In biology

Biology

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

, the imago is the last stage of development of an insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

, after the last ecdysis

Ecdysis

Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...

 of an incomplete metamorphosis

Metamorphosis

Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...

, or after emergence from the pupa

Pupa

A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...

 where the metamorphosis is complete. As this is the only stage during which the insect is sexually mature

Sexual maturity

Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...

 and, if it is a winged species, has functional wings, the imago is often referred to as the adult stage.

The Latin plural of imago is imagines, and this is the term generally used by entomologists

Entomology

Entomology is the scientific study of insects, a branch of arthropodology...

 – however, imagos is also acceptable.

The stage of subimago exists in the Ephemeroptera

Mayfly

Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...

(mayflies). Insects at this stage have functional wings but are not yet sexually mature.