Cuticular modified air sacs underlie white coloration in the olive fruit fly, Bactrocera oleae

Here, the ultrastructure and development of the white patches on thorax and head of Bactrocera oleae are analysed using scanning electron microscopy, transmission electron microscopy, and fluorescence microscopy. Based on these analyses and measurements of patch reflectance spectra, we infer that white patches are due to modified air sacs under transparent cuticle. These air sacs show internal arborisations with beads in an empty space, constituting a three-dimensional photonic solid responsible for light scattering. The white patches also show UV-induced blue autofluorescence due to the air sac resilin content. To the best of our knowledge, this research describes a specialized function for air sacs and the first observation of structural color produced by tracheal structures located under transparent cuticles in insects. Sexual dimorphism in the spectral emission also lays a structural basis for further investigations on the biological role of white patches in B. oleae. Manuela Rebora et al. use electron and fluorescence microscopy together with reflectance spectra to examine structural white patches present in the olive fruit fly, Bactrocera oleae. Their results suggest that white coloring is a result of transparent cuticle and modified air sacs within these patches, providing further insight into how structural white emerges in insects.

Automated summary

Researchers used electron and fluorescence microscopy to examine the ultrastructure and development of white patches in Bactrocera oleae. They found that the white patches are a result of modified air sacs under transparent cuticle, forming a three-dimensional photonic solid responsible for light scattering. This study sheds light on the biological role of white patches in insects and the use of structural color produced by tracheal structures.