Location: Crop Bioprotection Research
2022 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, evaluating diverse insect killing fungi for their potential to kill mosquito larvae. These studies are allowing us to identify fungal microbial agents that we can use in the aquatic environment and the appropriate concentration of fungal spores to attain maximal kill of mosquito larvae. Additionally, we tested two different species of insect pathogenic fungi against two important mosquito vectors in the United States: the Asian tiger mosquito (Aedes albopictus) and the house mosquito (Culex pipiens). These studies also evaluated whether another microbe, the symbiont Wolbachia (which these two mosquitoes naturally carry), could interfere with the killing activity of insect pathogenic fungi. Wolbachia is currently being used as a strategy for mosquito control and have potential implications for interactions with other biological control approaches.
For Objective 2, substantial progress was made testing different essential oils for toxicity against Aedes aegypti larvae. These compounds were tested in combination with the pesticide piperonyl butoxide for enhanced larval toxicity. Additionally, different essential oils from cedar wood oil, cilantro, parsley and pimento seed were tested for toxicity against adult mosquitoes. In a separate experiment, we tested the toxicity of cedarwood oil against hard tick species. The laboratory tests were conducted with immature stages of four hard-bodied tick species and using several doses of cedarwood oil, using DEET (N, N-diethyl-meta-toluamide) as a control group. This study found different degrees of repellency and toxicity to cedarwood oil across the different tick species. Our results indicate that cedarwood oil can be developed into an environmentally friendly repellent against ticks.
Accomplishments
1. Identified mosquito species that are resistant to insect killing fungi. Not all mosquitoes are equally susceptible to microbial-based biopesticides, and some carry the endosymbiont Wolbachia, a bacterium that can provide the mosquito protection against infection by viruses and bacteria. ARS researchers in Peoria, Illinois, in collaboration with scientists at Illinois State University tested the susceptibility to insect killing fungi of two field mosquitoes, the Asian tiger mosquito (Aedes albopictus) and the house mosquito (Culex pipiens). This study indicated that while Wolbachia does not interfere with the killing activity of insect fungal pathogens, it does impact mosquito overall health, with potential consequences to mosquito reproduction. Furthermore, this study showed that while both mosquito species are killed by insect fungal pathogens, Culex pipiens mosquitoes are highly resistant to the action of one common insect fungal pathogen. This study provides new susceptibility records of two important mosquito vectors in the United States that will guide vector control agencies when selecting the most appropriate biological control agent against these mosquitoes.
2. Determined cedarwood oil is an environmentally friendly biopesticide that kills and repel ticks. Ticks are one of the most important vectors of animal and human pathogens. Their control relies heavily on pesticides but the rapid evolution of pesticide-resistance in ticks underscores the need for new eco-friendly biopesticides. ARS researchers in Peoria, Illinois, tested the toxicity and repellency of cedarwood oil against four different tick species and observed a range of susceptibilities with the most significant toxicity being against the black-legged tick. Exposure to cedarwood oil repelled 80-94% of black-legged ticks, the same rate compared to the traditional DEET-based (N, N-diethyl-meta-toluamide) repellent currently on the market. This study indicates that cedarwood oil is a great candidate for further development of an environmentally friendly acaricide and repellent.
Review Publications
Flor-Weiler, L.B., Behle, R.W., Eller, F.J., Muturi, E.J., Rooney, A.P. 2022. Repellency and toxicity of a CO2-derived cedarwood oil on hard tick species (Ixodidae). Experimental and Applied Acarology. 86:299-312. https://doi.org/10.1007/s10493-022-00692-0.
Ramirez, J.L., Schumacher, M., Ower, G., Palmquist, D.E., Juliano, S.A. 2021. Impacts of fungal entomopathogens on survival and immune responses of Aedes albopictus and Culex pipiens mosquitoes in the context of native Wolbachia infections. PLOS Neglected Tropical Diseases. 15(11). Article e0009984. https://doi.org/10.1371/journal.pntd.0009984.
