Does body size predict the buzz‐pollination frequencies used by bees?

Abstract

Body size is an important trait linking pollinators and plants. Morphological matching between pollinators and plants is thought to reinforce pollinator fidelity, as the correct fit ensures that both parties benefit from the interaction. We investigated the influence of body size in a specialized pollination system (buzz‐pollination) where bees vibrate flowers to release pollen concealed within poricidal stamens. Specifically, we explored how body size influences the frequency of buzz‐pollination vibrations. Body size is expected to affect frequency as a result of the physical constraints it places on the indirect flight muscles that control the production of floral vibrations. Larger insects beat their wings less rapidly than smaller‐bodied insects when flying, but whether similar scaling relationships exist with floral vibrations has not been widely explored. This is important because the amount of pollen ejected is determined by the frequency of the vibration and the displacement of a bee's thorax. We conducted a field study in three ecogeographic regions (alpine, desert, grassland) and recorded flight and floral vibrations from freely foraging bees from 27 species across four families. We found that floral vibration frequencies were significantly higher than flight frequencies, but never exceeded 400 Hz. Also, only flight frequencies were negatively correlated with body size. As a bee's size increased, its buzz ratio (floral frequency/flight frequency) increased such that only the largest bees were capable of generating floral vibration frequencies that exceeded double that of their flight vibrations. These results indicate size affects the capacity of bees to raise floral vibration frequencies substantially above flight frequencies. This may put smaller bees at a competitive disadvantage because even at the maximum floral vibration frequency of 400 Hz, their inability to achieve comparable thoracic displacements as larger bees would result in generating vibrations with lower amplitudes, and thus less total pollen ejected for the same foraging effort.

Efficiency of using electric toothbrush as an alternative to a tuning fork for artificial buzz pollination is independent of instrument buzzing frequency

“…Our results also showed no differences in pollen amount extracted among different frequency levels. This was somewhat surprising because, recently, it has been found that larger bees that generate high floral vibration frequencies extract more pollen when compared to small bees in a given foraging effort [11], also suggesting that there may be additional effects of pollinator-specific buzzing that affect pollen removal [1].…”

“…Unlike other insect pollinators (e.g., Lepidoptera), buzz pollinators produce floral vibrations using their thoracic muscles and use their other body parts including mandibles, head and abdomen to release the pollen from these anthers [1,[5][6][7][8][9], an ability confined to a few insect genera. Although studies on ecology and evolutionary biology of buzz pollination have been carried out for more than a century [10], the biomechanics, pollinator physiology and behavior in relation to buzzing have only recently gained an increased interest [1,11,12].…”

Pollen dispensing schedules in buzz-pollinated plants: Experimental comparison of species with contrasting floral morphologies

“…However, some bee taxa might be able to adjust their vibration velocities or duration (Harder & Barclay, 1994;Morgan et al, 2016;Russell et al, 2016), resulting in increased pollen extraction at a higher energy cost to the insect. Field observations of the large flowered S. rostratum have shown that small buzzing bees frequently visit flowers (Solís-Montero et al, 2015), but larger taxa that produce higher velocity vibrations (De Luca et al, 2019), such as Bombus and Xylocopa, are common visitors (Whalen, 1978), as well as efficient pollinators (Solís-Montero & Vallejo-Marín, 2017).…”

“…Similarly, the vibration properties of bees vary across and within species (King & Buchmann, 2003;Arceo-Gómez et al, 2011;Corbet & Huang, 2014;Arroyo-Correa et al, 2019;De Luca et al, 2019;Pritchard & Vallejo-Marín, 2020), and previous empirical work demonstrates that vibration properties, particularly their amplitude, affect pollen release (Harder & Barclay, 1994;King & Buchmann, 1996;. However, we know relatively little about how plant species with different anther and floral morphologies vary in their pollen release schedules (but see Harder & Barclay 1994, Dellinger et al 2019, including their response to vibrations of different amplitudes.…”

Valuing biodiversity and resilience: an application to pollinator diversity in the Stockholm region

“…In order to quantify the differences in pollination potential, we assume that body size can be used as an indicator for pollination efficiency, thereby assuming that the larger pollinator species, B. terrestris (bumble bee), is a more effective pollinator due to its larger body size. This assumption is based on the reasoning that the ability of these types of pollinators to 'buzz pollinate', that is, to shake loose additional pollen by vibrating their wings, should become more effective with increasing body size (De Luca et al, 2019). It therefore follows, based on an average body size of 11-17 mm of a B. terrestris worker and an average body size of 8-10 mm of a male O. bicornis, that B. terrestris is, roughly, doubly as effective.…”