Composition and biological activity of essential oils from Labiatae against Nezara viridula (Hemiptera: Pentatomidae) soybean pest.

BACKGROUND: Plant essential oils have been recognised as an important natural source of insecticide. This study analysed the chemical constituents and bioactivity of essential oils that were isolated via hydrodistillation from Origanum vulgare L. (oregano) and Thymus vulgaris L. (thyme) against eggs, second instar and adults of Nezara viridula (L.). RESULTS: The major component of oregano was p-cymene, and, for thyme, thymol. The ovicidal activity was tested by topical application; the essential oil from thyme was more effective. The fumigant activity was evaluated in an enclosed chamber; the LC50 values for oregano were 26.8 and 285.6 µg mL(-1) for nymphs and adults respectively; for thyme they were 8.9 µg mL(-1) for nymphs and 219.2 µg mL(-1) for adults. To evaluate contact activity, a glass vial bioassay was used; the LC50 values for oregano were 1.7 and 169.2 µg cm(-2) for nymphs and adults respectively; for thyme they were 3.5 and 48.8 µg cm(-2) respectively. The LT50 analyses for contact and fumigant bioassays indicated that thyme was more toxic for nymphs and adults than oregano. Both oils produced repellency on nymphs and adults. CONCLUSION: These results showed that the essential oils from O. vulgare and T. vulgaris could be applicable to the management of N. viridula.

Biological activity of essential oils from Aloysia polystachya and Aloysia citriodora (Verbenaceae) against the soybean pest Nezara viridula (Hemiptera: Pentatomidae).

The objective of the current study was to determine the chemical constituents, ovicidal activity, fumigant, contact toxicity and repellent effects of essential oils isolated by hydrodistillation from Aloysia polystachya and A. citriodora against eggs and second instar nymphs of Nezara viridula. The major components were carvone (83.5%) for A. polystachya, and citronellal (51.3%) and sabinene (22.9%) for A. citriodora. The ovicidal activity of both oils was tested by topical application at different concentrations ranging from 1.2 to 12.5 microg/egg; all concentrations had a toxic effect. Data probit analysis showed that the LC50 value for A. polystachya was 2.3 microg/egg and for A. citriodora 1.9 microg/egg. The fumigant activity was evaluated in an enclosed chamber. The toxicity increased with concentration from 11 to 176 microg/mL air, and with exposure times from 1 to 48 h. The LC50 values for A. polystachya and A. citriodora were 29.9 and 13.5 microg/mL air 24 h after treatment, respectively. To evaluate contact activity a glass-vial bioassay was used. The toxicity increased with concentration from 2.8 to 45 microg/cm2 and with exposure time from 1 to 48 h. The LC50 for A. polystachya was 3.4 microg/cm2 and for A. citriodora 8.1 microg/cm2. The repellency bioassay demonstrated that both oils were active at the highest concentration (2.6 and 5.3 microg/mL air) and neutral at 1.3 microg/mL air. These results show that the essential oils from Aloysia polystachya and A. citriodora could be applicable to the management of populations of Nezara viridula.