Location: Crop Bioprotection Research
2019 Annual Report
Objectives
Objective 1. Utilizing transcriptomics to link gene function to fungal morphogenesis, develop liquid culture methods for producing propagules of fungal biocontrol agents such as Metarhizium spp., Beauveria bassiana, and Mycoleptodiscus terrestris by optimizing nutritional and environmental conditions during fungal growth for optimal biocontrol efficacy and storage stability to control pests in agricultural, urban, and natural ecosystems.
Objective 2. Develop novel fungal formulation technologies through the selection and application of innovative processes and ingredients that lead to improved storage stability, product delivery, field stability, and efficacy of fungal pathogens for biocontrol of insects [Beauveria bassiana, Metarhizium spp., and Isaria fumosorosea] and weeds [Mycoleptodiscus terrestris].
Subobjective 2A: Evaluate the compatibility of improved entomopathogen formulations with representative corn pest resistance mechanisms for control of sweet corn pests.
Objective 3. Identify, chemically and behaviorally characterize, and deploy natural insect semiochemicals (pheromones/kairomones and plant volatiles) with microbial biocontrol agents for management of important agricultural insect pests such as brown marmorated stink bug and coffee berry borer.
Approach
Our approach to the development of production methods for fungal biocontrol agents will focus on the use of liquid fermentation techniques. We will identify defined or semi-defined media that support the growth of our fungal biocontrol agents. Propagule form yield, storage stability, and biocontrol efficacy are critical “fitness” factors that will be considered during medium optimization. Initially, we will focus on producing propagules of fungal biocontrol agents such as Metarhizium spp, Beauveria bassiana, and Mycoleptodiscus terrestris. We also will use transcriptomics to identify pathways that may impact these factors. We will evaluate the impact of culture harvest techniques, stabilization processes, and formulation ingredients on the physical characteristics, biological activity, storage stability, and field efficacy of selected biocontrol agents. Also, we will identify and chemically characterize insect attractants and deterrents and evaluate formulations for management of important agricultural insect pests such as the brown marmorated stink bug, coffee berry borer, polyphagous shot hole borer, and tea shot hole borer.
Progress Report
Significant progress was made in FY19 on Objectives 1, 2, and 2a related to the production and formulation of microbial agents for controlling insects.
Under Objective 1, ARS scientists at Peoria, Illinois, continued to develop and optimize production processes by expanding techniques for liquid culture production to include additional beneficial fungi. Liquid culture production media were optimized for a newly discovered isolate of Isaria, an entomopathogenic fungi known to target crop pests like whiteflies and aphids. This isolate was discovered in cotton fields by ARS scientist at Byron, Georgia. Production media were optimized for maximum quantity of blastospore production by this new isolate and compared with that of a commercial strain. These samples are currently being evaluated for product quality as measured by long-term storage stability and pest control efficacy in laboratory and field experiment.
Previous research by ARS scientists at Peoria, Illinois, demonstrated synergistic (greater than expected) insecticidal activity from a two-microbe treatment that include the fungus Beauveria bassiana and the bacteria Bacillus thuringiensis. This observation prompted the research to develop liquid culture media for “dual microbe” production, to reduced production costs by simultaneous production of both microbes in a single liquid culture process. Although technically feasible, lower production yields by mixed cultures suggest additional improvements are needed to be economically competitive with current production technologies for individual microbes.
ARS researcher from Peoria, Illinois, collaborated with a Brazilian scientist to study the environmental stress tolerance of strains of an important insect killing fungus. This study characterized the interactions between environmental stress tolerance and the ability to kill insects (virulence) among a diverse set of beneficial fungal strains. The results demonstrated trade-offs between stress tolerance and insect virulence. This knowledge is necessary to identify strains with improved traits for crop protection applications.
To streamline the selection of beneficial microbes, ARS scientists in Peoria, Illinois, characterized the cabbage looper’s (Trichoplusia ni) host responses to infection by two different entomopathogenic fungi: Beauveria bassiana and Isaria javanica. These studies indicated that fungal exposure leads to an increase in the insect’s ability to melanize and sequester fungal cells. This response delayed fungal development and allowed larval survival to pathogen exposure. Insects also expressed contrasting responses in the production of other anti-microbial compounds when challenged with these two distinct entomopathogenic fungi. Understanding the pest response to fungal infection will improve our ability to select for more virulent fungal agents for improved control of lepidopteran pests by the screening of entomopathogenic fungi for their ability to circumvent these important host defenses.
Under Objective 2, an ARS scientist at Peoria, Illinois, evaluated several genes that promote resistance to diseases of corn and found some that also inhibited the growth of a beneficial fungal disease of insects used for biological control, while other genes did not. Understanding these interactions between crop plant genetics and beneficial microbes are necessary for optimizing implementation of integrated pest management strategies like host plant resistance and biopesticides. Additionally, the scientist observed an “induced-like” response, as a faster kill of a second infestation of pest insects when they fed on a corn leaf previously treated with a beneficial fungal biopesticide and previously exposed to insect feeding. This faster insecticidal action is an apparent interaction among the plant leaf, fungal biopesticide and initial feeding damage. Once the mechanism of this interaction is identified, further development may lead to enhanced insecticidal activity by fungal biopesticide treatments and result in reduced crop damage. These observations of both positive and negative interactions among host crop, crop pests, and beneficial microbes will direct future research to improve integrated pest management strategies that focus on simultaneous control of multiple pests of corn.
ARS researcher from Peoria, Illinois, collaborated with an Egyptian scientist to characterize the susceptibility of insect pests of mango to common insect pathogenic fungi. The insects were the white mango scale and the Seychelles fluted scale, which are important insect pests of mango. The study discovered that two insect-killing fungi provided effective control of the insects in lab and field assays. The study showed that natural fungi could effectively control orchard-pest insects. Understanding the environmental and ecological conditions that allowed the beneficial disease of pest insects to progress will improve the benefits provided by microbial biological control agents in integrated pest management systems. Further, identifying adverse conditions allows the opportunity to address these conditions through application of formulation technologies to protect beneficial microbes from environmental degradation.
Accomplishments
1. Discovery of a corn gene that improves plant resistance to insects and fungi. Corn plants have previously unidentified genes that improve plant resistance to insect and fungal pests that would otherwise greatly reduce corn yields and grain quality. Corn ear molds can produce toxins harmful to people and animals, causing hundreds of millions of dollars in losses in the U.S. ARS scientists in Peoria, Illinois, tested corn cell cultures after introducing a corn gene that produces a protein that could turn on several host-plant resistance mechanisms to insects and fungi and found increased resistance to both insects and fungi. If the correct form of this gene was bred into corn hybrids, the resulting cascade of corn’s natural biochemistry could reduce growth rates of insects that damage corn ears and reduce rates of corn ear rot fungal infection. Identifying and using beneficial genes for plant resistance is an economical means for growers to reduce corn ear damaged caused by insects and ear rots.
Review Publications
Weiler, L., Behle, R.W., Johnson, E.T., Strickman, D.A., Rooney, A.P. 2018. Evaluation of a granular formulation containing Metarhizium brunneum F52 (Hypocreales: Clavicipitaceae) microsclerotia in controlling eggs of Aedes aegypti (Diptera: Culicidae). Biocontrol Science and Technology. 29:68-82. https://doi.org/10.1080/09583157.2018.1530342.
Dowd, P.F., Johnson, E.T. 2019. Enhanced insect and fungal resistance of maize callus transgenically expressing a maize E2F regulatory gene. AGRI GENE. 12:100086. https://doi.org/10.1016/j.aggene.2019.100086.
Clifton, E.H., Gardescu, S., Behle, R.W., Hajek, A.E. 2019. Asian longhorned beetle bioassays to evaluate formulation and dose-response effects of Metarhizium microsclerotia. Journal of Invertebrate Pathology. 163:64-66. https://doi.org/10.1016/j.jip.2019.03.005.
Dowd, P.F., Johnson, E.T. 2018. Overexpression of a maize (Zea mays) defensin-like gene in maize callus enhances resistance to both insects and fungi. AGRI GENE. 9:16/23. https://doi.org/10.1016/j.aggene.2018.07.003.
Nisar, M.J., Behle, R.W., Dunlap, C.A., Goett, E.J., Iqbal, M., Gogi, M.D. 2019. Susceptibility of Rhagoletis suavis (Diptera: Tephritidae) maggots to entomopathogenic fungi. Southwestern Entomologist. 44(2):431-436. https://doi.org/10.3958/059.044.0208.
Addesso, K.M., O'Neal, P.A., Leahy, S., Trostel, K., Behle, R.W. 2018. Evaluation of a lignin-encapsulated nootkatone formulation against Tetranychus urticae (Acari: Tetranychidae). Florida Entomologist. 101(3):435-440. https://doi.org/10.1653/024.101.0321.
