Omphisa anastomasalis Guenee Lepidoptera Pyralidae

Natural History

Distribution. Sweetpotato vine borer is widespread in Asia where it is destructive in such countries as China, India, Indonesia, Japan, Philippines, and Vietnam. In the United States its distribution is limited to Hawaii, where it was first observed in 1900.

Host Plants. This species is associated with plants in the family Convolvulaceae. It is destructive only on sweet potato, but other Ipomoea spp. are common hosts. In Hawaii it is also reported from Stictocardia campanulata.

Natural Enemies. Larval parasitoids known from Hawaii include Chelonus blackburni Cameron (Hymen-optera: Braconidae), Enytus chilonis Cushman and Pris-tomeris hawaiiensis Perkins (both Hymenoptera: Ichneumonidae). Other parasitoids are known from Asia.

Life Cycle and Description. Phenology of sweet-potato vine borer is not documented. Considering the importance of the insect and crop, relatively little work has been done on this species.

  1. The eggs of sweetpotato vine borer are elliptical with a flat base, measuring about 0.6 mm long, 0.5 mm wide, and 0.35 mm in height. They are greenish and laid singly or in small clusters of 2-3 in crevices on leaves, petioles, and stems. The incubation period is 5-7 days.
  2. After hatching, larvae bore into the vine and move toward the base of the plant as they feed.

Sweetpotato vine borer larva.

Sweetpotato vine borer larva.

Larvae are only about 1 mm long at hatching and are whitish with a black head and prothoracic shield. Mature larvae attain a length of about 30 mm and may be yellowish-white or light purple. Large larvae are marked with brownish tubercles, which appear as spots over most of the body. The intersegmental membranes tend to be yellowish-brown, especially in the anterior region of the body. The head and prothorax are brownish and the body bears scattered stiff hairs. There are six instars. The duration of the larval stage is usually 30-35 days, but values of 2192 days have been reported.

  1. Pupation normally occurs within the base of the vine, but occasionally larvae pupate in the tubers if they are close to the soil surface. The larva spins a thin web-like cocoon and cuts an exit hole for the moth before pupation. The pupa is light to medium brown and measures about 16 mm long and 3 mm wide. Duration of the pupal stage is 14-18 days.
  2. The moth is white, but is heavily marked with yellowish brown. The base of the front wings bear a large, irregular dark spot. The abdomen is brown dorsally. The distal area of the front wings and the entire hind wings are marked with irregular dark lines. The wingspan is 30-40 mm. Moths are nocturnal and females produce sex pheromone. Adults survive for about 10 days, during which females deposit about 300 eggs.

Sweetpotato vine borer pupa.

Sweetpotato vine borer pupa.

Omphisa Anastomasalis
Adult sweetpotato vine borer.

Fullaway (1911) and Talekar and Pollard (1991) provided the biology of sweetpotato vine borer. Yoshiyasu (1975) described the adult stage.

Damage

Larvae mine the vines of sweet potato, disrupting the flow of water and photosynthates. Infested vines show weak growth, poor foliage development, and poor tuber development. Larvae also may bore into the upper portions of tubers. Yield reductions are directly related to infestation levels, and yield loss of 30% or more are common in Asia. In Hawaii, heavy infestations have been reported to kill plants (Talekar and Cheng, 1987; Talekar and Pollard, 1991). When infestation levels are low the feeding damage is much less pronounced. Sometimes, the only outward evidence of larval feeding is the accumulation of fecal material near the opening of the larval tunnel, which usually is at the crown of the plant.

Management

Insecticides. Insecticides can be applied for larval suppression, but the mining behavior of this insect requires that insecticides be in place at hatching, before larvae burrow into the tissue, or be systemic and translocated to the tissues where larvae feed. In areas of the world where sweetpotato vine borer is common, insecticide use often results in very sizable yield increases. Farmers are often discouraged from using insecticides, however, because of the low value of the crop.

Host-Plant Resistance. Considerable effort has been directed to screening varieties for resistance to sweetpotato vine borer. Although some cultivars display resistance, the yield potential of these selections is low, and additional work is needed by breeders to combine the insect resistance with high yield characteristics.

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