Wing coupling

Oiketicus spp. (family Psychidae). The frenulum can be seen at the top of the rear wing, which hooks onto the retinaculum, seen here as a small brush on the front wing, so that the wings travel together during flight. Magnification: 10x

Some four-winged insect orders, such as the Lepidoptera, have developed a wide variety of morphological wing coupling mechanisms in the imago which render these taxa as "functionally dipterous" (effectively two-winged) for efficient insect flight. All but the most basal forms exhibit this wing coupling.

The mechanisms are of three different types - jugal, frenulo-retinacular and amplexiform.