Fumigant toxicity of essential oils from three Thai plants (Zingiberaceae) and their major compounds against Sitophilus zeamais, Tribolium castaneum and two parasitoids

Abstract

Fumigant toxicity of essential oils from rhizomes of Alpinia conchigera, Zingiber zerumbet, Curcuma zedoaria and their major compounds; camphene, camphor, 1,8-cineole, α-humulene, isoborneol, α-pinene, β-pinene and terpinen-4-ol was investigated with adults of Sitophilus zeamais, Tribolium castaneum, Anisopteromalus calandrae and Trichogramma deion larvae. The last two insects are parasitoids commonly used to control stored-product weevils and moths. The trial was evaluated at 0, 37, 74, 148, 296, 444, 593 μL/L in air after 12, 24 and 48 h for S. zeamais, T. castaneum and A. calandrae, and 24 h for T. deion. Alpinia conchigera oils were toxic to S. zeamais, T. castaneum and T. deion, while the other two plant oils had low toxicity. Adults of S. zeamais and T. castaneum were more susceptible to A. conchigera oils than their eggs, larvae or pupae. Sitophilus zeamais adults (LC 50 85 μL/L in air) were slightly more tolerant of A. conchigera oils than T. castaneum (LC 50 73 μL/L in air) after 48 h exposure. Synthetic essential oils, a mixture of pure compounds in the same ratios of the extracted essential oils, were tested with S. zeamais and T. castaneum adults. Synthetic essential oils were more toxic than the extracted essential oils to both insects. Zingiber zerumbet oils (LC 50 26 μL/L in air) and C. zedoaria oils (LC 50 25 μL/L in air) were significantly more toxic to adults of A. calandrae than A. conchigera oils (LC 50 37 μL/L in air) whereas T. deion larvae were more sensitive to A. conchigera oils (LC 50 62 μL/L in air) than Z. zerumbet and C. zedoaria oils (LC 50 > 593 μL/L in air). Tribolium castaneum was more susceptible than S. zeamais to the eight pure compounds. Terpinen-4-ol was highly toxic to both insects.