Improving allometric models to estimate the proboscis length of tropical bees

The proboscis length of bees is a key morphological trait shaping communities and interaction networks. Despite its importance, it is rarely considered in ecological studies because of logistical limitations in obtaining accurate measurements. Although two studies have provided allometric models to estimate the proboscis length of temperate bee species based on body size, tropical bee taxa are likely to deviate from existing allometric models owing to different functional constraints. Thus, we sought to test and improve existing allometric equations to predict the proboscis length in three dominant tribes of tropical bees, using a database of proboscis length and intertegular distance measurements from 105 species collected from the field. We found that the previous model lacked accuracy when applied to tropical bees, particularly the tribes Meliponini and Euglossini. We developed new allometric equations estimating the proboscis length based on the intertegular distance, using (sub-)genera as an additional predictive variable to refine the estimations, resulting in high accuracy of estimates. Our results shed additional light on the nature of the proboscis length–body size allometric relationship in tropical bees and provide a tool for future studies on the functional ecology of bees and their interactions with plants.