Research Project: Basic and Applied Approaches for Pest Management in Vegetable Crops

Location: Vegetable Research

2024 Annual Report

Objectives
1. Develop and enhance germplasm for host plant resistance of sweetpotato and watermelon that are resistant or tolerant to economically important pests, including whiteflies and soil dwelling pests. 1.A. Develop and characterize watermelon germplasm with resistance to whiteflies and incorporate the resistance into advanced breeding lines. 1.B. Develop sweetpotato germplasm clones that are resistant to soil dwelling pests and have desirable horticultural traits. 2. Assess whitefly-virus-host plant interactions and effects of biotic and abiotic factors on vegetable pests and their biological control agents. 2.A. Determine the effect of biotic and abiotic factors on populations of whiteflies and biological control agents of whiteflies in vegetable production systems. 2.B. Assess the impact of biotic and abiotic factors on whitefly:host-plant:virus interactions and whitefly endosymbionts. 3. Develop new or improved methods for the management of insect pests (including whiteflies and soil dwelling pests) and whitefly-transmitted viruses in vegetable crop production systems. 3.A. Identify and characterize genomics factors and develop novel genomics-based biotechnologies that would impede virus acquisition and transmission from whiteflies to plants. 3.B. Characterize genetic diversity and population structure of the sweetpotato weevil within the U.S. 3.C. Characterize infochemicals and plant-based chemicals affecting vegetable pests (e.g., click beetles, sweetpotato weevil and whiteflies) for use in detection, monitoring, and biologically-based management. 3.D. Identify and characterize sources of pickleworm resistance in cucumbers. 4. Develop sweetpotato germplasm lines adapted to low input, sustainable production systems, especially lines that are productive under weed competition. 4.A. Identify and characterize sweetpotato germplasm that is tolerant/competitive with weed pressure within sustainable production systems.

Approach
Conduct laboratory, greenhouse, and field experiments to identify sources of resistance and evaluate genetic populations to determine resistance against the sweetpotato whitefly in watermelon, against soil insect pests, weeds and whitefly-transmitted viruses in sweetpotato, and resistance against pickleworms in cucurbits. Assay chemical and physical mechanisms of resistance to pests using tools including gas chromatography-mass spectrometry (GC-MS), and Y-tube olfactometers. Use PCR-markers and other genomic technologies, such as genotype by sequencing, to identify sequences linked to the studied characters and to locate controlling genes on linkage maps. Cross appropriate germplasm to facilitate the incorporation of resistance into advanced breeding lines or new cultivars. Assess the competitive advantage against weeds of sweetpotato genotypes with more vigorous growth habits in comparison to less competitive conventional cultivars, identify competitive genotypes with good horticultural quality, and evaluate them as a component in integrated management systems for conventional and organic growers. Use a recurrent mass selection breeding approach to generate sweetpotato clones with high levels of resistance and good horticultural characteristics. Continue ongoing searches for new resistances or tolerances among watermelon and sweetpotato accessions from the U.S. Plant Introduction System and other collections. Investigate the influence of climate and biotic factors on insect populations and secondary endosymbionts and virus transmission by using field and controlled environments. Study the epidemiology of whitefly-transmitted viruses using biological assays and molecular techniques. Infochemicals used by vegetable pests in mate- and host-finding will be assessed using chemical, electrophysiological and behavioral studies for pests such as click beetles. Make improved plant germplasm available for use by the vegetable industry.

Progress Report
Research addressing Objective 1 was conducted on host plant resistance in several vegetable crops. Research was continued on whitefly virus transmission assays with cucurbit leaf crumple virus (CuLCrV) to watermelon. Quantitative techniques for CuLCrV detection using digital PCR were used for measuring the quantity of viruses in whiteflies and in plant materials. Inoculation and CuLCrV transmission experiments were conducted on selected varieties of summer and winter squash and pumpkin. Inoculation with infectious clones, choice, and no-choice transmission experiments were evaluated, with differences in virus resistance among varieties and attraction of whiteflies demonstrated. A two-year field study was conducted on tracking sweet potato leaf curl virus (SPLCV) transmission to sweetpotato cultivated for breeding at the United States Vegetable Laboratory (USVL) in Charleston, South Carolina. Whitefly-transmitted SPLCV is widespread within sweetpotato and reservoir Ipomoea spp. at this site. Two consecutive plantings in both years were screened for SPLCV transmission from planting to harvest to determine timing and percentage of transmission into first year seedlings (FYS) plantings. Studies demonstrated that the first (early) planting remains largely free of whiteflies and SPLCV, with only one FYS becoming infected in year 1. SPLCV was detected at increasing percentages over the second (late) planting in both years. Results demonstrated that early planting can be used as a sustainable IPM strategy for avoiding virus transmission in regions with SPLCV reservoirs to generated virus-free planting slips. In the breeding program, these slips can be used to maintain virus-free selections and thereby bypass the time-consuming virus elimination step commonly needed prior to public release of new germplasm. Laboratory and greenhouse assays were conducted on the response of whiteflies to selected wild and cultivated watermelon and pepper lines based on phytochemicals and plant volatiles. In collaborative research with the University of Georgia, Fort Valley State University, and Auburn University, assessment were done on cultivars and plant introduction lines of yellow squash and zucchini for resistance against infestations of whiteflies and/or single infection of Cucurbit chlorotic yellows virus (CCYV) and Cucurbit leaf crumple virus (CuLCrV). Collaborative research with Auburn University was conducted on tomato plant leaf chemicals compounds that may help the plants to naturally repel whiteflies. Research addressing Objective 2 was conducted. The differences in CuLCrV transmission to watermelon by whiteflies harboring different secondary endosymbiont communities were evaluated. New digital PCR protocols are being used to quantify whitefly endosymbiont compositions and evaluate changes in whitefly endosymbionts after host plant, temperature, and field treatments. Evaluations of the effects of host plants, temperature, and field treatments on whitefly endosymbiont compositions continue. Changes in the quantities of secondary endosymbiont Rickettsia after whitefly feeding on healthy and infected tomato have been detected. The transcriptome of whiteflies after 24, 48, and 72 hours of acquisition of tomato yellow leaf curl virus was evaluated and several differentially expressed genes were identified. Select genes are in evaluation as candidates for RNAi-based control of whiteflies and whitefly-transmitted viruses. Cooperative research with the University of Georgia revealed that Begomovirus transmission to tomato plants is not hampered by plant defenses induced by feeding by the mirid insect Dicyphus Hesperus. In collaborative research with the University of Georgia, a study was done to assess the impact that a complex of pests and a complex of predators may have on changes in the population of insect pests in various cotton landscapes. The studied pests were whiteflies and aphids, and the primary predators of these insects in the study were lady beetles, spiders, minute pirate bugs, and big-eyed bugs. Crop diversity directly and indirectly suppressed whitefly and aphid abundances in the fields, and landscape types such as wetlands and pastures promoted aphid abundance. The results indicate that abundance of whiteflies and aphids in the cotton fields depends on landscape complexity and within field interactions among the insects. Cooperative research with the University of Georgia unlike good whitefly kill on plant in the greenhouse by a fungus (Wf GA17), presentence was needed to be enhanced in the field with an oil, and persistence still requires improvement under field conditions because the fungal spores declined rapidly, even after 24 hours. Research addressing objective 3 was continued. Field studies using a sex pheromone previously discovered at USVL were conducted in Virginia, North Carolina, and South Carolina on the reproductive biology of click beetles. A multi-year study was initiated to improve IPM strategies for wireworm in sweetpotato. The overarching goals are to optimize sex pheromone-based monitoring tools and improve adoption of new insecticides to replace chlorpyrifos. This will include using the recently discovered sex pheromone as a management decision support tool for sweetpotato, and to link seasonal activity of click beetle species complex to sweetpotato damage from larvae. The sex pheromone will also be used to evaluate the use of insecticidal small grain cover crops to suppress wireworm populations prior to planting sweetpotato. A study will be conducted to determine if pheromone trapping results can be used to inform timing of foliar sprays targeting click beetles to suppress subsequent wireworm injury to the crop. In the 3rd year of another study, a multi-modal trap, i.e., one combining sex pheromone and light cues was evaluated. Pheromone traps were used for 3rd and final year of the study to characterize the region-wide phenology of click beetles, to determine if pheromone trap captures can be used to time insecticide applications for click beetles in sweetpotato, and to determine the relationship between beetle captures in pheromone traps and wireworm densities in nearby soil samples. Sex attractants for several species of pestiferous click beetles were identified, and studies on trapping optimization were conducted. A field study evaluated use of sex pheromone lures of multiple species together in the same trap to improve cost efficiency. Data analyses were initiated for sweetpotato germplasm (~ 1600 samples) that were genotyped with a 3K SNP (single nucleotide polymorphisms) array developed in collaboration with Breeding Insight at Cornell University. Development of improved sweetpotato germplasm was continued with over 6,000 1st year seedlings and over 100 advanced clones evaluated in replicated field plots. A breeding nursery was established to create new insect and nematode resistant germplasm. Sweetpotato weevil samples were obtained from additional locations in Georgia, Florida, South Carolina, and Texas. Automated DNA isolation of specimens was initiated. Collaborative research with the University of Geogia resulted in the development of a quick (within 24-h) assay that revealed that among six commonly used insecticides for whitefly control, this pest had developed elevated resistance to some of the insecticides, while Cyantraniliprole killed the most whiteflies at both low and high dose rates. The use of this method and information will help the agricultural community in prioritizing insecticides for use or rotation in an insecticide resistance management program. Collaborative research with the University of Georgia was conducted to test the hypothesis that Dmnt1 influences reproductive cell division in developing whiteflies. In collaborative research with Auburn University and University of Georgia, the impact of row covers and reflective silver mulch on whitefly populations were assessed. The insect row covers reduced whitefly populations to zero until the covers were removed, and zucchini plants grown under the insect row covers and reflective silver plastic mulching had increased biomass accumulation due to the low insect counts in those treatments. The silver plastic mulch and row covers reduced the whitefly population (up to 87% in Georgia and up to 33% in Alabama), and increased both plant weight and total yield. Collaborative research with University of Georgia and University of Florida was conducted on the resistance to the commonly used insecticides in vegetable production including imidacloprid and cyantraniliprole. Research addressing Objective 4 was continued, with a total of 50 first year seedlings (FYS) of sweetpotato that had suitable storage root traits combined with upright vigorous plant habit were identified from over 6,000 FYS. Twenty-five advanced sweetpotato selections are being evaluated in replicated field trials in 2024, and the remaining FYS will be evaluated in 2025. An open pollinated breeding nursery was established to create new purple and yellow flesh colored sweetpotato germplasm resistant to soil dwelling pests and root-knot nematodes with modified plant architecture to be competitive with weed pressure.

Accomplishments
1. Sustainable strategies for virus avoidance and maintenance of virus-free sweetpotato breeding selections. Whitefly-transmitted sweet potato leaf curl virus (SPLCV) is endemic in most sweetpotato production and breeding areas. Nearly 100% of new sweetpotato germplasm advanced to public release is infected with SPLCV and requires laborious and time-consuming virus elimination before release. ARS researchers at Charleston, South Carolina, investigated early planting as a strategy for whitefly and SPLCV avoidance and generation of virus-free sweetpotato clones. The research demonstrated over two years of the breeding program that nearly all (98.7%) first year seedling selections remained SPLCV-free throughout early cultivation to harvest, whereas approximately 31% of first year seedlings became infected during late planting. This research provides a sustainable, environmentally friendly IPM strategy that can be used by growers and breeders for managing prevalent vector-transmitted viruses. Virus-free propagative material can be generated through early planting and used in production or for maintaining virus-free clones of breeding selections, thereby removing the need for virus elimination prior to public release of new germplasm.

2. Chemicals in wild tomato to help manage whiteflies. Wild types of tomato can serve as natural sources of pest resistance for improving cultivated tomato. Tomato plants produce a wide range of chemicals from specialized leaf hairs that can influence the behavior and biology of pests, predators, and pollinators. The amount of a group of chemicals called terpenes was determined to vary by leaves among several types of wild tomatoes as well as a commercial cultivar. One of these plant chemicals is called a-zingiberene, and it is known for helping plants to naturally repel whiteflies. In collaborative research with Auburn University, ARS researcher at Charleston, South Carolina, discovered that high quantities of this chemical was found in a particular line (accession PI209978) of the wild tomato Solanum habrochaites. These findings help researchers in understanding plant chemical diversity for plant defense, and will help researchers in developing pest-resistant tomato cultivars.

3. Genomic technology for managing whiteflies. Understanding the developmental process of insects is needed to develop ways to control them by disrupting their biology. Collaborative research between ARS researchers at Charleston, South Carolina, and researchers at the University of Georgia, previously demonstrated that Dnmt1 (DNA methyltransferase I) is important for forming both male and female reproductive cells in insects. Follow-up research by this collaboration tested the hypothesis that Dmnt1 influences reproductive cell division in developing whiteflies. No overall effect on the genes affecting cell division in sperm or egg cells was found. However, the results identified that genes in a pathway called Wnt were differentially expressed when Dnmt1 expression was experimentally reduced, and the biochemical process called methylation was characterized. The effect observed on Wnt presents an interesting new candidate pathway that will be useful to the scientific community in the development of molecular control strategies against whiteflies.

Review Publications
Adeleke, I.A., Kavalappara, S.R., Codod, C.B., Kharel, P., Luckew, A., Mcgregor, C., Simmons, A.M., Srinivasan, R., Bag, S. 2024. Evaluation of plant introduction lines of yellow squash (Cucurbita pepo) for resistance against single infection of Cucurbit chlorotic yellows virus (CCYV) and Cucurbit leaf crumple virus (CuLCrV). HortScience. 59(7):949-956. https://doi.org/10.21273/HORTSCI17861-24.
Alam, M.S., Khanal, C., Roberts, J., Rutter, W.B., Wadl, P.A. 2024. Enhancing reniform nematode management in sweet potato by complementing host-plant resistance with non-fumigant. Plant Disease. https://doi.org/10.1094/PDIS-07-23-1412-RE.
Andreason, S.A., Lahey, Z., Zhao, D., Mejia-Guerra, K., Williams Iii, L.H., Sheehan, M., Simmons, A.M., Wadl, P.A. 2023. Mitochondrial genome datasets for the sweetpotato weevil, Cylas formicarius elegantulus (Coleoptera: Brentidae), collected in the United States. Data in Brief. 49:1-8. https://doi.org/10.1016/j.dib.2023.109432.
Andreason, S.A., Mckenzie-Reynolds, P., Whitley, K.M., Coffey, J., Simmons, A.M., Wadl, P.A. 2024. Tracking sweet potato leaf curl virus through field production: Implications for sustainable sweetpotato production and breeding practices. Plants. 13:1267. https://doi.org/10.3390/plants13091267.
Cham, A.K., Adams, A.K., Wadl, P.A., Ojeda-Zacarias, M., Rutter, W.B., Jackson, D.M., Shoemaker, D.D., Bernard, E.C., Yencho, G.C., Olukolu, B.A. 2024. Metagenome-enabled models improve genomic predictive ability and identification of herbivory-limiting genes in sweetpotato.. Horticulture Research. 11(7). Article Uhae135. https://doi.org/10.1093/hr/uhae135.
Chen, X., Nowicki, M., Wadl, P.A., Zhang, C., Kollner, T.G., Paya-Milans, M., Staton, M., Chen, F., Trigiano, R.N. 2023. Chemical profile and biosynthesis of volatile terpenes in Pityopsis ruthii, a rare and endangered flowering plant. PLOS ONE. 18:6. https://doi.org/10.1371/journal.pone.0287524.
Cremonez, P.S., Perier, J.D., Nagaoka, M.M., Simmons, A.M., Riley, D.G. 2023. Precision and accuracy of field versus bioassay insecticide efficacy for the control of immature Bemisia tabaci. Insects. 14:645. https://doi.org/10.3390/insects14070645.
Cunningham, C.B., Shelby, E.A., Mckinney, E.C., Simmons, A.M., Moore, A.J., Moore, P.J. 2024. An association between Dmnt1 and Wnt in the production of oocytes in the whitefly Bemisia tabaci. Insect Molecular Biology. https://doi.org/10.1111/imb.12893.
Devendran, R., Kavalappara, S.R., Simmons, A.M., Bag, S. 2023. Whitefly-transmitted Viruses of Cucurbits in the Southern United States. Viruses. 15(11): 2278. https://doi.org/10.3390/v15112278.
George, J., Reddy, G.V., Wadl, P.A., Rutter, W.B., Culbreath, J.R., Lau, P.W., Rashid, T., Allan, M.C., Johanningsmeier, S.D., Nelson, A.M., Wang, M.L., Gubba, A., Ling, K., Meng, Y., Collins, D.J., Ponniah, S.K., Gowda, P.H. 2024. Sustainable Sweetpotato Production in the United States: Current Status, Challenges, and Opportunities. Agronomy Journal. 116(2):630-660. https://doi.org/10.1002/agj2.21539.
Gautam, S.; Gadhave, K.R.; Buck, J.W.; Dutta, B.; Coolong, T.;Adkins, S.; Simmons, A.M.; Srinivasan, R. Effects of Host Plants and Their Infection Status on Acquisition and Inoculation of A Plant Virus by Its Hemipteran Vector. Pathogens 2023, 12, 1119. https://doi.org/10.3390/pathogens12091119
Kavalappara, S.R., Bag, S., Luckew, A., Mcgregor, C.E., Culbreath, A.K., Simmons, A.M. 2024. Evaluation of squash (Cucurbita pepo L.) genotypes for resistance to cucurbit chlorotic yellows virus. Horticulturae. 10(3):264. https://doi.org/10.3390/horticulturae10030264.
Kheirodin, A., De Toledo, P., Simmons, A.M., Schmidt, J. 2025. Crop diversity and within field multi-species interactions mediate herbivore abundances in cotton fields. Biological Control. htpps://doi.org/10.1016/j.biocontrol.2023.105386.
Kumar, M., Kavalappara, A.R., Mcavoy, ., Hutton, S., Simmons, A.M., Bagg, S. 2023. Association of tomato chlorosis virus complicates the management of tomato yellow leaf curl virus in cultivated tomato (Solanum lycopersicum) in the southern United States. Horticulturae. 9(8):948. https://doi.org/10.3390/horticulturae9080948.
Legarrea, S., Latora, A.G., Simmons, A.M., Srinivasan, R. 2024. Begomovirus transmission to tomato plants is not hampered by plant defenses induced by Dicyphus hesperus Knight. Viruses. 16(4):587. https://doi.org/10.3390/v16040587.
Legaspi, J.C., Kanga, L.H., Haseeb, M., Simmons, A.M. 2023. Assessing the status of “push-pull” technology in worldwide agriculture and forestry. Subtropical Agriculture and Environments. 74:1-12.
Li, Y., Mbata, G.N., Simmons, A.M., Shapiro Ilan, D.I., George, S. 2024. Management of Bemisia tabaci on vegetables using entomopathogens. Crop Protection. 180. Article 106638. https://doi.org/10.1016/j.cropro.2024.106638.
Mbata, G.N., Li, Y., Warsi, S., Simmons, A.M. 2024. Susceptibility of yellow squash and zucchini cultivars to the sweetpotato whitefly, Bemisia tabaci Gennadius (MEAM1) in the southeastern United States. Insects. 15:429. https://doi.org/10.3390/insects15060429.
Perier, J.D., Cremonez, P.S., Parkins, A.J., Kheirodin, A., Simmons, A.M., Riley, D.G. 2024. Modified maximum dose bioassay for assessing insecticide response in field populations of Bemisia tabaci (Hemiptera: Aleyrodidae). Journal of Entomological Science. 59(4).000–000 (Month 2024). https://doi.org/10.18474/JES23-88.
Perier, J.D., Lagalante, A.F., Mccarthy, E.P., Simmons, A.M., Riley, D.G. 2023. Uptake and retention of imidacloprid and cyantraniliprole in cotton (Gossypium hirsutum) for the control of Bemisia tabaci (Hemiptera: Aleyrodidae). Journal of Entomological Science. 58(4):434-446. https://doi.org/10.18474/JES22-77.
Pizzo, J.S., Rutz, T., Ojeda, A.S., Kartowikromo, K.Y., Hamid, A.M., Simmons, A.M., Da Silva, A.L., Rodrigues, C. 2024. Quantifying Terpenes in Tomato Leaf Extracts from Different Species using Gas Chromatography-Mass Spectrometry (GC-MS). Phytochemistry. 689:115503. https://doi.org/10.1016/j.ab.2024.115503.
Rutz, T., Coolong, T., Srinivasan, R., Sparks, A., Dutta, B., Codod, C., Simmons, A.M., Da Silva, A.L. 2023. Use of insect row cover and reflective silver plastic mulching to manage whitefly for zucchini production. Insects. 14(11):863. https://doi.org/10.3390/insects14110863.
Trigiano, R.N., Boggess, S.L., Molnar, T., Moreau, E.L., Wadl, P.A. 2024. ‘Erica’s Appalachian Sunrise’: An apomitically derived cultivar from Cornus florida ‘Cherokee Brave’.. HortScience. 59:817-819. https://doi.org/10.21273/HORTSCI17833-24.
Wadl, P.A., Dattilo, A.J., Call, G., Hadziabdic, D., Trigiano, R.N. 2023. Pityopsis ruthii: an updated review of conservation efforts for an endangered plant. Plants. 12(14):2693. https://doi.org/10.3390/plants12142693.
Wu, S., Towes, M.D., Behle, R.W., Barman, A.K., Sparks, A.N., Simmons, A.M., Shapiro Ilan, D.I. 2023. Post-application field persistence and efficacy of cordyceps javanica against bemisia tabaci. The Journal of Fungi. 9(8):827. https://doi.org/10.3390/jof9080827.