Insect coloration as a defence mechanism against visually hunting predators

Abstract

Insects utilise a wide variety of defence coloration including crypsis, aposematic coloration, and deflection patterns. The traditional view is that animals can maximise their cryptic coloration only on one background. I demonstrated experimentally that a compromised coloration could confer equal protection in two visually different habitats where its wearer survived altogether better than perfectly cryptic forms. Contrary to the cryptic coloration, conspicuousness is the essence of aposematic coloration and it is this character that provides the advantage of reduced predation risk through predator learning. Experiments on this intensively studied subject (and prey detection in general) have mostly ignored the fact that vision of birds, which are important predators on insects, is based on at least four colour receptors ranging from ultraviolet to red. I conducted a series of experiments to test whether UV cues alone can signal unpalatability. I did not find strong evidence that UV cues alone would function effectively as aposematic signals, but on the contrary they increased the predation risk. Our knowledge on aposematism and other defence mechanisms are largely based on experiments in butterflies. Pieridae butterflies have been regarded to exemplify the Müllerian mimicry concept. I did not, however, find support for the idea that their white coloration would signal unpalatability. Many Lepidoptera species do not rely on warning or cryptic coloration as their defence mechanism but they possess conspicuous eyespots on their wings. Eyespots are hypothesised to increase the likelihood of escape of the detected butterfly by deflecting attacks away from the body. I compared the rate of successful escapes between spotted and spotless butterflies under laboratory conditions using lizards and birds as predators. The two butterfly forms did not differ in their survival rate and thus predation hypothesis cannot solely explain the occurrence of spotting.