Unveiling the chemical and behavioural ecology of Tribolium castaneum (Herbst, 1797) in wheat flour: Alterations in flour metabolic content and the role of chemical cues in modulating beetles' behaviour and regulating population growth.

Tribolium castaneum (Herbst, 1797) (Coleoptera: Tenebrionidae) is a notorious secondary pest of stored grains and flours, accounting for 10-15% of global annual losses in stored products. This study first evaluated the impact of T. castaneum infestation on the nutritional parameters of stored wheat flour. Infested flour exhibited reductions in total soluble sugars, triacylglycerol levels, and unsaturated fatty acids, particularly Oleic and Linoleic acid, while secondary metabolites such as phenolics, flavonoids, and tannins were increased. Behavioural assays revealed that adult beetles were significantly more attracted towards infested flour odour due to the presence of 4,8-Dimethyldecanal (4,8-DMD), an aggregation pheromone of T. castaneum. Another key compound in infested flour, 1-Pentadecene, derived from the beetles cuticular wax, was found to influence adult beetle behaviour. At higher concentrations, 1-Pentadecene acted as a repellent for the species. Molecular docking studies suggested that 1-Pentadecene competes with 4,8-DMD for binding to the odorant receptor TcOR1, which could potentially inhibit aggregation behaviour and reduce population growth. The docking analysis revealed that 1-Pentadecene interacts with the same binding pocket on TcOR1, sharing key amino acids (MET49, PHE69, THR72, GLN73, THR134, VAL135, TYR138, LEU154, ILE177, GLY180, ALA181, TYR286) and forming similar intermolecular bonds, such as a pi-alkyl bond, with a binding affinity ({Delta}G = -5.7) comparable to 4,8-DMD ({Delta}G = -5.8). Additionally, beetles reared in wheat flour containing higher concentrations of 1-Pentadecene exhibited lower population growth compared to those reared in flour with lower concentrations of this compound.