An Overview of Biological Control of Diaphorina citri

David G. HallSubtropical Insects Research Unit, USDA-ARS, Ft Pierce, FL

International Tamarixia Workshop 2010

An overview of natural enemies of the Asian citrus psyllid, Diaphorina citri Kuwayama

D. citri is subjected to various levels of biological control by a similar set of natural enemies throughout its geographic distribution, although the specific species complex varies geographically.

Entomopathogens: various fungal pathogens have been reported and have sometimes been considered important natural enemies.

Predators: The complex of predators usually includes various species of ladybeetles (Coleoptera: Coccinellidae); syrphid flies (Diptera: Syrphidae); lacewings (Neuroptera: Chrysopidae, Hemerobiidae); and spiders (Aranae)

Parasitoids: Two species are considered effective and occur in some geographic areas, either naturally or introduced.

Entomopathogens

D. citri killed by fungi

Isaria fumosorosea (= Paecilomyces fumosoroseus) (Samson 1974, Subandiyah et al. 2000)

Hirsutella citriformis (Rivero-Aragon and Grillo-Ravelo 2000, Subandiyah et al. 2000, Étienne et al. 2001)

Cephalosphorium lecanii (Verticillium lecanii) (Rivero-Aragon and Grillo-Ravelo 2000, Xie et al. 1988)

Beauveria bassiana (Rivero-Aragon and Grillo-Ravelo 2000, Yang et al. 2006)

Cladosporium sp. nr. Oxysporum (Aubert 1987)Capnodium citri (Aubert 1987)Acrostalagmus aphidum (Yang et al. 2006)Paecilomyces javanicus (Yang et al. 2006)

Entomopathogens reported to attack Diaphorina

Hirsutella citriformis – Florida, Guadeloupe, and other areasMycosed cadavers adhered to citrus leaves are point sources of infectionContact with conidial-bearing synnemataRain- or wind-dispersed conidiaDeath within 7 to 9 days, and synnemata first begin to appear about 7 days later.Infectious for more than 10 wkCadavers remain on leaves an average of 10 weeks, maximum of 24 weeks observed.

Adult D. citri killed by Hirsutella

Synnemata

Adult D. citri killed by Hirsutella (only adults have been observed to be attacked)

Hursutella citriformis is more common in older trees (more favorable microclimate).

Hirsutella citriformis

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Phenology of adult Asian citrus psyllid cadavers infected by Hirsutella citriformis over time. Thin downward arrows indicate application dates of petroleum oil for plant pathogenic fungi, bold downward arrows indicate application dates of petroleum oil plus copper.

A project is underway to assess copper, oil, and other chemicals for toxicity to Hirsutella

Hirsutella citriformis

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Phenology of healthy psyllids and diseased psyllids

Hirsutella citriformis

Percentage of adults per sample observed to be mycosed.

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Mycosed cadavers most common during the fall and winter

Three isolates. When healthy adult psyllids were exposed to one stain, 87.5 ± 2.5 % died and produced synnemata. When healthy adults were exposed to these dead cadavers, 77.5 ± 17.5 % died and produced synnemata.

Hirsutella culture media developed by Drion Boucias (UF)

Isaria fumosorosea Wize (= Paecilomyces fumosoroseus)Attacks all stages of Diaphorina citriFormulations already available for testing

Mycosed Nymph

Mycosed eggs

Mycosed adultsPhotos by Pasco Avery

There is considerable interest in microbial control of the psyllid

Presentations at this workshopJoe Patt

Alejandro ArevaloJesse de Leon

Entomopathogens of Diaphorina

Predators

An array of species of ladybeetles, lacewings, syrphid flies and spiders known to attack Diaphorina are reported in the literature.

I am going to address species reported in Florida

Coccinellid predators have been considered by some researchers to be the most important biological control agents of D. citri in Florida (in contrast to observations in India)

Olla v-nigrum Exochomus childerni Cycloneda sanguinea

Curinus coeruleusChilocorus stigma Harmonia axyridis

Olla v-nigrum is one of the most common predators of Diaphorina citri in Florida citrus.

Prior to the psyllids introduction into Florida, this coccinellid species was relatively rare in citrus.

Within several years after the psyllid was introduced, population levels of this ladybeetle greatly increased.

Harmonia axyridis, Cycloneda sanguinae and Olla v-nigrum were the dominant coccinellid species in two Florida citrus groves our lab studied.

In one 2-yr study, most abundant in citrus during January – June.

Not all coccinellid species will feed on Diaphorina citri!

Rodolia cardinalis

Coccinella septempunctataHippodamia convergins

Chilocorus circumdatus Coelophora inaequalis

Cryptolaemus montrouzeri

May actually feed on Diaphorina?

Zelus longipes: The milkweed assassin bug is an occasional predator of D. citri in Florida

Photo by Richard Leung

Allograpta obliqua

Syrphid fly larva predating on psyllid eggs and nymphs

Syrphid flies in the genus Allograpta have been found attacking D. citri in Réunion, Nepal and Florida.

Photo by Alan Cressler

Hibana velox: This spider has been noted as having some importance as a predator of D. citri in Florida

Two green lacewings, Ceraeochrysa sp. and Chrysoperla rufilabrisBurmeister, contribute to psyllid mortality in Florida. The green lacewings Chrysopa boninensis Okamoto and C. septempunctataWesmael attack D. citri in China

An unidentified brown lacewing has been observed attacking D. citri in Florida

There is considerable interest in predators of the psyllid, notably Coccinellids

Presentations at this workshopJawwad Qureshi

Mamoudou SetamouMark Hoddle

Hernán Camacho VindasEstéban Leyva

Predators of Diaphorina

Parasitoids

Tamarixia radiata (Hymenoptera: Eulophidae) and Diaphorencyrtus aligarhensis (Hymenoptera: Encyrtidae) are two well-known parasitoid species of D. citri.

In India, parasitoids of D. citri were reported to play a more important role in biological control of D. citri than predators (Husain and Nath 1927).

Other parasitoid species have been reported.Possible primary parasitoid: Psyllaephagus diaphorinaeProbably hyperparasites: Syrphophagus taiwanus, Syrphophagus

diaphorinae and Marietta sp. nr. exitiosaDiaphorencyrtus diaphorinae has been listed as a hyperparasite but

may be a primary parasitoid.

Diaphorencyrtus aligarhensis• Origin is India• Introduced into a number of citrus producing areas around the

world including Réunion Island, Taiwan, and Florida• Accidentally introduced into Philippines, Vietnam and China• A number of hyperparasitoid species are reported to attack this

parasitoid• Overall, usually less effective against D. citri than T. radiata

Diaphorencyrtus aligarhensis • An arrhenotokous endoparasitoid, but males are often absent due to

Wolbachia infections.• The female lays eggs inside 2nd, 3rd, or 4th instars• Adults host-feeds on younger instars causing more mortality than

parasitism• One strain was released during 1998 in Florida, from Taiwan (not

established) (males were absent)

A second collection of Diaphorencyrtus aligarhensis was imported from Vietnam during 2006.

• This strain had both males and females.• However, by January 2007, all males had disappeared from the

colony• Releases have been made over the past two years with little

evidence of establishment.A third strain of Diaphorencyrtus was imported from Pakistan during

2009 and is currently in quarantine. Both sexes are persisting in this colony.

Guest of Honor:

Tamarixia radiata

World distribution of Tamarixia radiata

T. radiata is becoming widespread in the New World even though it was intentionally only released in Guadeloupe and Florida.

Tamarixia radiata• Credited with reducing infestations of D. citri sufficiently in

Réunion to mitigate the impact of greening• Good levels of psyllid control by T. radiata have been reported in

Guadeloupe and Puerto Rico.• Attacked by hyperparasitoids in India• Regarded as a more effective than Diaphorencyrtus• An arrhenotokous ectoparasitoid, no reports of Wolbachia

suppressing males• The female lays eggs under 3rd, 4th and 5th instars• Up to 40% parasitism in the laboratory• Like Diaphorencyrtus, host feeding by adult parasitoids on younger

instars usually causes more mortality than parasitism

T. radiata egg T. radiata larva

Tamarixia radiata exit hole from mummy – thoracic or head region

• Tamarixia is widely distributed in Florida• But levels of biological control are erratic and generally low• Consistently higher percent parasitism has been reported in Puerto

Rico (upcoming Stansly report), and the parasitoid has been credited with exerting excellent control of Diaphorina in Réunion and Guadeloupe

Why doesn’t the strain of Tamarixia radiata in Florida provide better control?

Research has shown that there are at least minor genetic differences among some geographical populations of Tamarixia, for example the Florida strain can be distinguished from the Guadeloupe and Puerto Rico strains. Some ‘biotypes’ may be more effective in Florida than the established ‘biotype’.

Three new collections of the parasitoid were thus obtained (south China, north Vietnam, Pakistan)

AHPIS-PPQ granted permission for releases of these strains during November 2009. Dr. Stanlsy has initiated releases in southwest Florida, ARS will initiate releases this month in east-central Florida, Dr. Nguyen may have initiated releases.

In the future we may want to import additional ‘biotypes’ and perhaps other parasitoid species (forewarning to Bob Tichenor)

Thanks to Ru Nguyen for his continued dedication for importing Tamarixia and Diaphorencyrtus biotypes, interfacing with PPQ and NAPPO in bringing specimens in and getting permission for releases, and supplying parasitoids to many of us for releases.

Establishment and impact of these new Tamarixia strains in commercial citrus will be challenging given the intensive insecticide programs being used for psyllid control.

Some of the pesticides used for psyllid control are very toxic to Tamarixia for many days after they are applied.

Noted is that even before growers began intensive psyllid spray programs in Florida, a large array of natural enemies in citrus including Tamarixia failed to provide enough biological control of Diaphorina to solve the HLB problem.

An obvious current niche for Tamarixia is in urban settings, where increased biological control would contribute to area-wide psyllid management.

With this in mind, in addition to releases in conventional citrus settings, ARS will be making releases of the new strains in 12 different plantings of Murraya paniculata in east-central Florida.

The north Vietnam and Pakistan strains are distinguishable from the Florida strain via mitochondrial COI gene region, but they won’t be distinguishable after inter-mating occurs.

The development of microsatellite markers to distinguish these strains would be critical with respect to monitoring establishment of and biological control by the different strains.

Norman Barr - genetic diversity of Tamarixia.We are hopeful that one or more of the new Tamarixia strains will

establish and out-perform the Florida strain, yielding higher, more consistent levels of percent parasitism.

It would be prudent to investigate annually augmenting natural Tamarixia populations, perhaps even multiple times each year.

This could be especially strategic in areas where Tamarixia might have trouble bridging winter

Millions of parasitoids could be reared and released each year.Spatial-temporal issues: how many release points across an area,

what release rates would we use? (Jawwad Qureshi may give us some insight during his presentation)

Production issues: how could millions of parasitoids be produced and what would it cost?

An original focus of this workshop was to be on rearing procedures for Tamarixia, and thus we will hear a number of presentations on this specific topic and visit Dan Flores’ rearing operation.

There is only one publication I am aware of on rearing Diaphorina and Tamarixia (Skelley, L. H., and M. A. Hoy. 2004)

There is some helpful information on rearing Diaphorina (Tsai, J. H., and Y. H. Liu. 2000, Liu and Tsai 2000, Fung and Chen 2006, Nava et al. 2007

At this point in time we are forced to produce Tamarixia on Diaphorina reared on plants (Murraya, Citrus macrophylla, or other types of citrus).

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The Florida Experience

In spite of an array of biological control agents attacking Diaphorina citri in Florida, notable infestation levels continue to occur if insecticides are not regularly applied. Augmentative releases of natural enemies should be explored.

Microbial control has a potential current niche in citrus regularly sprayed with insecticides.

Biological control by parasites and predators has a current viable niche in urban landscape plants, dooryard trees, and abandoned groves.

If plant resistance to huanglongbing or to the psyllid can be developed and the use of pesticides reduced, biological control by parasitoids and predators could play a much more important role in commercial citrus.