What term is used to describe the larvae of masked chafer?

The term used to describe the larvae of the masked chafer is "grub." Grubs are the larval stage of beetles, and in the case of the masked chafer, they are typically C-shaped, pale white, and can be found in the soil, where they feed on the roots of grasses and other plants.

Choosing the other terms does not accurately describe the larval stage. "Raster" refers to specific characteristics of the setae or bristles on the larval body, generally considered in a more technical sense of insect morphology. "Pupa" refers to an intermediate stage in an insect's life cycle, following the larval stage, where significant transformation occurs into adulthood. "Adult" signifies the fully developed stage of the insect after it has emerged from the pupal stage. Therefore, "grub" is the correct term for the larval form of the masked chafer.