Variation of Apis cerana populations in the breeding area Phayao province (Thailand) based on forewing geometric morphometrics and mitochondrial DNA

The Asian honey bee (Apis cerana) is widely distributed in Thailand, where populations are structured across the Isthmus of Kra into northern and southern lineages. In 2018, a breeding project in Phayao Province was initiated to develop hybrid colonies between these populations, enabling assessment of morphological and genetic variation. Geometric morphometric analysis of 527 forewings using 19 vein junction landmarks revealed three venation patterns: regular (49.72%), irregular additive venation at the distal Rs of the marginal cell (46.11%), and disorder at the 2rs-m crossvein (4.17%). The highest variance occurred at landmark 15, confirming its diagnostic value for population differentiation. Discrimination functions and relative warp analysis achieved over 73% classification accuracy, with hybrid colonies showing overlap between northern and southern populations. Mitochondrial DNA markers (COI and intergenic COI-COII regions) further supported phylogeographic structuring, with northern haplotypes clustering with mainland lineages and southern haplotypes aligning with Sundaland lineages. Analysis of 27 sequences across 1,066 positions revealed high genetic diversity (π = 0.026; Hd = 0.986; H = 23), comparable to other Asian A. cerana populations. Phylogenetic trees and haplotype networks confirmed distinct northern and southern lineages, while hybrid colonies in Phayao acted as genetic bridges, connecting haplotypes from both regions. This connectivity enhances adaptability and resilience, traits critical for colony survival under environmental change. Together, morphometric and molecular approaches highlight the importance of conserving regional genetic diversity while leveraging hybridization to strengthen breeding strategies, biosecurity management, and the long-term sustainability of A. cerana in Thailand.