Abstract
Plant essential oils are an alternative source to pesticides due to their multiple modes of insecticidal action, easy biodegradability, and low mammalian toxicity. However, most botanical insecticides are sensitive to degradation, thus requiring frequent reapplication of large amounts of them in pest control practices. Mixing botanical insecticides with currently available insecticides is a feasible way to solve these issues. Therefore, plant oils were prepared from fruits of Zanthoxylum bungeanum Maxim. and Citrus maxima (Burm.) Osbeck (Sapindales: Rutaceae) through hydrodistillation. Fumigation toxicity of self-made Z. bungeanum oil and C. maxima oil, commercial garlic oil, phosphine and their binary mixtures against adults of Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae), Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), and Liposcelis entomophila (Enderlein) (Psocodea: Liposcelididae) was investigated in this study. Although adults of S. zeamais and C. ferrugineus were more sensitive to phosphine than to three plant oils, fumigation toxicity of garlic oil or Z. bungeanum oil against adults of R. dominica, T. castaneum, and L. entomophila was comparable to that of phosphine. The combination of Z. bungeanum oil and phosphine did not show any synergism against adults of five stored product pests. When C. maxima oil and phosphine were mixed at the mass ratios of 255: 1 and 1: 1, respectively, they showed the greatest synergistic toxicity against adults of T. castaneum and L. entomophila. When garlic oil and phosphine were mixed at the mass ratios of 13: 1 and 728: 1, respectively, they showed the greatest synergistic toxicity against adults of R. dominica and S. zeamais. In terms of the advantages of synergism in fumigation toxicity and low application dosages of botanical insecticides, fumigation with binary mixtures of plant oils and phosphine is a promising strategy for stored product pest control and management of phosphine resistance.
