Combination of biorationals against stored grain insect pests

The increasing demand for eco-friendly and safe pest management strategies has encouraged the exploration of plant-derived bioactive compounds as alternatives to synthetic pesticides. This study focuses on the evaluation of insecticidal and repellent properties of eugenol, cinnamaldehyde, and their binary combination (1:1) against major stored grain pests, Tribolium castaneum and Rhyzopertha dominica. These compounds are known for their bioactivity and potential use in sustainable pest control. The test compounds were analysed using Gas Chromatography–Mass Spectrometry (GC–MS) to confirm their chemical composition and purity. Bioassays, including fumigation, contact toxicity, and repellency tests, were conducted at different concentrations and exposure periods to assess their efficacy. The results showed that both eugenol and cinnamaldehyde were effective in controlling the insects, but cinnamaldehyde acted faster and was more potent, causing about 90–100% mortality and 75–100% repellency. In comparison, eugenol showed a slightly lower effect, with around 60–85% mortality and 70–85% repellency, depending on the concentration and exposure time. The biochemical mode of action was evaluated through acetylcholinesterase (AChE) inhibition assays, which indicated a concentration-dependent inhibitory effect of the compounds, suggesting their neurotoxic action on insects. Residual analysis of treated insects was performed using GC–MS; however, only trace levels of the compounds were detected, likely due to low sample quantity and rapid degradation of the test compounds. The efficacy of the binary combination was further analysed using expected mortality calculations and chi-square analysis. The results indicated varying interaction effects, including additive and antagonistic responses depending on the insect species, exposure method, and duration.
Overall, the findings of this study highlight the potential of eugenol, cinnamaldehyde, and their combination as effective and environmentally safe alternatives for the management of stored grain insect pests. This approach contributes to the development of sustainable pest control strategies with reduced reliance on synthetic chemicals.