Effect of gamma radiation on the protective efficacy of Thuja orientalis essential oil on stored cowpea against Callosobruchus maculatus and Callosobruchus chinensis

Abstract

Purpose Cowpea is an essential pulse food in several regions throughout the world. Essential oil isolated from Thuja orientalis unripe fruits exposed to gamma radiation at dose levels of 0, 1, 3 and 5 kGy was evaluated as cowpea seed protectant against Callosobruchus maculatus and Callosobruchus chinensis. Materials and methods Cowpea seeds were treated with three rates of the oils from non-irradiated and irradiated fruits, 0.5, 1.5 and 3.0 g kg−1. Mortality of C. maculatus and C. chinensis adults after 3 and 7 days, progeny reduction and weight loss of cowpea seeds after 45 days were recorded for all treatments. Results The pronounced mortality of C. maculatus adults was achieved at the highest rate 3.0 g kg−1 of the irradiated oil with 5 kGy (98.3%). While in the case C. chinensis, all tested application rates induced marked adult mortality and a complete mortality (100%) resulted at two application rates (0.5 and 1.5 g kg−1) of irradiated oil with 5 kGy and 3.0 g kg−1 after 7 days. Strong progeny suppression of C. maculatus and C. chinensis was resulted at the highest rate of 3.0 g kg−1 of irradiated oil with 5 kGy (11.3 ± 0.3) and (8.5 ± 3.8) after 45 days of treatment, respectively. High protection of cowpea seeds with weight loss 0.5 and 1.4% for C. maculatus and C. chinensis was achieved at 3.0 g kg−1 of irradiated oil dose of 5 kGy, respectively after 45 days. Conclusions Our results indicate that gamma irradiation of T. orientalis fruits improve the protective activity of their essential oil against C. maculatus and C. chinensis on stored cowpea seeds and the irradiated oil could be successfully used for management of these bruchid insects.