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The South American Palm Weevil Invasion in San Diego County, California


The South American Palm Weevil Invasion in San Diego County, California

By Mark Hoddle | October 18, 2018

The South American Palm Weevil Invasion in San Diego County, California

The Situation: The South American palm weevil (SAPW), Rhynchophorus palmarum, is a non-native pest of palms that has established populations in San Diego County in California. In December 2010, this weevil was discovered infesting ornamental Canary Islands date palms (CIDP) (Phoenix canariensis) in Tijuana, Baja California, Mexico. California Department of Food and Agriculture trapping programs detected SAPW in San Ysidro (~5 miles north of Tijuana) in San Diego County in 2011. Around 2014 reports of CIDP dying from SAPW attack were confirmed in San Ysidro. It is likely that SAPW established populations in San Diego County around 2014, or perhaps earlier than this date. Weevils have also been detected in Alamo Texas in 2012 and Yuma Arizona in 2015. SAPW has not established in Texas or Arizona.

Ornamental Canary Islands date palms are ubiquitous in California and they are a defining feature of southern California’s urban landscape

What Does the Weevil Look Like? Adult weevils are large, black in color, and about 1.5 inches in length. The adult weevils have wings and are strong fliers.  Weevil larvae are whitish in color and can grow up to five inches in length. Weevil larvae pupate inside fibrous cocoons that may be found in the infested crown region or in tunnels weevil larvae drill into the base of palm fronds. Adult weevils emerge from cocoons when pupation is complete.

(A) and (B) adult SAPW. (C) Mature SAPW larva. (D) SAPW cocoon. Photo credits: (A) Mike Lewis, Center for Invasive Species Research, UC Riverside, (B), (C), and (D), Ricardo Aguilar, Aguilar Plant Care.

Where is the Weevil? Tijuana (Mexico), San Ysidro, Imperial Beach, National City, Bonita, Chula Vista, El Cajon, and San Diego City (all in San Diego County) are infested to varying degrees with SAPW. The exact area of infestation in San Diego County is not known. We are relying on community scientists and concerned citizens to report palms that are suspected of having been killed by SAPW. To report an infested palm or one killed by SAPW an online form can be completed and submitted. Click here to report an infested palm.

A concern is that SAPW may invade the Coachella Valley and once established it could become a significant management issue for growers of edible dates, an industry with an annual value of around $68 million (US).

An aerial view of an edible date garden in Coachella Valley

What Species of Palms Does the Weevil Attack? In San Diego County, the weevil has shown a very strong preference for attacking CIDP to the almost complete exclusion of other palm species at this time. Attacks on other species of palms may occur when CIDP become less common. SAPW has been documented infesting and killing açaí palm (Euterpe oleracea), African oil palm (Elaeis guineensis), Canary Islands date palm (Phoenix canariensis), coco de palmito (Euterpe edulis), coconut (Cocos nucifera), edible date palm (Phoenix dactylifera), and sago palm (Metroxylon sagu).

How Does the Weevil Kill Palms? Infestations of weevil larvae in the crown of the palm can result in death if the infestation is not treated with insecticides. The apical meristem or “palm heart” produces new fronds and extensive feeding damage to this area can kill the palm as it is unable to continue growing. Once the palm heart is heavily damaged, the crown may tilt, appears collapsed, and in some instances the crown may become detached from the trunk and drop to the ground. Advanced stages of damage results in the palm trunk being ringed by a halo of fronds.

(A) CIDP crown showing damage from SAPW feeding. (B) Palms in varying stages of SAPW infestation. (C) Palm with a “halo” of fronds that has resulted from SAPW feeding in the apical meristem. (D) Palm crown that has dropped from a SAPW infested palm and rolled down the street

Infested palms present a significant dropping hazard to people, cars, and property. In addition to the risk of crown drop, dead fronds readily fall from SAPW infested palms. Wind and rain events can increase the probability of frond dropping. Palm fronds are heavy and in the case of CIDP fronds, the base has large strong spines that can cause injuries.

Identification of Potentially Infested Palms: Palms in the very early stages of weevil attack are hard to diagnose as infested because weevils are hidden in the crown and can be very hard to find. As the infestation progresses visible symptoms may become apparent. Evidence of SAPW attack can be found in the crown and some of the easiest and earliest symptoms to observe are damage to fronds that are emerging from the center of the crown. Weevil feeding damage to immature fronds becomes apparent as the fronds grow up out of the center of the palm and the leaflets as they expand appear to be “clipped,” “notched,” or “windowed.”

(A) Dead fronds that have dropped from a CIDP killed by SAPW and (B) fallen against a fence and blocking the drive way

Protecting Palms from Weevil Infestations: The best control option for protecting palms from SAPW are systemic insecticides that are either applied to the soil, trunk, or crown. These products move into the palm and accumulate in the apical meristem, the palm heart, where weevil feeding is concentrated. These products then poison weevil larvae and adults. Palms can be “cured” of moderate to heavy weevil infestations with applications of systemic insecticides. But applications need to be made before irreversible damage to the crown has occurred. In some instances all of the fronds will need to be removed, the crown thoroughly drenched, and then gradually over time, the damaged meristematic tissue will recover and new palm fronds will begin to develop. Once these pesticide programs begin they will need to continue indefinitely to protect palms from weevil attack.

Palm fronds showing damage from weevil feeding

What is Being Done in San Diego County?: The response to the establishment and spread of SAPW in San Diego County is following several different avenues. First, weevil population cycles over the course of a year are being monitored. Results so far suggest that weevils are flying all year round and don’t seem to stop over the winter. Second, more than 470 CIDP in urban areas are being monitored every six months for SAPW caused mortality. Over a two year period about 25% of palms monitored in urban areas have been killed by SAPW. Trials testing two different types of traps (bucket vs. Picusan) and types of fermenting bait with weevil aggregation pheromone are being evaluated. Insecticide trials evaluating different types of systemic pesticides for protecting palms from weevil attack have been set up with cooperators in several areas in San Diego County where weevil activity is high. These trials will likely run for two or more years until results become available. Finally, drones are being used to monitor palm mortality in riparian areas where foot access is difficult. Results of aerial monitoring of more than 760 palms indicate that over a 2 year period 28% have been killed by SAPW.

CIDP’s heavily pruned in Tunisia to facilitate crown drenches of systemic insecticides to “cure” palms of red palm weevil, Rhynchophorus ferrugineus, infestations

 

(A) Bucket and (B) Picusan traps are being evaluated for their ability to capture weevils. Traps are very useful for monitoring programs to determine whether adult weevils are active in an area of concern

 

Drone surveillance of Canary Islands date palms killed by SAPW in the Sweetwater Reserve, Bonita California

 

 

Topics: Rhynchophorus palmarum | No Comments »

Asian Citrus Psyllid Biocontrol Taskforce Awarded the 2017 California Department of Pesticide Regulation IPM Achievement Award

By Mark Hoddle | February 22, 2018

2017 IPM achievement award recipients

Left to Right (photo credit Anon):
Ruth Henderson (CRB), Raju Pandey (CRB), Mike Pitcairn (CDFA), Greg Simmons (USDA-APHIS), David Morgan (CDFA), Brian Leahy (Director, DPR), Jim Gorden (Chairman CRB), and Mark Hoddle (UCR).

Mark Hoddle, Director, Center for Invasive Species Research, University of California Riverside

On 13 February 2018 at the California Environmental Protection Agency Headquarters in Sacramento, the Asian Citrus Psyllid Biocontrol Taskforce was awarded the Integrated Pest Management (IPM) Achievement Award for innovation and leadership by the Department of Pesticide Regulation.

Asian citrus psyllid (ACP) was first detected in California in 2008. It spreads a bacterium that causes a lethal citrus disease, huanglongbing (HLB), which was found in California in 2012. ACP-HLB have devastated citrus industries in Florida and Texas, and California citrus producers are extremely worried something similar will happen to California’s iconic $3 billion per year citrus industry. Currently, ACP-HLB reside almost exclusively on backyard citrus in urban areas of southern California.

In response to this invasive pest, a biocontrol taskforce team was put together by the Citrus Research Board. Under the auspices of the Citrus Research Board, the ACP Biocontrol Taskforce has representatives from the following organizations and public groups: University of California Riverside (UCR), University of Agriculture Faisalabad (Punjab, Pakistan), USDA-APHIS, USDA-CPHST, CDFA, CRB, commercial insectaries, professional pest control advisors, citrus growers, and home owners. The Taskforce meets 2-3 times per year, coordinates research activities across agencies, provides opportunities for updates on ACP biocontrol programs, and facilitates conversations, program planning, and priority/policy alignment across all stakeholder groups. The success and impact of the ACP Biocontrol Taskforce, in terms of IPM program development with the focus on the critical objective of reduced pesticide use has been significant.

California Department of Pesticide Regulation poster

California Department of Pesticide Regulation poster

2017 IPM achievement stage before ceremony

2017 IPM achievement stage before ceremony

With the goal of reducing pesticide use for ACP management in urban areas, the priority of the taskforce was to develop a classical biological control (biocontrol) program for ACP in urban citrus in California with natural enemies imported from the home range of ACP (i.e., Pakistan). Foreign exploration with colleagues from the University of Agriculture Faisalabad in Punjab Pakistan resulted in the importation and release of two natural enemy species, Tamarixia radiata and Diaphorencyrtus aligarhensis in California. One of these natural enemies, T. radiata, established readily on ACP infesting urban citrus and spread quickly. Since the start of the biocontrol program targeting ACP, densities of this pest have declined substantially in many areas, perhaps as much as ~70% at some of the long term monitoring sites where ACP and natural enemy activity has been surveyed for three or more years. Research results strongly suggest that the Pakistani parasitoid, T. radiata and generalist predators, like syrphid fly larvae, contribute significantly to ACP mortality and have probably cause pest populations to diminish. These natural enemies are all self-sustaining, self-dispersing, self-regulating, pose zero environmental risk, and provide “free” ACP control 24/7/365!

The impact of the biocontrol program on ACP populations in California, especially urban citrus has been considerable. ACP biocontrol is a permanent pest management tool that needs no day-to-day management. The natural enemies saves CA millions of dollars annually in ACP control costs. The biocontrol agents eliminated the need for thousands of gallons of pesticides to be applied to backyard plants that provide food to millions of California families.

To learn more about the DPR IPM Achievement awardees and their accomplishments in using integrated pest management, see the DPR press release.

2017 IPM achievement award recipients

Standing Left to Right (photo credit Anon): Carolina Evangelo (CRB), Marilyn Kinoshita (Ag. Comm. Tulare County), Greg Simmons (USDA-APHIS), Mark Hoddle (UCR), Jim Gorden (Chairman CRB),  Brian Leahy (Director DPR), Gary Schulz (President CRB), 
Kneeling: Raju Pandey (CRB), Ruth Henderson (CRB), David Morgan (CDFA), Mike Pitcairn (CDFA)

Topics: Asian Citrus Psyllid, Mark Hoddle, News, Tamarixia radiata | No Comments »

The Red Palm Weevil Crisis in Tunisia: A Potential Threat to Food, Economic, Social, and Political Security?

By Mark Hoddle | May 16, 2017

Written by: Mark Hoddle
Department of Entomology, UC Riverside

Email: mark.hoddle@ucr.edu
More Research: UCR Biocontrol Website

Photos A and B illustrate high levels of Canary Islands date palm mortality caused by the red palm weevil (Photo C) in La Mersa, Tunis, Tunisia.

The red palm weevil (RPW), Rhynchophorus ferrugineus, is a highly invasive and extremely damaging pests of palms, especially ornamental Canary Islands date palms (Phoenix canariensis) (CIDP’s), and date palms (Phoenix dactylifera) that produce fruit for human consumption.

RPW is native to southeast Asia where it is a well-recognized pest of coconut palms. Movement of live palms for landscaping (e.g., beautifying new hotels and tourist resort areas with coconut and date palms) has resulted in the inadvertent introduction of this pest into areas outside of its home range.

Photos A and B illustrate high levels of Canary Islands date palm mortality caused by the red palm weevil (Photo C) in La Mersa, Tunis, Tunisia.

Regions that have been particularly devastated by the RPW invasion are Mediterranean countries (e.g., Italy, France, Spain, and Portugal where thousands of CIDPs have been killed), the Middle East (e.g., Egypt, Israel, Saudi Arabia, and the United Arab Emirates), and the Maghreb region of northwest Africa (e.g., Morocco, Tunisia, and Libya) where date palms and ornamental CIDP’s have been hard hit.

The threat RPW poses to date palms in the Middle East and northern Africa is immense and weevil attacks have possibly killed millions of date palms (unverified estimates from Egypt alone suggest that more than 1 million date palms have been killed by RPW) threatening a very important agricultural crop that has extremely high religious and cultural significance. The magnitude of this problem is of high concern in these regions and RPW is the focus of FAO missions that aim to develop control programs by training local staff on RPW management. Many of these FAO led missions appear to have been successful to varying degrees, but one program in particular stands out, it is appearing to be highly likely that in Mauritania RPW may be on the verge of eradication. RPW has been eradicated in the Canary Islands after an intensive management campaign, and a closely related palm weevil, R. vulneratus, also native to southeast Asia, was recently eradicated from California (Hoddle et al. 2017).

Red palm weevil adult (orange insect with black spots), larva (white grub), and pupa (beige with wing pads) extracted from an infected Canary Islands date palm.

In 2011, RPW was recorded in Tunisia killing CIDP’s in the northern cities of Tunis and Carthage. Management efforts have so far contained this pest in the north of Tunisia but infested areas are increasing.

Because of this ongoing spread and spectacular levels of palm mortality caused by RPW, this invasion is of high concern to the USA. Opening remarks made by Mr. Benjamin Moeling, Deputy Chief of Mission for the US Embassy in Tunis Tunisia at the recent International Conference on the Red Palm Weevil in Tunisia (3-5 May 2017) made it clear that the potential disruption to date production may cause a fragile political structure to collapse should RPW establish in the southern oases (Gafsa, Tozeur, Gabés, and Kébili) where dates are produced. The reason for this concern is potential economic, social, political, and food insecurity and consequently this is of high strategic interest to the US which views the RPW invasion as a national security issue in part of a much larger geopolitical area that is currently experiencing high political and social disruption.

The following statistics make it clear what is at risk from the RPW invasion. In 2016, 54,000 hectares of land was devoted to date production in Tunisia and exported dates were worth ~$207 million (US). Dates in Tunisia account for ~4% of global production, and an impressive 24% of global date revenue because of the high quality of this premium fruit. Dates account for 12% of agricultural exports from Tunisia (about 5% of exported dates are marketed in the USA) which makes up about 6% of agricultural production. Date farming is typically a small family run operation in Tunisia. There are an estimated 50,000 date growers farming plots that are ~ 0.85 hectare/producer. Harvested dates are managed by around 400 collection agencies, who pass this produce onto 72 exporters.

Date production in Tunisia is a high value agriculture enterprise that employs a lot of people in a country that in January 2017 had an estimated unemployment rate of ~15%. RPW has the capability of greatly reducing the long term viability of the iconic Tunisian date industry which could cause economic, political, and social instability in an area of Tunisia where the population is highly reliant on dates for their livelihoods and daily diet.

In response to this RPW invasion, the US Embassy sponsored a three day event, the International Conference on the Red Palm Weevil in Tunisia (3-5 May 2017). The conference had palm weevil experts from UC Riverside, Tunisia, FAO, France, India, Costa Rica, and Saudi Arabia who delivered talks over a two period on various aspects of date production, RPW biology, behavior, invasion ecology, and management.  The third day of the conference was a RPW monitoring training day in La Mersa in Tunis an area with very high numbers of dead and dying CIPD’s. The field day was devoted to discussing and demonstrating pheromone-based trapping programs, management of trap data, and emerging technologies such as “attract and kill” that support traditional pesticide applications to palms for RPW population suppression. The aim of this US-sponsored event was to assist Tunisian officials and RPW management teams with the development of containment and management programs to restrain populations in the north of Tunisia thereby preventing or greatly slowing the spread of this pest into date production areas 500 kilometers to the south. The ultimate goal of RPW management programs in is the eradication of RPW from northern Tunisia.

Conference Speakers and Presentations

Session 1. Overview of RPW in Tunisia: Containment, Control, and Eradication Efforts

1) Dorsaf Ben Ahmad Zaag, Directorate General for Agricultural Production, Tunis: The Economic Importance of Date Production in Tunisia

2) Mohamed Habib Dhouibi. Department of Entomology, National Institute of Agronomy, Tunis: The Major Pests of Date Palms in Tunisia and Research on Red Palm Weevil

3) Fetuhia Hellali, General Directorate of Protection and Control of the Quality of Agricultural Products, Ministry of Agriculture, Water Resources, and Fisheries, Tunis: Strategies Adopted to Control Red Palm Weevil in Tunisia.

Session 2: Overview of the Biology, Ecology, Behavior, Distribution, and Invasion History of Red Palm Weevil

4) Mark Hoddle, Department of Entomology, University of California, Riverside: Overview of the Biology, Ecology, Behavior, Distribution, and Invasion History of Red Palm Weevil.

5) Paul Rugman-Jones, Department of Entomology, University of California, Riverside: Identity, Phylogeny, and Invasion History of Red Palm Weevil

Session 3: Discovery of Palm Weevil Aggregation Pheromones and their Use in Pest Management

6) Cam Oehlschlager, CEO ChemTica International, Costa Rica: Discovery of Palm Weevil Aggregation Pheromones and their Use in Pest Management

7) Didier Rochat, Institute of Ecology and Environmental Sciences, Paris France: Synergists for Optimal Trapping of Red Palm Weevil Using Aggregation Pheromone

Session 4: Area-Wide Management Programs for Red Palm Weevils

8) Hamadttu El-Shafie, The Date Palm Research Center of Excellence, King Faisal University, Al Ahsaa, Kingdom of Saudi Arabia: Lessons Learned from the Experiences of Managing Red Palm Weevil in Saudi Arabia

9) Romeno Faleiro, FAO Goa India: Management of Red Palm Weevil: Development and Implementation of Small to Large-Scale Control Programs

Session 5: Future Directions and Emerging New Technologies for Red Palm Weevil Control

Agenor Mafra-Neto, ISCA Technologies, Riverside California: The Future of Red Palm Weevil Control in Tunisia: From Management to Eradication

Delegates from the International Red Palm Weevil Conference in Tunisia (3-5 May 2017) at the RPW field training day in La Mersa Tunis, Tunisia. This event was sponsored by the US Embassy in Tunisia.

 

 

References Cited:

Hoddle, M.S., C.D. Hoddle, M. Alzubaidy, J. Kabashima, J.N. Nisson, J. Millar, and M. Dimson. 2017. Rhynchophorus vulneratus palm weevil is eradicated from Laguna Beach. Cal. Ag. 71: 23-29.

Topics: Red Palm Weevil | No Comments »

The Making of a South American Palm Weevil Mini-Documentary for “Deep Look” with KQED

By CISR Team | April 5, 2017

The weevil killed palm in San Diego that was taken down for the KQED “Deep Look” science show.

The South American palm weevil, Rhynchophorus palmarum (Coleoptera: Curculionidae), is well established in parts of San Diego County in California and is responsible for killing numerous Canary Islands date palms. The spectacular damage this invasive pest causes and the large showy adult weevils and alien-looking larvae and pupae, captured the imagination of Elliott Kennerson and Joshua Cassidy, digital media producers for the science show Deep Look with KQED Public Television and Radio in San Francisco. After a few phone calls and ensuing discussions, Elliott made the pitch to KQED to develop a story on the palm weevil and the project was given approval for development.

A plan was made to drop a weevil infested Canary Island date palm tree in a residential area in San Diego County and from this palm weevil life stages would be collected and filmed. The first challenge was finding an infested palm, which we did, and the bigger challenge was to bring the palm down and then cut it up so we could examine the crown of the dying palm for weevils.

Paul Webb with RPW Services, Inc. put us in contact with Michael Palat from West Coast Arborists, Inc. who generously offered to taken the palm down and then dispose of it free of charge.

Paul Webb (RPW Services, Inc.) (left) and Michael Palat, West Coast Aborists, Inc. (right)

The take down of the palm was done on 27 March 2017 and filmed by Josh and Elliott. This involved a lot of camera work, including Go Pro’s strapped to the helmet of the arborist who was responsible for chain sawing the palm from the bucket lift!  Adult weevils, pupae, and one larva were recovered from the palm. The weevil life stages were photographed and filmed, and flight mill activity was all digitally recorded on 28 March 2017. Hours of digital footage was recorded and this will be condensed down to about 3 minutes when the final version is produced and released for public viewing in early July 2017.

 

 

 

 

Topics: Rhynchophorus palmarum | No Comments »

Stepping up to the Challenge of the UC Global Food Initiative: Improving Avocado Production in Tanzania

By CISR Team | March 30, 2017


Written by: Mark Hoddle

Email: mark.hoddle@ucr.edu
More Research: UCR Biocontrol Website

Written by: Mary Lu Arpaia

Email: mlarpaia@ucanr.edu
More Research: UCR Department of Botany & Plant Sciences

California is a recognized world leader in avocado production and is renowned for high quality Hass avocado fruit. The strength of the California avocado industry has resulted from research driven science, primarily by UC researchers, which addresses a variety of issues including plant nutrition and breeding, irrigation, canopy, pest, and disease management, and harvest and post-harvest practices.

Avocados are native to the New World and are recognized for having a highly nutritious fruit. To satisfy increasing demand, global fruit production is projected to continue to increase, especially in developing tropical countries, including Africa, where an estimated 2-3% increase in produ

(A) Participants in a Hass avocado outgrower meeting in Rungwe District.

ction per year is predicted (FAO 2003).

Tanzania’s fledgling Hass avocado industry has been in commercial production for less than 10 years and is aiming to increase exports to the lucrative European market (Anon 2015). A local private sector company, Rungwe Avocado Company (RAC), headquartered in Rungwe District in the Mbeya Region of the Southern Highlands of Tanzania, established a 100 hectare Hass avocado orchard in 2009. Associated with RAC are 118 staff and approximately 3,700 outgrowers who collectively exported > 1,000 metric tons of fruit in 2016.

Outgrowers are small land holder farmers who grow avocados under the umbrella of RAC which provides planting materials, extension and fruit harvest services, post-harvest processing of picked fruit, and logistical organization of exports to Europe (Anon 2015). Outgrower fruit is purchased by RAC through guaranteed off-take agreements which aim to lift the incomes of participating small land holders. This outgrower model is endorsed by many socially-responsible investors.

(B) Mary Lu Arpaia inspecting roadside avocados.

Managing outgrower fruit production is challenging as participating farms are spread over large areas and access can be difficult, the number of trees grown per farm is highly variable ranging from around 20 to more than 200, and farming and planting practices are not standardized. Coupled with these difficulties is a limited understanding of the pest and disease complexes associated with Hass avocado production in the Southern Highlands.

(C) Mark Hoddle sharing with children in Rungwe District insects collected from avocados.

One of the aims of the UCOP’s Global Food Initiative is to deploy UC’s best research and extension practices to address the key challenge of improving food production to sustainably feed an increasing world population. This challenge is regional, national, and international in scope. UC-ANR Extension Specialists with horticultural and pest management expertise in avocados have the required experience to develop research and extension driven programs to address issues affecting global food production, especially in developing regions of the world where food and economic security can be fragile. With respect to the UC Global Food Initiative, the goal we have set ourselves is to assist and improve outgrower avocado production in Tanzania.

A recent visit facilitated by RAC provided the opportunity for MSH and MLA to visit small and large outgrower avocado farms, the 100 ha RAC orchard, and the chance to interact with staff and extension technicians. Collectively, this provided critical insight into the unique growing conditions that typify the Southern Highlands of Tanzania and outgrower farming practices.

The week-long visit to the Southern Highlands, coupled with consultation and discussion with outgrowers, extension technicians, and packinghouse and export logistics managers, assisted with the identification of production, pest management, and fruit handling challenges. While different from problems faced in California (and Central and South America where we have also worked on avocado production issues), familiar themes were identified that can be addressed within a short (< 18 months [e.g., canopy management and pest identification]), medium (18-36 months [e.g., development of pest monitoring  programs]), and long-term (> 36 months [e.g., development of integrated pest management programs]) framework. The task in front of us now is to implement these suggestions and modify and adapt them as appropriate.

References Cited

Anon. 2015. Avocado farmers in Tanzania build export market with support from Feed the Future. https://feedthefuture.gov/article/avocado-farmers-tanzania-build-export-market-support-feed-future (last viewed 14 March 2017)

FAO. 2003. Medium term prospects for agricultural commodities – projections to the year 2010. http://www.fao.org/docrep/006/y5143e/y5143e00.htm (last viewed 14 March 2017)

 

Topics: Avocados | No Comments »

Psyllaphycus diaphorinae: Another Natural Enemy from Pakistan for ACP Biocontrol?

By Allison Bistline-East | January 11, 2016

Written by: Allison Bistline-East
Email: a.bistline-east1@nuigalway.ie
More Research: UCR Biocontrol Website

The Problem. In 2008, the Asian citrus psyllid (ACP), Diaphorina citri (Hemiptera: Liviidae), was first detected in California. Since its establishment in California, commercial citrus growers and homeowners alike have become familiar with this notorious pest and the threat it represents as a vector of the bacterium, Candidatus Liberibacter asiaticus, which causes the lethal citrus disease huanglongbing (HLB). As of July 2015, there have been two confirmed cases of HLB-positive citrus trees in California, both on residential properties in Los Angeles County.

pd_emergence_clip

Female Psyllaphycus diaphorinae emerging from a Diaphorencyrtus aligarhensis-ACP mummy.

Natural Enemies for ACP Biocontrol. Because ACP-HLB poses such a significant threat to the California citrus industry, which generates over $3 billion annually and provides over 26,000 jobs, ACP population control has been a primary focus of both UCR entomologists and the California Department of Food and Agriculture (CDFA). A classical biological control program to reduce ACP populations in urban areas began with the release of Tamarixia radiata in December 2011, and in December 2014, a second parasitoid, Diaphorencyrtus aligarhensis, was added to the release program with the intent of establishing a complementary set of parasitoids that attack ACP nymphs.  There has been some question as to how many different natural enemy species are optimal in biological control programs, and in several instances a complex of several species have been shown to be most effective, especially when the target pest infests different environments (Denoth 2002). In its home range, the Indian subcontinent and Asia, a guild of up to nine different parasitoid species were described attacking ACP nymphs by Mohammad Hussain and Dina Nath (1927). However, the identity of just one species, Tamarixia radiata, was determined. This led researchers in the Hoddle lab (UCR) on an investigation to determine the identities of the other parasitoid species putatively attacking ACP nymphs in Punjab Pakistan, with the intent of discovering additional natural enemies to use in the ACP control program in California.

It is likely one of the unnamed species recovered in Hussain and Nath’s (1927) study was Psyllaphycus diaphorinae. Nearly 50 years after the initial study, Mohammed Hayat (1972) formally described P. diaphorinae from specimens recovered in Punjab, India, a region immediately adjacent to Punjab, Pakistan where T. radiata and D. aligarhensis were collected and subsequently released in California for ACP biocontrol. In April 2013, six live female P. diaphorinae were returned to the Insectary and Quarantine Facility at UCR from a natural enemy collecting trip in Punjab, Pakistan. This collection was the first to return live P. diaphorinae, and the recovered females were immediately exposed to ACP nymphs at every juvenile stage to determine the preferred host stage of this  potential parasitoid of ACP nymphs.

P. diaphorinae Host Determination. To the surprise of UCR researchers, the preferred host of P. diaphorinae was not ACP at all. After exposing the P. diaphorinae females to 90 ACP nymphs no successful parasitism was observed. The females were then subjected to further exposure trials, this time sequentially to T. radiata larvae developing inside ACP (“mummies”), D. aligarhensis mummies, and additional unparastitized ACP nymphs. Contrary to the description given by Hayat, which was based solely on the morphology of preserved specimens, the results of these exposure trials determined that P. diaphorinae actually parasitizes developing T. radiata or D. aligarhensis within an ACP nymph, and not the ACP nymph itself! This type of parasitism, where one parasitoid targets another within a host, is known as hyperparasitism, and these types of parasitoids are known as hyperparasitoids. Basically, they’re parasitoids of parasitoids!

pd_male_female_combo_small

Female (top) and male (bottom) Psyllaphycus diaphorinae adults.

Investigating the Biology of P. diaphorinae. Once the hosts of P. diaphorinae were identified, an evaluation of many important biological traits, such as host preference, developmental rate, and adult longevity, were possible. Results from these experiments indicated that D. aligarhensis was a more suitable host than T. radiata, based on P. diaphorinae producing both more offspring overall and a higher ratio of female-to-male offspring on D. aligarhensis. P. diaphorinae offspring also developed slightly faster on D. aligarhensis (about 16.5 days on average, at 27°C) versus T. radiata (about 17 days average). Because D. aligarhensis was shown to be the better host, adult longevity was measured only for P. diaphorinae emerging from D. aligarhensis mummies. Male and female P. diaphorinae adults had an average lifespan of 17 days and 20 days, respectively, when held individually, and 20 days and 30 days, respectively, when held as male-female pairs. These experiments provided a valuable first glimpse into the biology of P. diaphorinae. Experiments also investigated the effects of various temperatures on developmental rate and adult longevity, which will allow researchers to determine the optimal conditions for this hyperparasitoid. For a more in-depth look at these experiments, see Bistline-East and Hoddle 2015.

Ecological interactions in the ACP-parasitoid complex. Hyperparasitoids exert negative effects on primary parasitoid populations, resulting in indirect positive effects on ACP

Ecological interactions in the ACP-parasitoid complex. Hyperparasitoids exert negative effects on primary parasitoid populations, resulting in indirect positive effects on ACP

Why Hyperparasitoids Matter. The existence of hyperparasitoids may greatly impact biological control programs. Because hyperparasitoids target the natural enemies that are being used to control a specific pest species, this causes a mediating effect on parasitoid impact, and an overall indirect positive outcome for the pest species. The good news is that there are no known species of hyperparasitoids in California that are found targeting T. radiata or D. aligarhensis in their native range, including P. diaphorinae. The bad news is that there are eight known genera that contain hyperparasitoids in both California and ACP’s native range, so there is still the possibility that over time one or more species within these genera that are native to California could eventually shift hosts and attack introduced ACP natural enemies. As far as we are aware, California is an “enemy-free zone” for T. radiata and D. aligarhensis, which is expected to allow incipient natural enemy populations to establish, spread, and potentially suppress ACP populations effectively.

References

  1. Bistline-East, A. and M.S. Hoddle. 2015. Biology of Psyllaphycus diaphorinae (Hymenoptera: Encyrtidae), a Hyperparasitoid of Diaphorencyrtus aligarhensis (Hymenoptera: Encyrtidae) and Tamarixia radiata (Hymenoptera: Eulophidae). Annals of the Entomological Society of America in press
  2. Denoth, M., L. Frid, and J. H. Myers. 2002. Multiple agents in biological control: improving the odds? Biol. Cont. 24: 20-30.
  3. Hayat, M. 1972. Descriptions of two new genera and species of Encyrtidae (Hymenoptera, Chalcidoidea), with notes on some described species. Acta ent. bohemoslov. 69: 207-214.
  4. Hussain, M. A. and D. Nath. 1927. The citrus psylla (Diaphorina citri) (Psyllidae: Homoptera). Mem. Dept. Agric. India, Entomol. Ser. 10: 5-27.

Topics: Asian Citrus Psyllid, Psyllids | 2 Comments »

The Palm Weevil, Rhynchophorus vulneratus, Successfully Eradicated from California

By Mark Hoddle | March 5, 2015

Fig. 1. Rhynchophorus vulneratus, the palm weevil discovered in Laguna Beach, California in October 2012.

Fig. 1. Rhynchophorus vulneratus, the palm weevil discovered in Laguna Beach, California in October 2012.

Fig. 2. Red palm weevil, Rhynchophorus ferrugineus, adult, larva (white grub), and pupa extracted from a Canary Islands date palm in France.

Fig. 2. Red palm weevil, Rhynchophorus ferrugineus, adult, larva (white grub), and pupa extracted from a Canary Islands date palm in France.

Fig. 3. Dead Canary Islands date palm  killed by R. vulneratus in Laguna Beach.

Fig. 3. Dead Canary Islands date palm killed by R. vulneratus in Laguna Beach.

Fig. 4. Red palm weevil Technical Working Group inspecting pheromone traps in Laguna Beach.

Fig. 4. Red palm weevil Technical Working Group inspecting pheromone traps in Laguna Beach.

Fig. 5. Collecting R. vulneratus from dead coconut palms in Java Indonesia.

Fig. 5. Collecting R. vulneratus from dead coconut palms in Java Indonesia.

Fig. 6. Collecting palm weevils in the Philippines.

Fig. 6. Collecting palm weevils in the Philippines.

Fig. 7. Testing aggregation pheromone and cut coconut logs in Sumatra Indonesia for attraction to R. vulneratus.

Fig. 7. Testing aggregation pheromone and cut coconut logs in Sumatra Indonesia for attraction to R. vulneratus.

Fig. 8. Aerating adult R. vulneratus for collection of aggregation pheromone in Sumatra Indonesia.

Fig. 8. Aerating adult R. vulneratus for collection of aggregation pheromone in Sumatra Indonesia.

Fig. 9. Enhanced trapping trial at Laguna Beach utilized freshly cut date palm trunks and aggregation pheromone.

Fig. 9. Enhanced trapping trial at Laguna Beach utilized freshly cut date palm trunks and aggregation pheromone.

Fig. 10. Injecting a systemic insecticide into the soil around the roots of a weevil infested palm tree in Laguna Beach.

Fig. 10. Injecting a systemic insecticide into the soil around the roots of a weevil infested palm tree in Laguna Beach.

Fig. 11. Eating cooked red palm weevil larvae for lunch in Thailand. These larvae were reared commercially in a weevil farm.

Fig. 11. Eating cooked red palm weevil larvae for lunch in Thailand. These larvae were reared commercially in a weevil farm.

Figure 12. USDA declaration of the successful eradication of R. vulneratus from Laguna Beach in January 2015.

Figure 12. USDA declaration of the successful eradication of R. vulneratus from Laguna Beach in January 2015.

In October 2010 a live large black weevil with a red stripe on the thorax (Fig. 1) was found inside the trunk of a dead Canary Islands date palm in Laguna Beach. This weevil was originally identified as the red palm weevil, Rhynchophorus ferrugineus (Fig. 2).  Subsequent work by researchers at UC Riverside using DNA analyses conclusively demonstrated that the weevil found in Laguna Beach was not R. ferrugineus, but a related species of palm weevil, R. vulneratus. These two species of weevils, R. ferrugineus and R. vulneratus, both native to southeast Asia, were incorrectly synonymized by Canadian researchers in 2004 and were subsequently referred to as R. ferrugineus, the red palm weevil, a notorious invasive pest of palms. The weevil-infested palm tree in Laguna Beach (Fig. 3) was promptly removed and a technical working group (Fig. 4) for “red palm weevil” was formed (at this stage of the invasion the correct identity of the weevil was not known and the weevil species in Laguna was referred to as red palm weevil [RPW]; for consistency across blog posts, this incorrect common name will be used here to refer to R. vulneratus).

Rapid action was taken against R. vulneratus and pesticide applications were applied to palm trees showing signs of probable infestation which were readily identified because of obvious feeding damage to palm fronds. As work on RPW was under way in Laguna Beach studies targeting R. vulneratus in Indonesia (Fig. 5) and the  Philippines (Fig. 6) were initiated and observations on R. ferrugineus management in France were made.

The studies conducted in Indonesia and the Philippines demonstrated that the commercially-available aggregation pheromone sold for R. ferrugineus was effective at attracting R. vulneratus in its native habitat. This was not a great surprise as the aggregation pheromone was originally isolated from R. vulneratus and not R. ferrugineus as originally thought (in fact the aggregation pheromone for R. ferrugineus is not known, but this weevil species finds the R. vulneratus aggregation pheromone very attractive, perhaps suggesting that they are similar).

The results of these field studies were important because trapping programs using the commercially-available aggregation by the California Department of Food and Agriculture in Laguna Beach were failing to capture adult weevils even though weevil feeding damage to palms was being observed. A key factor in the overseas field trials with the aggregation pheromone was the incorporation of cut palm trunks. The combination of cut palm trunks with aggregation pheromone greatly increased captures of weevils in Indonesia and the Philippines (Fig. 7). The aggregation pheromone from R. vulneratus was reanalyzed with new material that was collected during aeration trials in Sumatra Indonesia (Fig. 8). The pheromone was identical to the commercially-available pheromone that had been originally collected from R. vulneratus in Java Indonesia (this weevil species in Java was incorrectly identified as R. ferrugineus by the scientist that originally did this work.)

Field experiments in the home range of R. vulneratus demonstrated that the combination of commercially-available aggregation pheromone and cut palm trunks captured significantly more weevils than either treatment alone. Consequently, this lead to the initiation of “enhanced” trapping trials in Laguna (Fig. 9) that used a combination of cut date palm trunks provided by cooperators in the Coachella Valley and aggregation pheromone. These enhanced trapping trials also failed to capture weevils.

Removal and dissection of palm trees previously identified as being infested with R. vulneratus and treated with pesticides (Fig. 10) indicated that palms had been “cured” of infestations. This finding likely explained why the pheromone traps were not capturing weevils. Prompt action directed towards to infested palm trees while the R. vulneratus infestation was highly localized and weevil populations were very small was probably responsible for the eradication of this pest from Laguna Beach.

A big question that remains largely unresolved is how did R. vulneratus come to Laguna Beach, a relatively isolated coastal city with no international airports or seaports? Our working hypothesis for which we have no direct evidence is that this pest may have been deliberately introduced as a traditional food (Fig. 11) and that Bali Indonesia is close to the possible area of origin for the Laguna population.

The last live weevil was detected in Laguana on 18 January 2012. Three years subsequently passed with no further detections of. Because three consecutive years passed with no weevil detections in Laguna Beach USDA-APHIS declared this pest to be officially eradicated on 21 January 2015 (Fig. 12). This is a significant accomplishment against a notoriously destructive palm pest.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Topics: Mark Hoddle, Red Palm Weevil | 2 Comments »

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

By 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.

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.

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.

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 Michael Lewis, Center for Invasive Species Research, UC Riverside.

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.

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 77oF (25oC). 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.

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.

Topics: Asian Citrus Psyllid, Mark Hoddle, News, UC Riverside | 1 Comment »

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

By Erica Kistner | October 31, 2014

Erica Kistner

Erica Kistner, Ph.D.

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.

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.

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

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

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.

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.

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.

Topics: Argentine Ants, Asian Citrus Psyllid, Tamarixia radiata, UC Riverside | No Comments »

What’s in the Fridge?”: Collections of Invasive Insect Pests from Around the World

By Mark Hoddle | January 10, 2014

Anna Kuchment, Editor for Scientific American, produced a very nice article (“End of Orange Juice ” [Scientific American vol. 308 pp. 52-59, March 2013]) on the Asian citrus psyllid and huanglongbing situation in California, Florida, and other countries affected with this pest and disease.

During Anna’s visit to UC Riverside to cover this story, we pulled out insect specimens of other pests we are working on including the red palm weevil, gold spotted oak borer, and other potential invasive pests like the avocado seed moth, Stenoma catenifer . These collections, along with other insects like the big rhinoceros beetles that attack palms in Asia, interested Anna, and this led to her developing the “What’s in the Fridge?” series for Scientific American.

The inaugural release of “What’s in the Fridge? ” occurred in the July 2013 issue of Scientific American (vol 309 [1], pp. 18). Four insects are featured, the rhinoceros beetle that was collected in Sumatra Indonesia attacking newly planted oil palms. The coconut palm weevil, Rhynchophorus vulneratus , which has invaded Laguna Beach in southern California, but has not been detected for over 18 months despite trapping efforts. This species was synonomized with R. ferrugineus , the red palm weevil, but emerging results from molecular studies clearly show that R. vulneratus is a species distinct to R. ferrugineus, and the synomization of these two species was incorrect, hence we refer to this weevil as R. vulneratus. The gold spotted oak borer , an invasive pest native to southern Arizona, has killed > 22,000 native oak trees in southern California, and recent oak mortality estimates by Tom Scott , suggest that mortality may now be as high as 80,000 oak trees in affected areas in San Diego County. Avocado seed moth is a pest that is not yet in the USA, but increasing imports of fresh avocados from countries in Latin America where this pest is native may increase the chances of this pest accidentally invading and establishing in California, Florida, and Hawaii, states where avocados are grown commercially.

Claudia, Mark and Spencer examine insects for the shoot.

Claudia, Mark and Spencer examine insects for the shoot.

The photos for the “What’s in the Fridge?” piece were taken by Spencer Lowell who was assisted by Claudia Lucia . These guys made our disorganized lab freezer look amazing!

 

Topics: Invasive Species, Mark Hoddle | 1 Comment »

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