Occurrence Patterns and Control Methods of the Sweet Potato Hornworm

The sweet potato hornworm, Herse convolvuli (Linnaeus), belongs to the order Lepidoptera, family Sphingidae. It is distributed in Japan, and in China it is also found in Liaoning, Hebei, Henan, Shandong, Shanxi, Zhejiang, Taiwan, China, Guangdong and other provinces. It mainly damages plants of the Convolvulaceae, Solanaceae and Fabaceae. 

I. Morphological identification

1. Adult: body length 43-53 mm, wingspan 100-120 mm, head dark gray, thorax dorsum grayish brown, with 2 tufts of scales forming a “” (eight) shape. The mesothorax has grayish white markings. The abdominal dorsum has a gray longitudinal band. Each segment has white, red and black alternating transverse stripes on both sides. Forewings grayish brown, densely covered with serrated and cloud-like markings. Hindwings with 4 dark brown transverse bands, the fringe white mixed with dark brown.

2. Egg: spherical, about 2 mm in diameter, pale yellow-green.

3. Larva: mature larva body length 60-90 mm, body surface densely covered with small granules, abdominal segments 1-7 each with 7 dorsal folds. There are two color forms: in the green form the head is green, with pale yellow oblique lines on both sides, the thorax pale green, the dorsal line, subdorsal line and subspiracular line yellow, and abdominal segments 1-7 with yellowish white oblique lines on both sides. Spiracles orange-yellow, peritreme brown, caudal horn yellowish brown with a black tip, thoracic legs yellowish brown; in the brown form the head is yellowish brown with 2 black longitudinal stripes, the thoracic subdorsal line appears as a relatively broad pale stripe, the anal plate appears as a yellow band, abdominal segments 1-7 have pale yellow oblique stripes on both sides, and the spiracles and legs are black.

4. Pupa: brown, body length 56 mm, proboscis long and free, vermilion to dark red, wings reaching the fourth abdominal segment, anal spine triangular.

II. Occurrence patterns

Life history and habits: 1-2 generations occur each year in Beijing, and 3 generations each year in South China. It overwinters as a mature larva that pupates in the soil at a depth of 5-10 cm. In the Beijing area it appears in May or early October, is phototactic, and lays eggs scattered on the underside of leaves. In South China larvae are seen damaging plants at the end of May, with larger numbers occurring in September-October; the larvae feed on the tender stems of water spinach, and older larvae have a large appetite, and when damage is severe they can eat the leaves bare, leaving only the old stems. In South China the egg stage of this insect is 5-6 days, the larval stage 7-11 days, and the pupal stage 14 days. Adults hide by day and feed on nectar at night, mating and laying eggs. Where stems and leaves are luxuriant, more eggs are laid and larval damage is also severe.

III. Control methods

It generally occurs sporadically and can be eliminated manually along with field management, or controlled incidentally when controlling other pests.