Population genetic structure of Tribolium castaneum (Coleoptera: Tenebrionidae) populations in Malaysia

Tribolium castaneum (Herbst, 1979) (Coleoptera: Tenebrionidae), commonly known as the red flour beetle, is one of the most destructive pests of stored grain products worldwide. This study aimed to identify T. castaneum populations collected from Sabah, Penang, and Selangor using both morphological and molecular approaches and to assess their genetic structure and diversity. Morphological identification confirmed all specimens as T. castaneum. Molecular analysis using mitochondrial COX1 and 16S rRNA genes further verified species identity, with all samples showing 98% to 100% similarity to reference sequences in GenBank. Phylogenetic analysis revealed minor regional variation, with Penang and Selangor populations forming a distinct clade, suggesting greater genetic relatedness between these 2 Peninsular Malaysia populations than between them and Sabah. Microsatellite analyses indicated moderate genetic differentiation among populations (FSt = 0.162), accompanied by high within-population variation (FIs = 0.737). Complementary measures of genetic differentiation based on Jost's D and DEST (G'ST) revealed substantial allelic differentiation among populations (global Jost's D = 0.709; global DEST = 0.766), consistent with pronounced population structuring. Principal Coordinates Analysis (PCoA) and Bayesian clustering analysis (STRUCTURE, K = 5) further supported moderate substructuring and admixture among regions, suggesting ongoing gene flow. Overall, T. castaneum populations in Malaysia are genetically structured yet interconnected, likely influenced by trade and transportation activities. These findings provide baseline data on the dispersal dynamics of red flour beetles in Malaysia.