What is the term for the immature stages of insects?

The term for the immature stages of insects is known as "instars." Instars refer specifically to the various stages between molts that insects undergo as they develop from the egg stage to adulthood. During each instar, the insect can exhibit different physical characteristics and sizes, often increasing in size as it prepares for the next molt.

Larvae are generally considered to be a specific type of immature stage in certain insect groups, particularly in holometabolous insects, where the young often look very different from adults. Nymphs refer to the immature forms of insects that undergo incomplete metamorphosis, resembling smaller versions of adults, but are specifically used for certain groups rather than as a general term for all immature stages. Adults are the fully developed stage of insects, making this option incorrect in the context of the question about immature stages.

Thus, instars represent a broader group that encompasses the various developmental phases an insect experiences before reaching maturity, making it the most appropriate choice.