Final answer:
Option (A), An instar is the developmental stage of an insect's life cycle between two molting periods, with growth occurring only during these juvenile stages and not after reaching adulthood.
Step-by-step explanation:
An instar refers to the stage in an insect's life cycle between two periods of molting. Most insects undergo metamorphosis and the instar stages represent the developmental stages within this transformative process. In complete metamorphosis, each stage — egg, larva, pupa, and adult — is distinct in appearance. During the larval instar phases, the insect grows in size, and this period does not include the time after it has become an adult. The final molt usually results in the emergence of the adult form of the insect, ready to reproduce.
Insects such as ants, beetles, and butterflies experience complete metamorphosis where the larval form is considerably different from the adult form. In contrast, insects like cockroaches and crickets undergo gradual or incomplete metamorphosis, where early instars called nymphs may resemble the adult but lack fully developed wings. These stages allow insects to specialize in different habits and behaviors throughout their life cycle.
It's important to note that growth in insects occurs only during these juvenile instar stages, and not after the final molt into adulthood. This is because insect growth is regulated by hormones such as Juvenile Hormone (JH), which controls the transition from a larva to an adult through metamorphosis.