the egg hatches, the Tamarixia larva begins to feed on the under-surface of the ACP nymph. Eventually the larva completely excavates the body cavity of the ACP nymph and pupates inside the empty shell of its host.”

Hill explained the first releases of the tiny and harmless wasp will occur this fall in urban areas, “to help control ACP so that we do not have to do mitigations such as spraying in those areas. We hope to get to a point where we no longer need to go into people’s yards and ask if we can treat the trees.”

“The issue,” commented Valerie Melano, professor and chair, Cal Poly Pomona Plant Sciences and interim chair, Cal Poly Agribusiness & Food Industry Management/Agricultural Science, “is that we need to come up with the best possible ways to raise enough wasps for big releases to prey on ACP. We will have CDFA employees working in this green house, as well as student workers who have participated in our research program all along,” noted Melano.

Nick Hill, CPDPC chair
Nick Hill, a Tulare County citrus producer and Citrus Pest & Disease Prevention Program (CPDPC) chair.

Hill added, “The idea is to get enough Tamarixia out there so they start reproducing themselves and they become self sufficient. This is tough to accomplish, but researchers think if they can get big numbers of the wasp into the urban areas, they can put a big dent in lowering the populations of ACP.”

Cal Poly Pomona Greenhouse

The new Cal Poly 5,040-square-foot research greenhouse, built in collaboration with Citrus Research Board and constructed through a $400,000 grant from the Citrus Pest & Disease Prevention Program, will house the second Tamarixia production program in California. CDFA’s Mount Roubideaux facility in Riverside houses current production. Both facilities will support the CPDPC biological control program that oversees releases in urban areas with high ACP populations.

The new greenhouse should produce a 1-ACP Research Greenhouse1.5 million wasps. “It’s a very nice facility,” said Hill. “We are trying to boost the biological control program to produce four million Tamarixia a year.”

California Quarantine

The California Department of Food and Agriculture (CDFA) operates an extensive monitoring program to track the distribution of the insect and disease in both residential areas and commercial citrus groves. Results have determined quarantine zones, guided releases of biological control agents, and prioritized areas for a residential chemical control program. Nearly all of southern California is under quarantine for ACP, due to the fact that more than 15 residential trees have been discovered to be in infected with HLB.

The ACP quarantine in California includes parts of the following counties:  Fresno, Kern, Kings, Madera, Monterey, San Benito, San Joaquin, San Luis Obispo, San Mateo, Santa Clara, and Stanislaus; and the following entire counties: Imperial, Los Angeles, Orange, Riverside, San Bernardino, San Diego, Santa Barbara, Tulare County, and Ventura.

Asian Citrus Psyllid Cooperative Program California, Arizona, Baja California, and Sonora (USDA-APHIS)
Asian Citrus Psyllid Cooperative Program
California, Arizona, Baja California, and Sonora (USDA-APHIS). Visit our Citrus Diseases page to identify a plant infected by citrus greening, citrus canker, citrus black spot and sweet orange scab. If you detect an infected plant, report it  immediately.

ACP Quarantine in San Joaquin County, Guidelines and Scholarship

Expanded ACP Quarantine

Two portions of San Joaquin County have been placed under Asian citrus psyllid (ACP) quarantine following detections of one ACP within the City of Manteca and one within the City of Lodi. The quarantine zone in Manteca measures 105 square miles and in Lodi it measures 95 square miles.

The quarantine prohibits the movement of citrus and curry tree nursery stock out of the quarantine area and requires that all citrus fruit be cleaned of leaves and stems prior to moving out of the quarantine area. An exception may be made for nursery stock and budwood grown in USDA-approved structures that are designed to keep ACP and other insects out. Residents with backyard citrus trees in the quarantine area are asked not to transport citrus fruit or leaves, potted citrus trees, or curry leaves from the quarantine area.

Asian citrus psyllid (Source: UC ANR)
Asian citrus psyllid (Source: UC ANR)

The ACP, a tiny (0.125 in. length) mottled brown insect that is about the size of an aphid, is an invasive species of grave concern because it can carry the disease huanglongbing (HLB), also known as citrus greening. All citrus and closely related species such as curry trees are susceptible, and there is no cure. Once infected, a diseased tree will decline in health with yellowing shoots, asymmetrical leaf mottling and abnormally shaped bitter fruit until it dies—typically within three years.  HLB was detected once in California, in 2012, on a residential property in Hacienda Heights, Los Angeles County.  This plant disease does not affect human health.

Residents in the area who think they may have seen ACP or symptoms of HLB on their citrus trees are urged to call CDFA’s Pest Hotline at 1-800-491-1899.  For more information on the ACP and HLB, please visit: www.cdfa.ca.gov/go/acp

ACP Effective Treatments

The University of California Agriculture and Natural Resources’ Integrated Pest Management (IPM) Program  has developed treatment guidelines for citrus growers within the quarantine zones. A general principle when applying insecticides to control ACPs in commercial citrus is that no one insecticide fully controls ACP across all life stages because:

  • All stages are difficult to contact with insecticides; eggs and nymphs are tucked inside new foliage and adults can fly.
  • Some insecticides show better efficacy against one stage over another.
  • Because systemic neonicotinoid insecticides require root activity for uptake, they are best applied during June through September.

The UC IPM Guidelines for Citrus provides a ranked list of insecticides that are effective against the Asian citrus psyllid with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honeybees, and the environment are at the top of the table.

According to Mark Hoddle, UC Riverside (UCR) Director, Center for Invasive Species Research, “The science of biological control, the use of a pest’s natural enemies to suppress its populations to less damaging densities,” shows promise against the ACP with releases over the last three years of Tamarixia radiata–a parasitic wasp from Pakistan–in urban areas of southern California Thus far, this natural ACP enemy helps to control ACP growth in residential areas, but is inadequate for commercial application.

Biological Control Scholarship Fund

Harry Scott Smith (Source: Citrus Research Board, "Citrograph")
Harry Scott Smith (Source: Citrus Research Board, “Citrograph”)

Harry Scott Smith was the first to use the phrase “biological control” in 1919 at the meeting of Pacific Slope Branch of the American Association of Economic Entomologists at the Mission Inn in Riverside. Smith worked on the biological control of gypsy moth with USDA, then moved to the University of California Riverside where he eventually created and chaired the Department of Biological Control, which offered the only graduate degree in biological control in the world.

The Harry Scott Smith Biological Control Scholarship Fund at UCR aims to attract the brightest students to study biological control by providing assistance to its students to attend conferences to present their research or to participate in training workshops. More information on the Scholarship, past awardees, and a list of donors can be reviewed on the website.

Sources: CDFA; UC IPM; UC Riverside (UCR); UCR Center for Invasive Species Research; USDA Animal and Plant Health Inspection Service (APHIS)