Honey bee hairs and pollenkitt are essential for pollen capture and removal

Abstract

While insect grooming has been observed and documented for over one hundred years, we present the first quantitative analysis of this highly dynamic process. Pollinating insects, like honey bees, purposely cover themselves with millions of pollen particles that, if left ungroomed, would make sensing and controlled flight difficult. How do they get clean? We show that the hairs on insect eyes are tuned to the pollen they collect; namely, the hairs are spaced so that they suspend pollen above the body for easy removal by the forelegs. In turn, hair spacing on the foreleg dictates the leg's ability to store the pollen removed during each swipe. In tests with wax-covered honey bees, we show that hairy forelegs are necessary for pollen removal. Moreover, the viscous fluid found on the surface of pollen grains, or pollenkitt, greatly enhances adhesion. We find that bees accumulate twice as much pollen if pollenkitt is present. This study may help further understand pollination, as well as inform designs for mechanically-sensitive functional surfaces with micro- and nano-structures that are easier to keep clean.

A novel method to measure hairiness in bees and other insect pollinators

“…Some studies have found a negative relationship between bee hair length and ambient temperature (Peat, Darvill, Ellis, & Goulson, 2005;Peters, Peisker, Steffan-Dewenter, & Hoiss, 2016), suggesting that hairiness acts as a response trait to climate. Hairiness can also be considered an effect trait involved in pollen collection and transfer (Amador et al, 2017;Müller, 1995;Thorp, 2000), potentially affecting pollination effectiveness (Phillips, Williams, Osborne, & Shaw, 2018;Stavert et al, 2016;Woodcock et al, 2019). Hairiness may also be involved in antipredator strategies.…”

Sexual and natural selection on pollen morphology in Taraxacum

“…Size‐dependent movement of pollen by muscoids varies among host taxa; Kearns () found flies less effective at picking up large (~55.9 μm) pollen grains of Linum lewisi than smaller pollen grains of neighboring species. Kearns () posited that in flies, size‐dependent variation in pollen transfer efficiency could reflect the fit between spacing of the bristles and size of the grains (see also Thorp, ; Amador et al., ). Since larger pollen grains typically contain more nutrients than smaller grains (Simpson and Neff, ), the tendency of flies to pick up larger grains in the 20–30 μm diameter range of Taraxacum may increase nutritional rewards while satisfying the fit to bristle spacing.…”

“…Several features of pollen grains may mediate such advantages. For example, pollenkitt, the sticky lipid‐based compound that facilitates pollen clumping, is associated with animal pollination, aiding adherence of pollen to pollinators (Pacini and Hesse, ; Lin et al., ; Amador et al., ). Similarly, echinate (spiny) pollen has high prevalence in lineages dependent on insects for pollination, while closely related wind‐ or water‐pollinated species have relatively smooth sculpturing (Tanaka et al., ).…”

“…However, pollen size is a complex trait that varies with resources for provisioning, style length, and pollinator identity (Ganders, ; Cruden and Lyon, ). Regardless, pollen size may dictate the fit of the pollen grain between hairs of an insect pollinator or alter the amount of surface area contacting the hairs (Thorp, ; Kearns, ; Amador et al., ). Here we consider selection on quantitative variation in pollen traits within a hybrid zone of insect‐pollinated Taraxacum ceratophorum and its close congener, the apomictic T. officinale .…”

A ballistic pollen dispersal strategy hidden in stylar oscillation

“…Some animals, such as insects and elks, clean themselves by vibrating their hairs to remove accumulated particles 24,25 . In such systems, natural frequency governs particle detachment:…”