Instar

An instar (/ˈɪnstɑːr/ ⓘ, from the Latin īnstar 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (ecdysis) until sexual maturity is reached.

[1] Arthropods must shed the exoskeleton in order to grow or assume a new form.

that the number of instars can be physiologically constant per species in some insect orders, as for example Diptera and Hymenoptera.

For instance, environmental conditions may dramatically affect the developmental rates of species and still have no impact on the number of larval instars.

[3] On the other hand, temperature affects the development rates of a number of hymenopterans without affecting numbers of instars or larval morphology, as observed in the ensign wasp[4][5] and in the red imported fire ant.