CAREER: Prevalence, magnitude, and importance of gut microbial detoxification services in insect herbivory

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

Insects eat plants. This is both a basic process in nature and a major problem in agriculture, resulting in crop losses and costly pesticide treatments. Plants defend themselves by producing natural chemicals that are toxic to insects, but insects have many ways to overcome these toxins.

In addition to insects’ own abilities, which are well studied, recent evidence suggests that bacteria living in the insect gut can help to break down plant toxins. When and how this happens, and its overall contribution to plant damage by insects, are poorly understood. The goal of this research is to identify which bacteria break down toxins from two common crop families (the tomato family and the cabbage family) and measure how much these bacteria help insects eat these plants.

Understanding the different ways insects disable plant toxins will help us design more effective, targeted insect control strategies. Ultimately this could reduce crop losses and lessen the need for broad-spectrum pesticides. This project will also provide hands-on research experience for undergraduates at a Hispanic-serving institution, reaching a total of 120 students in the classroom and 30 students in the laboratory.

Students will rear insects, infect them with different bacteria, measure the effects on the insects’ health and plant consumption, and present their results in public and scientific venues. This will train both future members of our society and the next generation of STEM researchers in scientific thinking.

The overarching goal of this research is to predict the magnitude of detoxification assistance provided to insects by their gut microbiota, testing the hypothesis that host plant generalists will benefit more from microbial facilitation than specialists. Using beetles, grasshoppers and caterpillars feeding on Solanaceous and Brassicaceous plants, this research will: (1) Determine the abundance of allelochemical-degrading bacteria within wild insects’ gut microbiota.

Researchers will characterize gut microbial composition via 16S amplicon sequencing and simultaneously isolate live gut bacteria from the same insect individuals. The ability of these bacteria to degrade allelochemicals will be measured via culture-based assays. (2) Measure the magnitude of microbial detoxification in vivo. Researchers will inoculate generalist and specialist insects with toxin-degrading or non-degrading isolates and allow the insects to feed on plants.

Concentrations of allelochemicals excreted in insect frass will be measured to determine how much microbial degradation occurred. (3) Quantify the impact of gut microbial facilitation on insect fitness and plant consumption. Generalist and specialist insects will be reared on their host plants, inoculated with an isolate that does or does not degrade one of the plant’s major toxins.

Researchers will compare the insects’ growth rate, development time to adulthood, survival, and total leaf area consumed. This work will quantify the overall importance – or lack thereof – of gut microbiota in insect herbivory and launch a career-long investigation of the role of gut microbiota in the plant-insect chemical arms race, a process that has generated much of Earth’s terrestrial biodiversity.

This award was jointly funded by the Symbiosis, Infection and Immunity Program in the Division of Integrative Organismal Systems and by the Population and Community Ecology Program in the Division of Environmental Biology.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.