What is the adult form of the masked chafer?

The adult form of the masked chafer is indeed referred to simply as the adult. This stage is the fully developed insect that emerges from the pupal stage after undergoing complete metamorphosis, which includes the egg, larval, pupal, and adult stages. In the case of the masked chafer, the adult is a beetle characterized by its distinctive appearance and behavior.

In contrast, grubs represent the larval stage, which is a key life phase where the insect undergoes significant feeding and development. The pupa is an intermediate stage in the life cycle, where the insect transforms from the larval to the adult form, but is not the adult itself. Therefore, while these other options are crucial stages in the life cycle of the masked chafer, the adult is the correct identification of the insect in its mature and reproductive form.