Location: Natural Products Utilization Research
2019 Annual Report
Objectives
Objective 1: Discover new insecticidal active ingredients that are based on natural products and that are safe with respect to occupational exposure and with respect to the environment, including non-target effects.
Subobjective 1.1: Discover novel arthropod repelling biopesticides from mosquito repelling folk remedies.
Subobjective 1.2: Discovery of fungal compounds and natural product analogs with activity against permethrin-resistant and susceptible mosquitoes.
Subobjective 1.3: Discover novel bioinsecticide active ingredients from crude plant and fungal extract screening and bioassay-directed fractionation.
Objective 2: Participate in development of new products based on green biopesticides.
Subobjective 2.1: Develop and optimize fatty acids as natural topical and spatial arthropod repellents.
Subobjective 2.2: Development and optimization of the chromene derivative 131-1 as a biopesticide.
Approach
A bioassay-directed investigative approach will be performed on bioactive extracts in efforts to discover bioinsecticides and repellents for use against arthropod pests. General procedures for isolation of active compounds from plants and microbes will be utilized. Solvent extractions, liquid-liquid partitioning, column chromatography and thin layer chromatography will be employed as needed. Extracts, fractions and pure compounds will be tested for insecticidal and insect repellent activity in assays being carried out routinely at collaborator's laboratories. Identification of active compounds will be done using spectroscopic methods including mass spectroscopy (EI, CI, and high resolution ESI), Nuclear magnetic resonance (one- and two-dimensional). Chemical modification will be performed on compound(s) identified as "highly active" to improve activity or bioavailability.
Progress Report
This is the fourth full year of research for this project since it was newly created. For Objective 1, discovery of new insecticidal active ingredients that are based on natural products, milestones have been met and significant progress has been made.
Pineapple weed (Matricaria discoidea) has documented use as an insect repellent by various indigenous peoples of North America. This investigation was conducted to evaluate this practice and systematically identify chemical constituents responsible for any insect repelling effect by utilizing a mosquito (Aedes aegypti) biting deterrent assay approach. Essential oil from dried M. discoidea was the most bioactive crude extract generated and was as effective as DEET. The most active compounds were determined to be ¿-terpineol, spathulenol, and neryl isovalerate. Large cage in vitro evaluation of pure compounds isolated from M. discoidea indicated ¿-terpineol to be the most active compound providing complete protection similar to DEET. This is the first report on the mosquito repellency of neryl isovalerate and scientific evidence reported here validates the traditional use of M. discoidea as a biting-insect deterrent.
Members of the highly polyphagous Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) species complex cause major crop damage by feeding and by transmitting plant viruses. The Middle East-Asia Minor 1 (MEAM1) of the B. tabaci complex is by far the most problematic whitefly affecting crops including the cultivated watermelon (Citrullus lanatus). Watermelon cultivars share a narrow genetic base and are highly susceptible to whiteflies. However, there is wide genetic diversity among the species of Citrullus. A wild relative of the cultivated watermelon is C. ecirrhosus; it is a perennial desert species. We conducted a study to assess the potential of C. ecirrhosus as a source of whitefly resistance for cultivated watermelon. Results of this study indicate that C. ecirrhosus offers resistance against the MEAM1 B. tabaci based on, at least, antibiosis and antixenosis. Whitefly performance based on developmental survival, body size attainment, and non-preference were suppressed as compared with the watermelon cultivar Sugar Baby. Our olfactometer data support our other non-preference results. However, no detrimental effect of pungent odor from the leaves was observed on adult whitefly survival. We further demonstrated that plants of C. ecirrhosus can be clonally propagated from vine cuttings of the parent. Moreover, using traditional breeding procedures, we were able to cross C. ecirrhosus with cultivated watermelon and produce viable seeds. This study is the first report to establish pest resistance in C. ecirrhosus. This wild species offers a source of resistance against whiteflies for cultivated watermelon.
Diaporthe eres, a plant pathogenic fungus isolated from Hedera helix was cultured and the culture filtrate was investigated for mosquitocidal constituents. We have isolated an isochromone as the active compound. A series of analogs were synthesized and some analogs were found to be more active than the natural product particularly against the permethrin resistant mosquito larvae. We are synthesizing more analogs to optimize the activities targeting insecticide resistant larvae.
For Objective 2, participate in development of new products based on green biopesticides, milestones have been met and significant progress has been made.
Fatty acid methyl esters of C-11 and C-12 have been synthesized in an effort to both improve the mosquito repellency and improve the duration of activity of the natural C-11 and C-12 fatty acids. The optimum chain length for the esters has been determined and a highly active analog has been produced and shown to be more active than DEET in the K&D module bioassay system. Duration studies will be performed on these and other analogs produced synthetically. In-vivo evaluations of the most active compounds against Ae aegypti will be performed following the large scale synthesis of the analogs. A unique analog has been synthesized and shown to be more active than the parent compound C-11.
Large scale synthesis of 131-1 has been completed and a CRADA is ongoing with a private sector partner for the development of 131-1 into a commercial product. Additional arthropod tests will be completed by the commercial partner as part of the CRADA agreement. The chromene analog 131-1 has higher activity and three times longer duration of repellent activity than DEET. One of the drawbacks is the purification of 131-1. In the final step of cyclization of our synthetic scheme, two products are formed, 131-1 and its regioisomer. Both these products are active but the most active one is the 131-1. The separation of the two isomers is expensive and requires column chromatography. We have optimized the synthetic procedure to obtain these two regioisomers consistently in a isomer ratio of 80:20 using PEG-400 instead of N,N-diethylaniline as the solvent where the major isomer was 131-1. We have tested this isomer mixture in the mosquito repellent bioassay and found it to be slightly less active than the pure 131-1. We are in the process of developing the isomer mixture as an alternative to purified 131-1 to keep the production cost down. This endeavor is being conducted with a private company in developing the isomer mixture as a commercial mosquito repellent product.
Accomplishments
1. Pineapple weed (Matricaria discoidea). Pineapple weed (Matricaria discoidea) has documented use as an insect repellent by various indigenous peoples of North America. This investigation by ARS scientists at Oxford, Mississippi was conducted to evaluate this practice and systematically identify chemical constituents responsible for any insect repelling effect by utilizing a mosquito (Aedes aegypti) biting deterrent assay approach. Essential oil from dried M. discoidea was the most bioactive crude extract generated and was as effective as DEET. The most active compounds were determined to be alpha-terpineol, spathulenol, and neryl isovalerate. Large cage in vitro evaluation of pure compounds isolated from M. discoidea indicated alpha-terpineol to be the most active compound providing complete protection similar to DEET. This is the first report on the mosquito repellency of neryl isovalerate and scientific evidence reported here validates the traditional use of M. discoidea as a biting-insect deterrent.
Review Publications
Cantrell, C.L., Ali, A., Jones, A.P. 2018. Isolation and identification of mosquito biting deterrents from the North American mosquito repelling folk remedy plant, Matricaria discoidea DC. PLoS One. 13(10):e0206594. https://doi.org/10.1371/journal.pone.0206594.
Simmons, A.M., Jarret, R.L., Cantrell, C.L., Levi, A. 2019. Citrullus ecirrhosus: Wild source of resistance against Bemisia tabaci (Hemiptera: Aleyrodidae) for cultivated watermelon. Journal of Economic Entomology. https://doi.org/10.1093/jee/toz069.
Favaretto, A., Cantrell, C.L., Fronczek, F.R., Duke, S.O., Wedge, D.E., Abbas, A., Scheffer-Basso, S.M. 2019. New phytotoxic Cassane-like diterpenoids from Eragrostis plana (Nees). Journal of Agricultural and Food Chemistry. https://doi.org/10.1021/acs.jafc.8b06832.
