Variation in the Morphological Characters of the Hill and Plain Populations of Indian Honey Bee, Apis cerana indica (Fab.) in Tamil Nadu, India

The present study investigates the morphological differences between the hill and plain populations of the Indian honey bee, Apis cerana indica Fabricius, collected from six different locations in Tamil Nadu, India: Coimbatore, Karumandhurai, Coonoor, Madurai, Dindigul, and Chidambaram during 2023-2024. Significant differences were found between the two populations based on a comprehensive morphometric analysis of 29 characters. The hill populations from TNAU Insectary (Marudhamalai hills), Karumandhurai (Kalvarayan hills), and Coonoor (Nilgiri hills), the mean altitude of the locations being 1207 m a.s.l. exhibited significantly higher values in several morphometric traits than the plain populations from Madurai, Dindigul, and Chidambaram, with a mean altitude of 124 m above MSL (P<0.05). Component loading analysis highlighted the key morphometric characters contributing to the first and second components of both ecotypes. In the plain population, breadth of the radial cell, breadth of the forewing, and length of the radial cell demonstrated strong positive correlations with the first principal component, explaining 16.4% of the variance. The second principal component, influenced by characters such as the length of the femur and breadth of the metatarsus, showed 12.2% of the variance. In the hill population, the length of the radial cell, length of vein R.L., and length of the hindwing were the most influential traits for the first principal component, explaining 28.0% of the variance. In contrast, the second component, which included the breadth of the forewing and length of vein I.L., explained 12.3% of the variance. Further, the cubital index, a critical morphometric parameter, also showed a statistically significant difference, with the hill population (3.55) showing a higher value than the plain population (3.29). The significant morphometric differences observed between the hill and plain populations of A. cerana indica may suggest that they have undergone morphological divergence, likely due to adaptations to their specific environmental conditions.