Potential of three selected plant essential oils and their synergistic combinations in management of Tribolium confusum on wheat grains

Tribolium confusum (Duval) is one of the most common destructive pests of stored products, resistant to a wide range of insecticides. The present study aims to evaluate the insecticidal activities of essential oil (EOs) from three medicinal plants namely, Satureja calamintha (L.), Mentha piperita (L.) and Chenopodium ambrosioides (L.), and their combinations against T. confusum. Chemical analysis of EOs investigated by gas chromatography-mass spectrometry (GC/MS) revealed that the main constituents in S. calamintha EO were pulegone (36.8%), menthone (31%) and menthol (19.8%). Menthofuran (23.73%) and 1,8-cineole (20.23%) were the main compounds of M. piperita EO, while the EO of C. ambrosioides was characterized by the abundance of ascaridole (36.67%), p-cymene (34.32%), and isoascaridole (22.8%). The insecticidal activity of the three EOs and their combinations were evaluated by contact toxicity and repellent efficacy against T. confusum. Generally, ternary and binary combinations showed promising toxicity compared to individual EOs with LC50 = 0.022 μL/cm2 and LC50 = 0.057–0.078 μL/cm2, respectively. Considering the combination index (CI) and dose-reduction index (DRI) values, studied combinations showed synergistic and additive effects with favorable dose reductions. Interestingly, a high synergistic effectiveness was recorded for the ternary combination, with a CI value of 0.4. Moreover, both individual and combined EOs showed repellent effects against tested insect pest with an average repellency rate varying between 28.8% and 72%. The nanoemulsified ternary EO combination used at 1000 ppm, achieved the highest mortality (100%) of T. confusum adults whiting 4-day exposure in treated wheat grains, compared to the free form (68%). The nanoemulsion exerted high efficacy without significantly affecting the wheat germination. these findings highlight the potential of ternary EO combination and its nanoemulsion for developing environmentally-friendly insecticide to be used in the management of T. confusum in real-world conditions. [Display omitted] •Individual EOs showed high toxicity and repellent effect against T. confusum adults.•The EO combinations generated synergistic and additive insecticidal effects.•The EO ternary combination showed the highest toxicity and repellent effects.•Nanoemulsion of the ternary combination produced 100% pest mortality in wheat grains.•The nanoemulsion did not affect the germination of the treated wheat grains.