Pollen Gathering

My research in this area is published in the Journal of Hymenoptera Research, "A review and updated classification of pollen gathering behavior in bees (Hymenoptera, Apoidea)" https://doi.org/10.3897/jhr.71.32671

How a bee gathers pollen depends on many factors, including the structure of the host flower, the location of the pollen, and the behavioral and evolutionary limitations of the bee. I am interested in documenting the different types of pollen gathering behaviors and how they evolved. In particular, I am exploring the link between different floral and pollen morphologies and how they affect pollen gathering behavior in different bee species. ​
Active vs. incidental pollen gathering

Active pollen gathering occurs when when pollen is the primary objective or when nectar (or oil) and pollen are co-objectives. Active pollen gathering can be broken down into six types: scraping with the extremities, buzzing, rubbing with the body and/or scopa(e), tapping, rubbing with the face, and rasping. Each type is broken down below. 
Incidental pollen gathering occurs when pollen accumulates on the body, EITHER when a bee nectaring OR performing a primary pollen gathering behavior and pollen accumulates on non-target areas of the body. 

The different types of active pollen gathering behavior:
  • ​Scraping with the extremities: use of the legs or mouthparts to remove pollen directly from anthers, or, less commonly, to glean pollen from flowers. This is the most basic and primitive mode of pollen gathering. The video shows two bees, an Andrena chlorogaster and a Lasioglossum (Dialictus) species, gathering pollen by scraping with the extremities and biting with the mandibles. 




  • Buzzing: use of the flight muscles to vibrate a flower to assist with pollen release. This video shows a Bombus impatiens buzzing in a rig specifically designed to capture the buzzing noise (thanks to Avery Russell for use of the video). Next, a Bombus species is buzzing an open flower, alternating with scraping with the forelegs as it wades over the open flowers. The buzzing is a bit faint in this one, so I added a red bar when it buzzes. Thanks to youtuber sigma1920HD for this video. They have many more cool videos you can see on their youtube page. 
 
  • Rubbing with the body and/or scopa(e): the gathering of pollen through  direct and more or less continuous contact with the anthers by the main trunk of the body (thorax, abdomen) and/or the scopal hairs. This video shows a number of examples of the different types of this behavior. First are Ptilothrix bombiformis rubbing with the abdomen and scopae on Hibiscus. Thanks to Robert Klips for this video. Next is an Andrena species rubbing with the abdomen and scopae on Camissonia. Then a Macropis species rubbing with the venter of the thorax and abdomen on Lysimachia. The original Macropis video can be found at: https://doi.org/10.3203/IWF/Z-7083 and you can also watch the English-language version. Next is a Melissodes on Helianthus, which rubs with the apex of the abdomen. After that is Andrena helianthi, also on Helianthus. Similar to the Melissodes, the Andrena uses the apex of the abdomen to rub against the anthers, though this motion is much slower than the Melissodes. In both cases, the bees occasionally lift up the abdomen and transfer the pollen directly to the hind leg scopae. Finally, there is a Heriades on Monarda, which rubs directly with the abdominal scopa.
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  • Tapping: picking up pollen from anthers by a rapid up and down motion of  the abdominal venter. This video shows an Osmia species tapping with the abdominal scopa on Asteraceae. Tapping is similar to rubbing with the scopa, but differs in that the movement is more rapid and the abdomen is held parallel to the plane of anthers rather than curled over as in rubbing with the scopa. We chose to separate these two behaviors, though previous researchers have lumped them together and future research may demonstrate that they intergrade.

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  • Rubbing with the face: continuous and more or less direct contact with the  anthers by the face. This video was adapted from the excellent paper by Prosi et al. (2016). Rather than only moving the head, rubbing with the face is caused by the entire body jerking up and down which causes movement by the head against the anthers. 



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  • Rasping: rubbing of the thoracic dorsum against anthers, causing the anthers  to vibrate and release the pollen. This rather specialized behaviors occurs on certain species of Penstemon. This video shows as Osmia jerking the whole body in and out of the flower, and then immediately upon exiting the flower, she uses the middle leg to groom the pollen from the thoracic dorsum.





Incidental pollen gathering occurs when pollen accumulates on the body, EITHER when a bee nectaring OR performing a primary pollen gathering behavior and pollen accumulates on non-target areas of the body.  The bee then “decides,” based on pollen and floral characteristics, and on need, to discard or keep the pollen. This is demonstrated in the video where both honey bees are gathering pollen incidentally, but only one of them is currently packing the pollen into the pollen-transporting structures. 



Temporarily accumulating pollen is a behavior that doesn't fit into the active/incidental dichotomy, but it is an important and under-appreciated behavior performed by many different bees. Temporarily accumulating pollen is a two-step process that first involves the accumulation of a large amount of pollen on a specialized hair patch (as opposed to generalized body hairs). Then after a sufficient quantity of pollen has accumulated on the specialized hair patch, it is transferred to the pollen-transporting structures. This behavior is most well-documented in panurgine bees, but it has also been observed in many other groups such as Trigona and various Melittidae. 
There are two videos to demonstrate this behavior. The first video shows panurgine bees, led off Perdita sphaeralceae. Note how the bee first uses the forelegs to gather pollen  onto the venter of the thorax, then it rears back and transfers the pollen to the hind legs. This same behavior is shown for other bees on various flowers, including Perdita minima, Perdita multiflorae, Macrotera mortuaria, and Calliopsis subalpina.

The next video shows two melittid bees temporarily accumulating pollen. First is Macropis, which initially gathers pollen by rubbing with the venter of the thorax and abdomen, and then transfers the accumulated pollen in flight.  Next is Hesperapis on Eucnides, which initially accumulated pollen onto a specialized patch of hairs on the venter of the head, and then it flops onto its back and transfers the pollen to the scopa.