Polarized short odor-trail recruitment communication by a stingless bee, Trigona spinipes

Polarized odor-trail communication, in which a receiver can orient towards the correct endpoint from within the trail, is documented in relatively few animals and is poorly understood, although such directionality could significantly enhance resource localization. Among animals, stingless bees exhibit the unique behavior of depositing long substrate-borne odor trails that assist the orientation of flying nestmates to a specific three-dimensional food location. However, relatively little is known about the spatial structure of such odor trails, particularly vertical trails, and whether these trails are polarized to indicate the correct terminus. We show that a stingless bee, Trigona spinipes, can rapidly recruit nestmates in large bursts to a food source at a specific distance, direction, and height. In conjunction with a major recruitment burst, foragers deposited odor marks that attracted nestmates for up to 20 min. Surprisingly, these odor marks formed a short odor trail instead of a complete odor trail extending from the feeder to the nest (the classic description of a meliponine odor trail). The length of the odor trails varied between different feeder locations with different colonies, from a minimum of 3 m to a maximum of 29 m. The odor marks formed a polarized trail that newcomers followed to the end with the most concentrated odor marks (the feeder), even when the entire odor trail was rotated 180° and clean test feeders were set out at locations that foragers had never previously fed at. Thus locale odor or the potential communication of food location inside the nest do not account for the ability of newcomers to find the correct terminus. This result provides the first strong evidence for odor-trail polarization in social insects.