Location: Temperate Tree Fruit and Vegetable Research
2023 Annual Report
Objectives
Objective 1: Develop new tools and approaches for examining landscape-scale movement by Hemipteran vectors and plant pathogens between non-crop plant species and potato fields.
• Sub-objective 1A: Identify weedy plant sources of infective potato psyllids and beet leafhoppers entering potato fields of the Columbia Basin growing region.
• Sub-objective 1B: Characterize genetic variation in beet leafhopper populations across geographic areas and between host species within the Columbia Basin and use these data to evaluate host-linked dispersal of leafhoppers into potato fields.
Objective 2: Describe the biology of Hemipteran vectors of potato pathogens in crop and non-crop habitats, including reproduction and development, feeding ecology, chemical ecology, seasonal phenology, interactions with natural enemies, and transmission/acquisition of pathogens.
• Sub-objective 2A: Characterize beet leafhopper feeding behavior and stylet penetration activities to examine acquisition and inoculation of BLTVA across host species.
• Sub-objective 2B: Identify predator species important in reducing densities of potato psyllid and beet leafhopper in stands of weedy host plants.
Objective 3: Develop new or improved integrated management strategies to control emerging insect pests and insect-transmitted pathogens of potatoes.
• Sub-objective 3A: Produce a “risk matrix” that ranks non-crop weedy plants as to importance as sources of infective potato psyllid or beet leafhopper arriving in potato fields and forward those rankings to the potato industry.
Approach
Sub-objective 1A: Identify weed sources of psyllids and leafhoppers. Approach: Molecular gut content analysis will be used to identify plant DNA in insects and define their feeding histories. Both species will be collected as they enter potato fields. Specimens will be tested with PCR for presence of plant pathogens. Presence of a specific plant in insect guts and correlated presence of pathogen DNA will be evidence the plant is a source of infective insects. Contingencies: Plant DNA that cannot be identified to species based on representation in the NCBI database will be identified to genus. Sub-objective 1B: Characterize genetic variation in beet leafhopper populations across regions and host species. Approach: NextRAD sequencing will be used to identify genetically-defined leafhopper subpopulations collected from potato fields and weed hosts. Genetic differentiation among regions and plants will be assessed by analysis of molecular variance. Contingencies: NextRAD sequencing is time intensive which may make it difficult to evaluate all regions and host-sources. We will supplement NextRAD data as needed by analysis of the CO1 gene. Sub-objective 2A: Characterize beet leafhopper feeding behavior to examine acquisition and inoculation of plant pathogens. Approach: Electropentagraphy (EPG) technology to be used to examine how leafhopper feeding behavior affects pathogen acquisition and inoculation in cultivated and weedy hosts. We will record the time required to begin a feeding event and time spent in an event for three behaviors: xylem ingestion, phloem salivation, and phloem ingestion. Probability of pathogen acquisition and inoculation will be evaluated as a function of these time durations. Contingencies: If we encounter difficulties with the EPG assays, we will consult the literature on EPG work with other leafhoppers. Sub-objective 2B: Identify predator species that attack potato psyllid and beet leafhopper in non-crop habitats. Approach: Molecular gut content analysis will be used to identify predators feeding on potato psyllid and beet leafhoppers in non-crop habitats. Insects for molecular assay will be extracted from plant samples in Berlese funnels. The COI gene will be PCR amplified to detect psyllid or leafhopper DNA. We will identify which predatory taxa most readily attack potato psyllid and beet leafhopper by comparing presence vs absence of prey DNA across predator specimens. Contingencies: No difficulties in completing this work is anticipated. Sub-objective 3A: Produce a risk matrix that ranks weedy hosts by importance as sources of infective psyllids and leafhoppers. Approach: Rankings will color-code each plant species according to risk (red, yellow, or green). Host plants color-coded red will be those found to be sources of vectors and pathogens, and to be common in the study region. Rankings will be made available to growers at research meetings and publication in industry newsletter. We will include suggestions of how risk rankings can be used to assist IPM programs through monitoring of at-risk fields or by eradication of high-risk species. Contingencies: No difficulties in completing this work is anticipated.
Progress Report
This report documents fiscal year (FY) 2023 progress for project 2092-22000-022-000D, titled “New Technologies and Strategies for Managing Emerging Insect Pests and Insect Transmitted Pathogens of Potatoes.”
In a subordinate project related to Sub-objective 1A, ARS researchers in Wapato, Washington, analyzed molecular gut content to identify weed and crop hosts visited by aphid vectors of potato virus Y (PVY) in the San Luis Valley of Colorado. All aphid vector species regularly visit weedy plant species that host PVY, and regularly fed upon potato. Results suggested that the artichoke aphid and Russian wheat aphid may be more important vectors of PVY in potato than previously recognized.
In a subordinate project related to Sub-objective 1B, ARS researchers conducted 16S rDNA sequencing to identify microbial endosymbionts of beet leafhoppers, and polymerase chain reaction (PCR) to assess the frequency of Wolbachia infection across beet leafhopper sub-populations collected from various host plants within the Colombia Basin of Washington state and Elmore County, Idaho. Wolbachia infection did not vary by collection host, but beet leafhoppers with Wolbachia were significantly more likely to carry Candidatus Phytoplasma trifolii. Results were published in a scientific journal.
In support of Sub-objective 2A, the feeding/probing behavior of adult female beet leafhoppers was recorded in four-hour electropenetrograph (EPG) assays on radish and potato. Half of females carried Wolbachia infections. The resulting waveforms were compared with those in a previously established beet leafhopper waveform library to validate our methodology.
For Sub-objective 2B, ARS researchers conducted studies with several predatory arthropods including insects, spiders, and a predatory mite (Anystis) to determine how long following feeding the DNA signal of potato psyllid was harbored in the guts of the predators. DNA of potato psyllid was detected for up to one week following a meal of potato psyllid in the mite and the spiders, and for 2-3 days in the insect predators. These results confirm that the molecular tool developed in this sub-objective to identify predators which attack potato psyllid under field conditions detects DNA of the psyllid for at least several days following a single feeding event. A manuscript has been submitted to a scientific journal describing these results.
In support of Sub-objective 3A, ARS researchers in Wapato, Washington, sampled stands of matrimony vine for presence of potato psyllids. Data were used to update the psyllid prediction model being used by the Potato Pest Alert program of Washington State University for predicting risk of psyllid outbreaks in commercial potato fields. This is the 10th consecutive year that these samples have been taken and added to the psyllid prediction model. Risk rankings for weedy hosts of potato psyllid that are based upon psyllid use of the host plant and likelihood that the host harbors the zebra chip pathogen have been published in the industry newsletter (Potato Progress) and in a scientific journal. Plant species were color-coded (red, yellow, green) to describe their relative risk as potential sources of infective psyllids colonizing potato fields.
In a subordinate project related to Objective 3, initial studies were conducted to develop RNAi-based biopesticides targeting potato psyllid. Results identified three gene targets that increase mortality of potato psyllid adults. In addition, progress was made testing Symbiont technology for efficacy against the zebra chip pathogen in potato and tomato.
In a subordinate project related to Objective 3, ARS researchers initiated studies to identify new chemical management options for potato leafroll virus (PLRV) management. Afidopyropen treatments decreased PLRV transmission by green peach aphids in potatoes, although changes in feeding behavior related to PLRV transmission did not occur within the first four hours following afidopyropen exposure. These results suggest afidopyropen might be a useful tool for PLRV management, and the findings were published in a scientific journal.
Accomplishments
1. Discovery of a potentially important source of biological control in potatoes. Potato growers in the Columbia Basin have expressed interest in the use of commercially produced natural enemies for targeted release against aphid, mite, thrips, leafhopper, and psyllid pests. However, few if any natural enemy species which will attack the full suite of pests of concern to potato growers are available commercially. The whirligig mite (Anystis) discovered in Sub-objective 2B to readily attack potato psyllid on weedy host plants of the psyllid, was assayed to determine whether the mite also feeds on non-psyllid species which are pests of potatoes. ARS researchers in Wapato, Washington, and scientists at Washington State University, Pasco, Washington, collected mites from weedy hosts of the psyllid and assayed them to determine whether specimens harbored DNA of aphids, mites, thrips, or leafhoppers. All four pest taxa were detected in field-collected mites. Often a single specimen harbored DNA of multiple pest species, indicating that Anystis is a generalized and effective predator of arthropod pests common in potatoes. An insectary in Canada is now commercially rearing Anystis for purchase and release in Canada and has just recently expanded operations into Oregon, with aims to produce this mite in the US for release in greenhouses, vineyards, and other agricultural crops. This research indicates that Anystis should also be considered for targeted use against pests which are important in potatoes.
2. Bacterial endosymbionts of potato psyllid. Insects often harbor bacterial endosymbionts that provide them with nutrition, or protection from natural enemies, insecticides, pathogens, and plant defenses. ARS researchers in Wapato, Washington, and Washington State University scientists in Pullman, Washington, identified endosymbionts found in potato psyllid and compared them with endosymbionts found in two related non-pest psyllids, bindweed psyllid and atriplex psyllid. They found that bacterial communities were more similar in more closely related psyllids than in more distantly related psyllids and confirmed previous reports that both potato psyllid and bindweed psyllid harbor the pathogen that causes zebra chip disease of potato. They also discovered that potato psyllid harbors two distinct strains of the endosymbiont, Sodalis, which in other insects has been found to provide nutritional benefits. Results of this study provide a foundation to conduct more in-depth research on interactions and co-evolution between psyllids and their bacterial endosymbionts.
Review Publications
Cooper, W.R., Esparza-Diaz, G., Wildung, M.R., Horton, D.R., Badillo-Vargas, I.E., Halbert, S.E. 2022. Association of two Bactericera species (Hemiptera: Triozidae) with native Lycium spp. (Solanales: Solanaceae) in the potato growing regions of the Rio Grande Valley of Texas. Environmental Entomology. 52(1):98-107. https://doi.org/10.1093/ee/nvac109.
Angelella, G.M., Waters, T.D. 2023. Afidopyropen as a potential tool for potato leafroll virus management in post-neonicotinoid potato production. Journal of Economic Entomology. 116(3):713-718. https://doi.org/10.1093/jee/toad042.
Swisher Grimm, K.D., Horton, D.R., Lewis, T.M., Garczynski, S., Jensen, A., Charlton, B. 2022. Identification of three new ‘Candidatus Liberibacter solanacearum’ haplotypes in four psyllid species (Hemiptera: Psylloidea). Scientific Reports. 12. Article 20618. https://doi.org/10.1038/s41598-022-24032-9.
