Clover Root Curculio
Sitona hispidula (Fabricius), Curculionidae, COLEOPTERA

DESCRIPTION

Adult - The adult weevil (3 to 5 mm long) is shiny black or dark brown on top and ash gray on the underside. Small coppery or grayish scales on the back form three distinct stripes. The wing covers are deeply etched with parallel lines and minute spots; the beak is short, curved, and thick.

Egg - The tiny egg is ellipsoid or nearly round. Slightly yellow when laid, it turns dusky black in about 3 days.

Larva - The legless, fleshy grub is grayish-white with a light brown head. It is about 5 mm long when fully grown.

Pupa - The small pupa is curled in an oval cell 13 to 25.5 mm below the soil surface.

BIOLOGY

Distribution - The clover root curculio is found throughout the United States and southern Canada.

Host Plants - The clover root curculio larva feeds on many clovers (white, red, sweet, alsike), alfalfa, Kentucky bluegrass, soybeans, cowpeas, and other legumes.

Damage -The beetles feed by cutting small notches in the margins of leaves; they also consume leaf buds. The grubs, however, feed on the roots of legumes, causing more serious injury than the leaf feeding adults. Nodules and small roots are entirely eaten; larger roots are severed; the taproots are tunneled. Plants weakened in this manner are very susceptible to death during dry weather conditions. Although usually of little importance, the grubs have been known to destroy 60 to 80 percent of the plants in young stands of alfalfa.

Life History - Clover root curculios pass the winter as adults, young larvae or eggs. In spring, the grubs feed on small roots, nodules, or root crowns. In late March or early April, they mature and pupate for 17 to 22 days. Adults, which seldom fly, emerge in May or June and feed on leaves and stems for 4 to 6 weeks. During hot summer days, the beetles become active feeders again and mate. Although some females lay about 500 eggs in the crowns of the plants during October or November, most females do not lay their eggs at this time. Instead, they hibernate in field debris and lay their eggs the following spring. These eggs hatch in about 30 days. Some eggs laid in the fall hatch quickly; the young grubs feed for a short time and then hibernate. Other eggs do not hatch until the following spring, 150 to 200 days after being laid. A complete life cycle requires one year.

CONTROL

Cultural controls are most often employed. Rotating crops and planting infested fields with a grass or cultivated crop are effective control measures. Where possible, plowing during late fall or early spring has proven beneficial; early fall plowing, however, simply drives the beetles into another host field.

In North Carolina, chemical control is usually not warranted. Under some circumstances, however, insecticidal treatment may be necessary. For specific control information, consult current North Carolina State Agricultural Extension Service recommendations.