Biological Activity of Essential Oils from Aloysia polystachya and Aloysia citriodora (Verbenaceae) against the Soybean Pest Nezara viridula (Hemiptera: Pentatomidae)

Abstract

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 μg/egg; all concentrations had a toxic effect. Data probit analysis showed that the LC₅₀ value for A. polystachya was 2.3 μg/egg and for A. citriodora 1.9 μg/egg. The fumigant activity was evaluated in an enclosed chamber. The toxicity increased with concentration from 11 to 176 μg/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 μg/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 μg/cm² and with exposure time from 1 to 48 h. The LC₅₀ for A. polystachya was 3.4 μg/cm² and for A. citriodora 8.1 μg/cm². The repellency bioassay demonstrated that both oils were active at the highest concentration (2.6 and 5.3 μg/mL air) and neutral at 1.3 μg/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.