Japanese Beetle Life Cycle

Life Stages of the Japanese Beetle

The life cycle of the Japanese Beetles consists of four stages of development called complete metamorphosis. These stages are egg, larva, pupa and adult. The eggs are white and oval. They are laid in the soil about 2-4 inches down where they can absorb moisture and become roundish. The larvae are typical white grubs and go through 5 instars or molts before pupating into the adult form. The pupae are cream to reddish brown in color and are ½ inch wide. The adults are a metallic green color with copper – brown wings with a row of white hairs on each side of its abdomen.

Once the larva or grubs are fully developed they enter the pupation stage and become adults. Once the adult stage is reached in the early part of the summer months, they leave the ground and immediately begin to look for plants to feed on. These newly formed adult Japanese beetles begin to release pheromones. Pheromones are chemical substances that are released by insects or other organisms into the environment to communicate with others of the same species. These pheromones will attract other adult Japanese beetles that develop and leave the ground later. Once the other adult beetles arrive to the plants, they begin feeding as well until the mating process begins. Mating is common on the food plants and several mating’s by both males and females are common.

Female Japanese beetles will leave the plant that they are feeding on to find ideal conditions and soil to lay eggs in. The females will lay anywhere between 1 to 5 eggs throughout the area that they choose. When done with this egg laying process the females return to a food source to continue feeding until another mating cycle occurs where this process is repeated all over again. This process will repeat itself until the female lays over 40 eggs throughout her life cycle.

The eggs will develop into grubs and can spend the fall and winter months in the ground developing toward the pupation stage and ultimately into the adult. The grubs survive on a combination of things including proper soil moisture and the food sources. These food sources are often the grass or crop roots that they are laid by. As the grub develops it may become mobile and move toward either one of these conditions needed to survive, therefore causing an increased area of damage to the lawn or grass that they are developing and feeding in.