Repellent effects of methyl anthranilate on western corn rootworm larvae (Coleoptera: Chrysomelidae) in soil bioassays

Authors: BERNKLAU, ELISA - Colorado State University; Hibbard, Bruce; BJOSTAD, LOUIS - Colorado State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2018
Publication Date: 11/12/2018
Citation: Bernklau, E.J., Hibbard, B.E., Bjostad, L.B. 2018. Repellent effects of methyl anthranilate on western corn rootworm lLarvae (Coleoptera: Chrysomelidae) in soil bioassays. Journal of Economic Entomology. 112(2):683-690. https://doi.org/10.1093/jee/toy346.
DOI: https://doi.org/10.1093/jee/toy346

Interpretive Summary: The western corn rootworm is a major pest which has developed resistance to a number of management tactics. New tactics are needed to replace those being lost to resistance. We recently identified a compound from corn roots that is a repellent to western corn rootworm larvae and is potential area of vulnerability. Here, the repellent was tested in a soil environment for behavioral effects on newly hatched larvae. In tests with a single maize seedling surrounded by granules treated with the repellent, significantly fewer larvae located the roots and the number of larvae recovered from roots decreased with increasing rates of repellent. When the repellent was employed in a simple push-pull strategy between a repellent-treated seedling and an untreated seedling, concentrations of repellent as low as 0.01% caused significantly more larvae to be “pushed” to and recovered from roots of the untreated seedling. The effect strengthened as the dosage increased, with up to 90% repellency occurring with the highest dose tested (10%). Chemical analysis soil treated with the repellent showed that amounts remained high for 4 weeks in dry, sterilized or unsterilized soil, but levels declined rapidly in moist soil. After 7 days, levels in moist, sterilized soil were 50% lower than in dry soil and in unsterilized moist soil, only a trace of MA remained, suggesting that both moisture and microbial activity contributed to the degredation. A variety of carrier granules were coated with the repellent and tested in soil bioassays after aging in moist soil. After 1 day in the soil, all of the treatments were repellent at the 1% rate and clay granules were also effective at 0.1%. After one week in the soil, only the molecular sieve granules elicited repellency, but this activity was gone after two weeks of aging. These results documented repellent effect by western corn rootworm larvae in the soil environment and may have future potential as a rootworm treatment if formulations can be developed to protect the material from decomposition in the soil.

Technical Abstract: Methyl anthranilate, a natural compound in maize roots, was previously shown to be repellent to larvae of the western corn rootworm, Diabrotica virgifera virgifera LeConte. In this study, MA was tested in a soil environment for behavioral effects on neonate larvae. In tests with a single maize seedling surrounded by MA-coated granules, MA prevented larvae from locating the roots and the number of larvae recovered from roots decreased with increasing rates of MA. When MA was employed in a simple push-pull strategy between an MA-treated seedling and an untreated seedling, concentrations of MA as low as 0.01% caused significantly more larvae to be “pushed” to and recovered from roots of the untreated seedling. The effect strengthened as the dosage increased, with up to 90% repellency occurring with the highest dose tested (10% MA). A commercial product containing MA gave similar results, with 96% repellency observed for the highest dose tested. Chemical analysis showed that amounts of MA remained high for 4 weeks in dry, sterilized or unsterilized soil, but MA levels declined rapidly in moist soil. After 7 days, MA levels in moist, sterilized soil were 50% lower than in dry soil and in unsterilized moist soil, only a trace of MA remained, suggesting that both moisture and microbial activity contributed to the loss of MA. A variety of carrier granules were coated with MA and tested in soil bioassays after aging in moist soil. After 1 day in the soil, all of the MA granules were repellent at the 1% rate and clay granules were also effective at 0.1%. After one week in the soil, only the molecular sieve granules elicited repellency, but this activity was gone after two weeks of aging. These results demonstrate that MA elicits a repellent effect by western corn rootworm larvae in the soil environment and may have future potential as a rootworm treatment if formulations can be developed to protect the material from decomposition in the soil.