Psyllids

CISR: Asian Citrus Psyllid

Anonymous — Mon, 20 Jan 2020 21:31:31 +0000

CISR: Asian Citrus Psyllid Anonymous (not verified) Mon, 01/20/2020 - 13:31 More Blog Posts CISR Team May 26, 2009

The Situation: Asian citrus psyllid (ACP) is an efficient vector of the bacterial citrus disease huanglongbing (HLB), previously called citrus greening disease, which is one of the most destructive diseases of citrus worldwide. In the United States, the psyllid vector is found in Florida, Mexico, Louisiana, Georgia, South Carolina, Cuba, Belize and the Yucatan peninsula of Mexico. A federal quarantine restricts all movement of citrus and Rutaceae from into California in order to prevent introduction of the psyllid or the disease. The psyllid is under eradication in Southern California. If the psyllid and the disease were to become established in California, the disease would devastate the citrus industry.

Damage: ACP nymphs can only surive on the new flush tips of citrus. Because they produce a toxin, the flush tips die back or become twisted and the leaves do not expand normally. This problem can be reduced through pesticide control of the psyllid population or releases of natural enemies. A more important consequence of the introduction of ACP into California is its ability to vector the bacterial disease HLB. HLB causes assymetrical blotchy mottling of leaves (in contrast to Zinc deficiency that causes symmetrical blotching). Fruit from HLB-infected trees are small, lopsided, poorly colored, and contain aborted seeds. The juice from affected fruit is low in soluble solids, high in acids and abnormally bitter. The fruit retains its green color at the navel end when mature, which is the reason for the name citrus greening disease. The fruit is of no value because of poor size and quality. There is no cure for the disease and rapid tree removal is critical for prevention of spread.

Economic Impact: HLB is one of the most devastating diseases of citrus and since its discovery in Florida in 2005, citrus acreage in that state has declined significantly. Since the psyllid arrived in Southern California in 2008, the citrus nursery industry is rapidly moving its production under screenhouses. If the psyllid were to become established in citrus growing region, pesticide treatments for the psyllid would be instituted resulting in a direct cost of greatly increased pesticide use (3-6 treatments per year) and indirect costs due to disruption of the integrated pest management program. If the disease were to appear in California, a costly eradication program would need to be instituted to remove infected trees in order to protect the citrus industry.

Distribution of ACP and HLB: ACP is found in Asia, parts of the Middle East, South and Central America Mexico and the Carribean. Asian citrus psyllid was first detected in backyard citrus in Southern California in August 2008. Surveys have found infestations in areas of San Diego and Imperial counties. ACP is also found in Florida, Louisiana, Georgia, South Carolina, Texas and Hawaii. HLB is present in China, eastern and southern Africa, the Indian subcontinent, Madagascar, Mauritius, Reunion, the Saudi Arabian peninsula, and southeast Asia. In 2005, HLB was found in Florida and it is now known to occur in Cuba, Belize, and Eastern Mexico The presence of HLB in Mexico increases the risk for introduction of the disease into California via psyllids or infected plant material.

Research: Research centers on characterization of the bacteria, development of HLB detection methods, and control of the disease and the psyllid. To date, control of the disease is based on planting HLB-free citrus germplasm, eradication of infected citrus plants, and control of the vector with systemic insecticides. Countries with HLB learn to manage the disease so that they can still produce citrus. In California, the best strategy to keep this disease out is to continue to prevent spread of the psyllid into citrus growing regions through insecticide treatments and support both the federal and state quarantine regulations and the University of California’s Citrus Clonal Protection Program, which provides a mechanism for the safe introduction of pest and disease-free citrus germplasm into California.

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CISR: Tipu Psyllid

Anonymous — Mon, 20 Jan 2020 21:27:17 +0000

CISR: Tipu Psyllid Anonymous (not verified) Mon, 01/20/2020 - 13:27 More Blog Posts CISR Team May 30, 2009

The Situation: The rosewood tree, Tipu, or “Pride of Bolivia”,Tipuana tipu (Fabaceae), is native to South America (South Brazil, Argentina, Uruguay, Paraguay, Bolivia) and is widely grown as a landscape ornamental and shade tree in southern California and elsewhere in the world (e.g., Egypt, Portugal, and Israel.) Tipu trees are popular because they are drought and frost tolerant, are thornless, exhibit moderate height at maturity (~10m), and have attractive pinnate green leaves, and clusters of bright yellow flowers. Seeds are winged and look strikingly similar to those produced by maples. In October 2008, the Tipu psyllid, a new pest record for California, was found feeding on this urban plant in San Diego County.

Damage: Tipu psyllid nymphs and adults nymphs are tiny insects that feed on phloem. All life stages (except eggs which are non-feeding) attack young leaves and branches of Tipu trees. Extensive feeding causes the leaves on host plants to curl and drop prematurely. Nymphs produce pelletized wax-like residue. Adults and nymphs produce copious amounts of honeydew which fosters the growth of black sooty mold on leaves and branches. The wax pellets produces by nymphs are very similar to those seen in the Eugenia psyllid, an exotic pest from Australia that attacks Eugenia and Syzigium in California. Tipu psyllids feed exposed, without the protection of flocculent waxes or pit like depressions in leaves.

This pest was first detected in October 2008 in Carlsbad in San Diego County in California. Interestingly, this insect has recently emerged as a serious pest of Tipu trees in Curibita Brazil. Pest populations in Curibtia are very high, trees are being defoliated, excessive honey dew excretion is fouling concrete sidewalks and vehicles parked under Tipu trees. Tipu psyllid populations in several southern California communities have produced similar fouling of objects and sidewalks beneath infested trees. In Curitiba, high density pest populations are attacked by lady bug beetles (Coleoptera: Coccinellidae) which provide some control of outbreaks. In the absence of natural enemies (e.g., predators, parasites, or pathogens) or insecticidal controls, the establishment of Tipu psyllid in California poses a significant threat to the health and value of Tipu tree plantings in California landscapes.

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CISR: Potato Psyllid

Anonymous — Mon, 20 Jan 2020 21:14:07 +0000

CISR: Potato Psyllid Anonymous (not verified) Mon, 01/20/2020 - 13:14 More Blog Posts CISR Team August 13, 2009

The Situation: The potato psyllid is a major insect pest of solanaceous crops growing in Central and North America. Potato psyllid has historically been a sporadic pest in California, generally developing damaging populations for 6 months or a year and then disappearing for 20 or 30 years. However, since the year 2000, year-round populations have been causing damaging outbreaks in California and Baja, Mexico. Increases in damage have been reported on potatoes and peppers throughout the Central USA. In addition, this pest has recently spread to Canada and New Zealand, where tomatoes, potatoes, and peppers have suffered significant losses.

Damage: Potato psyllid causes yield loss by directly feeding on crop plants causing a significant reduction in quality and crop longevity. Yield losses of greater than 85% have been reported in potatoes and tomatoes. These yield losses are now known to be associated with the transfer of a bacterial pathogen. In tomatoes, the pathogen causes stunted plants and very low yields of marketable fruit. A potato defect associated with the pathogen is known as “zebra chip” (ZC), and has been documented in commercial potato fields in the U.S. (Texas, Nebraska, Colorado, Kansas, New Mexico, Arizona, Nevada, and California), Mexico, and Guatemala. The disease was named for the characteristic discoloration in potato chips produced from infected tubers. The phloem tissues in the tubers store sugars instead of starches, and these sugars caramelize upon cooking. The occurrence of zebra chip not only lowers yields of the potato crop, but also results in the rejection of chips processed from infected tubers. In peppers, in California, damage occurs when large populations of potato psyllids produce exceptional amounts of honeydew, a sticky waste product, which contaminates the fruit. Why the pathogen causes losses in peppers in New Zealand and Texas, but not in California, is an important research question.

Economic Impact: The U.S. potato industry, a nearly $4 billion dollar crop in 2008, has been devastated by the appearance of ZC. Losses have been in the millions of dollars in Texas alone, and the insect and pathogen have spread to major production areas across the U.S. The economic losses are likely to increase as Korea, Argentina, and Brazil have established quarantine restrictions on U.S. potatoes to prevent the accidental introduction of the agent that causes ZC. Tomato growers in Baja California, Mexico lost 85% of their crop in 2001, and tomato growers in San Diego Co., CA lost 50% of their crops in 2003.

Distribution: Potato psyllid is native to central North America, but has been resident in California and Baja, Mexico since 2000. In the U.S., the potato psyllid has been reported from Arizona, California, Colorado, Idaho, Kansas, Minnesota, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, Utah, Washington and Wyoming. In Canada, potato psyllid is found in Alberta, British Columbia, Ontario, and Saskatchewan. This pest also occurs in Mexico and has been recorded in the following states: Baja California Norte, Chihuahua, Coahuila, Districto Federal, Durango, Guerrero, Jalisco, Michiocan, Morelos, San Luis Potosi, Sinaloa, Tamaulipas, and Veracruz. Recently, potato psyllids have been collected from Guatemala and it has established itself in most parts of New Zealand as a pest of solanaceous greenhouse crops, as well as outdoor potatoes and tomatoes.

Research: At the UC Riverside campus, research is being conducted in the context of developing an integrated pest management program against this pest. This research focuses identifying and determining the role of natural enemies on potato psyllid population dynamics, the relative resistance of fresh market and chipping potato cultivars, characterizing the amount of variation that exists for the bacterium that cause ZC in potato psyllid populations, identification of potential non-crop hosts and studies on the impact of pesticides on ZC transmission.

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CISR: Red Gum Lerp Psyllid

Anonymous — Mon, 20 Jan 2020 20:59:41 +0000

CISR: Red Gum Lerp Psyllid Anonymous (not verified) Mon, 01/20/2020 - 12:59 More Blog Posts CISR Team October 22, 2009

The Situation: Red gum lerp psyllid is an insect that is native to Australia. In June 1998, this insect invaded California and was first found in Los Angeles County. This pest feeds exclusively on species of Eucalyptus and in California it exhibits high preference for river red gum (Eucalyptus camaldulensis), flooded gum (E. rudis), and forest red gum (E. tereticornis). Red gum lerp psyllid has demonstrated remarkable invasion potential. After its initial discovery in California, red gum lerp psyllid was found in Baja California, Mexico in 2000, Florida and Hawaii in 2001, Mauritius 2001, South America in 2002, and Portugal and Spain in 2007. This pest is a major threat to susceptible Eucalyptus species that are grown in urban landscapes, as wind shelters, or as commercial forests.

Psyllid Biology: Psyllid nymphs and adults feed on sugar rich phloem. Honeydew, is a sticky waste product excreted by nymphs and adult psyllids after digesting phloem. As nymphs feed they can use honeydew excretions to form a protective white cap called a “lerp,” the conspicuous white cone seen on eucalyptus leaves. Nymphs feed and grow to adulthood under this crystalline cap. Upon completing development, winged adults leave the protection of the lerp and fly to new plants to mate, feed, and lay eggs.

Damage: High density red gum lerp psyllid populations secrete copious amounts of honeydew and excessive feeding pressure causes premature leaf drop. Heavily infested leaves are readily noticeable because of the large numbers of white lerps encrusting the leaf surfaces. Falling leaves foul surfaces beneath infested trees such as vehicles parked under trees, and swimming pools, the bottoms of shoes are soiled when sticky leaves are walked on, and leaf drop results in the rapid accumulation of flammable material beneath trees and on the rooftops of houses and other buildings. Extensive and repeated defoliation events weaken trees, and contributes to the premature death of some highly susceptible species, in particular E. camaldulensis. In Southern California, thousands of mature E. camaldulensis were killed within 2-3 years by uncontrolled populations of red gum lerp psyllid. The removal costs for these dead trees must have cost home owners, city councils, community groups, and utility boards millions of dollars. Honeydew excretion promotes the unsightly growth of black sooty molds on leaves and branches, and honeydew dripping from heavily infested trees can stain concrete sidewalks.

Biological Control of Red Gum Lerp Psyllid: A biological control program against red gum lerp psyllid has used the parasitoid Psyllaephagus bliteus. This natural enemy is native to Australia and was widely released in California from 2000 through 2002 to control the red gum lerp psyllid, after quarantine studies indicated that it posed no significant risk to other species.

Laboratory studies have demonstrated that P. bliteus can lay eggs in psyllid nymphs of any age, but female parasitoids prefer third and fourth instars (red gum lerp psyllids have five nymphal stages or instars). To parasitize a psyllid nymph, female parasitoids use their ovipositor (an egg laying tube on the abdomen) to puncture nymphs and they then inject an egg into the body of the nymph once the ovipositor is inside the host. The parasitoid egg hatches and the P. bliteus larva then eats the host from the inside killing it. Once development is completed, the parasitoid pupates within the body of the host. To escape from the host’s body, the parasitoid uses its mandibles to chew a circular hole which provides an exit. The presence of these exit holes is a very good indicator that P. bliteus is present and attacking red gum lerp psyllid nymphs.

In addition to parasitizing red gum lerp psyllid nymphs, female parasitoids can kill nymphs through host-feeding. Female P. bliteus use their ovipositor to either drill through the protective lerp or they slide their ovipositor under the lerp and repeatedly stab the red gum lerp psyllid nymph. Females feed on the body fluids that leak from these wounds, and the trauma from host feeding is often lethal to nymphs. Female P. bliteus will host-feed on all nymphal stages and they will also feed on lerps to gain nutrition from sugars within the lerp. Adult female parasitoids can live for several months. Maximum egg deposition (i.e., 88%) occurs within 22 days of adult emergence. Female parasitoids can lay 34-302 eggs over their life time with an average of 126 eggs being laid before death.

The biological control program with P. bliteus against the red gum lerp psyllid has been very successful in California’s mild coastal regions, but has provided, only sporadic control in the hot dry interior regions of California. This result suggests that other strains of P. bliteus more tolerant to hot arid conditions need to be imported from Australia for potential release in California, or alternatively, a different species of parasitoid may be needed for areas where P. bliteus has provided inadequate control.

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Hunting for Natural Enemies of Asian Citrus Psyllid in Pakistan

Anonymous — Mon, 20 Jan 2020 02:03:46 +0000

Hunting for Natural Enemies of Asian Citrus Psyllid in Pakistan Anonymous (not verified) Sun, 01/19/2020 - 18:03 More Blog Posts CISR Team November 08, 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.

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

Anonymous — Wed, 18 Dec 2019 09:31:51 +0000

Psyllaphycus diaphorinae: Another Natural Enemy from Pakistan for ACP Biocontrol? Anonymous (not verified) Wed, 12/18/2019 - 01:31 More Blog Posts 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.

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!

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

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

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
Denoth, M., L. Frid, and J. H. Myers. 2002. Multiple agents in biological control: improving the odds? Biol. Cont. 24: 20-30.
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.
Hussain, M. A. and D. Nath. 1927. The citrus psylla (Diaphorina citri) (Psyllidae: Homoptera). Mem. Dept. Agric. India, Entomol. Ser. 10: 5-27.

Asian Citrus Psyllid, Psyllids

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Psyllids