Location: Subtropical Insects and Horticulture Research
2016 Annual Report
Objectives
Objective 1: Investigate biological control and ecological interactions of whiteflies with their natural enemies using banker plant systems to promote environmentally sound control in vegetable and ornamental crops.
Sub-objective 1a: 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, resistant to papaya ringspot virus and powdery mildew.
Sub-objective 1b: Determine the compatibility of insecticide regimes with beneficial insects and natural enemies used in banker plant systems.
Objective 2: Investigate structural, physiological, molecular and chemical aspects of the whitefly feeding process and identify inhibitor strategies/molecules such as but not limited to feeding disruptors and peptide inhibitors of disease transmission than 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.
Sub-objective 2a: Develop transgenic tobacco expressing enzymatic inhibitors of whitefly salivary sheath formation test for resistance to Bemisia tabaci feeding.
Sub-objective 2b: Test application of discovered small molecule inhibitors of sheath formation for their effect on whitefly feeding on tomato.
Sub-objective 2c: Conduct proteomic analysis of salivary exudates to identify salivary sheath structural and biosynthetic proteins.
Approach
Research will focus on constructing a nonflowering papaya banker plant through biotechnology that is resistant to both papaya ringspot virus and powdery mildew. Strategically timed insecticide applications including neonicotinoids in the rotation regimes will be evaluated against MED (Q-biotype whitefly) for whitefly efficacy and compatibility with two of the natural enemies used in our banker plant systems: the predatory mite, Amblyseius swirskii, and the whitefly parasitoid, Encarsia sophia. Development and testing molecular inhibitors of whitefly feeding processes with specific emphasis on the processes that must occur for the whitefly to develop a successful feeding event. Two main objectives include: 1) Continued characterization of the whitefly salivary sheath biosynthesis and composition. We already have basic compositional data and some knowledge on structural arrangement. Molecular, biochemical and structural analyses will continue to identify key biosynthetic enzymes and sheath structural components. 2) Evaluation of inhibitors of sheath formation as control agents. This evaluation will be performed using artificial diet assays and development of transgenic tobacco expressing inhibitors and conducting bioassays where the whitefly feed on the artificial diet or the transgenic plants.
Progress Report
Developed collaboration to use a transgenic papaya line developed by the University of Florida that has been engineered to be Papaya ringspot virus resistant.
The compatibility of insecticides used in rotation programs to control Bemisia tabaci (Mediterranean whitefly also known as biotype Q) with the predatory mite, Amblyseius swirskii used in biological control programs for whitefly control was evaluated on salvia ornamental plants in the greenhouse. Experiments testing dinotefuran (grower standard neonicotinoid) as a drench application was compatible with the predatory mite. No significant difference in mite life stages between mite treated and combination plots (mite + insecticide) were reported during the majority of study period. The mite was effective in suppressing MED whitefly life-stages throughout the study period and efficacy was overall comparable with plants treated with dinotefuran.
Cyantraniliprole (anthanilic diamide) in rotation with pymetrozine (pyridine azomethines), both new classes of insecticide, were evaluated for predatory mite compatibility for control of whitefly. Drench application of cyantraniliprole at the low rate was compatible with the mite, whereas their number was significantly reduced post application of pymetrozine. The combination insecticide/predatory mite treatment was the most effective and the chemical rotation was the least effective in suppressing MED whitefly during the study period.
To estimate the lethal concentration range of insecticides used in rotation greenhouse trials against swirskii mites used for biological control of whitefly pests, preliminary bioassays are underway where different solvent mixtures (benign to swirskii mite) for the preparation of insecticide concentrations have been tested and standardized. To ensure less than 5 percent control mortality, various bioassay arenas were designed and were tested for their suitability for the survival of swirskii mites. Solvent and solvent mixtures were optimized to ensure insecticide solubility and minimum residue accumulation in the Petri dishes. These parameters are critical to ensure the lowest control mortality.
Work on salivary sheath inhibition as a method of blocking B. tabaci feeding was advanced. Due to lack of funds, we chose to focus on topical application strategies for initial analysis instead of transgenic plant development. This decision was justified because of: 1) breakthroughs we have had in development of new topical applications strategies for the control of Asian citrus psyllid (ACP) sheath formation/sheath production; and, 2) our earlier demonstration that sheath inhibitors that work on ACP sheaths also work on B. tabaci sheaths. Therefore ARS Scientists developed and tested a topical application assay for direct evaluation of sheath inhibitors on B. tabaci feeding. This system uses excised spearmint leaves that ARS Scientists demonstrated to support the complete B. tabaci life cycle. It can be used in both choice and no choice experiments to monitor feeding deterrence, adult feeding, egg laying, and nymph development.
Because isolation and analysis of psyllid salivary sheaths was easier than that for the whitefly and because we previously demonstrated that the same sheath inhibitors worked for both insects, ARS scientists we used the psyllid system as a surrogate for the whitefly. Previous work has shown that the same salivary sheath inhibitors inhibit both Asian citrus psyllid and Bemisia tabaci whitefly salivary sheaths. Further, the availability of the whitefly genome and transcriptome will be used to identify the whitefly homologs to the proteins identified in the psyllid salivary proteome. We have conducted initial salivary sheath proteome analysis using the Asian citrus psyllid as a surrogate. This work was done in collaboration with a research molecular biologist, USDA-ARS, BioIPM Research Unit, Ithaca, New York. Also, a large batch of psyllid salivary sheaths was isolated for further compositional and structural analysis.
The pathogenicity of a naturally occurring entomopathogenic fungus, Isaria fumosorosea (PFR 97®) alone and in combination with an insect growth regulator (Talus®) was evaluated against a new invasive pest, Rugose spiraling whitefly (RSW) under field conditions for the second season. This study complemented earlier work. Overall, Talus alone and its combination with PFR was found to be the most effective treatment for control of RSW eggs, early instars and late instar nymphs during the 10 week period. PFR alone was found to be least effective. Results suggest that Talus alone and in combination with PFR could be efficacious against RSW and would help mitigate the spread of this pest in Florida.
Lab bioassay and greenhouse trials are underway to evaluate the biocontrol potential of two generalist predatory beetles Delphastus catalinae and Delphastus pallidus on two whitefly biotypes of Bemisia tabaci (MED and MEAM1). For the studies, separate colonies of the two beetles have been initiated.
Accomplishments
1. Compositions and methods for control of hemipteran insect stylet sheath structure formation. Final patent submission US15/140,666. Hemipteran insects collectively represent one of the greatest limitations (either yield or economics) to crop production in the United States and worldwide. During the probing process used to establish a successful feeding event on a host plant, agriculturally important hemipteran pest insects, including whiteflies, aphids, scales, mealybugs, leafhoppers, planthoppers etc., secrete a liquid saliva that hardens into a continuous feeding tube leading from the surface of the plant tissue to the site of feeding (the plant vascular tissues). Through analysis of composition and structure of this sheath, Agricultural Research Service (ARS) researchers at Fort Pierce, Florida, identified inhibitors that block this process and demonstrated that when they are applied to the surface of the leaf, establishment of a successful feeding event is inhibited. This work presents a novel method of preventing these pest insects from feeding on important United States crop plants without the use of toxic pesticides. Furthermore, this, interdiction method does not kill the insect, but produces a plant that cannot be used as a food source by the insect and therefore represents a sustainable control method that is compatible with other biocontrol methods as part of any Integrated Pest Management strategy, and should not have a deleterious effect on other beneficial insects. As a result of this work, a CRADA with a private company has been initiated to support development of a commercializable product.
2. Geographical distribution and genetic analysis reveal recent global invasion of an agricultural pest whitefly, Bemisia tabaci primarily associated with three genetic types. The whitefly Bemisia tabaci is a cryptic species complex in which one member, Middle East-Asia Minor 1 (MEAM1) has invaded globally. After invading large countries like Australia, China and United States, MEAM1 spread rapidly to occupy most of the climatically suitable geography. In contrast, our analysis of MEAM1 in India showed a very different pattern. Despite the detection of MEAM1 being contemporaneous with invasions in Australia, United States and China, MEAM1 has not spread across the country and instead remains restricted to the southern and southwestern regions. An assessment of MEAM1 genetic diversity in India showed a level of diversity equivalent to that found in its presumed home range and much higher than what is observed across the invaded range. This high level of genetic diversity and restricted distribution of MEAM1 raises the prospect that its home range extends into India. To test this we explored diversity across the invaded range and observed that 84.5 percent of records are accounted for by 3 haplotypes of which one, Hap1, accounts for 79.8 percent. In 823 records pertaining to Australia, China and United States, Hap1 accounts for 88.6 percent whereas in India it remains restricted to only one part of one Indian State despite its first detection in 1999. This study not only unifies our understanding of B. tabaci diversity in India, it increases our understanding of species invasions. In particular, it shows clearly that the global invasion by MEAM1 has been driven primarily by a single haplotype rather than the entire species.
None.
