Research Project: Chemical Communications of Plants, Insects, Microbes, and Nematodes

Location: Chemistry Research

2023 Annual Report

Objectives
Objective 1: Investigate semiochemicals of agricultural plant-insect-microbe interactions, with emphasis on mites, weevils, leaffooted bugs, and fruit flies; and, volatile biomarkers from insect or microbe infestations of agricultural products. Objective 2: Collect, analyze, and identify semiochemicals of pollinator pest-host and nematode-plant-microbe interactions, including varroa mites, hive beetles, entomopathogenic nematodes, or associated soil/root microbes. Objective 3: Survey floral nectar microorganisms occurring in flowering crops and determine their impacts on nectar chemistry, pathogen loads, and pollinator affinity.

Approach
Investigate the chemical communications of agricultural plant-insect-microbe systems, such as those involving mites, weevils, leaffooted bugs, and fruit flies, as well as entomopathogenic nematodes and their associated soil/root microbes. This work will also include investigating how pheromones and multitrophic signaling can be utilized for effective control of pest organisms. Provide new or improved biological, behavioral, or cultural control methods to reduce agricultural reliance on broad spectrum chemistries. To address the ever-changing abiotic stressors, will provide flexible pest management tools for agricultural ecosystems, including those that protect plant-pollinator habitats or hosts. Will address these pollinator issues by identifying semiochemicals of pollinator pest-hosts, including varroa mites and hive beetles, and providing cost-effective, environmentally safe pest management strategies. This research will utilize numerous interactive laboratory- and field-based bioassays with insects, mites, microbes, nematodes, and plants, as well as purified biochemicals and other organisms. Isolation and identification of new bioactive chemicals that mediate arthropod and nematode behaviors and other inter-organismal interactions will be achieved using a combination of approaches including HPLC, LC-MS, preparative flash chromatography, GC-MS, FT-IR, NMR, micro-degradation, and synthesis where applicable. Major target insects for this research will include those listed above, with other target insects selected as needed during progression of the project.

Progress Report
Progress has been made on Research Project 6036-22430-001-000D by Gainesville, Florida scientists. In Objective 1, progress includes: Nematodes – we successfully collected volatiles (odors) from roots of weevil host plants such as blueberry and corn but could not get field access to weevil-infected plants (due to farmers quick removal and burning of potentially infected plants). Since Citrus root weevil (Diaprepes abreviatus) are rapidly increasing their host and geographic range, ARS scientists established a citrus root weevil lab colony. With this colony we will be able to work with a wider range of infested agricultural plants and cultivars under controlled conditions rather than trying to rely on field samplings; to establish host insect related compounds functioning as entomopathogenic nematodes (EPN) signaling odor were collected daily from insects infected by several different EPN species. Thus far, one potential repellent, released 1 to 2 days after infection, has been identified; the sampling technique that we developed for root odor collections has also been used for field collection of odors released by aggregating mature citrus root weevils to establish a more potent attractant than the previously identified aggregation pheromone (an odor that signals the insect or nematode to gather). It has also been used for collection of blueberry gall midge attractants (UF graduate studies); laboratory reared nematodes are “activated” by insect cadaver extracts prior to field release. However, in addition to aggregation pheromones, the cadaver extracts also contain species-specific dispersal pheromones which are not part of, and may interfere with, host searching and mass infestation of new hosts. This suggests that prerelease treatments with pure pheromone preparations are likely to improve artificially reared EPN host infectivity. Maize weevil – a major stored-product pest that can cause significant economic losses to maize crops. The maize weevil uses host plant-derived (odors) to locate a suitable host as adults, but the function of individual compounds remains unknown. Our research used a combination of odor composition and identification, choice behavioral assays, and chemical treatments (methyl salicylate, geranyl acetate, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-alpha-bergamotene) to identify and assay specific compounds from maize lines W22, B104, and B73 that may influence maize weevil host location. We found that (E)-alpha-bergamotene and the maize line W22 were the most attractive to the maize weevil. Ongoing research into understanding the factors that contribute to the attraction of maize weevils to maize is essential for effective pest management. Leaffooted bug (LFB) – LFB colony is well established and routinely producing adults sufficient for electrophysiological and behavioral bioassays. Examination of attractive semiochemicals (odors that influence insect behavior) has been expanded to include LFB pheromones and possible overlap between kairomones of previously identified, attractive host plant and putative LFB aggregation pheromones; Infestation – odors of maize seed infested with maize weevil have been measured in time course experiment to identify changes in the volatile profile of stored grain. Preliminary experiments conducted to examine odors in cowpea infested with cowpea weevil; a cowpea weevil colony was established in the lab. Objective 2, progress included the following: Using behavioral studies (submitted manuscript) and chemical analyses (manuscript in preparation), we found species-specific as well as overlapping “follow the leader” aggregative EPN host searching behaviors and discovered overlaps when analyzing corresponding aggregation/trail pheromone blends. These results suggested that these behaviors can be correlated with conserved pheromone components. This investigation was made possible by HQ and Area funds to purchase high-resolution/high-accuracy LC/MS equipment. Varroa mites – we developed a novel method to assay the Varroa mite and the honey bee to carbon dioxide sensitivity. Our previous research indicated that the Varroa mites’ tolerance is much less than that of the honey bee. Ongoing research will assay the honey bee and Varroa mites’ carbon dioxide tolerance and exploit these finding as a possible control measure for Varroa mite population reduction within the honey bee hive. Objective 3, progress included identification of several nectar microbe species that inhibit the growth of fungicide-resistant plant pathogens from the genus Colletotrichum, which cause the disease anthracnose or ripe rot in blueberry. To assess pollinator responses to the protective nectar microbes and pathogens, we evaluated honey bee consumption of microbial cultures, finding that bees did not exhibit preferences for or against the microbes tested. In a separate project, we have identified the odors emitted from whole flowers, nectar, and pollen in sunflowers inoculated with a floral yeast, bacteria, both species, and a control water spray, identifying odors that differ between microbial treatments and floral contexts. These odors may be relevant to pollinator foraging behavior. Additionally, results from a collaborative study with academic researchers recently demonstrated that multiple almond orchard management practices can influence the microbe composition on flowers thus possibly affecting flowering and pollination.

Accomplishments

Review Publications
Stuhl, C.J., Romero, M.I., Noble, I.I. 2023. Respiration levels of honey bee casts as a possible indicator in varroa mite attraction. Journal of Apiculture Research. 10:1-3. https://doi.org/10.1080/00218839.2023.2179773.
Stuhl, C.J. 2022. A novel method in small hive beetle rearing. Journal of Apiculture Research. 29:1-5. https://doi.org/10.1080/00218839.2022.2130596.
Kleckner, K., De Carolis, A., Jack, C., Stuhl, C.J., Formato, G., Ellis, J. 2022. A novel acute toxicity bioassay and field trial to evaluate compounds for small hive beetle control. Applied Sciences. 12:9905. https://doi.org/10.3390/app12199905.
Cheseto, X., Kirwa, H., Mohamed, S.A., Ekesi, S., Beck, J.J., Torto, B. 2022. Field evaluation of glutathione and glutamic acid as host marking pheromones for control of tephritid fruit flies in a mango orchard in Kenya. Pest Management Science. 97:1585-1592. https://doi.org/10.1002/ps.7331.
Visser, B., Le Lann, C., Nieberding, C.M., Lammers, M., Hahn, D.A., Alborn, H.T., Enriquez, T., Scheifler, M., Harvey, J.A., Ellers, J. 2023. Many parasitoids lack adult fat accumulation, despite fatty acid synthesis: A discussion of concepts and considerations for future research. Current Opinion in Insect Science. 3:100055. https://doi.org/10.1016/j.cris.2023.100055.
Cheseto, X., Rering, C.C., Broadhead, G.T., Torto, B., Beck, J.J. 2022. Early infestation volatile biomarkers of fruit fly Bactrocera dorsalis (Hendel) ovipositional activity in mango (Mangifera indica L.). Phytochemistry. 206:113519. https://doi.org/10.1016/j.phytochem.2022.113519.
Schaeffer, R.N., Crowder, D.W., Gutierrez Illan, J., Beck, J.J., Fukami, T., Williams, N.M., Vannette, R.L. 2022. Disease management during bloom affects the floral microbiome but not pollination in a mass-flowering crop. Journal of Applied Ecology. 60:64-76. https://doi.org/10.1111/1365-2664.14320.
Gaffke, A.M., Shapiro-Ilan, D., Alborn, H.T. 2022. Deadly scents: Exposure to plant volatiles increases mortality of entomopathogenic nematodes during infection. Frontiers in Physiology. 13:978359. https://doi.org/10.3389/fphys.2022.978359.
Adeleye, V.O., Seal, D.R., Liburd, O.E., Mcauslane, H., Alborn, H.T. 2022. Pepper weevil, Anthonomus eugenii (Coleoptera: Curculionidae) suppression on jalapeño pepper using non-host insect repellent plants. Crop Protection. 154:105893. https://doi.org/10.1016/j.cropro.2021.105893.
Stuhl, C.J., Teal, P.E. 2023. A potential sexual pheromone of Aethina tumida (Coleoptera: Nitidulidae). Florida Entomologist. 106:83-89. https://doi.org/10.1653/024.106.0203.
Yactayo Chang, J.P., Hunter III, C.T., Alborn, H.T., Christensen, S.A., Block, A.K. 2022. Production of the green leaf volatile (Z)-3-hexenal by a zea mays hydroperoxide lyase. Plants. 11(17):2201. https://doi.org/10.3390/plants11172201.
Yactayo Chang, J.P., Boehlein, S., Libertini, G., Beiriger, R., Resende, M., Bruton, R.G., Alborn, H.T., Tracy, W.F., Block, A.K. 2022. The impact of post-harvest storage on sweetcorn aroma. Phytochemistry Letters. 52:33-39. https://doi.org/10.1016/j.phytol.2022.09.001.
Mbata, G., Shapiro Ilan, D.I., Alborn, H.T., Strand, M. 2019. Preferential infectivity of entomopathogenic nematodes in an envenomed host. International Journal for Parasitology. 49(9):737-745. https://doi.org/10.1016/j.ijpara.2019.05.002.