Toxicity of vapours of three essential oils to the immature stages of Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae)

Fumigant toxicity of the essential oils from Lavandula hybrida, Rosmarinus officinalis and Eucalyptus globulus against the larvae and pupae of Acanthoscelides obtectus was assessed. The relationships between the application period and mortality, and between temperature and mortality, were investigated. The essential oil vapours were toxic to all immature stages tested with LC₅₀ values ranging between 0.6 and 76 μl/l air, depending on the insect's stage and the essential oil. The larvae of A. obtectus appeared progressively more tolerant to the essential oil vapours as they grew older, but were more susceptible than pupae. Increase of exposure time from 6 to 48 h resulted in an increase of larval mortality, whilst further increases of exposure time gave no additional detrimental effect. The essential oil vapours were more effective at 10°C and 18°C than at 4°C, 26°C, 32°C and 36°C.