An alternative to reduce the use of the synthetic insecticide against the maize weevil Sitophilus zeamais through the synergistic action of Pimenta racemosa and Citrus sinensis essential oils with chlorpyrifos

Abstract

Sitophilus zeamais attacks stored corn kernels and is traditionally controlled using synthetic pesticides. However, the frequent use of these toxic compounds leads to environmental and health damage and to the development of resistant insect populations. Essential oils (EOs) represent an alternative to conventional pesticides for pest control. The objective of the present study was to evaluate the effect of the combination of EOs with chlorpyrifos against S. zeamais in order to reduce the effective applied dose of the synthetic insecticide. The most active EOs against S. zeamais were Rosmarinus officinalis, Pimenta racemosa var. ozua and Citrus sinensis. Moreover, all the binary mixtures (1:1 volume EO:volume EO) of these EOs (P. racemosa-R. officinalis, P. racemosa-C. sinensis and R. officinalis-C. sinensis) showed a higher fumigant activity and repellency than the individual EOs, with the combinatory index (CI) values of these binary mixtures indicating synergism for fumigant activity. The P. racemosa-C. sinensis-chlorpyrifos (16:1 volume of binary mixtures of EOs:volume of chlorpyrifos) combination had a lower LC95 value compared to the respective binary mixtures of EOs, revealing a synergistic effect. In addition, this combination did not produce phytotoxicity on maize grains. The binary mixture P. racemosa-C. sinensis in combination with chlorpyrifos synergized the effect of the synthetic pesticide without affecting germination of the maize grains. In addition, the use of this mixture (P. racemosa-C. sinensis-chlorpyrifos) decreased the net quantity of the synthetic insecticide, thus making it an interesting alternative for the control of the maize weevil S. zeamais.