Comparative Toxicity of Methanolic Extracts of some Indigenous and Exotic Flowers against Subterranean Termites Odontotermes obesus (Isoptera: Termitidae)

Abstract

Subterranean termites are destructive pests and cause massive damage to agricultural crops, forest plantations, wooden infrastructures and other cellulosic products. Their control is usually done by the application of highly persistent synthetic insecticides which often cause different non-target effects such as environment contamination. This laboratory study evaluated the toxicity of methanolic extracts of eight flowers i.e. Mexican marigold (Tagetes lucida), African marigold (Tegates erecta), tecoma (Tecoma stans), calendula (Calendula officinalis), basil (Ocimum basilicum), oxeye daisy (Leucanthemum vulgare), lily (Lilium longiflorum) and chrysanthemum (Glebionis segetum) against the worker individuals of subterranean termite Odontotermes obesus (Isoptera: Termitidae). Bioassays were conducted using filter paper disc method according to completely randomized design with four replications for each treatment. Termite mortality data was recorded at 6, 12, 24 and 48 h post-treatment. Median lethal concentration (LC50) and median lethal time (LT50) values were calculated for each treatment using log-dose probit analysis. Results revealed a mortality response of termites directly proportional to the extract concentration for all treatments. The floral extracts of basil (O. basilicum) and Tecoma (T. stans) exhibited maximum termite mortality (i.e. 55.5 and 50.0%, respectively) with minimum LC50 and LT50 values, followed by the extracts of chrysanthemum (G. segetum) and African marigold (T. erecta). Overall study results suggest that above mentioned floral extracts can be further characterized for potential botanical pesticide formulations against insect pests such as subterranean termites.