Are Stingless Bees a Broadly Polylectic Group? An Empirical Study of the Adjustments Required for an Improved Assessment of Pollen Diet in Bees

Abstract

This research describes simple calculations for pollen diet studies to improve the understanding of bee natural history. The stingless bees (tribe Meliponini) have been classified as broadly polylectic as they utilize more than 10% of the pollen host species of the entire melittophilous flora at a site or more than 25% of the available plant families. However, when considering pollen types, it was not possible to classify three bee species in this manner. For this reason, different calculation adjustments on foraged and available items were applied. For the former, two threshold values (10% and 5%), to identify abundant and discard minor and contaminant pollen resources, were used. For each threshold value, the number of pollen types and the number of pollen species ascribed to each pollen type were calculated. For the available items, spatial and temporal adjustments were estimated. When these adjustments were applied, in some cases bees were identified at higher specialization categories; broad polylectic was recorded only in six cases for Melipona orbignyi and Tetragonisca fiebrigi. As previously suggested for the other categories, contaminant and minor pollen types should also be excluded in polylectic bees. The threshold values of 10% for species and 25% for families are too high to reach broad polylecty. In addition, no direct comparisons between pollen types and pollen species could be made when working with the palynological data. Thus, simple values were proposed to assess pollen diet of generalist bees: the maximum number of foraged items per nest (contaminants not considered) and the maximum percentage value of foraged versus available items (adjusted). These belong to a wider range of values that can be recognized as degrees of polylecty, allowing for a more precise identification.