Helicoverpa Assulta Guenee Research Articles

Resistance selection and mechanisms of oriental tobacco budworm (Helicoverpa assulta Guenee) to indoxacarb

The oriental tobacco budworm, Helicoverpa assulta, is one of the most destructive pests for numerous commercial crops, and these organisms are responsible for enormous economic losses in Chinese agriculture. Insect larvae often feed within host plant fruits, providing protection from many currently used insecticides and making field control of H. assulta very difficult. Owing to its novel mode of action, high insecticidal activity, and low mammalian toxicity, the nonsystemic insecticide indoxacarb has been considered a promising alternative for the control of lepidopterous pests of agricultural significance. Indoxacarb evidences an elevated insecticidal activity against H. assulta. After 13 generations of selection with indoxacarb and bifenthrin insecticides under laboratory conditions, the LC50 of these compounds for H. assulta increased by 4.19-fold and 10.67-fold, respectively. The synergists diethyl maleate (DEM) and triphenyl phosphate (TPP) increased indoxacarb toxicity by 2.76-fold and 4.10-fold in resistant strains and, comparatively, 1.58-fold and 1.75-fold in susceptible strains, suggesting that carboxylesterase (CarE) and glutathione-S-transferases (GSTs) may be involved in the development of indoxacarb resistance in H. assulta. Activity and kinetic parameters observed in detoxification enzymes further demonstrated that the enhanced activity of CarE and GSTs may be critical in development of indoxacarb resistance in H. assulta. The data provides a foundation for further study of the indoxacarb resistance mechanism observed in H. assulta and the rational use of indoxacarb as a rotation insecticide with other insecticide classes for the control of H. assulta.

Induction of nicotine in tobacco by herbivory and its relation to glucose oxidase activity in the labial gland of three noctuid caterpillars

TobaccoNicotiana tabacum L. is a host plant ofHelicoverpa armigera (Hubner),Helicoverpa assulta Guenee andSpodoptera litura (Fabricius) (Lepidoptera, Noctuidae). The difference in leaf nicotine response to the feeding by these three larvae and the mechanical simulation of their feeding was examined by HPLC. Results indicated that nicotine induction was suppressed byH. armigera andH. assulta larvae feeding or by simulated damage treated with their labial glands extracts. The production of nicotine was also suppressed by the glucose oxidase fromAspergillus niger when it was treated on mechanically wounded leaf area. On the contrary, the nicotine production was stimulated byS. litura larva feeding or by simulated damage treated with its labial gland extract. Heat denature can not counteract the stimulation effect of theS. litura labial gland extracts to tobacco nicotine production. The glucose oxidase activity was detected in labial gland extracts of bothH. armigera andH. assulta, but the activity inH. armigera was significantly higher than that inH. assulta. No glucose oxidase activity was detected in labial gland extracts ofS. litura. It is shown that the glucose oxidase activity in labial glands of caterpillars plays an important role in the nicotine response to herbivory. The glucose oxidase was mainly contained in the labial gland ofH. armigera larva, and had the highest activity at pH 7.0. D-Glucose was the optimal substrate of the glucose oxidase. Labial gland glucose oxidase activities varied daily during larval development with high activities found when larvae were actively feeding.