Isomeric Flavonoids of<i>Artemisia annua</i>(Asterales: Asteraceae) as Insect Growth Inhibitors Against<i>Helicoverpa armigera</i>(Lepidoptera: Noctuidae)

Abstract

Artemisia annua (Asterales: Asteraceae) is one of the important natural sources of antimalarial compounds i.e., artemisinin and artemisinic acid. Also this plant is cultivated on a large area in India under industry-farmer partnerships. With a view to enhance the added value of the raw material of A. annua and its chemical constituents, we evaluated methanolic extract of powdered A. annua leaves and different compounds isolated from the extract for toxicity and inhibition and disruption of growth and development of the African pod borer, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). Methanol extract of A. annua and eight known constituent compounds [artemisinic acid, artemisinin, scopoletin, arteannuin-B, deoxy-artemisinin, artemetin and isomeric flavonoids (casticin and chrysosplenetin)] were bio-assayed for larval mortality, abnormal development, and growth inhibition. The methanol extract severely affected 100% of the larva treated, i.e., larvae gained very little weight, some larvae died, some formed larval-pupal intermediates, some pupae died and a few abnormal adults (adultoids) emerged. The mean weight of treated larvae reached only 0.026 g compared to the 0.270 g in the control and at par with larvae treated with 2% neem seed kernel extract (0.035 g) and 0.02% w/w azadirachtin (0.059 g).Among A. annua constituent compounds, the isomeric flavonoids exhibited a strong reduction in mean larval weight (58.5%), and growth inhibition (50.0%) as compared to the control. Extracts of A. annua and its isomeric flavonoids appear to have potential for developing novel biopesticides.