Final answer:
Adult frogs are secondary consumers as they prey on insects, which are primary consumers.
Step-by-step explanation:
Adult frogs, which feed on insects, are classified as secondary consumers in the food chain. This is because they consume primary consumers, the insects, which in turn feed on producers like plants. Frogs play a significant role in maintaining the equilibrium of the ecosystem by regulating the insect population. It is important to note that the trophic levels are based on the diet at each stage of an organism's life, and the adult frog specifically fits into the category of a secondary consumer due to its carnivorous diet.