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