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Insect eyes are generally sensitive to ultraviolet, blue and green light. With the exception of some butterflies, they cannot see the color red. Nevertheless, bees and other insects are also attracted to red flowers such as poppies. In this case, however, they are not attracted by the red color, but because they recognize the UV light reflected by the poppy flower.

However, two beetle species from the eastern Mediterranean region can indeed perceive the color red, as an international research team was able to show. The beetles are Pygopleurus chrysonotus and Pygopleurus syriacus from the family Glaphyridae. They feed mainly on pollen and prefer to visit plants with red flowers, such as poppies, anemones and buttercups.

Beetles have photoreceptors for long-wave light

"To our knowledge, we are the first to have experimentally demonstrated that beetles can actually perceive the color red," says Dr. Johannes Spaethe from the Chair of Zoology II at the Biocentre of Julius-Maximilians-Universit盲t (JMU) W眉rzburg in Bavaria, Germany. He gained the new insights together with Dr. Elena Benc煤rov谩 from the W眉rzburg Bioinformatics Chair and researchers from the Universities of Ljubljana (Slovenia) and Groningen (Netherlands). The study has been in the Journal of Experimental Biology.

The scientists used electrophysiology, behavioral experiments and color trapping. Among other things, they found that the two Mediterranean beetles possess four types of photoreceptors in their retinas that respond to UV light as well as blue, green and deep red light. Field experiments also showed that the animals use true color vision to identify red targets and that they have a clear preference for red colors.

New model system for ecological and evolutionary questions

The researchers consider the Glaphyrid family to be a promising new model system for investigating the visual ecology of beetles and the evolution of flower signals and flower detection by pollinators.

"The prevailing opinion in science is that flower colors have adapted to the visual systems of pollinators over the course of evolution," says Spaethe. However, based on the new findings, it is now possible to speculate whether this evolutionary scenario also applies to Glaphyrid beetles and the flowers they visit.

Why do the researchers think this? The three genera of this beetle family (Eulasia, Glaphyrus and Pygopleurus) show considerable differences in their preferences for flower colors, which vary between red, violet, white and yellow. This suggests that the physiological and/or behavioral basis for seeing red and other colors is relatively labile.

The great variety of flower colors in the Mediterranean region and the considerable variation in the color preferences of the beetles made it plausible that the visual systems of these pollinators may adapt to flower colors better than was commonly assumed.