Spodoptera latifascia Walker Lepidoptera Noctuidae

Natural History

Distribution. These native armyworms are found in eastern states, primarily along the Gulf Coast. They also are found in the Caribbean and in Central and South America. Adults and sometimes larvae of sweetpotato armyworm, Spodoptera dolichos (Fabricius), may occur as far north as Kentucky and Maryland. Velvet armyworm, Spodoptera latifascia (Walker), rarely is numerous outside the Gulf Coast area and is more damaging than sweetpotato armyworm in Florida and Central America.

Host Plants. These insects are general feeders, and only occasionally damage vegetables in the United States. Among vegetable crops damaged are asparagus, bean, corn, cowpea, pepper, potato, sweet potato, turnip, and probably others. Sweetpotato armyworm is known to damage cotton, and has also been called the "larger cotton cutworm." Velvet armyworm also is a common pest of ornamental plants in Florida.

In studies conducted in Honduras, velvet army-worm oviposited preferentially on Amaranthus spp. and Ixophorus unisetus weeds relative to corn and sorghum; however, only amaranths, Amaranthus spp., were good hosts for larvae (Portillo et al., 1996b). Other weeds known to sustain larvae are sea purslane, Thrianthema portulacastrum; sena, Cassia leiophila; mor-ningglory, Ipomoea sp.; Melampodium divaricatum; and purslane, Portulaca oleracea (Portillo et al., 1991,1996a).

Natural Enemies. Sweetpotato armyworm is parasitized by Winthemia quadripustulata (Fabricius) (Diptera: Tachinidae). Velvet armyworm is parasitized by Archytas marmoratus (Townsend) and Winthemia sp. (Diptera: Tachinidae), Chelonus sp. (Hymenoptera: Braconidae), Euplectrus plathypenae Howard (Hymen-optera: Eulophidae), and Trichogramma sp. (Hymenop-tera: Trichogrammatidae). Velvet armyworm is also known to be infected with a Vairimorpha sp. (Micro-sporidia: Nosematidae) and a nuclear polyhedrosis virus.

Life Cycle and Description. The biology of these insects is poorly known. Larvae have been collected from July-November, and "several" broods of S. doli-

chos are reported to occur annually in Tennessee (Crumb, 1956). Development from the egg to adult stage requires 35-50 days.

  1. The egg closely resembles that of yellow-striped armyworm, Spodoptera ornithogalli. It is a slightly flattened sphere, and measures about 0.46 mm in diameter and 0.36 mm in height. The egg bears about 50 narrow ridges that diverge from the center. They are laid in clusters of 200-500 eggs on the undersides of leaves, and bear scales from the female's abdomen. Apparently females produce 5003000 eggs. Duration of the eggs stage is 4-8 days.
  2. Larvae are gregarious during the early instars but disperse thereafter. There likely are 5-7 instars in both species. Crumb (1929) gave head capsule widths of 0.27, 0.41, 1.0-1.1, 1.5-1.6, 2.2-2.5, and 3.1-3.3 mm for instars 1-6 of S. dolichos. Santos et al. (1960) indicated head capsule widths of 0.3, 0.45, 0.75, 0.95, 1.4, 2.20, and 3.25 mm for instars 1-7 in S. latifascia. Duration of the larval stage is reported to be 23-30 days in S. dolichos and 15-27 days in S. latifas-cia. Instar-specific development time is reported to be about three, four, four, four, three, four, and five days for instars 1-7, respectively, in S. latifascia. Larvae of S. latifascia completed their larval period in about 15 days when fed cotton, and 18 days when soybean; no larvae completed development on lettuce. Larvae are variable, ranging from light gray or green to blackish, and well marked with spots and stripes. Larvae bear prominent dark triangular spots subdorsally along the abdomen, consistent with many other Spodoptera spp., and lateral yellowish lines are usually present both above and, to a lesser extent, below the spiracles. The subspiracular yellowish line is not interrupted by a spot on the first abdominal segment, as is usually the case with southern armyworm, S. eridania, but the supraspiracular line does bear a dark spot. Dark subdorsal markings found on the mesothorax are small and semicircular in S. latifascia but large and trapezoidal in S. dolichos. In contrast, the mesothoracic markings of yellowstriped armyworm, with which these species are easily confused, are triangular. Larvae attain body lengths of 43 and 48 mm in S. dolichos and S. latifascia, respectively, which makes them quite large for the genus. (See color figures 60 and 62.)

Sweetpotato armyworm larva.

Sweetpotato armyworm larva.

Anterior region of sweetpotato (left) and velvet (right) armyworms. Adult sweetpotato armyworm.

dark brown and measures 20-30 mm long. Duration of

Adult velvet armyworm.

dark brown and measures 20-30 mm long. Duration of

Adult velvet armyworm.

the pupal stage is 9-20 days.

Adult. The adults are grayish-brown moths with few distinguishing characters, but heavily mottled forewings. The forewing of sweetpotato armyworm usually bears an irregular orangish streak distally, and the thoracic region is marked with two broad-dark bands running from the head to the abdomen; the moths of velvet armyworm lack these characters. In both species, the hind wing is white, with a narrow dark band along the distal edge. The wingspan of these moths is 40-50 mm. (See color figure 249.)

Descriptions of sweetpotato armyworm are found in Crumb (1929, 1956). Velvet armyworm was described by Levy and Habeck (1976), developmental biology was given by Habib et al., 1983, and the sex pheromone discussed by Monti et al. (1995). Larvae of both species were described briefly by Passoa (1991), and keys for many Spodoptera were presented by Levy and Habeck (1976), Passoa (1991), and Hepp-ner (1998). These species also occur in a key to Louisiana noctuids (Oliver and Chapin, 1981) and in a key to armyworms and cutworms in Appendix A. Keys to adults were presented by Todd and Poole (1980) and Heppner (1998). King and Saunders (1984) discussed biology in Central America.

Damage

Larvae are defoliators, and because of their large size inflict considerable damage late in the larval stage. They can function as cutworms, severing young plants at the soil surface, and also may burrow into tomato and other soft fruits.

Management

Larvae are most often controlled by application of foliar insecticides. These insects are not frequent pests, however. In Central America, velvet armyworm sometimes feeds on corn and sorghum, but if weeds are present the larvae of this insect feed preferentially on them. Corn and sorghum, because they are not suitable for larval development, serve as sink habitat, whereas certain broadleaf weeds serve as a source habitat (Portillio et al., 1991).

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