Life Cycle

Japanese beetles have a one-year life cycle in most parts of their range. Adults occur from June to August. Upon emergence

FIGURE 1 (A) Japanese beetles with characteristic feeding damage. (B) Japanese beetle grub.

from the soil, virgin females emit a volatile sex pheromone that attracts clusters of males. Subsequent matings occur on food plants. The beetles typically feed from the upper surface of leaves, chewing out the tissue between the veins and leaving a lacelike skeleton. Adults also feed on petals of flowers such as roses, and on developing fruits or berries. Food plants growing in sunny locations are preferred. Usually the beetles begin to feed on foliage near the top of a plant, regardless of its height. They often aggregate on particular shoots or plants. This phenomenon results from both sexes being attracted to blends of aromatic volatile compounds released from beetle-damaged leaves. Despite the beetles' broad host range, some plant species are rarely or never fed upon. Closely related cultivars within species may also differ in susceptibility. Resistance probably results from presence of feeding deterrents (e.g., certain phenolics) or other secondary plant compounds. Some plants (e.g., geranium, Pelargonium hortorum) are palatable to the beetles but cause paralysis or other toxic effects.

After feeding, gravid females fly to moist turf, pasture, or agricultural fields, where they burrow down to lay small clutches of eggs in the upper 8 cm of soil. Females alternate between feeding and egg laying; each female may emerge from the soil, fly to host plants, feed, mate again, and return to the soil 15 or more times, laying 40 to 60 eggs in her lifetime. The pearly white eggs, oval when first laid, swell with soil moisture to a diameter of about 1.5 mm. Larvae hatch in 2 to 3 weeks, usually by early to mid-August. Larvae feed just below the soil surface, consuming plant roots and organic matter. When grubs are numerous, the root system of turf grasses may be completely severed, such that the turf wilts and dies, and can be pulled from the soil like a loose carpet. Most grubs are third instars by September. About the time of first frost, the grubs move deeper (about 15—30 cm) to overwinter. In early spring, as soil temperatures warm to about 10°C, the grubs move back to the upper 2.5 to 5.0 cm of soil and resume feeding for about 4 to 6 weeks, after which they again go deeper and form an earthen cell in which to pupate. The first adults begin emerging a few weeks later.

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