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Has the Asian Citrus Psyllid Parasitoid, Tamarixia radiata, Established in California?


Has the Asian Citrus Psyllid Parasitoid, Tamarixia radiata, Established in California?

By Mark Hoddle | July 19, 2012

Tamarixia radiata (female)

The Problem: Tamarixia radiata, a tiny parasitic wasp has been imported into California from the Punjab of Pakistan to attack nymphs of Asian citrus psyllid (ACP), a serious citrus pest that has established wide spread populations in the counties of Los Angeles, San Bernardino, and Riverside (significantly smaller populations are known in Imperial and San Diego Counties too). Releases of Tamarixia commenced in December 2011 after USDA-APHIS cleared this natural enemy for release from the Quarantine Facility at the University of California Riverside. Since these initial releases in December, approximately 8,500 parasitoids have been released at about 50 different sites in Southern California by July 2012.

The Biocontrol Release Program: Parasitoid releases have been made in the cities of Azusa, Bell Gardens, Chino, Duarte, Fontana, Los Angeles, Mira Loma, Montclair, Ontario, Pico Rivera, Pomona, Rialto, Riverside, San Bernardino and Whittier. In these areas, citrus in residential gardens with ACP infestations were selected for parasitoid releases. Ideally release sites had lemons or limes, and other types of citrus too (e.g., oranges or grapefruit.) Lemons and limes are good hosts for ACP because they tend to produce a lot of flush growth that is favored by ACP females for egg laying, and lemons in particular, tend to produce flush growth more frequently when compared to other types of citrus (e.g., oranges.)

A mixture of different citrus types in gardens is desirable for a release site because it increases the possibility that there will be flush present on different citrus types at different times of the year that will be available for ACP can infest. We’ve also noticed that semi-regular pruning of citrus, good fertilization, and decent watering schedules can also help garden citrus produce strong flush.

Tamarixia Recoveries: Parasitoids have been recovered at about 4-6 release sites in Azusa and Bell Gardens, and some of these sites have not received parasitoid releases for 2-3 months suggesting that Tamarixia has likely established and is breeding on its own (the life cycle of the parasitoid is about 12-14 days depending on the temperature). DNA analyses suggest that the parasitoids that have been recovered from release sites have a unique genetic signature that is very similar to the parasitoids imported from Pakistan for the biological control of ACP in southern California. This result tentatively suggests that the parasitoids recovered from release sites are most likely those that were mass reared and released by the

Tamarixia radiata parasitizing an Asian citrus psyllid nymph in Bell Gardens Los Angeles County

University of California Riverside. Further, at one site in Azusa, it appears that Tamarixia has self-dispersed about 65 m from where it was released on citrus and it established new populations on ACP infested curry plants (curry plants are really good hosts for ACP too.) Additionally, the genetic signal from captured parasitoids is reasonably diverse which suggests that the foreign exploration, rearing, and release program at UCR has preserved a lot of genetic variation which could be very important for local adaptation by parasitoids to citrus growing areas from the coast to the inland valleys.

How Does Tamarixia Kill ACP? Tamarixia can kill ACP nymphs in two different ways. First is parasitism, and in this instance a female parasitoid lays an egg underneath a fourth or fifth instar (instar refers to the developmental stage of the nymph, so a fifth instar is the fifth nymphal stage before the nymph becomes an adult) nymph. These larger nymphs are most preferred by Tamarixia for parasitism. When the egg hatches, the parasitoid larva begins to feed on the under surface of the ACP nymph. Eventually the Tamarixia larva will completely excavate the body cavity of the ACP nymph, and it will pupate inside the empty shell of its host. Often you will see beige colored silk strands radiating out from the edge of a mummified ACP nymph. The parasitoid larva spins this silk to hold the ACP shell onto to the twig that the nymph was feeding on. This ensures that the husk of the host won’t fall off the twig prematurely exposing the parasitoid pupa to predators or inclement climatic conditions. Once the parasitoid has finished pupating, the adult wasp chews a perfectly circular hole near the head of the mummified ACP husk and the parasitoid emerges. After emergence it will mate and if it is a female, it will hunt for more ACP nymphs to attack. The presence of these emergence holes near the head of dried up ACP nymphs is very strong evidence that Tamarixia emerged from that host.

The second way Tamarixia can kill ACP nymphs is by host feeding. When Tamarixia host feeds, the female uses her ovipositor or egg laying tube at the posterior end of her abdomen to stab and mutilate the ACP nymph. This physical injury causes hemolymph (the equivalent of insect blood) to leak from the body and the parasitoid feeds on this fluid. Hemolymph is an important source of protein for female parasitoids, and the trauma of being stabbed then feed upon is sufficient to kill ACP nymphs. Only females can attack ACP nymphs in this manner because males lack an ovipositor because they don’t lay eggs.
Laboratory studies on the biology of Tamarixia suggest that through the combined actions of parasitism and host feeding, individual female parasitoids have the capacity to kill several hundred ACP nymphs during their life time.

Argentine ants tending an infestation of Asian citrus psyllid nymphs. Ants may hamper biological control of ACP by Tamarixia

Ants and ACP Biocontrol: At some release sites, ants, in particular the invasive Argentine ant, may have the potential to interfere with the biological control of ACP. Field observations strongly suggest that ants tend ACP nymphs and as a reward for guarding them, the ACP provide the ants honeydew, a sweet waste product that they excrete. We’ve also seen ants capture and eat Tamarixia parasitoids foraging in clumps or patches of ACP nymphs, and in some instances the ants have chased Tamarixia off the patch if they could not catch it. It is possible that when ACP infestations are heavily tended by ants, some sort of ant control may be needed if the natural enemies are to attack the pests. This problem is not unique to ACP, honeydew producing scales and mealybugs, for example, are also tended by ants, which in turn hampers effective biological control of these pests too.

Future Plans: Monitoring and release programs are ongoing, and UC Riverside is now ramping up the mass production of Tamarixia for expanded releases throughout ACP infested zones. It is hoped that as more Pakistani Tamarixia are released in southern California greater establishment rates will occur and natural spread will begin to fill in areas between release sites.

Topics: Asian Citrus Psyllid, Mark Hoddle, Tamarixia radiata | 4 Comments »

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

By 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:

  1. 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.
  2. Densities of RPW in Laguna Beach are simply too low to be captured in the bucket traps with the pheromone.
  3. 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.

Topics: Mark Hoddle, Red Palm Weevil, UC Riverside | No Comments »

Huanglongbing Detected in Hacienda Heights, Los Angeles County

By 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 psyllid found 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

Topics: Asian Citrus Psyllid, Huanglongbing, Invasive Species, Mark Hoddle, News, UC Riverside | No Comments »

Entomophagy: Collecting and Eating Red Palm Weevil Larvae from Nipa Palms in Sumatra, Indonesia

By Mark Hoddle | March 9, 2012

The red stripe form of red palm weevil (referred to here as Rhynchophorus vulneratus) is harvested for food from nipa palm trunks in parts of Sumatra by rural and semi-rural agrarians. Nipa palms (Nypah fruticans; known as buah atap in Indonesia) typically grow in swampy muddy areas (in either fresh or brackish water conditions) and the fronds are used as thatch roofing, or basket making. Most of the trunk of the nipa palm grows underground and the leaves and flower stalks grow above ground. The sap and flowers are sweet, rich in sugars, and can be fermented. The trunk is high in starch and can be harvested, pounded, and dried to form a type of sweet “sago” flour.

Another use of the palm is for the deliberate rearing of R. vulneratus larvae for harvesting and eating. Adult weevils are attracted to exposed damaged trunks and in some instances salt may be applied to the cut area which reportedly increases the attractiveness to breeding weevils. Adult weevils attracted to the palm trunk release an aggregation pheromone which further amplifies the attractiveness of the palm for breeding and feeding. Female weevils use their long rostrum or snout to chew holes into the trunk and eggs are laid (oviposited) into these holes. After several days, the eggs hatch and the small first instar weevil larvae burrow into the trunk to feed.

Palm trunks prepared for weevil attack are opened with an axe and machete after about six weeks. If the trunk is infested with weevil larvae a distinctive fermenting odor emanates from the trunk when it is opened, the internal tissue has oxidized and taken on a brownish color with interspersed ginger-colored gelatinous globs. This fed upon and fermenting material has the consistency of sloppy oatmeal (porridge). Weevil larvae feeding inside the palm trunk are easy to find because they make large diameter tunnels, and disturbance and probing of tunnels causes the legless larvae to wriggle vigorously and once they start to move they are easy to pick out of the tunnels.

The larvae are very high in protein and are considered by FAO to be an insect food that has potential to be commercialized because it requires low inputs for the quantity and quality of nutrition provided. About 1,700 species of insects are eaten by humans, mainly in the tropics because they are available year round, diversity is high, and the harvest and sale of insects for human food is a good income supplement. Human consumption of insects is called entomophagy.

Large R. vulneratus larvae harvested from nipa logs in Sumatra can sell for as much as 1000 rupiah (~ $0.11 US) each while smaller larvae fetch around 500 rupiah. Larvae can be cooked before being eaten. To prepare larvae, the large head capsule is removed, larvae may be blanched quickly in boiling water before being battered and deep fried or prepared as a type of curry. When prepared this way weevil larvae are reminiscent of cooked shrimp or squid. Another selling point for these larvae is their apparent potency as an aphrodisiac (something I can’t confirm or deny after eating many). One of our field assistants refused to eat the larvae because he was working away from his village and wouldn’t see his wife for the next two weeks. This may be a powerful testimony to the power of this aphrodisiac.

Alternatively, larvae can be eaten raw straight from the nipa trunk. Smaller larvae are preferred because they are easier to chew and swallow. However, large larvae are no problem to eat alive. The best way to eat palm weevil larvae raw is to hold them by the head capsule between your thumb and forefinger, place the larva’s body in your mouth, and bite behind the head severing it from the body and leaving the head capsule between your fingertips. Palm weevil larvae from nipa palms are surprisingly sweet, the texture internal body contents is smooth and agreeable, and they don’t have a foul or weird taste (you’d expect them to taste like rotting wood but they don’t!) The larva cuticle or skin is very chewy and can be spat out or easily swallowed.

I was very surprised at how easy these larvae were to eat straight from the nipa palm trunk in the jungle. We washed the larvae with some drinking water to remove the fermenting palm mush prior to eating them. Our guides indicated that the most preferred weevil larvae are taken from nipa palms while those harvested from the crowns of coconuts have a less agreeable taste and texture.

For more info:
Red Palm Weevil on CISR
Edible Forest Insects – Humans Bite Back!!
Beastly Bugs or Edible Delicacies?
Time for a ‘Bug Mac’? The Dutch Aim to Make Insects More Palatable
Entomophagy: Edible forest insects
Could you please pass me the bug kabobs? 

 

Topics: Entomophagy, Invasive Species, Mark Hoddle, Red Palm Weevil | 4 Comments »

Tamarixia radiata release video

By 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

Topics: Asian Citrus Psyllid, Christina Hoddle, Invasive Species, Mark Hoddle, News, Tamarixia radiata, UC Riverside | 5 Comments »

First Release of Tamarixia radiata in California for the Biological Control of Asian Citrus Psyllid

By Mark Hoddle | December 20, 2011

Provost and Executive Vice Chancellor of UC Riverside Dallas Rabenstein (left) and Mark Hoddle (right) made the first release of Tamarixia in Southern California.

At 11:00 am on the 20 December 2011, approximately 30-40 people assembled at the UC Riverside Biological Control Grove to participate in the first release in California of the Asian citrus psyllid natural enemy, Tamarixia radiata. Representatives from the University of California, California Department of Food and Agriculture, Citrus Research Board, and Citrus Pest and Disease Prevention Committee were in attendance. The event was covered by local media including Riverside’s Press Enterprise. After a brief introduction and description of the problem California faces with Asian citrus psyllid, and a quick review of the approximately two year process to reach this point, Mark Hoddle invited Provost and Executive Vice Chancellor Dallas Rabenstein to make the first release of Tamarixia in Southern California.

The Issue: In 2008, Asian citrus psyllid (ACP) was first found in California. This insect feeds on citrus and close relatives of citrus. The major problem with ACP is that is spreads a bacterium that causes a lethal disease in citrus known as Huanglongbing (HLB) . There is no cure for this disease. HLB is NOT in California.
ACP is widely established in LA County and pest populations are increasing and spreading in Riverside and San Bernardino Counties. This pest is almost exclusively restricted to backyard citrus. Spray programs to control ACP are difficult and expensive, and not every infested tree can be found and treated. Additional tools are needed for controlling ACP in California and biocontrol is one of these additional control options for ACP.

An adult Asian Citrus Psyllid on a citrus leaf.

The Biocontrol Program: ACP is native to Asia and the Punjab of Pakistan and India and this area is thought to be part of the native range where this insect evolved. People have accidently moved this pest and HLB around the world through the accidental movement of infested citrus plants.
Over the last two years Mark and Christina Hoddle (Department of Entomology, University of California, Riverside) have worked in Faisalabad Pakistan looking for natural enemies of ACP. Faisalabad Pakistan was chosen for this research effort because this part of Pakistan has a very good climate match (~70-75%) with the major citrus producing areas of California which will mean the natural enemies released in California will be pre-adapted to very hot dry summers and cold foggy winters.

An ACP Natural Enemy from Pakistan: One parasitoid found attacking ACP in the Punjab of Paksitan is Tamarixia radiata. This is a very small insect that kills ACP nymphs either by parasitizing them (i.e., females eggs laid underneath ACP nymphs and the parasitoid larvae burrow into the nymph to feed which kills the pest) or by host feeding (i.e., female parasitoids stab the nymph with their ovipositor, a tube that they use to lay eggs, and they feed on the body juices that leak from these wounds. This kills the nymph too.)

An adult female Tamarixia (left) and a dead Asian Citrus Psyllid nymph with an exit hole (right) from which an adult Tamarixia emerged after successfully parasitizing it.

Quarantine Studies: Safety tests conducted by Dr. Raju Pandey in Quarantine at UC Riverside clearly demonstrated that this parasitoid posed no undue risk to California’s environment, other species of insects, or humans. A 60 page Environment Assessment Report on Tamarixia that summarized the results of these studies was prepared by Mark Hoddle and Raju Pandey for review by USDA-APHIS. On 7 December 2012, APHIS issued a permit (P526P-11-04159) authorizing the release of Tamarixia from Quarantine for establishment in California for the biological control of ACP.

The Release Event: On 20 December 2011 at 11:00am, 12 glass vials containing 186 female Tamarixia and 95 male Tamarixia (total 281 parasitoids) were opened to release the parasitoids in the Biocontrol Grove at UC Riverside. The eight colonies in Quarantine from which these parasitoids were sourced for release were tested using DNA analyses to ensure that they were free of the bacterium that causes HLB. All tests were negative for HLB indicating that the parasitoids were free of this bacterium.
The Biocontrol Grove is a repository for natural enemies that have been imported for the biological control of citrus pests (e.g., scales, mealybugs, whiteflies, etc) in California over the last 50+ years. With the releases of Tamarixia in the Biocontrol Grove, one more natural enemy is being established here to combat an invasive pest that threatens California’s agricultural prosperity.

Expected Outcomes: This release of 281 Tamarixia is the first salvo against ACP in California. Over the next year or so it is anticipated that thousands of these parasitoids from Pakistan will be mass reared and released throughout LA, Riverside, and San Bernardino Counties and other areas as the pest continues to spread. Once Tamarixia establishes it will move by itself to find new populations of ACP to attack and kill. The parasitoids will have the ability to enter areas to kill ACP that may be difficult or impossible to reach for pesticide applications.

Tamarixia will *NOT* eradicate ACP from California but this natural enemy should reduce the populations of ACP in California. Every ACP killed by Tamarixia will be one less pest for homeowners and commercial citrus growers to worry about.

For More Information: These websites have more information on ACP and the work in Pakistan looking for natural enemies of ACP.
http://cisr.ucr.edu/asian_citrus_psyllid.html
http://cisr.ucr.edu/citrus_greening.html
http://cisr.ucr.edu/blog/psyllids/hunting-for-natural-enemies-of-asian-citrus-psyllid-in-pakistan/

Topics: Asian Citrus Psyllid, Christina Hoddle, Mark Hoddle, News, Tamarixia radiata | 12 Comments »

Looking for the Asian Tiger Mosquito in Southern California

By CISR Team | December 9, 2011


In September 2011, Asian Tiger Mosquito (Aedes albopictus) was found in Southern California. Small pockets of communities were reporting extremely aggressive, daytime biting mosquitoes – a telltale sign of the Asian Tiger Mosquito. The Asian Tiger Mosquito was first found in isolated pockets of California in the early 1970’s. It was eradicated, but showed up again in the late 80’s and again in the early 2000’s. This time, the potential vector-carrying mosquito was reported in the city of El Monte, about 10 miles East of Los Angeles.

In response, two LA based agencies worked together to inform the public about its new mosquito resident and to determine the extent of its establishment in the area. The Greater Los Angeles County Vector Control District (GLACVCD) and the San Gabriel Valley Mosquito & Vector Control District (SGVMVCD) cooperatively began surveying a 20 square mile grid of homes in El Monte. Officials knocked on doors to inform residents of the new pest, and asked for permission to check each property for potential breeding grounds around their homes.

Truc Dever, Director of Community Affairs and Steven Vetrone, Assistant Vector Ecologist are two officials from GLACVD who participated in the sweep in El Monte.

“If the Asian tiger mosquito becomes established here in LA County, it would be a game changer for all of us. Residents would need to be concerned about disease-transmitting mosquitoes biting them during the day,” Dever said.
Dever and Vetrone participated in a 20 square mile grid by knocking on doors in a South El Monte neighborhood. They had two primary goals: help increase the public’s awareness of the Asian Tiger Mosquito and check for areas that could provide a breeding ground. They walked around with the home owners to point out potential problems. Each pool of standing water was carefully examined for larva and eggs, and a few samples were taken back to the lab for further examinations.

The Asian Tiger Mosquito differs from other mosquito’s in that it is an aggressive day time biter. It can also carry a number of vectors like dengue, yellow fever and west nile virus. Breeding grounds can include anything that holds standing water. Trash can lids turned upside down proved a popular culprit, as well as water trays under garden pots. Even some unsuspecting plants that hold water on their leaves were potential candidates for mosquito eggs.

“We need the public’s help in order to control and eradicate this dangerous pest. We are asking everyone to call us if they are getting bitten by mosquitoes during the day.” Dever said.

For more information on the Asian Tiger Mosquito, visit the CISR page

Los Angeles officials are asking residents to call and report if they see any black and white mosquitoes that bit during the day. Please contact the Greater Los Angeles County Vector Control District at (562) 944-9656 (www.glacvcd.org) or the San Gabriel Valley Mosquito & Vector Control District at (626) 814-9466 (www.SGVmosquito.org)

Topics: Asian Tiger Mosquito, Invasive Species, News | 3 Comments »

Hunting for Natural Enemies of Asian Citrus Psyllid in Pakistan

By CISR Team | November 8, 2011


Asian citrus psyllid (ACP) was found in California in late 2008 in San Diego and Imperial Counties. This invasive pest sucks sap from citrus and is a major concern for California because when feeds ACP inject into trees bacteria that cause a lethal disease of citrus known as huanglongbing (HLB). This plant disease is incurable, is restricted to citrus, and poses zero (i.e., no) risk to humans. HLB is also known as yellow shoot disease or citrus greening.

This ACP-HLB combination has been particularly devastating following its arrival in major citrus producing areas. In Florida for example, 60,000 acres of citrus, about 10% of commercial production, was taken out by HLB within 4-5 years of the first detection of the disease. At the time this blog was written (November 2011), HLB had not been detected in California. However, many suspect that the disease is present in California, and could be residing undetected in backyard citrus, possibly in plants that were smuggled into the state from areas where HLB is present (e.g., Asia, Mexico, or Florida).

Since 2008, large ACP populations have developed in Los Angeles (LA), Riverside, and San Bernardino, Counties. The vast majority of infestations found by the California Department of Food and Agriculture’s (CDFA) monitoring program have been detected in urban areas. Citrus is a very popular backyard fruit tree and homeowners grow a large variety of different citrus including oranges, mandarins, lemons, limes, kumquats, and grapefruit. It has been estimated that there is more citrus growing in people’s gardens than there is in all of California’s commercial citrus production areas combined. Surveys by UC Riverside scientists working on ACP in LA have found that ACP is encountered most often on lemons and limes, and populations can reach very high levels on Mexican limes, which appear to be a highly favored host.

Containing ACP in urban areas is a major challenge that the CDFA and Citrus Research Board (CRB) have jointly undertaken. The management plan involves treatments of residential trees that have ACP and neighboring trees within a prescribed distance of the infested tree that triggered treatments. Pesticide applications may include foliar sprays to kill ACP eggs, nymphs, and adults, and soil drenches with approved systemic insecticides that move inside the plant killing ACP when they suck sap. Finding and treating ACP infested citrus is a difficult and expensive task, and some homeowners don’t like the idea of pesticides being applied to citrus in their gardens.

UC Riverside with support from CDFA, CRB, and the Citrus Health Response Program (CHRP) has initiated a classical biological control program for ACP. This approach to ACP control involves finding natural enemies of the pest in its native range. Most scientists who work on psyllids, the group to which ACP belongs, agree that this insect is probably native to parts of central and southern Asia and has been moved unintentionally on citrus into areas where it is not native. Once in these new areas, with lots of citrus to feed on, favorable year round climates, and a lack of specialist natural enemies, ACP populations increase and spread rapidly.

Part of the native range of ACP is the Indian subcontinent, and the very first study on ACP was published by two scientists Mohammad Hussain and Dina Nath in 1927 . They conducted their research on this citrus pest in the Punjab region of modern day Pakistan and India where is it was associated with declines in lemons and oranges. Hussain and Nath (1927) also reported that there were nine species of parasitoid attacking the nymphs of ACP and that parasitism of this pest could sometimes exceed 90-95% at certain times of the year. One species of parasitoid, Tamarixia radiata, an eulophid that preferentially attacks the fourth and fifth instars of ACP was reared described from specimens that emerged from ACP infesting lemon leaves in Lyallpur in 1922!! This parasitoid has been used in Florida, Texas, Mexico, the Caribbean, Central and South America for biological control of ACP.

The Punjab has a very good climatic match (about 70% similar) with the major citrus producing areas in the Central Valley of California. Biological control theory suggests that climates that are similar in the pest’s region of origin and the intended receiving range for natural enemies is important because it increases the likelihood that biological control agents will be well adapted to the climatic conditions in the area into which they could be introduced. There are basically three seasons in the Punjab; cool and foggy (October – February), hot (March-June), baking hot and humid (monsoon season July – September).

UAF Pakistan

The Central Valley is characterized by very hot dry summers and cold foggy winters (Tule fog). It is anticipated that parasitoids of ACP sourced from the Punjab of Pakistan will be well adapted to California’s citrus growing areas.

Agri Entomology

Foreign exploration for natural enemies of ACP in the Punjab of Pakistan was initiated with a trip over the period 28 August 2010 to 5 September 2011 to assess the potential for collaboration with scientists in the Department of Agri-Entomology at the University of Agriculture Faisalabad (UAF) (Faisalabad was formerly known as Lyallpur). It was quickly determined that UAF would be an excellent base for this project because it had research plots of citrus infested with ACP that were not treated with insecticides, UAF is closely positioned to Sargodha and Toba Tek Singh important commercial citrus production areas in the Punjab, and the Vice Chancellor of UAF, Dr. Iqrar Khan, a MS and Ph.D. graduate from UC Riverside (supervised by Dr. Mikeal Roose) and world leader in HLB research was extremely enthusiastic about developing a joint project between UAF and UC Riverside.

Mark and Christina Hoddle with VC Khan

Zaman taking field data

A four week trip to Pakistan over the period 11 March 2011 to 10 April 2011, resulted in the setting up of two research plots in Square 9 and PARS, both of which are UAF citrus research areas. In these two plots ACP and natural enemy population dynamics and flush growth patterns are being studied weekly on two different types of citrus, kinnow and sweet orange. Kinnow, a type of mandarin bred at UC Riverside by H.B. Frost in 1935 and introduced to UAF in 1940 and the first tree was planted in Square 9 one of our current study sites! Kinnow accounts for about 85% of citrus produced in the Punjab and it is an export crop for Pakistan. A Masters Student in Agri-Entomology, Mr. Shouket Zaman Khan was trained to do this work, and he is supervised by Dr. Mohammed Jalal Arif. At the end of this period, 80 Tamarixia radiata (24 males and 56 females) and 70 Diaphorencyrtus aligharhensis (25 males and 45 females) were returned to Quarantine at UC Riverside and used to establish colonies. All living material for this project is moved under USDA-APHIS permit and is cleared at LAX by Homeland Security Personnel before being moved to the Quarantine Facility at UCR.

Dr. Mohammad Jalal Arif working three phones

The third trip to Pakistan to look for ACP natural enemies was conducted over the period 6 June 2011 to 13 June 2011. This trip was very successful and 406 T. radiata (151 males and 255 females) and 25 D. aligarhensis (21 males and 4 females) were returned to UCR’s Quarantine facility.

The fourth collecting trip to Pakistan was completed over 28 October to 4 November 2011. From this collecting trip about 800 T. radiata and approximately 30 D. aligarhensis were brought back to UC Riverside. From all of these collections, just two parasitoids of ACP have been collected, T. radiata and D. aligarhensis. Consequently, we are questioning the validity of Husain and Nath’s (1927) claim that ACP nymphs were attacked by nine different species of parasitoid. Based on our experiences with collecting and rearing large numbers of specimens from Pakistan and from three different time periods it seems unlikely that the parasitoid fauna associated with this pest is diverse.

Shipments of natural enemies carried from Pakistan to UCR are processed in a receiving room in Quarantine. During this initial inspection phase, shipments are checked for accidental contaminants which are eliminated and destroyed immediately. Colonies of these natural enemies are set up in Quarantine at UC Riverside and are maintained as isocage lines to preserve genetic diversity. Maintaining colonies of ACP and its natural enemies in Quarantine is very difficult, time consuming, and requires meticulous attention to detail. Colonies of ACP and natural enemies are double caged, kept in secure rooms that are within secure rooms, and workers must wear coveralls which are removed in a designated changing room once work in the colonies is finished for the day.

T. radiata and D. aligarhensis are undergoing safety testing to ensure that they will pose no undue risk to the environment in California. Release of T. radiata for biological control of ACP in California is anticipated for Spring 2012 once the Environment Assessment Report has been reviewed and approved by USDA-APHIS.

Topics: Asian Citrus Psyllid, Christina Hoddle, Mark Hoddle, Psyllids, Tamarixia radiata | 7 Comments »

Testing Red Palm Weevil Pheromone Traps in the Philippines

By CISR Team | November 7, 2011


In August 2010, red palm weevil (RPW), was officially detected in Laguna Beach, Orange County California. This insect was recovered from a dying Canary Islands palm in a residential property and has been declared by FAO to be the world’s most destructive palm pest. At least 2-3 additional palms are thought to have been killed by this insect in Laguna Beach, and two Canary Islands palm trees showing RPW damage have been treated with insecticides. Intensive trapping efforts by CDFA for more than one year using the commercially-available RPW aggregation pheromone, ethyl acetate (weevil magnet), and fruit additives placed together in bucket traps have failed to capture RPW in the immediate vicinity of previous detection sites.

LEFT: The orange form of R. ferrugineus RIGHT: The black with red stripe form of R. ferrugineus

This pheromone-based trapping program has been used successfully for monitoring in other countries where the orange and black form of R. ferrugineus has invaded, and it is an important management component of IPM programs in Middle Eastern commercial date plantations for this pest.

A major point of interest regarding the trapping program in California using the commercially available RPW pheromone is whether or not it is attractive to the red palm weevil morph found in Laguna Beach. The RPW color morph found in Laguna Beach is black with a prominent dorsal red stripe that runs from the rear margin of the head across the thorax to the anterior margin of the abdomen. Until its detection in southern California this red stripe form of RPW was only known from southeast Asia (e.g., south Thailand, Malaysia, Indonesia, and the Philippines.)

To assess the attractiveness of the commercial RPW pheromone used by CDFA in Laguna Beach to the “vulneratus” morph, a small trial was run in a 60 ha commercial coconut plantation in Quezon on Luzon Island in the Philippines from 20 October 2011 to 26 October 2011. This area has been reported previously to have both RPW color morphs in sympatry. Three treatments were set up and checked twice per day at 6:00am and 4:00pm for captures of RPW:

Treatment one:This treatment consisted of traps with RPW aggregation pheromone + ethyl acetate (weevil magnet) + fermented dates. The aggregation pheromone and weevil magnet were supplied by CDFA and are the same products being used to monitor for RPW in Laguna Beach. Previous studies have demonstrated that fermented dates are an extremely potent “additive” to this set-up for attracting the orange and black morph of RPW. Dates were used for 3 days and then replaced with cut pieces of palm hearts. Traps were hung either in immature coconuts (a highly preferred host stage for RPW to attack) (see photo below) or on dead coconut trunks ~ 2.0 m above the ground (a height similar to that of CDFA deployed traps in Laguna Beach). This treatment was replicated three times in the plantation. 

Treatment 2: Freshly felled coconut palms that were bucked, stacked, and had palm hearts arranged on the wood pile were inspected for RPW attracted to this resource. This treatment was replicated three times. The plantation owner was asked to fell five palms that were suspected to be infested with RPW. All five palms exhibited extensive internal damage, but no RPW life  stages were found and it is was difficult to determine if feeding damage had been caused by RPW or another serious coconut pest, Oryctes rhinoceros beetles. 

Treatment 3: This treatment consisted of Treatment one (bottle trap with RPW pheromone + ethyl acetate + fermented dates or palm hearts) and Treatment two combined and was replicated three times at different sites in the plantation. 

Results: The results of these trials were clear cut and consistent. Treatments one and two did not result in the capture of any RPW over the 6 day monitoring period. Treatment three, pheromone bottle traps placed on freshly cut stumps of coconut palms with cut sections of palm trunk and palm hearts resulted in the capture of 23 RPW over the course of the trial. All three replicates of Treatment three resulted in the capture of RPW and the first captures were made ~ 24 hr after the palms were felled, sectioned, and stacked with the pheromone bottle trap. Captures ranged from 1 – 5 RPW at a site. RPW were found either inside the bottle traps, or more often underneath the wood stacked on top of the palm stump, or in chainsaw blade width slices made into bucked pieces of palm trunk. Adults are exceptionally thigmotactic and can push themselves deeply into very tight crevices, hence the notches on the cut pieces of palm trunk.

The color morphs of RPW that were captured in Treatment three included R. ferrugineus, “R. vulneratus”, and a color and pattern spectrum between these two distinct forms.

In the photo above, the global invading RPW morph (orange and black) is seen on the extreme left (two specimens), the “vulneratus” morph that has invaded Laguna Beach is third from the left, and the remaining “vulneratus” variants exhibit various red and black markings and at the extreme end (last two specimens on the right), these dorsal markings have been lost entirely. All of these weevils were captured in one night across all three replicates of Treatment three.

 

A Red Palm Weevil inside a bottle trap in Treatment 3 is covered in phoretic mites

The sex ratio of captured RPW was highly female biased (n = 18 females [78%]; n = 5 males [22%]). Unidentified phoretic mites were found on 60% and 67% of males and females, respectively. Phoretic mites have been recorded previously on RPW adults but their potential role as control agents of RPW is uncertain.

The majority, 78% (n = 18) of RPW were captured when treatments were examined at 6:00am, the remaining 22% (n = 5) were captured at 5:00pm. This result suggests the RPW flight activity in the Philippines may be crepuscular or nocturnal.

Conclusions: The RPW traps baited with pheromone and weevil magnet (ethyl acetate) used by CDFA in Laguna Beach failed to capture any weevils in a commercial coconut plantation in the Philippines unless they were deployed in conjunction with freshly felled coconut palms. The pheromone + weevil magnet + fruit additives alone did not catch any weevils, nor did the fresh-cut palm logs attract any weevils.  The reasons for this are not clear. This small study had low treatment replication and treatments were not blocked to account for site effects – although they were dispersed widely through the plantation. The bottle traps may not have been adequate for retaining RPW attracted to Treatment 1. This trial was run at the end of the monsoon season, a time of year reported to have low RPW activity. This situation may have been worsened by a wetter than normal “dry” season (the owner of the coconut plantation indicated that the dry season had been unusually wet this year) that preceded the monsoon season and RPW densities may have been lower than normal for this time period.

Thus, our results suggest that the bait combinations being used in Laguna Beach may not attractive to the RPW morph that is present.  Our results suggest that at a minimum, pheromone and weevil magnet baits should be deployed in combination with fresh-cut palm material, especially newly cut palm trunks and if possible this treatment should be set up and trialed in Laguna Beach to see if it can attract and retain RPW.

Topics: Christina Hoddle, Mark Hoddle, Red Palm Weevil | 1 Comment »

Invasive species rise after 9-11

By CISR Team | October 21, 2011

Recently CISR Director, Mark Hoddle, was interviewed on the Voice of Russia Radio about new research on invasive species after 9-11. The Associated Press reported hundreds of agricultural scientist who normally conducted inspections for invasive species were redirected to Homeland Security, causing a huge spike of invasive species coming into the US. AP reports its cost the US billions of dollars in cleanup. Follow the link for the interview on this problem.

“American anti-terror measures prompt insect invasions” 

Topics: Invasive Species, Mark Hoddle, News | No Comments »

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