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

Fumigant toxicity of essential oils from rhizomes of Alpinia conchigera, Zingiber zerumbet, Curcuma zedoaria and their major compounds; camphene, camphor, 1,8-cineole, alpha-humulene, isoborneol, alpha-pinene, beta-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 mu L/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 (LC50 85 mu L/L in air) were slightly more tolerant of A. conchigera oils than T. castaneum (LC50 73 mu L/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 (LC50 26 mu L/L in air) and C. zedoaria oils (LC50 25 mu L/L in air) were significantly more toxic to adults of A. calandrae than A. conchigera oils (LC50 37 mu L/L in air) whereas T deion larvae were more sensitive to A. conchigera oils (LC50 62 mu L/L in air) than Z. zerumbet and C. zedoaria oils (LC50 > 593 mu L/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. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.