It's the term for an adult insect after metamorphosis
The Latin plural of 
imago is imagines, and this is the term generally used by entomologists  
however,... [DOC] [TLE] imagines (insect) - Memidex dictionary/thesaurus [PAR] Definition: an adult insect produced after metamorphosis ... the last stage an 
insect attains during its metamorphosis, its process of growth and development;... [DOC] [TLE] How Insects Grow & Change Form [PAR] After it reaches the adult stage, it does not molt or grow any more.