
The first winged stage of a mayfly, not reproductively mature.
Found on
http://nhguide.dbs.umt.edu/index.php?c=insects&m=glossary

• (n.) A stage in the development of certain insects, such as the May flies, intermediate between the pupa and imago. In this stage, the insect is able to fly, but subsequently sheds a skin before becoming mature. Called also pseudimago.
Found on
http://thinkexist.com/dictionary/meaning/subimago/

(from the article `mayfly`) ...As many as 50 molts (periodic shedding of skin) may occur, depending on the species and the environment. When growth is complete, the nymphal skin ...
Found on
http://www.britannica.com/eb/a-z/s/177
Sub`i·ma'go noun [ New Latin See
Sub- , and
Imago .]
(Zoology) A stage in the development of certain insects, such as the May flies, intermediate between the pupa and imago. In this stage, the insect is able to fly, but subsequently sheds a skin before becoming mature. Calle...
Found on
http://www.encyclo.co.uk/webster/S/222

First adult instar of the first imaginal instar of mayflies.
Found on
http://www.geog.ubc.ca/biodiversity/efauna/InsectGlossary.html
No exact match found.