The warmth of flowers

Pollinators use precise cues to identify flowers rich in pollen or nectar: colour, scent … Researchers have discovered that bees are also sensitive to temperature variations between different parts of a flower. These “thermal patterns” enable them to locate the flowers richest in food.

British scientists have investigated a new cue, in addition to colour or scent, that allows pollinating insects to distinguish nectar-rich flowers from others.

Pollinating insects are known to rely on various cues to select suitable flowers. While some of these are also perceptible to humans, such as colours or floral scents, others remain hidden. In a study published on 19 December 2017 in the journal eLife, researchers from the University of Bristol (United Kingdom) present one such cue. They demonstrated that bees and bumblebees are able to perceive temperature differences between different parts of a flower and that these “thermal patterns” allow them to differentiate between flower species and thus select those richest in nectar.

Temperature differences of up to 11 °C

The British researchers found that the majority of flowers—even very common ones such as poppies or daisies—exhibit these distinctive temperature variations. Of the 118 species examined using thermal imaging, 55% showed temperature differences exceeding 2 °C across their petals, a level sufficient for insects to perceive using thermal sensors located on their antennae and legs. According to the scientists, these patterns are on average 4 to 5 °C warmer than the rest of the flower and can even reach differences of up to 11 °C. This heat may be produced by thermogenesis or supplied by daylight.

The scientists also created artificial flowers reproducing the patterns observed on natural flowers. “We thus showed that these insects are capable of distinguishing artificial flowers that display thermal patterns similar to those observed on real flowers,” they note in the study, and of preferentially visiting them. The lead author, Dr Heather Whitney, stated in a press release that “the presence of multiple cues on flowers improves the ability of bees to forage efficiently, thereby maximizing the amount of nectar they can collect to feed the rest of the colony.” Thermal patterns therefore play an important role by enabling insects to save time by directly visiting suitable flowers.

The threat of climate warming

The discovery of this phenomenon also heightens concerns about the consequences of climate change: “If pollinators are partly influenced by subtle temperature differences on the surface of petals, even a small change in environmental temperature could have significant and unforeseen effects on the efficiency of bees and other pollinators when visiting flowers with thermal patterns,” the researchers suggest.

Source: www.sciencesetavenir.fr