UC Riverside

INFORMATIONAL MEETING ON A NEW PEST IN ORANGE COUNTY – THE RED PALM WEEVIL

Anonymous — Mon, 20 Jan 2020 02:26:10 +0000

INFORMATIONAL MEETING ON A NEW PEST IN ORANGE COUNTY – THE RED PALM WEEVIL Anonymous (not verified) Sun, 01/19/2020 - 18:26 More Blog Posts CISR Team October 28, 2010

CALIFORNIA DEPARTMENT OF FOOD AND AGRICULTURE COUNTY AGRICULTURAL COMMISSIONER’S OFFICE

~OFFICIAL INVITATION~

INFORMATIONAL MEETING ON A NEW PEST IN ORANGE COUNTY –
THE RED PALM WEEVIL (Rhynchophorus ferrugineus)

Meeting – Friday, November 05, 2010
10:00 AM – 12:00 PM

City Council Chambers
505 Forest Avenue
Laguna Beach, CA

The California Department of Food and Agriculture (CDFA), the Orange County Agricultural Commissioner, the United States Department of Agriculture, and the University of California Cooperative Extension are hosting the first of several informational meetings. The goal of this meeting is to inform local government officials, arborists, public works, landscapers, and pest control advisors about the current RPW situation including properly identifying the pest and its feeding damage. Future meetings will target other industry members and the public.

Worldwide, the Red Palm Weevil (Rhynchophorus ferrugineus) is considered the most destructive pest of palms. A red palm weevil (RPW) discovery on a residential plant in Laguna Beach is the first time this beetle has been detected in the United States. The presence of the red palm weevil in California represents a serious threat to landscape palms as well as to the date palm industry.

Because you are an important member of California’s pest surveillance system, your participation in this meeting is needed to assist us in responding to this harmful, invasive pest before it becomes established. If you cannot attend this important meeting and require additional information, please contact our toll-free PEST HOTLINE at (800) 491-1899 or visit our red palm weevil website at: www.cdfa.ca.gov/phpps/rpw

(Note: Free Parking is available at the corner of Laguna Canyon Road and Forest Avenue, located one block away from the City Council Chambers)

Meeting Agenda:

Welcome – Rick LeFeuvre or designee (Orange County Agricultural Commissioner)
Red Palm Weevil Biology and Identification – Nick Nisson, Orange County Entomologist
Trapping and Surveillance – John Hooper or designee (CDFA)
Potential Regulatory Impacts – Nawal Sharma or designee (CDFA)
What you can do to Help – Dr. John Kabashima (UCCE)
Public Outreach Campaign – CDFA Public Information Officer
Question and Answer Session – CDFA will moderate

(Note: Special thanks to the City of Laguna Beach for providing free parking!)

For More Details Please Contact:
John Kabashima, M.B.A., Ph.D.
County Director/Environmental Horticulture Advisor
University of California Cooperative Extension, Orange County
1045 Arlington Dr.
Costa Mesa, CA 92626
Ph: 714-708-1611
Fax: 714-708-2754
Email: jnkabashima@ucdavis.edu

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News

Red Palm Weevil

UC Riverside

Tamarixia radiata release video

Anonymous — Mon, 20 Jan 2020 01:53:31 +0000

Tamarixia radiata release video Anonymous (not verified) Sun, 01/19/2020 - 17:53 More Blog Posts CISR Team January 12, 2012

Christina Hoddle explains the release of Tamarixia radiata at UC Riverside. Video recorded on December 20, 2011 at University California Riverside.

For more information about Tamarixia radiata and Asian Citrus Psyllid, visit the CISR website: http://cisr.ucr.edu/asian_citrus_psyllid.html

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Huanglongbing Detected in Hacienda Heights, Los Angeles County

Anonymous — Mon, 20 Jan 2020 01:50:18 +0000

Huanglongbing Detected in Hacienda Heights, Los Angeles County Anonymous (not verified) Sun, 01/19/2020 - 17:50 More Blog Posts Mark Hoddle April 13, 2012

The Situation: On Thursday April 5 2012, after about a week of testing, the California Department of Food and Agriculture (CDFA) removed a pumelo tree with a lemon graft from Hacienda Heights in Los Angeles County after the tree and an Asian citrus psyllidfound on the tree both tested positive for a lethal citrus disease, Huanglongbing(pronounced Wong-Long-Bing [HLB]). HLB is caused by a bacterium, and HLB-causing bacteria kill citrus by affecting the food transportation systems of infected trees. There is no known cure for the disease, and the HLB-bacterium does not pose a threat to humans, pets, or other plants.

Asian Citrus Psyllid

The Problem: Huanglongbing, also known as yellow shoot disease, yellow dragon disease (these are English translations from the Chinese Huanglongbing indicating that the leaves of infected citrus appear an irregular mottled yellow color) or citrus greening (because fruit don’t ripen properly and remain green in areas) is spread from tree-to-tree by the Asian citrus psyllid (ACP), This small insect acts as a flying syringe carrying bacteria in its needle-like mouthparts and when infected psyllids feed on citrus they inject bacteria into trees. The disease can also spread by grafting infected branches onto healthy trees. The possibility that an infected branch was brought into California and used for a graft is being investigated.

Infected trees typically die within 5-8 years after being infected, but disease symptoms may take as long as 2 years to become obvious. This long latency period provides ample time and opportunities for ACP to visit infected plants, feed on them, acquire the bacteria and fly onto healthy trees to feed which puts these trees at risk of becoming infected with bacteria.

HLB has been a particularly devastating disease problem in Florida. In 2005, HLB was first detected and it was estimated that 10% or 60,000 acres of citrus was destroyed by HLB by 2009, just four years after the first find. This reduction of citrus acreage in Florida corresponded with an estimated loss of 6,600 jobs, $1.3 billion in lost revenues to growers, and $3.6 billion in lost economic activity associated with the citrus industry in Florida.

The commercial citrus industry is worth about $1.2 billion in California and about 300,000 acres are farmed.

Where are ACP and HLB in the USA? ACP and HLB are present in Florida, Texas, Louisiana, Georgia, and South Carolina. ACP is present in Arizona, Mississippi, and Alabama, but HLB has not yet been found. In California, ACP was first found in San Diego and Imperial Counties in 2008. Since this initial detection ACP has been found in Ventura, Orange, Santa Barbara, Los Angeles, Riverside, and San Bernardino Counties. ACP populations at this time are heaviest in Los Angeles County.

The quarantine for HLB in Los Angeles and Orange Counties

The Response: On April 5 2012, the CDFA held an open house meeting at Industry Hills Expo Center in the City of Industry. The purpose of the meeting was to provide the public with information on HLB and ACP and to respond to requests to examine citrus with disease symptoms that look suspiciously like HLB. Additionally, all citrus within an 800 meter (about 2,400 feet) radius of the infected tree have been treated with insecticides by the CDFA to kill any Asian citrus psyllids that may be carrying bacteria that cause HLB. A 93 square mile quarantine has been established in Hacienda Heights in Los Angeles County and part of northern Orange County. This quarantine prohibits the movement of all citrus nursery stock out of this area in case they are infected with HLB and these plants, if infected, could start new disease infestations in different areas of California. Any fruit from residential properties must not be moved to other areas in case ACP or HLB accidentally hitch-hike into new areas on this fruit.

A description of the Quarantine has been prepared by CDFA and maps of the Quarantine Zone are available.

What is the Future for Citrus in California? Following the find of HLB in Hacienda Heights there has been concern that a massive citrus die off in gardens is now imminent. This is unlikely because surveys have failed so far to find more than one tree infected with HLB. Further, it is unlikely that trees dying from HLB be initially widespread, it is probable that if there are other HLB infected trees in California, they are uncommon and widespread. The difficult problem facing the CDFA and USDA is finding these infected trees (should they exist) and eradicating them before ACP finds them, feeds, acquires HLB bacteria, and spreads them to healthy citrus. Because the disease is slow in killing trees, the loss of trees will be slow, and probably patchily distributed in the early stages of the spread.

What Can you Do to Help? The CDFA has set up a Pest Hotline 1-800-491-1899 and a Report-a-Pest website http://www.cdfa.ca.gov/plant/reportapest/ to help in the fight against invasive species coming into California.

Recent News Articles
Los Angeles Times: Gardeners’ Common Bond May Have Introduced Deadly Disease.
Los Angeles Times: San Gabriel Valley Homeowners Swarm to Meeting about Citrus Disease

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Testing a New Trapping Program for Red Palm Weevil in Laguna Beach California

Anonymous — Mon, 20 Jan 2020 01:48:38 +0000

Testing a New Trapping Program for Red Palm Weevil in Laguna Beach California Anonymous (not verified) Sun, 01/19/2020 - 17:48 More Blog Posts CISR Team June 28, 2012

Since the first official detection of red palm weevil (RPW) in September 2010, the California Department of Food and Agriculture has been running a pheromone trapping program for this pest in Laguna Beach. As part of this trapping program, CDFA is monitoring 153 traps that are set up in two different patterns. The core area around the initial RPW finds is being trapped at a rate of 50 traps per square mile. Outside of this intensive trapping area the remaining traps are deployed at 25 per square mile. Traps were monitored weekly until March 2012, after this time, servicing has been reduced to once every two weeks. The first RPW adult caught as part of this monitoring program was collected from a trap on 18 January 2012 that was last serviced 9 January 2012. The trap that caught the single RPW was on a Washingtonia palm close to the Pacific Coast Highway in Laguna Beach.

It is surprising that despite the intensive and long-term trapping effort by the CDFA that so few RPW have been trapped. In overseas countries were RPW is either native (e.g., India) or invasive (e.g., the Mediterranean and Saudi Arabia) the pheromone traps are very effective at luring and trapping RPW. However, it should be noted that the color form of the RPW caught in these trapping programs is the orange and black form, and not the red stripe form that is present in Laguna Beach.

Orange and red stripe on the Red Palm Weevil.

There could be several reasons for the lack of RPW captures in Laguna Beach using the pheromone bucket traps:

The RPW pheromone that is being used in the trapping program, while very attractive to the orange and black form RPW, is not particularly attractive to the red stripe form in Laguna Beach. May be it is not even the correct aggregation pheromone.
Densities of RPW in Laguna Beach are simply too low to be captured in the bucket traps with the pheromone.
The pheromone trap set up being used is not very attractive to the red stripe form of RPW in Laguna and dispersing RPW simply ignore it because they find infested palm trees more attractive and they tend to aggregate here with other RPW instead of going to the traps.

To address these potential issues a couple of research projects were executed overseas with funding from the CDFA’s Specialty Crops Program. This program was designed to investigate possible factors affecting the success of the trapping program in Laguna Beach, and if possible, to figure out ways to make it more effective.

Three key research questions were addressed with research projects that were run in the Philippines and Indonesia: (1) can the commercially-available RPW pheromone that is being used in Laguna Beach attract the red stripe form of RPW in countries where this color form is native? We had to do the work in these overseas countries because there are no other areas in the world which have the red stripe form of RPW. (2) Is there a more attractive trap set up that could increase the chances of capturing the red stripe form of RPW? (3) Does the pheromone for the red stripe form of RPW have the same chemical make up as the commercial RPW pheromone used for trapping the orange form of RPW?

Assessing the Attractiveness of the RPW Trapping Program Used in Laguna Beach to the Red Stripe Form of RPW. Two large field experiments were conducted in the Philippines and Sumatra Indonesia to assess the attractiveness of the CDFA’s bucket trap to the red stripe form of RPW. Three different trap set ups were tried: (A) cut coconut logs only (coconuts are a highly preferred host palm for RPW in countries where it is native and volatiles released from cut coconut palms are very attractive to RPW), (B) pheromone traps only, and (C) pheromone traps with freshly cut coconut logs.

The daily RPW harvest from the field trials in Indonesia

The results of these trials in the Philippines and Indonesia were crystal clear – RPW was highly attracted to stacks of cut coconut palm logs that had the pheromone traps sitting on the log stack. This suggested to us that perhaps the missing element in Laguna was a lack of freshly cut palm material to help attract RPW to the pheromone traps that the CDFA is using to monitor for this pest.

The results of this study also indicated that the commercially-available pheromone seemed to be quite important for attracting the red stripe form of RPW to stacks of cut coconut logs. But did this mean that the pheromone was actually the correct one used by the red stripe form, or did these RPW simply find it O.K., but not as attractive as the pheromone that they produce themselves (assuming the red stripe RPW have a similar but different pheromone to that used by the orange and black forms)? To answer this question we collected aggregation pheromone for red stripe RPW captured in the field in an oil palm plantation in Sumatra Indonesia.

Cut coconut palm trunks and a RPW pheromone trap set up in Indonesia to test the efficacy of the commercially-available RPW aggregation pheromone

Collecting Aggregation Pheromone from the Red Stripe Form of RPW in Sumatra Indonesia. Adult red striped RPW collected from oil palm trees that had collapsed in a commercial oil palm plantation were used for the pheromone collection experiments. The process was quite simple in concept, but a little challenging to execute in an outdoor shed in an oil plantation! Field collected RPW (all red stripe forms) were set up in oven bags that had hoses hooked up to an aquarium pump. The aquarium pump pulled air through a special set of filters to remove any potential volatile contaminants before it passed into the oven bags and over the contents of the bags. The RPW were contained in mesh cages inside the oven bags so they couldn’t chew holes in the bags and escape. Four oven bags were set up each time pheromone aeration trials were run. The bags contained either an empty sterilized mesh cage (to capture the chemical signature of the mesh cage), RPW food only in a mesh cage.

RPW set up in oven bags and being aerated for pheromone capture in Sumatra Indonesia

Sugar cane or oil palm hearts were the food used for the RPW – it really likes to eat both types, but we didn’t know whether sugar cane or oil palm would be needed to stimulate RPW to release aggregation pheromone, so we tried both. RPW in a mesh cage only, or RPW with food inside a mesh cage. Aerations were made for these different treatments continuously for about 3-4 days. The volatiles released were trapped on ultra-pure charcoal filters as purified air was pulled through the oven bags containing the treatments. After this exposure time the charcoal filters were removed, new treatments were set up again, and then randomly assigned to a new set of oven bags. The process was repeated three or four times over a 14 day period.

The RPW field crew who assisted daily with the field experiments in Indonesia

The charcoal filters with aeration product were air expressed from Sumatra to Riverside, California. Jocelyn Millar at UC Riverside analyzed the aggregation pheromone captured on the charcoal filters that had been released from the red stripe RPW inside the oven bags. Millar’s analyses clearly showed that the aggregation pheromone released by the red stripe form in Sumatra was exactly the same as the commercially-available pheromone used to trap the orange and black form of RPW. We concluded from this work that we were using the correct aggregation pheromone to attract the red stripe form of RPW in Laguna Beach.

A New Trapping Plan for the Red Striped RPW in Laguna Beach. So after the completion of these studies in the Philippines and Indonesia, the pieces were now in place to consider a modified trapping program for the red stripe RPW in Laguna. We know that the aggregation pheromone released by the red stripe RPW is exactly the same as the commercially-available pheromone used to trap the orange and black form of RPW, so there is no problem in using this pheromone. We also learned that red stripe RPW are strongly attracted to stacks of freshly cut palm logs that have aggregation pheromone sitting on top of these log stacks. The challenge after figuring this out is to replicate this set up in Laguna Beach.

Setting up the RPW pheromone aeration experiment in Sumatra Indonesia

The CDFA gave permission to set up a new trapping plan in May 2012 using freshly cut date palm logs and pheromone traps. This program was a replication of the successful trapping programs that had been tested in the Philippines and Indonesia. In June 2012, three stacks of cut date palm logs with RPW pheromone traps were deployed at three different sites in Laguna Beach. This project was a major collaboration between UC Riverside with date palm producers in the Coachella Valley, in particular Duane Young with Cocopah Nurseries in Indio California, and Albert Keck with Hadley Dates in Vista Santa Rosa (both businesses operate out of the Coachella Valley.)

Cocopah Nurseries donated 3 date palms that were felled, and from which the top most third was removed from the trunk and cut with a chainsaw into sections for deployment at Laguna Beach. These palm sections were transported to Laguna Beach and set up at three different sites with pheromone traps. These sites were selected based on their close proximity to previous find sites for RPW and to palms which have had evidence of recent RPW attacks. The log stacks and pheromone buckets are checked daily and trap checking is a cooperative effort between CDFA (Mohammed Alzubaidy), the Orange County Agricultural Commissioner’s Office (Nick Nisson), UC Cooperative Extension (John Kabashima), and UC Riverside (Mark and Christina Hoddle). At the time this blog was written, this new trapping program had been out for one week and no RPW had been caught.

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Mark Hoddle

Red Palm Weevil

UC Riverside

Tamarixia radiata and Natural Enemy Impacts on the Invasive Asian Citrus Psyllid in southern California

Anonymous — Wed, 18 Dec 2019 10:14:57 +0000

Tamarixia radiata and Natural Enemy Impacts on the Invasive Asian Citrus Psyllid in southern California Anonymous (not verified) Wed, 12/18/2019 - 02:14 More Blog Posts Erica Kistner October 31, 2014

Written by:
Erica J. Kistner (Postdoctoral Scholar, UC Riverside)

Photos by:
Mike Lewis, Mark Hoddle and Nayham Melhem

The Problem: Since its accidental introduction in 2008, the invasive Asian Citrus Psyllid (ACP) is now widespread throughout southern CA including San Diego, Imperial, Riverside, Los Angeles, Orange, and San Bernardino counties. ACP may present the greatest economic threat that California’s citrus industry has ever faced. This little insect is an efficient vector of a bacterium that causes a lethal citrus disease, huanglongbing (HLB), which is one of the most destructive diseases of citrus worldwide. There is currently no cure for this bacterial disease which kills susceptible commercial citrus varieties in as little as 5-8 years. California’s citrus industry is currently valued at $2 billion per year. Since 2005, Florida’s citrus industry has been hit hard by HLB. The spread of HLB in Florida by ACP has been estimated to have cost the Florida citrus industry $1.6 billion in losses over a 5 year period. In April 2012, the first case of HLB was detected in a residential site in Los Angeles County.

The remains of Tamarixia killed Asian citrus psyllid nymphs. The circular holes near the head indicate where the wasp emerged from its mummified host.

Ongoing Biocontrol Efforts: To reduce the spread of HLB into California’s commercial orange groves, a tiny parasitic wasp, Tamarixia radiata, sourced from Pakistan is currently being massed reared and released as a biocontrol agent throughout southern California. As of July 2014, approximately ~700,000 Tamarixia wasps have been released by the California Department of Food and Agriculture. This parasitoid has multiple stable populations and has even spread to sites where it was never released and it had likely established in southern California. Despite these massive rearing and distribution efforts, the efficacy of Tamarixia in controlling urban ACP population growth and spread remains unknown. Preliminary results of biweekly ACP surveys across 27 sites in Riverside and LA County suggest that Tamarixia may be limiting ACP densities.

Asian Citrus Psyllid, Diaphorina citri, life stages. UCNFA, G.O. Conville 1970.

ACP Life Cycle: ACP hatch from eggs and transition through 5 juvenile life stage known as nymphal instars before reaching adulthood (see photo above). ACP adults have wings and are excellent fliers. ACP generation time is short with development from egg to sexually mature adult taking ~2-4 weeks.

Natural Enemies and Allies: In addition to Tamarixia, ACP may have other enemies including naturally occurring predators. Generalist predators, including lady beetles are known to signficantly reduce ACP numbers in Florida, but their impact in California is unknown. To complicate matters further, the Argentine ant, another invasive pest, may be helping ACP thrive in southern CA. These ants have been observed to protect ACP colonies from their enemies (including Tamarixia). In exchange, colonies of ACP nymphs provide ants with honeydew, a sweet waste product that nymphs excrete (See photo above).

Argentine ants tending Asian citrus psyllid nymphs on our experimental colonies. These ants may interfere with biocontrol efforts by protecting ACP from Tamarixia and predators.

ACP Survival Experiments: To access the impact of natural enemies on ACP population growth, experimental ACP cohorts are currently being monitoring at three sites within Riverside County, CA where Tamarixia has been released and established. ACP cohorts of ~200 eggs are established in the lab on four citrus plants that are placed at field sites to assess the impact of natural enemies on these experimental ACP cohorts. Four treatments are evaluated to assess natural enemy impact on immature ACP: (1) potted plants are completely enclosed with a fine mesh bag to exclude all natural enemies, this treatment acts as a control to determine ACP survivorship rates in the absence of natural enemies (we expect survivorship rates to be high in this treatment is nothing is able to access the ACP and feed on it). (2) Potted plants are enclosed within a coarse mesh bag to prevent access by large predators while still allowing entry of small natural enemies like Tamarixia. This treatment provides information on how much mortality Tamarixia alone can inflict on ACP if these parasitoids can find ACP cohorts in the field. (3) A sticky barrier is applied to potted plant bases to prevent access to ACP by walking natural enemies (e.g., lacewing larvae). Only natural enemies that can fly (e.g., ladybugs and Tamarixia) will be able to land on plants to attack ACP eggs and nymphs, (4) Potted plants are fully exposed thereby allowing free access to ACP life stages by all natural enemies (i.e., walkers and flyers). Plants are examined every other day using a 10x lens and numbers of ACP by life stage are recorded per treatment. Predators observed on ACP patches or trapped in tangle foot barriers are identified. Parasitism by Tamarixia is easy to detect in the field since emerging adult wasps leave a circular exit hole in the body of the deceased ACP host (see photo above).

Experimental ACP cohorts at the UC-R Biocontrol Plot. Each potted citrus plant is home to families of ACP (known as cohorts) whose survival is monitored from egg to adulthood.

Results to Date: Preliminary results suggest that both predators and Tamarixia reduce experimental ACP numbers in California. Protection from natural enemies can increase ACP survival by 6-fold. Thus far, hover fly (Syrphidae) and green lacewing (Chrysopidae) larvae have been the most commonly observed predators, but spiders (Aranae) and lady beetles (Coccinellidae) have also been seen on experimental ACP colonies. Hover fly and green lacewing larvae have voracious appetites and may consume over 100 ACP nymphs before pupating (the non-feeding stage between insect larvae and adult life stages). ACP mortality from these hungry larvae can reach as high as 93% in some instances.

One experimental site with ACP cohorts in Riverside exhibited a 66.3% parasitism rate by Tamarixia when ACP cohorts were protected from walking predators and only a 1.4% parasitism rate when exposed to all enemies. Could this reduction in parasitism be the work of the Argentine ant? These ants have been observed tending experimental ACP colonies which likely protects them from natural enemies.

Green Lacewing (right) and hover fly larvae (left) found on experimental potted plants with ACP cohorts. Adults of both species lay their eggs next to psyllid and aphid colonies.

Future Plans: Argentine ants are abundant at all experimental sites and their interactions with ACP and natural enemies are being investigated. These experiments will continue over a year’s time (2014-2015) to compare seasonal variation in ACP densities through time.

Take Home Message: Our results suggest that predators as well as Tamarixia are helping limit ACP numbers at urban sites. In turn, your friendly neighborhood insects may help prevent the future spread of HLB in California by reducing ACP populations and this in turn helps to protect our commercial citrus production areas from ACP and HLB.

Argentine Ants, Asian Citrus Psyllid, Tamarixia radiata, UC Riverside

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First Official Release of Diaphorencyrtus aligarhensis in California for the Biological Control of Asian Citrus Psyllid

Anonymous — Wed, 18 Dec 2019 10:03:05 +0000

First Official Release of Diaphorencyrtus aligarhensis in California for the Biological Control of Asian Citrus Psyllid Anonymous (not verified) Wed, 12/18/2019 - 02:03 More Blog Posts Mark Hoddle December 19, 2014

The Problem

Figure 1. An adult male (left) and female (right) Diaphorencyrtus aligarhensis on a citrus leaf. Photo Mike Lewis, Center for Invasive Species Research, UC Riverside.

Asian citrus psyllid (ACP) is a serious threat to California’s citrus because it spreads a bacterium that causes a lethal disease of citrus, huanglongbing, which was first detected in Hacienda Heights, Los Angeles County in March 2012. One way to reduce the rate of spread of HLB is to reduce the populations of ACP living on citrus in urban areas. This will have two important impacts: (1) it will reduce the rate of spread of HLB by ACP, and (2) fewer ACP will migrate from urban areas into commercial citrus production areas threatening organic and conventionally-grown citrus. One way to suppress ACP populations in urban areas without the use of pesticides is through biological control, the use of natural enemies to reduce pest population densities.

On 16 December 2014, the biological control project targeting ACP took a significant step forward when 556 Diaphorencyrtus aligarhensis (Hymenoptera: Encyrtidae) (Fig. 1) were released at the University of California Riverside (UCR) Biological Control Grove. The release occurred at 9:00am and was attended by approximately 40 people representing UCR, the Citrus Research Board (CRB), the California Department of Food and Agriculture (CDFA), local pest control advisors, and media representatives.

Figure 2. UC Riverside’s Chancellor Kim Wilcox (right) and Divisional Dean of Agricultural and Natural Sciences, Jodie Holt (left), releasing Diaphorencyrtus at the Biological Control Grove. Photo Mike Lewis, Center for Invasive Species Research.

The first of 15 vials that contained parasitoids was opened by Chancellor Kim Wilcox (Fig. 2), the remaining vials were distributed amongst attendees, who opened and tied them to branches of lemon trees in the Biocontrol Grove. The sex ratio of this Pakistani parasitoid is ~50% female and ~50% male. The road to releasing Diaphorencyrtus in California was long. The parasitoid was first collected from Punjab Pakistan in March 2011 and recovered from ACP nymphs until a sixth and final collecting trip was completed in April 2013. A total of 1,023 Diaphorencyrtus were collected in Pakistan and returned to the quarantine facility at UCR.

How Safe is Diaphorencyrtus for California?

Figure 3. Diaphorencyrtus sitting on the nose of Abraham Lincoln on a US penny. Photo Mike Lewis, Center for Invasive Species Research.

Diaphorencyrtus is a tiny parasitic wasp (Fig. 3), it can’t sting people or animals, it doesn’t eat plants, and unlike ACP it can’t spread the bacterium that causes huanglongbing, the disease that kills citrus. Safety testing to determine the host specificity of Diaphorencyrtus took almost 18 months to complete in quarantine at UCR. This process involved exposing this parasitoid to non-target psyllid species that included native psyllid species and psyllids used as weed biocontrol agents to determine its host range (i.e., the number of psyllid species it can attack) and host specificity (i.e., which psyllid species are most preferred for parasitism). Results from no-choice and choice tests were used to prepare an 84 page Environment Assessment Report that was submitted to USDA-APHIS for review on 1 November 2013. The results of experiments demonstrated that Diaphorencyrtus has a very strong preference for ACP nymphs and likely poses little environmental risk. On 24 November 2014, USDA-APHIS issued the official release permit, P526P-14-04034, to move Diaphorencyrtus out of quarantine for release and use in California as a biocontrol agent of ACP.

Overview of Diaphorencyrtus Biology

Figure 4. Diaphorencyrtus ovipositing in a third instar ACP nymph. Photo Mike Lewis, Center for Invasive Species Research, UC Riverside.

Diaphorencyrtus is an endoparasitoid that can parasitize second through fourth instar ACP nymphs, but second and third instars seem to be preferred (Fig. 4). All parasitized ACP nymphs, regardless of stage that is parasitized, continue to feed, develop, and molt to the fifth and final instar before they turn into mummies. Curiously, Diaphorenyrtus is unable to develop in late stage fourth instar (i.e., nymphs that are older than 7.5 days of age) as for some unknown reason parasitoid eggs don’t hatch (. Fifth instar ACP nymphs are also unsuitable for oviposition because the cuticle maybe too thick to pierce with the ovipositor and defensive twitching by these large nymphs may deter ovipositing females.

Figure 5. Asian citrus psyllid mummies showing the position of exit holes chewed by adult Diaphorencyrtus (left, hole is in posterior of the ACP mummy) and Tamarixia (right, hole is in anterior of the ACP mummy). Photo Mike Lewis, Center for Invasive Species Research, UC Riverside.

Development from egg to adult parasitoid emergence takes about 16 days at 77^oF (25^oC). During this developmental period parasitoid larvae passes through four larval instars, or developmental stages, before reaching a pre-pupal stage that transitions into the pupa. Developmental times for Diaphorencyrtus eggs, first and second instar larvae are about 2 days; the third, fourth, and pre-pupal stages last around 1 day, while the pupal stage takes seven days to complete. During the third instar, Diaphorencyrtus larvae use secretions from the tip of the abdomen to anchor themselves within the thoracic region of body cavity of the ACP nymph. Once secured, parasitoid larvae then position themselves with the posterior of their bodies aligned with the head of the ACP nymph and the larval head or anterior region facing the posterior of the host.

Figure 6. An adult female Diaphorencyrtus feeding on Asian citrus psyllid nymph honeydew. Photo Mike Lewis, Center for Invasive Species Research, UC Riverside.

Therefore, when adult Diaphorencyrtus emerge, they chew an exit hole at the posterior end of the ACP mummy through which they escape. In contrast, Tamarixia chews an exit hole in the anterior or head region of the ACP nymph to emerge (Fig. 5). Diaphorencyrtus females obtain protein for maturing eggs by host feeding on ACP nymphs. To host feed, females use their ovipositor to pierce the body of the ACP nymph, hemolymph or insect blood, leaks from these wounds and is eaten by females. The trauma of being stabbed and then fed upon is often sufficient to kill ACP nymphs. Additionally, adult Diaphorencyrtus may gain nutrition from eating ACP honeydew, the dried white material that is exuded by feeding nymphs (Fig. 6).

The Diaphorencyrtus Release Plan for California

Releases of Diaphorencyrtus are planned for areas where Tamarixia has either not been released or surveys indicate that selected areas near Tamarixia release sites have little or no activity associated with this parasitoid. The reason for this strategy is to minimize competition between Diaphorencyrtus and Tamarixia so as to give Diaphorencyrtus the best possible chance to establish. To select sites for Diaphorencyrtus releases we are working closely with the CDFA to identify suitable sites that encompass a variety of different climatic conditions. For example, Tamarixia-free sites in the Coachella Valley have been identified and scouting is underway to look for suitable release areas in Riverside and Los Angeles Counties. Past experience suggests that establishing more than one natural enemy of a citrus pest in California can increase the chances of successful biological control. Perhaps one of the best recognized cases is that concerning the cottony cushion scale, Icerya purchasi, with the predatory beetle, Rodolia cardinalis, and the parasitic fly, Cryptochaetum iceryae. Surveys indicate that the beetle provides control in arid desert interior regions, while the fly dominates in cooler coastal areas where citrus is grown. Parasitoid releases will be made when ACP stages are abundant for parasitism and host feeding. Site security needs to be ensured to minimize preventable accidents such as pesticide sprays or pruning of trees which could accidentally eradicate incipient Diaphorencyrtus populations.

How Well Will Diaphorencyrtus Control ACP in California?

Diaphorencyrtus populations sourced from Taiwan, Vietnam, and China (these are all female colonies) have failed to establish in Florida despite multiple release efforts involving more than 11,000 parasitoids. Reasons for this are unknown, but could be due to heavy pesticide use to control ACP, lack of synchrony between releases and ACP life stages suitable for parasitism, competition from Tamarixia, and possible predation of parasitized nymphs. Other factors may include low genetic diversity (because these parasitoids in Florida are all female they don’t reproduce sexually) and too little investment put into release and establishment efforts.

In many countries Tamarixia and Diaphorencyrtus coexist (e.g., Vietnam, China, and Taiwan) and in Pakistan the results of ~ 2.5 year long surveys in kinnow mandarin and sweet orange suggest that average year round parasitism of ACP nymphs by Diaphorencyrtus is ~ 20% while Tamarixia accounts for ~30% parasitism each year (Khan et al., 2014). In Saudi Arabia, Diaphorencyrtus may be the only parasitoid species attacking ACP nymphs infesting Mexican limes with maximum parasitism rates of 64-71% being recorded.

It is impossible to predict what level of ACP suppression Diaphorencyrtus is likely to provide in California. It is anticipated that if Diaphorencyrtus establishes it will complement the activity of Tamarixia thereby increasing overall ACP mortality. It is possible that if Diaphorencyrtus does establish in may have ecoclimatic preferences different to that of Tamarixia which may allow it to provide control in areas where Tamarixia is not effective. The only way to determine these potential outcomes is through a multi-year research program that tracks the establishment, spread, and impact of Diaphorencyrtus on ACP in urban and commercial citrus production areas in California.

Asian Citrus Psyllid, Mark Hoddle, News, UC Riverside

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