The nature of Drosophila melanogaster

they form juxtaposed pointillistic colour centres which, to our eyes, create the stimulus of the colour green (the same principle is used in many neo-impressionist paintings). One further special feature of this structurally coloured system, and possibly the reason it evolved, is that only the blue colour component is significantly linearly polarised; linear polarisation is sometimes used for intra-specific signalling in Lepidoptera, so this system seems ideally designed to be cryptically green to, say, predator visual systems that do not see differences in the polarisation of light, while broadcasting linearly polarised blue signals to conspecifics. A separate small family of swallowtails, the Nireus group that is indigenous to the Afrotropics, concurrently employs a fluorescent pigment and not one, but two forms of specialised photonic structure: a multilayer and a two-dimensional photonic crystal slab. These carefully control the emission direction of the fluorescent light and make the butterfly a much brighter object than it would be without them. This is the first known example in which fluorescent pigment and colour-producing or colour-controlling nanostructures are so closely tied together. There are a vast number of other examples. Lepidopteran structural colour systems, and those in other orders too, truly exhibit a remarkable ability to control the flow of light and colour in so many ways and for so many purposes. Why is this subject worth investigating? Textbooks tell us that a colour pattern is a slice in time; a frozen moment in the dynamic processes of development and evolution. Genetic information is translated into the manipulation of cell systems and cuticle assembly to give final patterns and appearances. To understand these processes in Lepidoptera, we examine the biological components that underpin their wing colours and patterns. We seek to know how changes in genes and development can control colour and pattern; how larval food plant quality affects male sexual quality indicators; how the forms and relative weighting of inter-specific and intra-specific selection pressures affect wing colour intensity, hue, polarisation and angular visibility. A study of the biology of the wing colours and patterns of Lepidoptera is a study of evolution itself. Now, within this field, it is increasingly clear that structural colour, and the many ways in which it is produced, is a fundamental component. From the perspective of technological photonics, these lepidopteran systems are amazingly elaborate. They feature self-assembled highly complex biological engineering for photonic purposes (amongst others) that, given the limited …