Dated 8/93
Placed on the Web 4/95 by the Department of Entomology, NCSU
Revised: 03/05
The sweetpotato weevil is the most destructive insect pest of sweetpotatoes in the United States. It lives primarily on the sweetpotato and other plants of the genus Ipomoea (morning glories) and is believed to be native to Asia.
The sweetpotato weevil was first discovered in India in 1792 and in the U.S. in 1875 near New Orleans, LA. In 1878 it was found on the west cost of Florida and in 1890 in Texas. It is thought that this insect was introduced from the West Indies. The weevil was found in Mississippi and Georgia in 1917, in Alabama in 1918, in Oklahoma in 1922, in South Carolina in 1966, in Arkansas in 1982, in Tennessee in 1983 and in California in 1993. The sweetpotato weevil was detected in North Carolina in 1967 and 1971. The weevil has been reported most recently in the NC counties of New Hanover and Brunswick. Infestations in 1967 were reported in Columbus, Brunswick, Robeson, and New Hanover counties. Outbreaks in Johnston County in the 1990s and later in Nash County in 2002 resulted in quarantines. Infestations in NC are currently confined to the Ft. Fisher area on seaside morning glory, Ipomoea sagitta, a native host.
Most damage by sweetpotato weevils is through infestation of mature sweetpotatoes. Tunnelling in the vines by larvae does not cause appreciable losses in yield. However, adult feeding, oviposition, and emergence holes mar the appearance of the sweetpotato, and larval tunnelling imparts a bitter taste to the crop. The presence of sweetpotato weevil and/or quarantine has a detrimental effect on seed and plant industries and on producers who lose markets for their product. Hence, the threat posed by the weevil has serious implications for the North Carolina sweetpotato industry. An external state quarantine exisits in three counties in South Carolina.
Adult - Adult weevils resemble ants, with a narrow head and thorax, long legs and a distended body. The wing covers are metallic dark blue, the head and snout dark blue, and the thorax and legs brick red. The weevil is 5.5 - 8 mm (1/4 - 3/8 inch) in length.
Egg - The egg is creamy white, broadly oval, and narrowed at the attached end. It is convex in outline and is 1/40 inch long and 1/50 inch wide.
Larva - When newly hatched, the larva or grub is nearly pure white and when mature it is ivory white. When full grown, the grub is 5 - 8.5 mm (3/16 - 5/16 inch) long. It is wrinkled, fat and somewhat crescent-shaped. The head is yellowish-brown, small and narrower than the body.
Pupa - The pupa is initially pure white but later the eyes, wing pads, and legs become darker while the remainder of the body becomes yellowish. The head and snout are folded down along the ventral surface. The pupa is about 5 mm (1/6 - 1/5 inch) long.
There are usually 3 and sometimes 4 larval instars which require a total of 12-154 days to complete development, depending on the temperature. The larva tunnels throughout the sweetpotato and returns to feed near the surface as it matures. The full grown larva excavates a pupal cell near the surface of the sweetpotato and becomes quite for one or more days before pupating. Pupation time varies with the temperature and ranges from 5 to 49 days.
Upon emerging from the pupal stage, 4 to 37 days are required for the adult to tunnel to the surface of the sweetpotato and emerge. Oviposition begins about 15 days after adult emergence. Females lay an average of 119 eggs during a period of about 62 days.
The adult weevil will feed on any exposed part of the plant but prefers the storage root. Feeding punctures occur in patches and are very shallow. In the field, more feeding occurs at the more accessible stem end. The upper surface of the larger sweetpotatoes beneath or near cracks in the soil are more susceptible to feeding. When exposed to light, the weevil feeds on the undersurface of the sweetpotatoes. Feeding on the vines by the adult does not occur as distinct punctures but as gnawing. On the main stems, petioles, and leaf veins the feeding scars often run together or overlap. The weevil feeds in the crown or basal part of the vines, stems, petioles, and leaf veins in approximately that order.
The sweetpotato weevil can survive the winter months provided extended periods of freezing temperatures do not occur. This is especially important in North Carolina since many growers have modern storage houses that can provide a favorable environment for the weevil to overwinter. Grass and weeds furnish some protection to the weevils. Activity is sluggish below 70 degrees F and nearly ceases below 60 degrees F. Weevils become completely inactive at 40 degrees F.
Adult weevils fly freely during the warm part of the year and capable of flying at least 1 mile per season. Weevils in NC have been collected year round. However, peak activity is from July through October in the Ft. Fisher area. Since the weevil spreads readily from infested storage areas to field plantings, precautions are necessary to prevent natural movement from storage houses to beds or plantings. Flights take place primarily at night but also during the day if the insects are disturbed. Adults fly most freely during calm weather or when there are gentle breezes. Flight activity tends to be more general or dark nights than on bright moonlit nights.