Location: Crop Bioprotection Research
2024 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
For Objective 1, ARS researchers in Peoria, Illinois, made significant progress in evaluating 17 species of insect- killing fungi for larvicidal activity against the yellow fever mosquito, Aedes aegypti. These fungal strains, spanning five genera, exhibited varying levels of spore production and pathogenicity against mosquito larvae and pupae. Two forms of fungal inocula were evaluated (blastospore and conidia), providing insights into optimal fungal stages to use during formulations for enhanced efficacy and shelf life. These would serve as leads for microbial biopesticide formulations to suppress mosquito larvae.
In a separate project to evaluate the potential impact of climate change on mosquito control, ARS researchers in Peoria, Illinois, collaborated with Bradley University to evaluate the effect of elevated carbon dioxide, a key contributor of climate change, on susceptibility of mosquito larvae to microbial biopesticides. Larvae of the yellow fever mosquito were maintained under normal or elevated carbon dioxide levels and challenged with fungi known to kill mosquitoes. Our results indicated that elevated carbon dioxide has complex effects on susceptibility of mosquito larvae to microbial biopesticides, with one microbial biopesticide losing its effect under elevated carbon dioxide levels. Our findings provide valuable insights into how climate change may affect mosquito physiology and host-pathogen interactions, with implications for their potential control under likely future elevated carbon dioxide conditions.
In a collaboration with Brazilian scientists, five entomopathogenic fungi were evaluated for activity against the dog tick (Rhipicephalus sanguineus), an important vector of Rocky Mountain spotted fever in humans. Two entomopathogenic fungi were found to have acaricidal properties and studies are currently being conducted to elucidate how ticks defend themselves against infection by entomopathogenic fungi.
Substantial progress was also made in testing crude secondary metabolite extracts from five fungi for toxicity against mosquito larvae and ability to inhibit microbial growth. Crude extracts of entomopathogenic fungi Beauveria brongniartii were toxic to mosquito larvae and had antimycobacterial activity against Mycobacterium smegmatis (Mc2155). Additional research is currently being conducted to determine the bioactive molecules responsible for killing the mosquito larvae and inhibiting microbial growth.
For Objective 2, The bioactivity of brassica seed meals was tested for toxicity against three medically important ticks. This study indicated that Garden cress and Pennycress seed meals have synergistic activity against the black-legged tick, the American dog tick, and the lone star tick. These results have been submitted for an invention disclosure (“DEFATTED GLUCOSINOLATE CONTAINING SEED MEALS AS EFFECTIVE ACARICIDES TO CONTROL TICKS” (Docket No: 0099.23)).
Accomplishments
1. Identification of beneficial fungi that are lethal to mosquito larvae and pupae. Synthetic insecticides are harmful to the environment and mosquitoes have developed resistance to nearly all classes of synthetic insecticides approved for public health use. Therefore, there is an urgent need for alternative approaches for mosquito control. Insect-killing fungi and bacteria are promising alternatives to chemical insecticides due to their high specificity to the target organisms and low toxicity to humans and the environment. ARS researchers in Peoria, Illinois, tested 17 strains of insect-killing fungi from five fungal genera and identified six fungal strains that were highly effective at killing larvae of the yellow fever mosquito. Some of these fungal strains were also effective at killing the pupal stage, effectively preventing emergence of adult mosquitoes. This study expands our list of insect-killing fungi for further study and application on mosquito control. The application of these mosquito-killing fungi could be applied in both urban and rural areas, reducing our reliance on synthetic insecticides and preventing the outbreak of mosquito-borne diseases. These findings are invaluable to public health and vector control agencies seeking sustainable alternatives to chemical insecticides.
2. Use of mustard seed meals to control ticks. Ticks are one of the most important vectors of animal and human pathogens. Unfortunately, they are becoming resistant to pesticides, which makes it harder to control them using the traditional methods. Plant-derived biopesticides are promising options to manage ticks. These biopesticides often contain several active compounds that work in different ways, thus preventing ticks to develop resistance. ARS researchers in Peoria, Illinois, evaluated the activity of mustard plant seed meals against three important tick species (the lone star tick, American dog tick, and black- legged ticks). Of the four mustard seed meals that were evaluated, three were found to be toxic to ticks. A combination of garden cress and Pennycress seed meals was particularly effective at killing the three tick species compared to either seed meal alone. These findings suggest that combining seed meals from different mustard plants could be harnessed as a natural and effective way for controlling ticks, while at the same time preventing the development of resistance in tick populations. These plant-based biopesticides provides public health agencies and farmers a sustainable alternative to synthetic acaricides to control ticks, reducing the incidence of human and animal tick-borne diseases.
Review Publications
Yan, J., Kim, C., Chesser, L., Ramirez, J.L., Stone, C.M. 2023. Nutritional stress compromises mosquito fitness and antiviral immunity, while enhancing dengue virus infection susceptibility. Communications Biology. 6. Article 1123. https://doi.org/10.1038/s42003-023-05516-4.
Njoroge, T.M., Berenbaum, M.R., Stone, C.A., Kim, C., Dunlap, C.A., Muturi, E.J. 2024. Culex pipiens and Culex restuans larval interactions shape the bacterial communities in container aquatic habitats. FEMS Microbes. https://doi.org/10.1093/femsmc/xtae002.