Adults live four to six weeks and females lay eggs during most of their lives. Eggs hatch in about two weeks. Maturing in the fall, the grubs overwinter in the soil and resume feeding in the spring. After two to four weeks, the grubs mature and pupate in cells in the soil. Adults emerge three to four weeks later and remain in the cells for several days before digging to the surface.
Adults are active during the day, returning to the turf in late afternoon.
Full-grown grubs are about an inch long. Sampling and Control Japanese beetle grubs spend most of their time near the surface unless dry soil conditions drive them deeper. They are easily exposed by laying the sod back and looking in the top 1 to 2 inches of soil and in the roots of the grass. Irrigate thoroughly several hours prior to sampling if the soil is dry. Irrigation is also needed before application of control materials under dry conditions.