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Introduction: Structural colour patterns and their functions in insect wings are less known. Wing interference patterns (WIPs) are colour patterns apparent when wings are viewed against black backgrounds; the angle of incident light and wing surface structures also influence the resulting wing colour pattern. To date, WIPs are correlated with mate attraction, while the impact of geography and environment on WIPs remains unexplored. We explore WIP variation in Drosophila melanogaster populations collected from three altitudes and also compare WIP variation in sibling species D. melanogaster and D. simulans reared at three different temperatures to understand if local selection pressures could also influence WIPs. Methodology: Wings of D. melanogaster males were collected from three different altitudes, and D. melanogaster and D. simulans males reared at three different temperatures were imaged. Images were analysed for their relative red, green and blue content in the RGB colour space. In representative images, wing thickness was assessed using the Newton colour series. Results: An altitudinal cline in WIPs was observed in the cosmopolitan D. melanogaster collected from the Western Himalayas. Relative RGB values and increase in altitudes were negatively correlated. Thermal responses in WIPs were parallel for both D. melanogaster and D. simulans. Relative RGB values were negatively correlated with rearing temperature. In both species, wing thickness measurements indicated that the wings of flies reared at low temperatures had greater blueness (cyan and magenta) compared to flies reared at moderate to high temperatures; the latter had more green and yellow content. Wing thickness pattern was also consistent for D. melanogaster flies collected from low versus higher altitudes. Discussion: We find WIPs to be a plastic trait in response to temperature. WIP response to thermal variation corroborates with the temperature of the geographic origin in D. melanogaster. The adaptive significance of WIP variation and associated wing thickness remains unclear. Future studies could explore the underlying adaptive significance of structural colour patterning under different environmental conditions. [ABSTRACT FROM AUTHOR]

The pupal colour of many butterflies is plastic, being green or brown depending on the environment in which they develop. In most species with pupal colour plasticity (PCP), larvae that pupate on leaves tend to develop into green pupae whereas those that pupate off‐leaf (e.g., on the stem or soil) tend to become brown. This correlation between background and pupal colour has been hypothesized to protect the butterflies against predation by allowing them to match their background, although experimental evidence is scarce. Furthermore, not all butterflies exhibit PCP, and the extent to which substrate choice influences PCP remains unclear. We use a comparative approach involving multiple, closely related species varying in the degree of PCP to test predictions related to the correlation between pupal colour and pupation substrate. We studied PCP in response to larval density in five common satyrine species (Nymphalidae), two dimorphic and three monomorphic. As predicted, species with monomorphic green pupae preferred to pupate on leaves whereas those with monomorphic brown pupae preferred off‐leaf substrates. In species with dimorphic pupae, pupal colour correlated with pupation substrate. We also predicted that higher larval density induces a greater proportion of off‐leaf pupation in the dimorphic species, but not in the monomorphic species. However, this prediction was not supported. Overall, we found a strong across‐species correlation between pupation substrate choice and pupal colour plasticity, and our results support the idea that pupal colour plasticity can be an adaptation against predation. [ABSTRACT FROM AUTHOR]