Location: Crop Bioprotection Research
2020 Annual Report
Objectives
Objective 1. Enable the commercial production of microorganisms pathogenic to mosquitoes.
Objective 2. Enable the commercial production of bioactive compounds/metabolites derived from plants and microorganisms to control mosquitoes and/or the viruses they carry.
Approach
Our approach will focus on the discovery of novel microbial and plant-based biopesticides that could be commercialized for the control of mosquitoes or the pathogens they transmit. A variety of entomopathogenic fungi will be evaluated for their effect on survival of adult mosquitoes. Selection of candidate mosquito entomopathogens will be done initially by focusing on the isolates with known pathogenicity and strains that have previously been isolated from dipteran species. Transcriptomic analysis coupled with functional assays (through reverse-genetic techniques) will be used to identify the fungal mode of action as well as the mosquito responses to infection. Attempts will be made to isolate and identify microbe-derived molecules with biological activity against mosquitoes and selected arboviruses. We will also evaluate plant-based compounds effective for activity against mosquitoes. We will integrate standard insecticide testing bioassays with modern and conventional approaches in chemical ecology to identify the chemical compounds in selected plants that are attractive to gravid females and deleterious to mosquito larvae.
Progress Report
This is the final report for Project 5010-22410-020-00D. This research project focused on the discovery of novel compounds from plants, bacteria, and fungi for controlling mosquitoes and the diseases they vector. The overall goal was to discover new vector control tools for application in integrated vector management.
Bacterial communities that inhabit the mosquito body play an important role in mosquito survival and development and can also interfere with the mosquito’s ability to transmit diseases. Identifying these microbes and factors that influence their composition and diversity can facilitate identification of bacterial species that could be harnessed for mosquito control. ARS scientists in Peoria, Illinois, made significant progress in Objective 1 by determining that parental background, host sampling location, and host blood meal source are factors that influence the diversity and composition of bacterial communities associated with mosquitoes. We successfully used fluorescent proteins as markers to study the functions of bacterial communities inhabiting the mosquito gut. Additionally, the scientists identified new fungal strains that are lethal to mosquitoes, increasing the list of fungal microbes that could be developed as biopesticides for vector control. In addition, the scientists successfully identified previously unrecognized molecules that enable the mosquito to detect and overcome attack by fungal infections. These molecules allow the mosquito to survive infection by some fungal strains but not others.
For Objective 2, ARS scientists demonstrated under field conditions that leaf litter of common blackberry is an ecological trap for the northern house mosquito, the primary vector of West Nile virus in northeastern United States. Storm water catch basins “treated” with leaves of common blackberry were highly attractive to egg-laying female mosquitoes but detrimental to the hatching larvae. The detrimental effects on mosquito larvae were not due to the presence of toxic chemicals from decaying leaves, but rather due to blackberry leaves serving as a low-quality food resource for mosquito larvae. The microbial communities present in blackberry leaf infusions served as a poor food resource for mosquito larvae yet emitted chemical cues that were attractive to egg-laying adults. Because the results could not point to specific chemical compounds from blackberry leaves that were responsible for these bioactivities, research was expanded to identify botanical sources for mosquito control by investigating the biological activity of various plant essential oils on eggs and larvae. These studies have led to the identification of novel plant-based compounds and oil emulsion formulations for further development as commercialization tools for mosquito control.
Substantial progress was made at screening several fungal strains for their potential to generate compounds that can be used as biopesticides and as drugs for the treatment of human microbial pathogens (i.e., bacteria). Our efforts identified several fungal strains with quantifiable activity against bacteria. Fungal growth media were manipulated to induce and maximize fungal production of bioactive compounds. The optimum media for the initial species continues to be tested with new fungal species.
Accomplishments
1. Mechanisms behind the mosquito resistance to fungal infection. Specific fungi are very effective at attacking and killing insects and are environmentally friendly alternatives to synthetic insecticides. However, mosquitoes are also able to survive attack by some of these fungi. ARS scientists in Peoria, Illinois, have identified the specific molecules that the mosquito produces to successfully detect and defend itself against fungal infection. These molecules were highly effective against some fungal strains but ineffective against other strains. Overall, ARS scientists have uncovered and published significant new findings that will be exploited in our continuing research during the selection of fungal strains with different modes of action to accelerate the rate kill of mosquitoes and prevent the development of resistance. This research provides critical knowledge that can be used to exploit the use of fungal biopesticides to limit and manage mosquito resistance to synthetic insecticides.
2. Plant-based compounds for mosquito control. Plants are well-known sources of effective and environmentally friendly compounds for mosquito control. Some plants produce essential oils that kill mosquitoes. Unfortunately, these oils tend to evaporate quickly when applied to terrestrial habitats for adult mosquito control and are insoluble in water limiting their use in larval control. ARS scientists in Peoria, Illinois, discovered components from manuka essential oil that were very toxic to mosquito larvae and could be developed as effective natural pesticides. Researchers also developed a method that enhanced the toxicity of garlic, asafoetida and manuka essential oils against mosquito larvae and improved their solubility when applied in water bodies where mosquito larvae reside. This research provides critical knowledge that can be used to develop essential oil-based biopesticides for mosquito control.
3. Microbial metabolites for mosquito control. Beneficial fungal pathogens produce molecules that allow them to infect, propagate and kill targeted insect hosts. Identification of these molecules and their biological activity against mosquitoes is a critical step towards the discovery of new biopesticides for mosquito control. ARS scientists in Peoria, Illinois, identified several fungal isolates with ability to produce compounds that inhibit bacterial growth and control mosquitoes. Researchers also enhanced the production of these compounds by optimizing the growth conditions of the fungal isolates. The optimized growth of fungal isolates with antimicrobial and insecticidal properties has the potential to yield novel agents for mosquito control and for the treatment of human/animal diseases.
Review Publications
Muturi, E.J., Hay, W.T., Behle, R.W., Selling, G.W. 2019. Amylose inclusion complexes as emulsifiers for garlic and asafoetida essential oils for mosquito control. Insects. 10(10):337. https://doi.org/10.3390/insects10100337.
Muturi, E.J., Selling, G.W., Doll, K.M., Hay, W.T., Ramirez, J.L. 2020. Leptospermum scoparium essential oil is a promising source of mosquito larvicide and its toxicity is enhanced by a biobased emulsifier. PLoS One. 15(2):e0229076. https://doi.org/10.1371/journal.pone.0229076.
Barletta, A.F., Trisnadi, N., Ramirez, J.L., Barillas-Mury, C. 2019. Mosquito midgut prostaglandin release establishes systemic immune priming. iScience. 19:54-62. https://doi.org/10.1016/j.isci.2019.07.012.
Tchouassi, D.P., Muturi, E.J., Arum, S.O., Kim, C., Fields, C., Torto, B. 2019. Host species and site of collection shape the microbiota of Rift Valley fever vectors in Kenya. PLOS Neglected Tropical Diseases. 13(6):e0007361. https://doi.org/10.1371/journal.pntd.0007361.
Caceres Carrera, L., Victoria, C., Ramirez, J.L., Jackman, C., Calzada, J.E., Torres, R. 2019. Study of the epidemiological behavior of malaria in Darien Region, Panama. 2015–2017. PLoS ONE. 14(11):e0224508. https://doi.org/10.1371/journal.pone.0224508.
Ramirez, J.L., Muturi, E.J., Flor-Weiler, L.B., Vermillion, K., Rooney, A.P. 2020. Peptidoglycan recognition proteins (PGRPs) modulates mosquito resistance to fungal entomopathogens in a fungal-strain specific manner. Frontiers in Cellular and Infection Microbiology. 9:465. https://doi.org/10.3389/fcimb.2019.00465.
