Dimorphic Pollen of Heterostylous Waltheria indica Identified in Honey Bee Pollen Loads: Implications for Pollination Ecology

During an analysis of the pollen load composition in the Apis cerana Fabr. honey bee colonies maintained in the Pondicherry region of southern India, an unidentified and taxonomically unresolved pollen morphotype was repeatedly recorded. Subsequent field observations, corroborated by light microscopic pollen studies, revealed that this morphotype corresponded to Waltheria indica L. (Malvaceae), a heterostylous shrub or subshrub that produces distinct long- and short-styled floral morphs associated with pollen dimorphism. Archived bee pollen slides were re-examined and compared with reference pollen collected from both floral morphs of W. indica using light microscopy (LM). The two pollen morphotypes differed considerably in size, shape and exine ornamentation: long-styled (pin) flowers produced smaller, reticulate pollen grains, whereas the short-styled (thrum) flowers yielded larger, microechinate grains. Pollen recovered from bee loads corresponded primarily to the larger morphotype from the thrum flowers. Field observations confirmed that A. cerana foraged on both floral morphs, supporting the potential for intermorph pollen transfer. This study demonstrates that heterostyly-associated pollen dimorphism can influence pollen spectra obtained from bee foraging studies, underlining the need to consider floral polymorphism for accurate palynological identification and pollination interpretations.