White Grubs
Larvae of the green June beetle, Cotinis nitida (Linnaeus) and the May beetle, Phyllophaga spp.
Scarabaeidae, COLEOPTERA

DESCRIPTION (several species)

Adult - The May beetle is about 19 to 25.5 mm long, and shiny reddish-brown to black in color. It is robust, oblong, and hardshelled. The June beetle is dull velvety green on top, brownish yellow on the sides, and shiny green and orange yellow underneath.

Egg - The egg is a dull, pearly white when laid, but it turns dark just before hatching. Oval to spherical shaped, it is 1.5 to 3 mm in diameter and encased in a cell of soil particles.

Larva (Grub) - Young May beetle grubs are creamy white and about 5 mm long. Fully grown grubs range from 20 to 45 mm long depending upon the species. They are C-shaped and creamy white, with distinct brown heads. Except for scattered hairs and six distinct forelegs, the body is shiny and smooth. Two rows of hairs on the underside of the last segment distinguish white grubs from similar grubs. Green June beetle larvae are about 48 mm long when fully grown and have the curious habit of crawling on their backs. Color plate.

Pupa - Approximately the same size as the adult, the pupae may be creamy white, pale yellow, or dark brown.

BIOLOGY

Distribution - More than 200 species of white grubs are found throughout North America. Common species include May beetles and green June beetles. May beetles are most injurious throughout the North Central states and into New England. During summer, they are often seen flying around lights at night. In North Carolina, green June beetles are most commonly reported in the Piedmont and mountain areas, maybe because forage and pasture acreage is concentrated in these areas. Populations of most grub species tend to be highest in older plantings of sod, or in soils high in decomposing organic matter.

Host Plants - White grubs feed on the roots of corn, timothy, lespedeza, Kentucky bluegrass, sorghum, soybean, strawberry, potato, barley, oat, wheat, rye, bean, turnip, and other cultivated crops. They also infest various pasture grasses, lawns, and nursery plantings. In addition, green June beetle grubs occasionally infest alfalfa and may be a major pest of Ladino clover. They also feed on decaying organic matter in the soil.

May beetles and June beetles feed on the foliage of forest and shade trees. They are strongly attracted to fragrant flowers and ripe fruits.

Damage - White grubs are among the most destructive soil insects in North America. They destroy root systems by their feeding and tunneling activities. When numerous, the larvae can cause severe mechanical plant damage by uprooting plants during movement. Under these conditions the soil may become soft and fluffy due to grub movement and stolon establishment is affected.

Life History - In spring, overwintering adults emerge from the ground at dusk, feed on the leaves of trees, and mate during the night. At dawn, they return to the ground, where the females lay 15 to 20 pearly white eggs in cells several centimeters below the surface. Female green June beetles prefer to lay their eggs in manure, decaying vegetable matter or humus; May beetles usually return to the cultivated crop or pasture to lay their eggs. Eggs hatch in 3 to 4 weeks. The newly hatched grubs feed throughout the summer. Green June beetle grubs reach maturity the same summer they emerge, whereas May beetle grubs complete only 1/3 their development before the fall. In the fall, grubs of both species burrow below the frostline (sometimes to a depth of 1.5 meters) and hibernate.

The following spring, a new generation of green June beetle adults emerges, but May beetle grubs resurface to feed and grow. In fall, the May beetle grubs migrate downward to overwinter. The third spring, they move upward again to feed on the plant roots. In late spring, the fully grown grubs encase themselves in earthen cells and pupate. In late summer, adults emerge from pupal cases, but they do not leave the ground. These beetles overwinter, emerging the next spring to feed and mate.

Green June beetles complete one generation each year. May beetles produce one generation approximately every 3 years. In spite of the length of this life cycle, generations overlap so that both beetles and grubs are present every year.

CONTROL

The cultural control practice of late-spring and early-fall plowing provides control in areas where predaceous birds occur (Coastal Plain primarily). Crop rotation is the most effective control method. Susceptible crops should be rotated with resistant or less susceptible crops (e.g. oats, rye, clovers, orchard grass, or alfalfa). In areas where green June beetle grubs are the primary problem species, avoid planting small-seeded legumes or grasses immediately after plowing under larger amounts of vegetative matter.

For current control recommendations, consult the current North Carolina Agricultural Chemicals Manual.