Which term describes the transformation from larva to adult in an insect's life cycle?

The term that describes the transformation from larva to adult in an insect's life cycle is metamorphosis. This process involves significant physiological changes, where the larval form undergoes development to emerge as an adult. Insects exhibit different types of metamorphosis, primarily complete (holometabolous) and incomplete (hemimetabolous), which affect how they develop from the immature stages to full-grown insects.

The concept of metamorphosis is crucial in entomology because it explains how insects adapt to different environments and life stages, influencing their survival and reproduction strategies. Understanding metamorphosis provides insights into the unique biological processes behind insect development.

Other terms in the question have specific meanings related to insect development, but they do not describe the complete transformation process. For example, instar refers to the developmental stage between molts, ostia are openings in the heart of insects, and eclosion is the act of emerging from an egg or pupal case. These terms highlight other aspects of insect physiology and development, but metamorphosis remains the overarching term for the change from larva to adult.