Synergistic combinations of essential oils and their major constituents against Tribolium species: A systematic review

Stored product insects represent a major threat to food security by causing significant postharvest losses. Tribolium species are among the most destructive pests affecting stored grains and processed food commodities worldwide. To control these pests, synthetic pesticides are widely used. However, the overreliance on those chemicals has raised major concerns associated with health risks and the development of insect resistance. Hence, to reduce reliance on these chemicals, plant-derived biopesticides, particularly essential oils (EOs) and their constituents (EOCs), have shown promising potential as eco-friendly alternatives. Adopting a PRISMA-based approach, this systematic review aims to summarize the insecticidal and behavioral effects of EOs and EOCs mixtures, to identify potential interactions and key research gaps. In this context, out of the 25 studies included, only 15 used a validated quantitative interaction model, with Wadley’s being the most used statistical model (in 7 studies). The articles included covered both insecticidal (ingestion, contact, and fumigation) and behavioral effects (repellency and antifeedant) of EOs and EOCs mixtures against larvae and adults of Tribolium species, with a major focus on Tribolium castaneum (Herbst, 1797) (Coleoptera: Tenebrionidae). The effectiveness of these combinations depended on the insect species, age, developmental stage, exposure duration, and mixture ratio. The findings revealed that numerous combinations displayed a distinct synergistic effect, leading to significant improvement in various bioactivities. This was illustrated in various insecticidal bioassays. Not only that, but other studies also reported additive and antagonistic interactions, underscoring the impact of the ratio on the type of interaction observed. This study highlights the ongoing effort to better understand synergistic interactions in order to develop stable and effective mixtures for the control of Tribolium species. Future research should therefore focus on the development and optimization of formulations based on these active combinations to enhance their stability, sustainability, and practical applicability under real storage conditions.