Do fungi make caterpillars picky eaters? Effects of endophytic Metarhizium robertsii on corn, Zea mays, growth and fall armyworm, Spodoptera frugiperda
Open Access
- Author:
- Flonc, Brianna Evelyn
- Graduate Program:
- Entomology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 25, 2019
- Committee Members:
- Mary Ellen Barbercheck, Thesis Advisor/Co-Advisor
Nina Ellen Jenkins, Committee Member
Maryann Victoria Bruns, Committee Member - Keywords:
- Metarhizium
Fall Armyworm
Spodoptera frugiperda
Zea mays
Biological Control
Endophyte
Agriculture
Pest Control
Metarhizium robertsii
Entomopathogenic Fungus - Abstract:
- Biological control plays an integral part in regulating pest populations in agroecosystems. On organic farms, biological control provided by natural enemies including predators, parasitoids, and pathogens, is of critical importance because farmers cannot apply synthetic insecticides. Soil fungi in the genus Metarhizium Sorokin (Hypocreales: Clavicipitaceae) are entomopathogens found in a wide range of soils, including agricultural soils, that can infect and kill a variety of insects. Recently, Metarhizium was found to be able to grow in plants as an endophyte that can promote plant growth. Therefore, my research examined the effects of endophytic Metarhizium robertsii on corn (Zea mays L.) and larvae of the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae), an economically important pest of corn. My research provides insight into the potential for endophytic Metarhizium to be used as a plant growth promoter and natural biological control for pest insects. My research objectives were to determine: 1) the ability of an isolate of M. robertsii J.F. Bisch, Rehner and Humber obtained from an organic field experiment to endophytically colonize corn leaf and root tissue at different growth stages; 2) effects of endophytic M. robertsii on corn growth; 3) the effect of M. robertsii-colonized corn leaf tissue on the relative growth rate (RGR) of FAW larvae; and 4) effects of endophytic M. robertsii on the feeding behavior of FAW larvae in choice and no-choice assays. In experiments to address Objective 1, I recovered endophytic M. robertsii in the tissue of 201 out of 295 inoculated plants across five trials with a mean percent recovery ± standard error per trial of 60.5% ±10.6. Out of the 295 treated corn plants with M. robertsii recovery, 42 plants (12% ±2.70) had root recovery, 65 plants (14.0% ±6.2) had leaf recovery, 94 plants (21.7% ±9.71) had concurrent leaf and root recovery, and 94 plants (39.5% ±10.6) had no recovery. Corn grown from inoculated seed had similar leaf and root tissue colonization, which was unexpected due to previous research showing endophytic colonization occurring almost exclusively in plant roots. In greenhouse experiments to address Objective 2, there were no consistent differences between the height, dry aboveground biomass, or chlorophyll content of corn grown from inoculated seed and control corn. In detached-leaf assays and on-plant assays to address Objective 3, the mean relative growth rate (RGR) of larval fall armyworm (FAW), Spodoptera frugiperda, that fed on M. robertsii-colonized leaf tissue was similar to the mean RGR of FAW that fed on control corn leaf tissue. In choice assays to address Objective 4, FAW showed no feeding preference for control corn leaf tissue over leaf tissue from M. robertsii-inoculated corn plants, or vice versa. Endophytic fungi are wide-spread and diverse in nature and their effects on the relationship between plants and arthropods are not well understood. Because the isolate of M. robertsii used in this study had no previously known relationship with corn as an endophyte or with FAW as an infective entomopathogenic fungi, it is necessary to repeat experiments with M. robertsii recovered from corn tissue and sporulating FAW cadavers exhibiting mycosis. It remains unclear whether this isolate of M. robertsii would be able to promote corn growth and act as a natural biological control for FAW through endophytic means. Future studies should also include field trials to determine if M. robertsii can colonize corn endophytically in competition with other soil microbes and impact FAW field distribution.