A team of scientists from Oregon State University and the University of Minnesota, Saint Paul, has learned that blue fluorescent light in the 430- to 480-nm range set wild bees abuzz.
Fluorescent light is what’s seen when a fluorescent substance absorbs ultraviolet (UV) rays or some other type of lower-wavelength radiation and then immediately emits it as higher-wavelength visible light.
Like humans, bees have trichromatic vision: they have three types of photoreceptors in their eyes.
Both people and bees have blue and green receptors, but the third type for people is red while the third kind for bees is UV.
Flowers’ vibrant colors and patterns — some of them detectable only with UV sight — are a way of helping pollinators like bees find nectar, a sugar-rich fluid produced by plants.
Bees get energy from nectar and protein from pollen, and in the process of seeking food they transfer pollen from a flower’s male anther to its female stigma.
Building on their earlier research, Dr. Oksana Ostroverkhova, a researcher in the Department of Physics at Oregon State University, and colleagues set out to determine if green fluorescence, like blue, was attractive to bees.
They also wanted to learn whether all wavelengths of blue fluorescence were equally attractive, or if the drawing power tended toward the green or violet edge of the blue range.
In field conditions that provided the opportunity to use wild bees of a variety of species, the team designed a collection of bee traps (non-fluorescent and fluorescent via sunlight).
Under varying conditions with a diverse set of landscape background colors, blue fluorescent traps proved the most popular by a landslide.
The scientists examined responses to traps designed to selectively stimulate either the blue or the green photoreceptor using sunlight-induced fluorescence with wavelengths of 420 to 480 nm and 510 to 540 nm, respectively.
They found out that selective excitation of the green photoreceptor type was not attractive, in contrast to that of the blue.
“And when we selectively highlighted the blue photoreceptor type, we learned the bees preferred blue fluorescence in the 430- to 480-nm range over that in the 400-420-nm region,” Dr. Ostroverkhova said.
The findings, published in the Journal of Comparative Physiology A, are a powerful tool for assessing and manipulating bee populations — such as, for example, if farmers needed to attract large numbers of bees for a couple of weeks to get their crop pollinated.
Oksana Ostroverkhova et al. Understanding innate preferences of wild bee species: responses to wavelength-dependent selective excitation of blue and green photoreceptor types. Journal of Comparative Physiology A, published online June 5, 2018; doi: 10.1007/s00359-018-1269-x