The synergistic effects of five essential oils and eight chiral compounds on deltamethrin-piperonyl butoxide insecticide against Sitophilus zeamais (Coleoptera: Curculionidae)

Abstract

Sitophilus zeamais is a major cause of damage to corn and its preventive control is performed with Deltamethrin-Piperonyl Butoxide (deltamethrin-PBO). However, due to the intensive use of conventional insecticides, the population of S. zeamais has developed resistance to nearly all classes of insecticides. In order to establish new control practices through the reduction of the use of conventional insecticides for management of S. zeamais, the present study was to evaluate the insecticidal activities and synergistic interaction between five essential oils, as well as six chiral constituents with deltamethrin-PBO used in the preventive control of S. zeamais. The chemical analysis revealed a high percentage of monoterpenes in the oils investigated. Limonene was the major component found in the oils from Citrus aurantifolia and C. reticulata. Citronellal, terpinen-4-ol and menthol were the major constituents in the oils from Eucalyptus citriodora, Melaleuca alternifolia and Mentha piperita, respectively. Oil from M. alternifolia exhibited greater toxicity. Among chiral constituents, (R)-(+)-Limonene, (1R,5R)-(+)-α-pinene and (1S,5S)-(-)-α-pinene were the most toxic against the pest. Binary mixtures prepared with synthetic insecticide and oils exhibited two synergistic interactions. Mixtures prepared with deltamethrin-PBO and (R)-(+)-limonene showed one synergistic interaction. These results are promising, particularly the Citrus oils and its main constituent, (R)-(+)-limonene, which increased the mortality of S. zeamais by 56.41; 43.58 and 35.89 %, respectively. The present findings suggest that the impacts on the environment and human health with the indiscriminate use of deltamethrin-PBO can be minimized with the preparation of a formulation of this insecticide combined with Citrus oils.