Which of the following is a common soil-inhabiting insect pest of Iowa turfgrass?

The Japanese beetle is identified as a common soil-inhabiting insect pest of Iowa turfgrass primarily due to its life cycle and behavior. This pest primarily affects turfgrass in the larval stage, known as grubs, which reside in the soil. These grubs feed on the root systems of grass, leading to significant damage and weakening of turf.

The adults emerge from the soil, usually in late spring to early summer, and they can further impact the health of turfgrass and other plants by feeding on the foliage. The combination of their presence in the soil as grubs and the damage they cause to turfgrass makes the Japanese beetle a significant concern for lawn care and management in Iowa.

The other options, while they may affect turfgrass, do not inhabit the soil as grubs or larvae in the same manner, making them less relevant to this particular question about soil-inhabiting pest species.