Comparative repellent activity of single, binary and ternary combinations of plant essential oils and their major components against Sitophilus oryzae L. (Coleoptera: Curculionidae)

In the present study, repellent activity of three plant essential oils (EOs) [anise (Pimpinella anisum L.), eucalyptus (Eucalyptus camaldulensis Dehn.) and peppermint (Mentha piperita L.)] and their major components (trans-anethole, 1,8-cineole and L-menthol, respectively) was evaluated at five concentrations (3.6, 7.1, 14.3, 28.6 and 57.1 µl/l air) through Y-tube olfactometer against the rice weevil, Sitophilus oryzae L. (Coleoptera: Curculionidae), under laboratory conditions. The binary (1:1) and ternary (1:1:1) combinations of the EOs and/or components were also evaluated for their possible combination effects (synergism, antagonism and additive effect). The results showed that all the EOs and components tested, both alone and in binary and ternary combinations, had a repellent activity on adult S. oryzae. However, repellency was concentration dependent (P = 0.05). None of the combinations tested had a statistically significant influence on the repellence against adult S. oryzae (P = 0.05). Based on the estimated RC50 (the concentration required to obtain 50% repellency) values, binary and ternary combinations generally had lower RC50 values, indicating that they were more repellent to S. oryzae than the single application of EOs or components, except for anise EO and 1,8-cineole. Considering the combination index (CI) values, most of the binary and ternary combinations showed synergistic effects (CI   1). Overall results suggest that EOs and their components may help prevent the rice weevil infestations and can be used to develop new products that meet expectations.