Nanomorphology of the blue iridescent wings of a giant tropical wasp Megascolia procer javanensis (Hymenoptera)

The wings of the giant wasp Megascolia procer javanensis are opaque and iridescent. The origin of the blue-green iridescence is studied in detail, using reflection spectroscopy, scanning electron microscopy, and physical modeling. It is shown that the structure responsible for the iridescence is a single homogeneous transparent chitin layer covering the whole surface of each wing. The opacity is essentially due to the presence of melanin in the stratified medium which forms the mechanical core of the wing.

Figure 1

(Color online) A collected specimen of male Megascolia procer javanensis (Hymenoptera). Note the dark wings of this Scoliid, showing bluish reflections.

Figure 2

(Color online) The wings of Megascolia procer are highly sophisticated organs, balancing low inertia, strength, and optimized aerodynamics. Note the rippled surface, which produces a wavy cross section for the bearing membrane.

Figure 3

Megascolia Procer Javanensis wing section (scanning electronic microscopy picture) and model used for simulations.

Figure 4

(Color online) Wing reflection as a function of the wavelength for various incidence angles. Experimental data (solid line) and simulations results (dashed line).

Figure 5

(Color online) (a) In this upper panel, the wing on the left has been kept dry as a reference, and the wing on the right is covered with a macroscopic layer of liquid ethanol (refractive index 1.4). The wet wing loses its blue-green iridescence and shows a dark-brown appearance, due to the strong attenuation of the outer interface refractive index contrast. (b) When ethanol is removed by evaporation, the wing returns to its original iridescent appearance.

Figure 6

Schematic representation of the wing structure, showing how the reflection takes place through the multiple paths of light.

Figure 7

(Color online) Colorimetric trajectories for light reflected from the wing of the wasp, for varying incidence angles, in the range from 0° to 60°. Solid line is from experimental data; dashed line is from the model calculation.