Preprint: Sweet signals: Using floral traits to predict nectar sugar availability

Floral nectar is a crucial energy source for many insects, yet its availability is rarely quantified at broad taxonomic and geographic scales. Mosquitoes are opportunistic nectar feeders whose survival and vectorial capacity depend on access to sugar resources, but the extent to which nectar sugar availability can be predicted from floral morphology across floras remains poorly understood.

We analysed relationships between corolla morphology and nectar traits in 156 flowering plant species from the UK and Zambia. Corolla length, base width and floral shape were measured alongside nectar volume and sugar concentration. Linear and linear mixed-effects models were used to assess predictive relationships in tubular and non-tubular flowers, and phylogenetic statistics (Blomberg’s K and Pagel’s λ) were applied to test for evolutionary signal.

Nectar volume and sugar content increased with tube length and width in tubular flowers, while corolla width and shape were strong predictors in non-tubular flowers. Phylogenetic analyses across 154 species (42 families) indicated weak phylogenetic signal in nectar volume.

Simple floral traits provide proxies for nectar sugar availability across lineages. Shape-specific scaling relationships suggest convergent responses to ecological and morphological constraints, offering a practical framework for predicting nectar resources and linking floral diversity to mosquito and pollinator ecology.