Paradigm shift in mayfly flight (Insecta: Ephemeroptera): Multi-methodological approach reveals true function of wing bullae

DOMÍNGUEZ EDUARDO; VAN DE KAMP, T.; MIKO, ISTVAN; CUEZZO, M. G.; STANICZEK, A.

Ilheus

Conferencia; VII Simposio de Insetos Aquáticos Neotropicais; 2022

Universidade Estadual de Santa Cruz

Unlike wings inother insect orders, mayfly forewings are equipped with so-called bullae. Theseoval, blister-like spots are found in some of the main negative veins.Traditionally, it has been suggested that bullae might play a central role inflight (Edmunds & Traver 1954). According to these authors, bullae wouldallow the distal part of the wing membrane to bend in the upstroke, thus diminishingpressure and reducing resistance. However, our own observations by high speedvideography did not confirm this generally adopted theory. Instead of bendingduring upstroke, mayfly wings remain straight for the whole wing cycle, only intheir basal wing half its membrane cambers to produce uplift. This observed wingmovement contradicts a function of bullae in wing bending during flight, whichled to further investigations by SEM, µCT, and fluorescence microscopy. In bothwinged 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 containresiline and have no elastic properties. They resemble well-defined,desclerotized areas in otherwise heavily sclerotized veins. This still suggestsa role of bullae in wing bending, but this does not happen in flight. Instead, videorecordings reveal a crucial function of bullae in subimaginal moulting: Halfwaythrough the moult, wings fold over at bullae position, thus facilitatingextraction of the imaginal wings from the subimaginal skin. This theory is alsosupported by the lack of bullae in species, which remain in their subimaginalstage.