What is the primary function of the epicuticle in insects?

The primary function of the epicuticle in insects is to protect them from moisture loss. This outermost layer of the exoskeleton is made up of a waxy substance that acts as a barrier to reduce water loss and help maintain the insect's internal hydration levels. Insects are especially vulnerable to desiccation due to their small size and high surface-area-to-volume ratio; thus, the epicuticle plays a critical role in their survival by regulating water retention.

The other options refer to functions that are not associated with the epicuticle. Digestion is a process managed by the digestive system organs, reproduction involves internal and external structures related to the reproductive system, and movement is facilitated by the muscles and joints within the exoskeleton rather than the epicuticle itself. Therefore, the correct answer emphasizes the protective role of the epicuticle regarding moisture retention, which is essential for an insect's overall survival and function.