White Grubs
Phyllophaga spp., Scarabaeidae, COLEOPTERA


DESCRIPTION

Adult - Robust, oblong, and hard-shelled, May beetles are about 19 to 25 mm long and reddish brown to black in color.

Egg - The small, white, spherical eggs turn dark just before hatching. They are 1.5 to 3 mm in diameter and are encased in soil particles.

Larva - White grubs have a brown head capsule, a C-shaped body, three pairs of legs, and a slightly enlarged abdomen. On the underside of the last abdominal segment there are two nearly parallel rows of spines. Fully grown grubs average 35 mm in length but range from 20 to 45 mm long. Color plate.

Pupa - The 20- to 24-mm long pupae may be creamy white, pale yellow, or dark brown.


BIOLOGY

Distribution - White grubs are common throughout North America, although species distribution varies greatly.

Host Plants - White grubs feed on the roots of corn, timothy, Kentucky bluegrass, sorghum, soybean, strawberry, potato, barley, oat, wheat, rye, bean, turnip, and to a lesser degree, other cultivated crops. They also infest various pasture grasses, lawns, and nursery plantings. The adults, which are strongly attracted to fragrant flowers and ripe fruits, feed on the foliage of forest, shade and fruit trees.

Damage - Damage by white grubs is usually most severe when corn is planted following sod. In this case, root feeding can be so severe that plants may grow no taller than 30 to 60 cm (1 or 2 feet). If the root system is badly damaged, injured plants will eventually die and can be easily pulled from the ground. Even light infestations usually result in increased lodging and reduce yield.

White grubs are sensitive to differences in soil moisture and texture. Since these factors are not uniform throughout any given field, a white grub infestation, likewise, is not uniform. Therefore, within the same field, some areas may be completely destroyed while others are undamaged.

Life History - In spring, overwintering May beetles 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 eggs in earthen cells several centimeters below the surface. Most May beetles lay eggs in grassy sod. Eggs hatch 3 to 4 weeks later. The young grubs feed on plant roots throughout the summer; in the fall, they burrow below the frost line (to a depth of 1.5 meters) and hibernate. The following spring, they return near the soil surface to feed and grow. In fall, the grubs again migrate downward to overwinter. The third spring, they move upward to feed on plant roots. By late spring, they are completely grown. These large grubs form earthen cells and pupate. In late summer, adults emerge from the pupal stage, but they do not leave the ground. These beetles overwinter, emerging the next spring to feed and mate.

The usual length of time for one complete generation (adult to adult) is 2 to 4 years depending upon latitude. Generations, however, are staggered so that grubs and beetles are present every year. Grubs are usually most numerous and damaging the second season following a large beetle flight.


CONTROL

White grubs are among the most destructive soil insects in North America. True white grubs may be easily confused with several other grubs infesting corn roots. However, the damage inflicted and the control methods employed are identical for most grubs and their close relatives. (In the strictest sense only species of Phyllophaga are white grubs. Other similar larvae of the insect family Scarabaeidae are often referred to as "white grubs" also. These include larvae of the Japanese beetle, Newman; the green June beetle, Cotinis nitida (Linnaeus); and annual white grubs, Cyclocephala spp.

The cultural practices of late-spring and early-fall plowing or disking provide control in areas where predaceous birds occur (e.g., the Atlantic Coastal Plain). Crop rotation, however, is the most effective cultural control method. Deep-rooted legumes, like alfalfa and clovers, are excellent crops with which to rotate corn or small grains, especially following years of unusually heavy May beetle flights. For specific control information consult the current North Carolina Agricultural Chemicals Manual.