Effects of Crude and Partially Purified Extracts from UV‐B–irradiated Rice Leaves on Helicoverpa armigera (Hübner)‡

The effect of crude and partially purified extracts from ultraviolet-B (UV-B)-irradiated rice (Oryza sativa L.) leaves on the growth and development of corn earworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), was investigated. Fifty muL droplets of a liquid diet containing different concentrations of the crude and partially purified extracts were fed to H. armigera neonates to determine possible short-term toxicity effects. A choice test using a solid artificial diet was also performed to determine larval feeding preferences and antifeedant effects. To study effects on the life history of the insect, different concentrations of the crude and partially purified extracts were also incorporated in the artificial diet and fed to individually confined neonates of H. armigera. The neonates were reared up to the adult stage. Results showed that crude and partially purified extracts of UV-B-irradiated rice leaves demonstrated antifeedant, growth-inhibitory and antibiotic properties against H. armigera. At high concentrations, the extract initially stimulated larval feeding; however, there were subsequent negative effects on pupal and adult traits, thereby reducing the reproductive potential of adults. These partially purified extracts appeared to have an antifertility effect because adults laid fewer eggs and, of those eggs laid, viability was lower. These results suggest that the accumulated flavonoids or other phenolics in UV-B-irradiated leaves, extracted from UV-B-resistant rice cultivar 'M202,' affected the growth, development and reproduction of H. armigera, a polyphagous insect pest.