Herpetogramma bipunctalis Fabricius Lepidoptera Pyralidae

Natural History

Distribution. Hawaiian beet webworm, Spoladea recurvalis (Fabricius), is found throughout the world in tropical and subtropical regions. In North America, it is found in the southern states from Florida west to California and Hawaii, and also in Puerto Rico. It sometimes causes damage as far north as Virginia, but it cannot overwinter there and must reinvade annually; thus it inflicts injury only late in the season. Its origin is uncertain, but it is not native to North America.

Spotted beet webworm, Hymenia perspectalis (Hubner), and southern beet webworm, Herpetogramma bipunctalis (Fabricius), are closely related to Hawaiian beet webworm. They are not well known, but also are tropical pests with a wide geographic range. In the United States, they similarly are southern insects but can occasionally cause injury as far north as Illinois and Virginia.

Host Plants. Hawaiian beet webworm is largely restricted to plants in the family Chenopodiaceae. Among vegetable crops, beet, chard, spinach, and New Zealand spinach are normally injured. Sugarbeet is readily attacked, but this crop is rarely grown in the warm environments favored by Hawaiian beet web-worm. When they face starvation, this insect may feed on other crops, but it is much less damaging than the better-known webworms—beet webworm, Loxostege sticticalis (Linnaeus); alfalfa webworm, L. cereralis (Zeller); and garden webworm, Achyra rantalis (Guenee). Weed hosts are pigweed, Amaranthus spp., lambsquar-ters, Chenopodium album, and purslane, Portulaca oleracea. Pigweed is preferred even over cultivated hosts. Spotted beet webworm and southern beet web-worm display the same dietary preferences as does Hawaiian beet webworm. Tingle et al. (1978) indicated that southern beet webworm was the dominant caterpillar on Amaranthus hybridus in Florida corn fields during the late summer months.

Natural Enemies. Hawaiian beet webworm is known to be parasitized by Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), Venturia infesta (Cresson) (Hymenoptera: Ichneumonidae), Argyrophy-lax albincisa (Weidemann), Chaetogaedia monticola

(Bigot), Eucelatoria armigera (Coquillett), and Nemorilla pyste (Walker) (all Diptera: Tachinidae).

Not surprisingly, the parasitoid complex attacking spotted and southern beet webworms is similar to Hawaiian beet webworm. Venturia infesta (Cresson) (Hymenoptera: Ichneumonidae) has been reared from all three webworms. Also, Apanteles mimoristae (Muesebeck) (Hymenoptera: Braconidae) is associated with spotted beet webworm, whereas Gambrus ultimus (Cresson), Temelucha sp. (both Hymenoptera: Ichneu-monidae) and C. marginiventris (Hymenoptera: Braco-nidae) attack southern beet webworm. Argyrophylax albincisa (Weidemann) is associated with spotted beet webworm and Nemorilla pyste (Walker) with southern beet webworm (both Diptera: Tachinidae).

Life Cycle and Description. In Hawaii, Hawaiian beet webworm is active throughout the year and about 10 generations occur annually. During warm weather, one generation is completed in about 30 days. The biology of spotted and southern beet webworms is less certain, but seems to be basically the same as Hawaiian beet webworm except as noted below.

  1. The egg is elliptical, iridescent white, and flattened, and may be deposited singly or in rows of up to several eggs. The egg measures 0.6 mm long, 0.4 mm wide, and 0.25 mm in height. They most often are laid on the lower surface of leaves adjacent to large veins. Duration of the egg stage is about four days.
  2. Young larvae of Hawaiian beet webworm feed beneath the leaves, and occasionally spin light webs in which they rest. The larvae initially are pale green, though a few dark spots are found on the head and thoracic plate. As larvae attain maturity they develop broad, irregular, whitish lateral stripes that contrast strongly with a dark stripe dorsally. The larvae also become uniformly pinkish or rust-colored as they prepare to pupate. The head capsule increases in width from 0.25 to 1.2 mm as the larva grows. The body bears numerous stout hairs over the length of its body, but lacks the dark spots or rings found with such hairs on many webworms. The larval development period is normally 9-13 days. (See color figure 73.)

Larvae of spotted beet webworm also are green, but as its common name suggests, bear numerous spots. The thorax and abdomen are equipped with raised-dark spots from which arise dark hairs. The head bears purplish dots, though the center is unmarked. The thoracic plate has black borders.

Larvae of southern beet webworm are dark-green with a dark, nearly black, head. The thoracic plate is similarly dark except for the central area. The body bears numerous large, dark, raised spots from which

Hawaiian beet webworm larva.

Spotted beet webworm larva.

Spotted beet webworm larva.

arise black hairs. The spots are light in color centrally, however, resulting in a ring-like appearance and causing this insect to resemble garden webworm, Achyra rantalis (Guenee). (See color figure 72.)

Pupa. Mature larvae drop to the soil to pupate. They burrow slightly beneath the soil surface and form firm, compact, elliptical cocoons of silk covered with grains of soil. The pupa is light brown and the posterior end is equipped with terminal spines bearing hooked tips. The pupa measures about 10 mm long

Southern beet webworm larva.

Southern beet webworm larva.

and 2.5 mm wide. Duration of the pupal stage is 7-14 days.

Adult. The moth of Hawaiian beet webworm is dark brown, and often tinted purple. The front and hind wings are marked with a white transverse band that nearly crosses the wings. The forewing also bears one elongate and two small white spots distally. The margin of the front wings is alternating dark and light. Narrow light bands are found on the abdomen. The wingspan measures 17-23 mm. (See color figure 210.)

Spotted beet webworm is similar to Hawaiian beet webworm in general appearance. The spotted species is lighter brown, however, with a reddish tint, and the white wing markings are less discrete and pronounced. The wingspan is about 20 mm.

Southern beet webworm moths are light yellowish-gray, sometimes with an iridescent purplish cast. The front wings bear three dark spots along the leading edge, but the markings are not very distinct. The hind wings are not distinctly marked. The abdomen is

Hawaiian beet webworm pupa.

Hawaiian beet webworm pupa.

darker. The wingspan is 22-26 mm. (See color figure 214.)

The biology of Hawaiian beet webworm was given by Marsh and Chittenden (1911b) and Walker and Anderson (1939). Spotted beet webworm was described by Davis (1912) and Chittenden (1913a). Southern beet webworm was described by Chittenden (1911a).

Damage

Young larvae remain on the lower surface of foliage, not eating entirely through the leaves. When nearly mature, however, they consume the entire leaf. Unlike some other webworm species, webbing is not very pronounced.

Adult Hawaiian beet webworm.
Herpetogramma Bipunctalis Amaranthus
Adult southern beet webworm.
Pyralidae Dark Brown Whitish Bands
Adult spotted beet webworm.

Management

Infestations often result from the presence of weeds in crop fields. Destruction of weeds can deter oviposi-tion. Insecticidal suppression of webworms is normally accomplished by foliar applications, though this is seldom warranted except, perhaps, for Hawaiian beet webworm in Hawaii. The bacterium Bacillus thuringiensis provides some control.

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