Labellar Structure of the Maxillaria splendens Alliance (Orchidaceae: Maxillariinae) Indicates Floral Polyphenols as a Reward for Stingless Bees

Several studies have reported stingless Meliponini bees gathering hairs from the labella of Maxillaria spp., including M. ochroleuca, a member of the M. splendens alliance. Such hairs usually contain food materials and are thought to have nutritional value. The papillose labella of representatives of the Maxillaria splendens alliance, however, bear scattered, simple 1-5-celled uniseriate trichomes (hairs) that lack food materials. By contrast, here, as well as polyphenolic compounds, typical labellar papillae usually contain small quantities of starch, protein, and minute droplets of lipid, the last probably involved in the production of fragrance. Towards the labellum apex occur elevated groups of papillae that lack food materials, but contain volatile compounds, probably fragrance precursors. In the past, the terms 'trichomes' or 'hairs' and 'papillae' have been used interchangeably, causing some confusion. Since the trichomes, however, unlike the papillae, are easily detachable and can fragment, it is most likely they, not the papillae, that have previously been observed being collected by bees, but their poor food content indicates that they do not function as food-hairs. Even so, our field observations of M. ochroleuca reveal that stingless bees scrape polyphenol-rich labellar tissue and possibly use this material to produce a resinous, complex, heterogeneous substance commonly referred to as 'bee glue', used for nest construction and repair.

Automated summary

Several studies have shown that stingless bees collect hairs from the labella of Maxillaria spp., which are believed to have nutritional value. However, the labella of Maxillaria splendens alliance actually contain trichomes that lack food materials. These trichomes can be easily detached and do not function as food-hairs. Field observations of M. ochroleuca suggest that stingless bees scrape polyphenol-rich labellar tissue and use it to produce "bee glue" for nest construction and repair.