The efficacy of essential oil of Alpinia calcarata (Rosc.) and its major constituent, 1,8-cineole, as protectants of cowpea against Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Abstract

The bruchid, Callosobruchus maculatus, (F.) causes major losses during the storage of cowpea seeds [Vigna unguiculata (L.) Walp.] in Sri Lanka. Essential oil was extracted from Alpinia calcarata (Rosc.) and 1,8-cineole, identified as the major constituent of the essential oil, was tested for its potential insecticidal activity against C. maculatus. The adults of C. maculatus were susceptible to both fumigant toxicity and contact and fumigant toxicity of 1,8-cineole and A. calcarata oil. In the fumigant toxicity assay, the LC50 (0.685 g L-1) value of 1,8-cineole was similar to that of A. calcarata oil. However, LC50 values of 0.068 g L-1 and 0.141 g L-1 were obtained for the contact and fumigant toxicity of 1,8-cineole and A. calcarata oil, respectively. Oviposition and F1 adult emergence were significantly inhibited by 1,8-cineole and A. calcarata oil at concentrations higher than 0.80 g L-1 in the fumigant toxicity and 0.123 g L-1 in the contact plus fumigant toxicity. Repellent activity of A. calcarata oil was more potent to C. maculatus than 1,8-cineole at doses ranging from 10 to 40 mg. This study reveals that 1,8-cineole is the most toxic component present in A. calcarata oil, and that the repellent activity of A. calcarata oil could be due to 1,8-cineole as well as the other constituents present in the essential oil. Key words: Callosobruchus maculatus (F.), Alpinia calcarata (Rosc.), 1,8-cineole, essential oils, cowpea