Location: Subtropical Insects and Horticulture Research
2021 Annual Report
Objectives
Objective 1: Investigate the interactions of subtropical invasive pests of vegetables and ornamental crops (e.g., tomato, pepper, floriculture) with their natural enemies and use this information to develop biocontrol-based banker plant systems for environmentally sound pest management. [NP304, C3, PS3A, 3B and 3C]
Sub-objective 1a: Expand the utility of the papaya banker plant system by incorporating predators and/or entomopathogenic fungi simultaneously or in combination with the parasitoid.
Sub-objective 1b: Build a better banker plant through biotechnology by genetically engineering papaya to contain attributes that make it more suitable for banker plant use: i.e. nonflowering, papaya ringspot virus and powdery mildew resistant.
Sub-objective 1c: Develop a mealybug banker plant system using ornamental muhly grass (Muhlenbergia capillaris), the native mealybug (Stemmatomerinx acircula), and predatory beetles (Diomus austrinus, Cryptolaemus montrouzieri) for control of pest mealybugs.
Objective 2: Investigate structural, physiological, molecular, and chemical aspects of whiteflies and identify inhibitor strategies/molecules such as but not limited to feeding disruptors and peptide inhibitors of disease transmission that can be used in the development of novel interdiction strategies envisioned to work either through production of transgenic plants or application of chemical treatments that block feeding/disease transmission. [NP304, C3, PS3A, 3B and 3C]
Sub-objective 2a: Identify interdiction molecules that can be expressed in transgenic or Plant-Host Activated-Cell Transplantation (PHACT) adapted plants for controlling hemipteran insects and their transmitted diseases.
Sub-objective 2b: Development of transgenic vegetables and ornamentals with increased resistance to hemipteran pest insects and/or their transmitted diseases
Sub-objective 2c: Plant-Host Activated-Cell Transplantation (PHACT) as a strategy to induce plant resistance to hemipteran insects and their transmitted diseases.
Approach
This project focuses on two control strategies for whitefly and subtropical invasive. The first approach will be the development of banker plant systems for whitefly and mealybug management that will be used to establish, augment and increase the numbers of natural enemies in vegetable and ornamental production. We will expand the utility of the papaya banker plant system to include general predators and/or entomopathogenic fungi to enhance the pest control capability of the system by increasing the number and diversity of pests controlled. We will construct a nonflowering papaya banker plant through biotechnology that is both Papaya ringspot virus and powdery mildew resistant to increase the utility of the banker plant system. Mealybug banker plant systems will be developed to provide viable biologically control alternatives for environmentally sound pest management for nursery, greenhouse ornamental and vegetable growers. The second approach focuses on the development of a biological interdiction strategy through identification of entomotoxic biomolecules (primarily peptides) that target the pest insect or the transmitted pathogen and delivering these molecules either through transgenic expression or through a novel Plant-Host Activated-Cell Transplantation (PHACT) organoid-biofactory strategy. The outcomes of this research range from development of improved and sustainable IPM strategies employing banker plant systems to identification of new biologically-based control strategies incorporating either resistant transgenic plants or deployment of an engineered plant organoid biofactory system for hemipteran pest insect control.
Progress Report
Host prey preference experiments for the predatory beetle, Delphastus pallidus, determined the following ranking from high to low preference of seven exotic whitefly species: Middle East-Asia Minor 1 > pepper whitefly > ficus whitefly > Bondar’s nesting whitefly > rugose spiraling whitefly > Ixora whitefly, > giant whitefly. Currently we use papaya and the papaya whitefly as the host plant and surrogate to rear the predatory beetle. Host preference for papaya whitefly and life table studies are currently underway.
Five fungicides were evaluated for mortality effects on papaya whitefly. One residual followed by three contact sprays were demonstrated to be suitable fungicides for colony maintenance and banker plant development to control powdery mildew. A second trial to screen six additional fungicides has been initiated.
The success of Objective 1b demands the involvement of researchers from several disciplines especially plant pathology and plant breeding. We have assembled a team and developed a strategy. The introduction of transgenes of powdery mildew resistance requires the suitable papaya genotype, target genes, and working transformation protocols. Bioinformatic analysis was used to identify two genes candidates, CpMLO1A and CpMLO1B, for genome editing-based knock out to induce powdery mildew resistance in papaya.
Determined the host preference, population potential of phantasma scale on common palms grown in Florida and a protocol for assessing scale infestations as efficiently and accurately as possible. The variety trial included eight palm varieties: Foxtail, Windmill, Phoenix roebelenii, Triangle, Queen, Saw Palmetto, Adonidia and Areca. Number of frowns per palm were recorded at least monthly and each frown was rated as infested or not infested (% palm infested). The most heavily infested frown per palm was rated for number of scale with 1 equaling no scale and 6 equal to over 500 scale (severe infestation). At the last evaluation Windmill was the most heavily infested followed by Saw Palmetto, Foxtail = Areca, Triangle, Robellini = Adonidia, and Queen Palm. Phantasma scale did not find Queen palms attractive at all with no infestation recorded until 301 days after introduction into the nursery. This study will be terminated at 2 years in December 2021.
Determined the efficacy of a pepper-based banker plant system utilizing Amblyseius swirskii and Amblydromalus limonicus predatory mites for control of chilli thrips on rose. Results showed that both mite species successfully reduced populations of thrips on roses down to nearly undetectable levels compared to the predator-free controls. There was no difference however, in the level of control achieved between the two predatory mite species. Manuscript is currently under review.
Assessed the suitability of Artemia cysts commonly known as brine shrimp eggs for development and reproduction of predatory thrips, Franklinothrips vespiformis compared to poinsettia thrips as prey. Results showed that Artemia cysts alone were sufficient for complete development of F. vespiformis, however, Artemia cysts were not a superior food source compared to poinsettia thrips although predation was reduced when alternative food was provided. Manuscript is in preparation.
Conducted greenhouse studies to determine if the application of Artemia cysts as an alternative food source for predatory thrips (Franklinothrips vespiformis) enhanced biological control of poinsettia thrips. Results showed that F. vespiformis is a very effective predator of poinsettia thrips. Artemia cysts application did not enhance their biological control which was likely due to the strong predatory response exhibited by F. vespiformis. However, Artemia cyst application did promote the persistence of F. vespiformis in the cash crop. These findings demonstrate that Artemia cysts provided as a supplemental food for F. vespiformis is a promising tactic for the long-term management of poinsettia thrips. Manuscript is currently under review.
Conducted greenhouse studies to test the host specificity of potential banker plant mealybug candidate, Stemmatomerinx acircula, on economically important target crops and plants that are taxonomically similar to its primary grass host, Muhlenbergia capillaris. Crops included pepper, tomato, hibiscus, and poinsettia, while taxonomically similar plants included Tripsacum dactyloides, Tripsacum floridanum, Muhlenbergia schreberi and Muhlenbergia sericea. Native natural enemies of S. acircula in Florida are also being surveyed. Data collection is ongoing.
We collected over 700 sequences of sweetpotato whitefly, Bemisia tabaci, cryptic species MED (aka Q biotype) from Genbank. After removing short, erroneous ones with missing bases and ones with stop codon; we have about 500 sequences of MED from all over the world. All sequences were divided into 25 unique haplotypes. Among them, three haplotypes are the most prevalent all over the world. Hap1 comprises >30% of all records of MED and Hap2 and Hap3 comprise more than 10% and rest >60% are singleton. Hap1 and Hap3 are the most common in the USA. Hap1 and Hap2 are most common in the rest of the invasion ranges. Interestingly MED from Eastern Mediterranean never moved to Asia or any other invaded country except Canada and USA. Our analyses show multiple invasion incidences of MED in the world. One with Hap1 then Hap2 and most recent with Hap3. Manuscript is in preparation.
Ficus whitefly, an invasive species causing damage to ficus hedges and trees in Florida, is still challenging to manage almost 15 years after its first Florida record. We reinvestigated its status, resurveyed its biological control agents and overview of its management. Ficus whitefly has been distributed all over Florida with wide distribution towards east, west and south and its natural enemies are available in the field. Among its natural enemies, Baeoentodon balios, ficus whitefly specific parasitoid in Florida is dominant in the field. Two manuscripts are in preparation.
Support was provided to a regulatory agency to identify several new records and at least one new species of whiteflies. Two new USA continental records of whitefly species were found: Aleurovitreus pueblensis, piper whitefly, identified on Piper auritum and Aleuroplatus validus, Jamaican whitefly, identified on Mosiera longipes. The interception records of A. pueblensis show Piper species as its primary host. However, we determined that A. validus has been intercepted several times at USA ports from Antigua, Barbuda, Dominican Republic, Haiti, and Jamaica on leaves of wide range of host plant species including Annona muricata (soursop), Canella winteriana (wild cinnamon), Citrus sp., Eucalyptus sp., Guatteria blainii (haya minga), Pimenta sp. including Pimenta dioica (allspice). In addition, a new state record of the recent new USA continental record, Aleurotrachelus anonae, Annona whitefly, was identified in Washington DC from non-Annona host plants species. The whitefly slides collection at the Smithsonian National Museum of Natural History was used to determine that this species can infest several important ornamentals and fruit crops, including bananas and avocados. Initially, this species was thought to infest only Annona host plants species. In addition, an undescribed species of Aleurovitreus genus was identified on succulent species, crown of thorns. Manuscript is in preparation.We tested 2,635 specimens of 57 mealybug species from 26 genera of Pseudococcidae collected from Florida to discover an alternate of slide-mounting for an invasive species, Nipaecoccus viridis. N. viridis is an emerging polyphagous pest of regulatory concern in the USA and its distribution is limited to Florida. Our hemolymph color test can help identify all life stages promptly and allows early detection even when an adult female is not available. In addition, we identified its first report on organic blue berries and hemp in Florida. Two manuscripts are in preparation.
We identified for the first time Phenacoccus madeirensis, Madeira mealybug, on hemp in Florida. All of our collected mealybug samples from hemp in Florida were classified into three groups. Two of them are P. madeirensis and P. nr. gossypii, and the third one could be a new species. This is first report of two circullii species in the genus Phenacoccus.
We performed extensive analyses for hemp arthropod pests and prepared the list of 188 pest species (insects=180, mites=6, springtail=1, snail=1) from 55 families of 12 orders of arthropods ever reported from hemp all over the world with their references. Among Insects: Coleoptera (51), Dermaptera (1), Diptera (11), Hemiptera (55), Hymenoptera (3), Lepidoptera (32), Orthoptera (21), Thysanoptera (5); Non-Insect: Mites; Sarcoptiformes (1), Trombidiformes (5), Springtail; Symphypleona (1) and Snail; Mollusca (1). Out of 188, 21 have limited distribution, 5 have moderate distribution, 138 are not present at all and 24 are widely distributed in Florida. There are 29 which can be considered potentially major pests, 10 are widely distributed, 5 have limited distribution and 14 are not present in Florida. This work will help governmental agencies and growers in hemp pest management and regulations in Florida. Manuscript is in preparation. A new method of modifying plant traits without modifying plant genes was advanced. This method of creating host plant cells that can be grown as symbionts attached to crop plants and grow by producing their own growth regulatory molecules was demonstrated on tomato and sunflower. We have demonstrated that such symbionts can be engineered to produce Bacillus thuringiensis toxins that kill 100% of Lepidopteran larvae after just 3 days of their feeding on artificial diet supplemented with the engineered symbiont tissue. This was done as proof of concept and is now being advanced to identify molecules that can also kill hemipteran crop pests.
Accomplishments
1. New predatory mite identified for Chilli thrips control. The chilli thrips, Scirtothrips dorsalis Hood, is a recently established pest in the USA and poses a serious risk to many economically important ornamental and food crops. ARS researchers at Fort Pierce, Florida, in collaboration with the University of Florida conducted lab studies to compare the biological control potential of the phytoseiid mites Amblydromalus limonicus (Garman and McGregor) and Amblyseius swirskii (Athias-Henriot) by examining their predation and oviposition rates when fed different developmental stages of chilli thrips. Leaf disc bioassays determined there were no significant difference in predation and oviposition rates between mite species fed specific chilli thrips life stages and the larval stage was the most preferred stage for both mite species. Although the results showed that the biological control potential of both mite species was similar, having an additional predator available that may be as effective as A. swirskii, a proven control agent against chilli thrips in the field, warrants additional research into its potential utility.
2. A parasitoid vectors a plant disease, potentially diminishing the benefits it confers as a biological control agent. Parasitoids are frequently used in biological control and integrated pest management strategies all over the world. ARS researchers at Fort Pierce, Florida, illustrated, for the first time, an unappreciated risk posed by the use of such control agents. Deployment of parasitoids has been promoted as a means of suppressing the vector pest, Asian citrus psyllid (ACP), which naturally transmits citrus greening disease (Huanglongbing) in citrus orchards. However, while controlling ACP, the parasitoid Tamarixia radiata can inadvertently vector the Huanglongbing pathogen (CLas) thus diminishing its biological control efficiency; particularly in orchards where CLas infected and uninfected asymptomatic citrus trees coexist. Finding present a new and significant caution to the strategy of implementing biological control using parasitic wasps.
3. Cultivating next generation of whitefly taxonomists/identifiers for Florida state regulatory agency. Florida receives 2–3 exotic pest species every month. Whiteflies are ranked on the top among them. There are over 75 whitefly species in Florida, and this number is consistently increasing every year. The objective of the state regulatory agency in Florida is to prevent the introduction and spread of pests through inspection, detection, identification, eradication, mitigation, and public education. Taxonomic expertise plays a vital role among all these entities. There was no trained taxonomic in Florida state regulatory agency. It takes continuous efforts of several years for someone to identify Floridian whiteflies, and it can become almost impossible if there is no one to mentor or train. ARS researchers at Fort Pierce, Florida have provided comprehensive training to three identifiers working at Division of Plant Industry, Florida Department of Agriculture and Consumer Services this year. They are successfully conducting whiteflies identifications and playing an important role in halting the spread of exotic whiteflies in Florida and the USA.
4. Development of the first diagnostic framework for field detection, identification and management of phantasma scale in the USA. Fiorinia phantasma Cockerell & Robinson (Diaspididae: Hemiptera), phantasma scale, is an economically important pest of nursery plants, particularly of ornamental palms and can be transported to new localities by movement of live nursery stocks. The first USA continental record was collected on Phoenix canariensis Hort, Canary Island date palm, in 2018 from Miami-Dade County, Florida, where it was abundant and causing damage to fronds in ornamental palms. Its preference for palms may be of concern in Florida where palms are important components of natural and ornamental environments. The presence of all life stages and dense populations of phantasma scale on palm trees in Miami-Dade County indicate the infestation had been there for an extended period. It is not surprising that the Florida infestation remained undetected, as the scale is identical in field appearance to other species in the genus Fiorinia that occur in Florida on similar or identical hosts. ARS researchers at Fort Pierce, Florida, for the first time established diagnostic framework for detecting, identifying and managing its infestations.
5. Development of morphomolecular diagnostic tools for immature Fiorinia species in the USA. One of the main challenges in armored scale control is early detection. Fiorinia phantasma is geographically restricted in two Florida counties and is usually found on palms. The presence of its closely related species, F. fioriniae on palms complicates the detection of F. phantasma in Florida. Heavy infestations of another Fiorinia species, F. probocidaria, were recently recorded on citrus from residential areas in Florida. Regulatory efforts aimed at preventing its introduction to and establishment in commercial citrus growing areas in Florida are being implemented. In addition, there are three species, F. japonica, F. pinicola, and F. externa that are not established in Florida and 63 Fiorinia species that are not in the USA that could be introduced and could cause additional damage. These contemporary dynamics demand morphomolecular diagnostic tools for immature Fiorinia species. ARS researchers at Fort Pierce, Florida, provide diagnoses of immature of males and females, DNA barcodes, and extensive records of seven Fiorinia species distribution. Overall, the combined use of morphological and molecular data yield effective methods for early detection of new infestations and assist in making regulatory and control decisions.
6. Characterization of entomopathogenic fungus on the scale insect pest infesting the Christmas tree in the USA. Elongate hemlock scale, Fiorinia externa, one of the notable invasive pest species of Christmas trees, is not established in Florida, which has led to interdict the movement of F. externa on infested cut Fraser fir Christmas trees, Abies fraseri (Pinaceae, Tracheophytes) into Florida. Interdicted Christmas tree shipments in Florida have been quarantined, confiscated, destroyed, or returned to North Carolina for several years. It has been causing substantial economic loss since Florida businesses buy around 15% of its total production. The infestation of F. externa on Fraser fir Christmas trees is inevitable since they are usually grown outdoor for years before harvesting. Broad-spectrum insecticides do not effectively control armored scales in general. The growers of Christmas trees have been struggling to find a way to control F. externa for the last several years, mostly to resolve the regulatory challenges they are facing in Florida. During the last Christmas, ARS researchers at Fort Pierce, Florida, found most of the individuals of F. externa intercepted on Fraser fir Christmas trees imported from North Carolina covered with entomopathogenic fungus species, Conoideocrella luteorostrata. Most of the F. externa individuals were infested with this fungus suggesting a potential use of this fungus species as pre- or post-harvest biocontrol of F. externa in North Carolina and avoiding the rejection of shipments since interdiction does not apply if scale insects are dead. These findings will immediately appeal to growers, extension agents, and researchers working on the management of F. externa on Fraser fir Christmas trees because they bring new and robust evidence that entomopathogenic fungus can be used commercially to help the Fraser fir Christmas trees industry controlling F. externa and solve the ongoing regulatory issues related to F. externa.
7. Development of a new method of modifying plant traits without modifying plant genes. A new method of creating host plant cells that can be grown as symbionts attached to crop plants and grow by producing their own growth regulatory molecules was demonstrated on tomato and sunflower. ARS researchers at Fort Pierce, Florida, have demonstrated that such symbionts can be engineered to produce Bacillus thuringiensis toxins that kill 100% of Lepidopteran larvae after just 3 days of their feeding on artificial diet supplemented with the engineered symbiont tissue. This was done as proof of concept for using these to produce molecules that can also kill hemipteran crop pests. This is being developed for two applications: 1) the ability to inoculate crop plants for insect (whitefly and other crop insect pests) resistance, and 2) using the symbionts as a harvestable biofactory that produces biological insecticide molecules. Implementation of this pest insect control strategy will allow rapid response to emerging pest insect threats and easier delivery of therapeutic technologies to diverse germplasms. Using the symbionts as harvestable biofactories for biomolecule production could create new crop systems for rural agriculture and greatly reduce the production cost of biological pesticide molecules for use in agriculture.
Review Publications
Schoeller, E.N., McKenzie, C.L., Osborne, L.S. 2020. Comparison of the phytoseiid mites Amblyseius swirskii and Amblydromalus limonicus for biological control of chilli thrips, Scirtothrips dorsalis (Thysanoptera: Thripidae). Experimental and Applied Acarology. 82:309-318. https://doi.org/10.1007/s10493-020-00556-5.
McKenzie, C.L., Sparks, A.N., Roberts, P., Oetting, R., Osborne, L. 2020. Survey of Bemisia tabaci (Hemiptera: Aleyrodidae) in agricultural ecosystems in Georgia. Journal of Entomological Science. 55(2):163-170. https://doi.org/10.18474/0749-8004-55.2.163.
Kumar, V., Mehra, L., McKenzie, C.L., Osborne, L. 2020. Functional response and prey stage preference of Delphastus catalinae and D. pallidus (Coleoptera: Coccinellidae) on Bemisia tabaci (Hemiptera: Aleyrodidae). Biocontrol Science and Technology. https://doi.org/10.1080/09583157.2020.1749833.
