Flower color offers a warm welcome to bees
often use floral color signals as an indication of nutritional reward. Because bees
have to maintain a certain body temperature, floral heat could be an additional
incentive for them to land on one flower instead of another. Scientists at the Universities
of Cambridge and London in the UK speculated as to whether bees prefer warmer flowers
and if they can use floral color as a cue to decide which plants to visit.
As described in the Aug. 3 issue of Nature,
the team introduced bees to two identical feeders: one at 18.5 °C and the other
at 18.5, 22.5, 27 or 29.5 °C. The bees chose the warmer feeder, especially
when the temperature difference was greater than 4 °C. Although this confirmed
the first part of the hypothesis, it only exhibited the bees’ ability to use
spatial positioning to identify heat.
Next, they exposed the bees to four
purple flowers at 28.8 °C and four pink flowers at 20.8 °C. The flowers
were positioned randomly and offered solutions with equal amounts of sucrose. The
bees landed on the purple flowers 58 percent of the time. Conversely, when the pink
flowers were warmer, the bees chose the pink flowers 61.6 percent of the time. They
demonstrated no color preference when the flowers were the same temperature, nor
did they exhibit a temperature preference when the flowers were the same color.
This led the researchers to conclude
that bees use color, rather than other perceptual mechanisms, to gauge which flowers
are warmer. They speculate that their findings may have evolutionary implications,
suggesting that flora within and between species may adapt their temperature to
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