Location: Subtropical Insects and Horticulture Research
2025 Annual Report
Objectives
Objective 1: Investigate biological control and ecological interactions of invasive pests of subtropical orchard crops (especially citrus) with their natural enemies, including signaler compounds that influence pest and natural enemy behaviors, and use this information to develop biologically based pest control strategies.
Sub-objective 1a: Identify plant species that can function as nectar sources or as banker plants (= ‘conservation plants’) to support the natural enemies of ACP in commercial citrus groves and nearby residential areas.
Sub-objective 1b: Determine whether the addition of conservation plants to a target landscape results in increased numbers of natural enemies with a concomitant decrease in ACP and, if so, determine if this effect decreases as a function of distance between conservation plants and citrus trees.
Sub-objective 1c: Perform scale-up of conservation plant arrays for use in citrus groves and evaluate their effectiveness in reducing ACP populations.
Sub-objective 1d: Determine whether plant signaler compounds can be used to: 1) increase recruitment of D. citri natural enemies to citrus; and, 2) influence ACP settling on citrus shoots.
Objective 2: Identify structural, physiological, molecular and chemical aspects of the Asian citrus psyllid and its hosts that can be used in the development of novel interdiction strategies such as feeding disruptors and peptide inhibitors of disease transmission that can be deployed either through biotechnology or exogenous application.
Sub-objective 2a: Screen dsRNAs in silico.
Sub-objective 2b: Identify interdiction molecules that can be expressed in transgenic or PHACT adapted plants for controlling hemipteran insects and their transmitted diseases.
Objective 3: Develop delivery methods to control ACP and HLB using approaches such as biotechnology, optimal chemical formulation, plant infusion, and attract and kill devices.
Sub-objective 3a: Develop direct delivery strategies for RNAi inducing and peptide interdiction molecules.
Sub-objective 3b: Development of transgenic citrus with increased resistance to hemipteran pest insects and/or their vectored diseases.
Sub-objective 3c: Plant-Host Activated-Cell Transplantation (PHACT) as a strategy to induce plant resistance to hemipteran insects and their transmitted diseases.
Sub-objective 3d: Develop Attract and Kill (AK) devices that will effectively suppress ACP populations in citrus groves and residential citrus. The devices will be capable of being charged with soft pesticides, entomopathogens or other killing agents. They will attract and manipulate psyllids using a combination of sensory stimulants and attractants.
Approach
Orchard crops, a major contributor to the U.S. agriculture industry, are long-lived trees that are threatened by the continuous invasion of exotic pests and the pathogens they transmit. This project’s focus is to increase the sustainability of U.S. orchard crops by reducing economic losses to invasive pests and pathogens. Current pest management practices rely on broad-spectrum pesticides, which are problematic because of their adverse effects on the health of humans, beneficial organisms, and the environment. Reliance on pesticides promotes pesticide resistance in the targeted insects. Thus, there is a need for novel tools and alternative control methods. The biotechnology and biocontrol methods proposed here complement existing IPM strategies and will lead to sustainable solutions for insect vectors of crop pathogens. The project will focus on the citrus/Asian citrus psyllid/Candidatus Liberibacter asiaticus crop/pest/pathosystem. Candidatus Liberibacter asiaticus (CLas) is the presumed causal agent of Huanglongbing (HLB), also known as citrus greening, a fatal disease that threatens citrus production worldwide. CLas is vectored only by the Asian citrus psyllid (ACP) (Diaphorina citri), a phloem feeding hemipteran restricted to Citrus and related genera. The objectives of the project are to develop: 1) Sustainable, biologically-based pest control strategies for area-wide management of HLB-ACP; 2) Interdiction molecules, with a focus on RNAi inducing molecules and bioactive peptides, that block key pathosystem processes; and, 3) Novel delivery methods for improved and effective uptake of interdiction molecules, killing agents, and entomopathogens to control ACP and HLB. The deliverables of this research will be sustainable management strategies that will allow citrus to remain an economically viable commodity in the presence of HLB. These approaches are also broadly applicable to a range of subtropical orchard crops.
Progress Report
ARS researchers from Fort Pierce, Florida used field trials to identify which plant species can be used to attract and sustain natural enemies of the Asian citrus psyllid. This ‘conservation biological control’ strategy can be used in commercial citrus groves as well as residential landscapes. The expectation is that, by improving the local habitat of the psyllid’s natural enemies, they will remain and reproduce in the area. This, in turn, will lead to increased predation of the psyllid, by both adult predators and their offspring. Experiments to demonstrate the veracity of this concept are ongoing.
A ‘Grove First’ concept was developed by USHRL scientists to evaluate injecting citrus trees with biopesticide and antimicrobial molecules that have potential to reduce pathogen levels in citrus trees and alleviate citrus greening symptoms. This work led to the identification of several treatments that improved citrus tree health and that are being evaluated in cooperating growers’ groves.
Methods were developed for producing and identifying small single-domain antibodies, termed ‘Mantabodies’, from manta rays. Our tests demonstrated that novel mantabodies bind proteins produced by pathogenic bacteria such as Escherichia coli and Vibrio. We are currently using computational biology and AI to alter the binding domain of these antibodies. This will permit us to rapidly produce mantabodies that bind to critical molecules within pests and pathogens, which incapacitates or kills them. We are identifying the mantabodies that bind to: 1) the bacterium that causes citrus greening disease to prevent disease symptom development, and 2) the precursor molecules that form the salivary sheaths produced by psyllids and other sap-sucking insects to prevent them from feeding and transmitting pathogens to crop plants.
A major hurdle to use of biomolecules to control crop pests and pathogens is the “cost of goods”. USHRL scientists developed a novel low-cost strategy for growing multiple PHACTs on plants that function as biofactories and biowarehouses of biomolecules that treat plant diseases. We have identified an Agrobacterium system that prolifically produces multiple PHACTs that, in turn, can produce biomolecules in crop plants. This system is now being coupled with the Gaantry gene introduction system, developed by ARS scientists, that delivers to 50 to 70 Kb of DNA to crop plants. This approach will result in the formation of numerous PHACTs that can produce targeted biomolecules to protect crop plants from pests and pathogens. The successful delivery of this strategy will create new economic opportunities to rural U.S. agriculture and open the door to the production of a multitude of biological molecules to protect crop plants.
Accomplishments
1. Screening multiple antibacterial treatments against HLB. ARS researchers from Fort Pierce, Florida have developed a ‘Field First’ screening pipeline to advance antibacterial treatments into trials with field grown citrus trees. Over 80 antibacterial molecules have been injected into citrus trees in the largest outdoor trial ever conducted. This has permitted USHRL scientists and their cooperating growers to rapidly screen these antibacterial molecules with respect to ability to improve tree health, fruit retention, and tree recovery.
2. Using coriander to protect citrus trees. An ARS scientist from Fort Pierce, Florida showed that co-sowing the seeds of quick-flowering coriander with slow-flowering cilantro resulted in flower production that lasted weeks longer compared to sowing each variety alone. The long-lasting flowering period provides nutritional resources, such as nectar, pollen, and alternate prey to ladybugs and hoverflies, which are the major predators of the Asian citrus psyllid. Co-sowing the two varieties will provide citrus growers with longer lasting natural enemy habitat while reducing their labor time and costs.
Review Publications
Sirmans, S., Avery, P.B., Cicero, J., Hunter, W.B., Cave, R.D., Carrillo, D. Persistence of three biopesticides containing entomopathogenic fungi under tree canopy conditions in Florida, USA. Biocontrol Science and Technology. 35(2):159–171. 2024. https://doi.org/10.1080/09583157.2024.2433534.
Stuehler, D.S., Hunter, W.B., Qureshi, J., Cano, L.M. Transcriptomic characterization of Wolbachia endosymbiont from Leuronota fagarae (Hemiptera: Psylloidae). Popular Publication. 4:19. 2025. https://doi.org/10.20517/mrr.2024.84.
Shippy, T.D., Hosmani, P.S., Flores-Gonzalez, M., Mann, M., Miller, S., Weirauch, M.T., Vosberg, C., Massimino, C., Tank, W., De Oliveira, L., Paris, T.M., Shatters, R.G., Heck, M.L., Hunter, W.B. Diaci v3.0: Chromosome-level assembly, de novo transcriptome, and manual annotation of Diaphorina citri, insect vector of Huanglongbing. Gigascience. 2024. 13:Article giae109. https://doi.org/10.1093/gigascience/giae109.