Insect feeding deterrent and growth inhibitory activities of scopoletin isolated from Artemisia annua against Spilarctia obliqua (Lepidoptera: Noctuidae)

Abstract

Artemisia annua (Asteraceae) is well known for its antimalarial activities due to presence of the compound artemisinin. We isolated a methoxy coumarin from the stem part of A. annua and confirmed its identity as scopoletin through mass spectral data. The structure was established from 1H-nuclear magnetic resonance (NMR), 13C-NMR. The compound scopoletin was evaluated for its feeding deterrence and growth inhibitory potential against a noxious lepidopteran insect, Spilartctia obliqua Walker. Scopoletin gave FD50 (feeding deterrence of 50%) value of 96.7 μg/g diet when mixed into artificial diet. S. obliqua larvae (12-day-old) exposed to the highest concentration (250 μg/g diet) of scopoletin showed 77.1% feeding-deterrence. In a growth inhibitory assay, scopoletin provided 116.9% growth inhibition at the highest dose of 250 μg/g diet with a GI50 (growth inhibition of 50%) value of 20.9 μg/g diet. Statistical analysis showed a concentration-dependent dose response relationship toward both feeding deterrent and growth inhibitory activities. Artemisinin is found mainly in the leaves of A. annua and not in the stems, which are typically discarded as waste. Therefore identification of scopoletin in stems of A. annua may be important as a source of this material for pest control.