Enhancing the insecticidal efficacy of inert dusts against stored food insect pest by the combined action with essential oils
Abstract: Inert dusts (IDs), as Kaolin (K) and diatomaceous earth (D) powders, and aromatic plant essential oils (EOs) are among the most appealing alternatives to traditional chemical insecticides, against stored-products and field crops pests. IDs and EOs are environmentally friendly and very low toxic to mammalian. In addition, it has been proven that insects are not able to develop resistance to IDs. Recent studies indicate that, when used in combination, aromatic plant EOs may enhance the insecticidal efficacy of IDs. Such effect could be due both to the physical action of IDs on the cuticle and the supposed neurotoxic effects of EOs.The aim of the present study was to evaluate the efficacy of the two aromatic plants Pistacia lentiscus and Foeniculum vulgare EOs, of K and D powders and of the IDs-EOs mix as grain protectants against the maize weevil Sitophilus zeamais (Motschulsky) (Curculionidae). The EOs were tested at 10, 40, 80 and, 100 ppm, IDs at 25, 50 and 100 ppm while the EOs + IDs at 20, 40 and 60 ppm in 330 ml pots containing 150 g of maize grains and 10 unsexed insects. Results were recorded after three, six and nine days of treatment. Orthogonal contrasts analysis shows that the action of IDs was higher when used in combination with the EOs (P < 0.05). These results indicate that the combined use of IDs and EOs could effectively enhance the insecticidal efficacy of IDs reducing the costs of the management of stored grains.