Optimization of the insecticidal response of combined essential oils from Satureja alpina, Rosmarinus officinalis and Ammodaucus leucotrichus using a designed mixtures approach

The main objective of the present study is to investigate the fumigant toxicity of EOs extracted from Satureja alpina (L.) Scheele (Lamiaceae), Rosmarinus officinalis (L.) (Lamiaceae) and Ammodaucus leucotrichus(Coss. & Durieu) (Apiaceae) and to predict specific EO mixtures that provide optimal insecticidal activities against two common secondary insect pests, namely Stegobium paniceum (L.) (Coleoptera: Anobiidae) and Tribolium confusum du Val (Coleoptera: Tenebrionidae). GC/MS analysis showed that A. leucotrichus EO was characterized by the abundance of L-perillaldehyde and D-limonene, while the main constituents of R. officinalis EO were 1.8-cineole, camphor, and α-pinene. S. alpina EO was mainly composed of pulegone. Concerning the insecticidal activity, the results showed that all EOs tested individually exerted high efficacy, with LC50 from 3.4 to 6.6 µL/L air for S. paniceum, and from 25.3 to 41.9 µL/L air for T. confusum. The various combinations of these EOs were generally found to possess greater activity than when used individually, and synergistic interactions were recorded. The optimal mixtures predicted were 48% S. alpina, 31% R. officinalis and 21% A. leucotrichus EOs, corresponding to LC50 of 1.47 µL/L air; and 57% A. leucotrichus and 43% S. alpina EOs corresponding to LC50 of 8.26 µL/L air, for S.paniceum and T. confusum, respectively. Our findings showed that the use of these optimized EO combinations from the tested plants could be a promising insecticidal alternative to reduce the use of harmful synthetic insecticides.