Definition of "subimago"

Subimago, Fem.—Dull piceous: antennæ black: abdomen more than twice the length of the thorax: setæ brownish testaceous, mutilated: legs dull testaceous; fore-legs brown: wings gray; veins black, not strongly marked.

1853, Francis Walker, Catalogue of the Specimens of Neuropterous Insects in the Collection of the British Museum‎, page 538

The subimago (a winged, but usually sexually immature stage) in the life cycle of mayflies is unique among living insect orders. The Ephemeroptera have two winged-instars, the subimago and the adult (or imago).

1996, Richard W. Merritt, An Introduction to the Aquatic Insects of North America‎, page 126

Subimagos emerge at the surface, fly to a support, molt immediately to the adult stage, live only a few hours, swarm, and mate shortly after ecdysis.

2009, James H. Thorp, Ecology and Classification of North American Freshwater Invertebrates‎

Subimagines flutter away immediately and rest at protected sites near the stream for up to 2-3 days, until the molt to the very short-lived adult occurs.

2011, Rüdiger Wagner, Central European Stream Ecosystems: The Long Term Study of the Breitenbach‎