subimago

noun plural -imagoes or -imagines (-ɪˈmædʒəˌniːz)

the first winged stage of the mayfly, with dull opaque wings, known to anglers as a dun, before it metamorphoses into the shiny gauzy imago or spinnerSee also dun 2 (def. 3), spinner (def. 6)

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Examples from the Web for subimago

Historical Examples of subimago

This is what is called the subimago, and precedes the imago or perfect state of the insect.
Scientific American Supplement, No. 385, May 19, 1883
Various
Perhaps the subimago in this genus of Ephemerids, as in certain others, is the permanent aerial state of the female.
Scientific American Supplement, No. 385, May 19, 1883
Various