Sweetpotato Hornworm Agrius cingulatus Fabricius Lepidoptera Sphingidae

Natural History

Distribution. Sweetpotato hornworm is native to the western hemisphere, where it is found throughout the tropical and subtropical areas. In the United States, it occurs throughout the southern states, and is found throughout the year in Florida and southern Texas. Each summer the moths are found as far north as Arkansas, and occasionally a stray is found in such northern locations as Michigan and Nova Scotia. Sweetpotato hornworm also occurs in Hawaii and Puerto Rico.

Host Plants. Larvae feed on various species of Ipomoea in the plant family Convolvulaceae. Among vegetable crops, only sweet potato is injured. The adults feed on nectar from various deep-throated flowers.

Natural Enemies. The eggs of this species are heavily parasitized by Trichogramma semifumatum (Perkins) (Hymenoptera: Trichogrammatidae). Several fly parasitoids are known, including Agryophylax spp., Belvosia bifasciata (Fabricius), Chaetogaedia monticola (Bigot), Drino inca (Townsend), D. incompta (Wulp), and D. rhoeo (Walker) (all Diptera: Tachinidae) (Arnaud, 1978). The aforementioned tachinids attack the larval stage and have a wide host range; they also have been reared from many other species of Lepidoptera.

Life Cycle and Description. The biology of this insect is not well documented. The number of generations is reported to be at least two in North Carolina, and probably more in Gulf Coast states.

  1. The eggs are deposited singly on the underside of the foliage. They are nearly spherical in shape, whitish or greenish, and measure about 1.35 mm in diameter. The female is reported to produce about 30-40 eggs. Duration of the egg stage is 6-10 days.
  2. Young larvae measure only about 3 mm long when they hatch, and are greenish-white with white granulations. The head, however, is greenish-yellow. There are five instars and the larvae attain a length of about 115 mm at maturity. Head capsule widths are about 0.5,1.0,1.8, 3.2, and 6.0 mm, respectively. Duration of the larval stage is about 30-60 days, depending on temperature. The appearance of the larva is variable, the body color ranging from light green or brown to almost black. Typically, in the early instars the body is green and marked by oblique black stripes along each side on a whitish or light background, or with a narrow white band along the lower edge of the oblique stripes. The oblique lines may also form "V"-shaped lateral markings. The spiracles and anal appendage, or "horn" are blackish. In the final instar, the larva may remain green or becomes mostly brown. The green form has dark bands on the head capsule, and the oblique bands are found in the earlier instars; the posterior oblique band terminates in the horn. In the brown form, the body is gray with brown spots. The lateral oblique lines are weak, lighter beneath, and less likely to be "V"-shaped markings. The black spiracles are surrounded by a dark ring, and give the appearance of very large spiracles. The prolegs are dark brown or purplish. As in the green form, the head is marked with dark bands and the posterior oblique lines terminate in the dark horn. (See color figures 85 and 86.)
  3. At maturity the larva pupates in the soil. The pupa is dark brown or mahogany red and measures 55-65 mm long. Duration of this stage is 20-30 days. (See color figure 269.)
  4. The moth is sometimes known as the "pink-spotted hawk moth." The adult is fairly typical in form for sphingids, heavy bodied with long pointed front wings, and short hindwings. The front wings are dark gray mottled with brown and black. The hind wings are pinkish basally with 2-3 dark bands that run parallel to the wing border. The abdomen bears a dark band dorsally and transverse pink or rose transverse bars on each side. The moth measures about 45 mm long and 90-100 mm in wingspan. Moths are often observed feeding from flowers at dusk.

Sweetpotato hornworm larva.

Sweetpotato hornworm larva.

Adult sweetpotato hornworm.

The biology of the sweetpotato hornworm was given by Fullaway (1911), with additional notes provided by Hodges (1971). Larvae were described by Dyar (1895).

Damage

The larvae of this species feed on foliage. They rarely are abundant enough to be considered a serious pest, though sometimes they have been so abundant as to defoliate entire fields and to acquire the "armyworm''-like habit of dispersing in groups (Watson, 1944).

Management

Larvae are easily suppressed with foliar insecticides, including the microbial insecticide Bacillus thuringiensis.

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