“Cambio de paradigma en el vuelo de las efímeras (Insecta: Ephemeroptera): un enfoque multi-metodológico revela la verdadera función de las bullas del ala”

DOMINGUEZ, E.; CUEZZO M.G.

Illheus

Simposio; VI Simpósio de Insetos Aquáticos Neotropicais; 2022

Universidade Estadual de Santa Cruz

Unlike wings in other insect orders, mayfly forewings are equipped with so-called bullae. These oval, blister-like spots are found in some of the main negative veins. Traditionally, it has beensuggested that bullae might play a central role in flight. According to this assumption, bullae would allow the distal part of the wing membrane to bend in the upstroke, thus diminishing pressure and reducing resistance. However, our own observations by high speed videography did not confirm this generally adopted theory. Instead of bending during upstroke, mayfly forewings remain straight for the whole wing cycle, only in their basal halves their membrane cambers to produce uplift. This observed wing movement contradicts a function of bullae in wing bending during flight, which led to further investigations by SEM, μCT, and fluorescence microscopy. In both winged stages, bullae are present at half-length in negative wing veins Sc, R2, R4+5, and MP1 at most. Unlike the entire wing membrane, bullae do not contain resiline and have no elastic properties. They resemble well-defined, desclerotized areas in otherwise heavily sclerotized veins. This still suggests a role of bullae in wing bending, but this does not happen during flight. Instead, video recordings reveal a crucial function of bullae in subimaginal molting, which is unique to mayflies. Halfway through the molt from the winged subimago to imago, wings fold over at bullae position, thus facilitating extraction of the imaginal wings from the subimaginal skin. This theory is also supported by the lack of bullae in species, which remain in their subimaginal stage.