Location: Crop Bioprotection Research
2021 Annual Report
Objectives
Objective 1: Enable the commercial production of microorganisms and their bioactive metabolites to control mosquitoes and the viruses they carry.
Goal 1.1: Evaluate larval-specific fungal/bacterial entomopathogens for mosquito control.
Goal 1.2: Characterize and select microbial isolates with potential for bioactive factor production.
Objective 2: Enable the commercial production of bioactive compounds from plants to control mosquitoes.
Goal 2.1: Identify essential oils with adulticidal activity against mosquitoes and their potential application as ingredients of attractive toxic sugar bait.
Goal 2.2: Develop essential oil emulsions that are effective against mosquito larvae.
Approach
Mosquito control is a fundamental component of mosquito-borne disease prevention and outbreak control. The conventional approach to mosquito control relies heavily on synthetic chemical insecticides, but there is an urgent need for alternative vector control tools to tackle the rising problem of insecticide resistance and limit pesticide-related environmental hazards. Biopesticides are pest management agents based on living organisms or natural products and have a proven potential as ecofriendly alternatives to synthetic chemical insecticides. To date, only a limited number of biopesticides have been commercialized for use in mosquito control. Thus, the discovery of new biopesticide agents is one of the key priorities of vector biology research. This project will apply technologies allied with the fields of medical entomology, molecular biology, microbiology, chemical ecology and natural products chemistry to discover new microbial- and plant-based biopesticide agents to be developed and commercialized for mosquito control. Plant-based compounds that are highly effective against mosquitoes will be identified and developed into water-soluble and environmentally stable formulations for effective delivery to the target mosquitoes. The potential to harness bioactive compounds from plants as active ingredients for attractive toxic sugar-baits for mosquito control will also be explored. The project will focus primarily on plant essential oils because of their proven potential for pest and vector management. Additionally, we will explore and identify new entomopathogenic fungi and bacteria that kill different life stages of the mosquito. The bioactive compounds contributing to entomopathogenic activity of these fungi/bacteria will be isolated, characterized and examined for mosquitocidal and anti-arboviral activity. Successful completion of this project will lead to new discoveries that have great potential to propel the development and eventual commercialization of novel plant- and microbial-based agents for mosquito control.
Progress Report
We made significant progress in Objective 1 by developing and optimizing the media components and incubation time that supports production of fungal spores from different fungal entomopathogens. Preliminary tests were conducted to confirm maintenance of fungal pathogenicity in mosquitoes. In efforts to discover new bacterial pathogens that are lethal to mosquitoes, bacteria isolated from diseased crickets were tested against mosquito larvae. Additional experiments are currently ongoing to define the toxicity of these bacterial isolates to mosquitoes. In collaborative efforts with the University of California Merced, we described for the first time the presence of the symbiont Wolbachia, in five mosquito species from California. This bacterium is currently being used as a strategy for mosquito control. International collaborations with the Gorgas Institute in Panama, focused on the interaction of mosquitoes and their associated microbes, which led to the first records in Panama of natural malaria infections in a mosquito species that is widely distributed in this country. We also demonstrated that blood meal source and mixed blood feeding affects the composition and structure of microbial communities residing in mosquito guts.
For Objective 2, significant progress was made in the development and optimization of protocols for evaluating the toxicity of essential oils against adult mosquitoes and their potential application as active ingredients in the attractive toxic sugar bait system. Twenty essential oils were evaluated for toxicity against adult mosquitoes using modified Centers for Disease Control and Prevention bottle assays. Ten essential oils were shown to be toxic against adult mosquitoes and are currently being investigated further to determine their chemical composition, and lethal concentrations. A simple system for delivering sugar solution poisoned with essential oils to adult mosquitoes using glass bottles was developed and is currently been employed to evaluate the 10 essential oils with adulticidal activity for potential application in the attractive toxic sugar bait system. We have also developed essential oil emulsions that were highly effective against larvae of three mosquito species of medical significance regarded as such because of their ability to transmit human pathogens.
Accomplishments
1. Discovery of new mosquito-bacteria associations to advance mosquito control. Wolbachia is known for its ability to suppress mosquito populations and to reduce mosquito susceptibility to pathogens that affect human health. It is therefore being evaluated for potential application in controlling diseases transmitted by mosquitoes. Not all mosquito species carry Wolbachia and their identification in diverse mosquito species is crucial for the design of future Wolbachia-based mosquito control applications. ARS researchers at Peoria, Illinois, in collaboration with researchers at the University of California Merced, identified new mosquito species that harbor the bacterium Wolbachia and that reside along the Central Valley of California. This study provides new mosquito records that can be used by vector control agencies interested in utilizing this technology or by medical entomologist interested in expanding the development of new Wolbachia-based mosquito control applications.
2. Blood meal source and mosquito gut microbial communities. The microbial communities residing in mosquito gut can influence “vector competence,” which is the ability of mosquitoes to transmit disease such as dengue and Zika viruses. ARS researchers at Peoria, Illinois, in collaboration with researchers at the University of Illinois, discovered that the microbes in mosquito gut can change dramatically in response to the animal species that the mosquito feeds on. Given that some gut microbes can prevent the mosquitoes from transmitting disease, these findings suggest that the blood feeding pattern of mosquitoes is likely one of the key factors responsible for population variation in vector competence that is commonly documented in nature. These findings provide new microbial database that can be utilized by public health experts and the scientific community to better describe mosquito populations in a given area and device appropriate mosquito control methods.
3. Essential oil emulsions. Currently, there is an urgent need for environmentally friendly solutions for controlling mosquitoes that transmit diseases important for public health. ARS scientists at Peoria, Illinois, developed environmentally friendly emulsions of opoponax essential oil that were highly toxic to larvae of three mosquito species known to vector human disease pathogen. These emulsions improved the mixing of the opoponax essential oil with water where mosquito larvae live, killing more larvae than when the oil was applied alone. This research provides critical knowledge that can be used to develop essential oil-based biopesticides for mosquito control.
Review Publications
Muturi, E.J., Njoroge, T.M., Dunlap, C.A., Caceres, C.E. 2021. Blood meal source and mixed blood-feeding influence gut bacterial community composition in Aedes aegypti. Parasites & Vectors. 14. Article 83 https://doi.org/10.1186/s13071-021-04579-8.
Muturi, E.J., Hay, W.T., Doll, K.M., Ramirez, J.L., Selling, G.W. 2020. Insecticidal activity of Commiphora erythraea essential oil and its emulsions against larvae of three mosquito species. Journal of Medical Entomology. 57(6):1835-1842. https://doi.org/10.1093/jme/tjaa097.
Juma, E.0., Allan, B.F., Kim, C., Stone, C., Dunlap, C.A., Muturi, E.J. 2020. Effect of life stage and pesticide exposure on the gut microbiota of Aedes albopictus and Culex pipiens L. Scientific Reports. 10. Article 9489. https://doi.org/10.1038/s41598-020-66452-5.
Muturi, E.J., Dunlap, C.A., Caceres, C.E. 2020. Microbial communities of container aquatic habitats shift in response to Culex restuans larvae. FEMS Microbiology Ecology. 96(7). Article fiaa112. https://doi.org/10.1093/femsec/fiaa112.
Juma, E.O., Allan, B.F., Kim, C., Stone, C., Dunlap, C.A., Muturi, E.J. 2021. The larval environment strongly influences the bacterial communities of Aedes triseriatus and Aedes japonicus (Diptera: Culicidae). Scientific Reports. 11. Article 7910. https://doi.org/10.1038/s41598-021-87017-0.
Munywoki, D.N., Kokwaro, E.D., Mwangangi, J.M., Muturi, E.J., Mbogo, C.M. 2021. Insecticide resistance status in Anopheles gambiae (s.l.) in coastal Kenya. Parasites & Vectors. 14. Article 207. https://doi.org/10.1186/s13071-021-04706-5.
Raddi, G., Barletta, A.B.F., Efremova, M., Ramirez, J.L., Cantera, R., Teichmann, S.A., Barillas-Mury, C., Billker, O. 2020. Mosquito cellular immunity at single-cell resolution. Science. 369(6507):1128-1132. https://doi.org/10.1126/science.abc0322.
Torres-Cosme, R., Rigg, C., Santamaria, A.M., Vasquez, V., Victoria, C., Ramirez, J.L., Calzada, J., Carrera, L.C. 2021. Natural malaria infection in anophelines vectors and their incrimination in local malaria transmission in Darien, Panama. PLoS ONE. 16(5). Article e0250059. https://doi.org/10.1371/journal.pone.0250059.
Torres, R., Hernandez, E., Flores, V., Ramirez, J.L., Joyce, A.L. 2020. Wolbachia in mosquitoes from the Central Valley of California, USA. Parasites & Vectors. 13. Article 558. https://doi.org/10.1186/s13071-020-04429-z.
