ARS | Publication request: Isolation of three diterpenoid acids from sunflowers, as oviposition stimulants for the banded sunflower moth, Cochylis hospes

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 28, 2008
Publication Date: January 29, 2009
Citation: Morris, B.D., Charlet, L.D., Foster, S.P. 2009. Isolation of Three Diterpenoid Acids from Sunflowers, as Oviposition Stimulants for the Banded Sunflower Moth, Cochylis hospes. Journal of Chemical Ecology. 35:50-57.

Interpretive Summary: The banded sunflower moth is native to North America and one of the most important pests of cultivated sunflower in the U.S. Larvae feed primarily on different species of sunflowers, Helianthus spp., and a few other composite weeds. Previous research on cultivated sunflower resulted in the isolation of two diterpenoids which stimulate egg laying by female banded sunflower moths, and also showed that other, more polar compounds also stimulated oviposition. Using a bioassay-guided approach, we isolated three further diterpenoids, grandifloric acid (1), 15a-hydroxy-ent-trachyloban-19-oic acid (2), and 17-hydroxy-16a-ent-kauran-19-oic acid (3), from polar fractions of extract of pre-bloom sunflower heads. In laboratory experiments, purified natural samples of each of these compounds stimulated oviposition by female moths. A comparison of the five diterpenoids showed that a specific chemical structure common to each may be responsible for stimulating oviposition by female moths. These chemicals are likely perceived only by the moths when in contact with the plant. Further research is needed to identify volatile compounds which attract the females to the sunflower plant.

Technical Abstract: The banded sunflower moth (BSFM), Cochylis hospes Walshingham (Lepidoptera: Cochylidae) is a specialist insect, the larvae of which feed on sunflowers, Helianthus spp., and a few other species of Compositae. It is one of the most important pests of sunflower in the USA. Previous work on H. annuus, the cultivated sunflower, resulted in the isolation of two diterpenoids which function as oviposition stimulants for female BSFM, and also showed that other, more polar compounds also stimulated oviposition. Using a bioassay-guided approach, we isolated three further diterpenoids, grandifloric acid (1), 15a-hydroxy-ent-trachyloban-19-oic acid (2), and >17-hydroxy-16a-ent-kauran-19-oic acid (3), from polar fractions of extract of pre-bloom sunflower heads. In laboratory bioassays, purified natural samples of each of these compounds stimulated oviposition by female BSFM. Structure-activity relationships of the five diterpenoids known to stimulate oviposition by female BSFM are discussed.