Oriental Cabbage Webworm Hellula undalis Fabricius Lepidoptera Pyralidae

Natural History

Distribution. Cabbage webworm, Hellula rogata-lis, apparently is an American insect, and is found in the southern states from Virginia and Florida to California. Occasionally it is reported from a more northern location, such as Nova Scotia, but is not a pest in northern climates. When first studied in Georgia in the late 1800s, it was confused with the closely related H. undalis. This latter species, sometimes called the oriental cabbage webworm, is found in tropical and subtropical areas of Europe, Africa, and Asia. It also is found in Hawaii.

Host Plants. These insects feeds on several cruci-fer crops, including broccoli, cabbage, collards, kale, kohlrabi, mustard, radish, rutabaga, and turnip. Studies by Latheef and Irwin (1983) failed to demonstrate significant preference among collards, kale, mustard, and turnip. Weed hosts include shepherdspurse, Capsella bursa-pastoris; and purslane, Portulaca oleracea.

Natural Enemies. Despite a report by Chittenden and Marsh (1912) of several fly (Diptera: Tachinidae) and wasp (Hymenoptera: Braconidae and Ichneumo-nidae) parasitoids, more recent studies have failed to identify natural enemies of cabbage webworm (Ru and Workman, 1979; Kok and McAvoy, 1989).

Life Cycle and Description. Cabbage webworm generation time is 43, 34, and 23 days at 26°, 30°, and 35°C, respectively. They breed continuously in southern Florida and Hawaii, but in more temperate areas such as Virginia they become numerous enough to cause damage only during the autumn months.

  1. The eggs are gray or yellowish-green when first deposited, but turn pink as embryonic development proceeds. The flattened eggs, which are often marked with a distinct nipple at one end, measure about 0.3 mm wide and 0.5 mm long. Oviposition does not occur at 15°C, though eggs incubated at this temperature can hatch. Temperatures of 20-30°C are suitable both for oviposition and egg hatching. Eggs hatch after about three days. They are normally deposited singly or in small masses on the terminal leaves.
  2. The first and second instars feed singly as a leaf miner between the upper and lower epidermis. Initially, the larva is yellowish gray, but soon takes on an appearance resembling the mature larva. At about the third instar, larvae begin to web and fold the foliage. Much of the damage occurs on the lower surface of the leaf, but large larvae also feed on the leaf midrib. There are five instars. The head capsule widths are 0.2, 0.3, 0.5, 0.8, and 1.2 mm, respectively. Average body length for the five instars is 0.9, 2.4, 4.8, 6.4, and 9.9 mm, respectively. Development time of the larval instars at 30°C is 2.8, 2.4,1.9, 2.4, and 4.3 days, respectively. The mature larva is yellowish-gray, with five brownish purple longitudinal bands running the length of the insect, and attains a maximum length of 15 mm. The head capsule is black. The body is sparsely covered with moderately long yellow or light brown hairs, and tapers at both the anterior and posterior ends. (See color figure 69.)

Cabbage webworm larva.

Cabbage webworm larva.

  1. Pupation occurs in the soil, in a webbed cocoon comprising grains of soil. The duration is 5.05.5 days at 30°C. The pupa is yellowish-brown, and measures about 7-9 mm long.
  2. The moth consists of yellowish-brown front wings which are marked with white bands and a dark kidney-shaped spot. The hind wings are grayish white, though the margin is darker. The wingspan of the moth is about 18-21 mm. Oviposition begins about 3-5 days after moths emerge. About 150-300 eggs are produced by each female. Adult longevity is normally 7-14 days.

The biology of cabbage webworm was presented by Chittenden and Marsh (1912) and McAvoy and Kok (1992).

The oriental cabbage webworm, H. undalis, is very similar in appearance to H. rogatalis (Munroe, 1972). The genitalia are used to distinguish these species. The biology of H. undalis was given by Youssef et al. (1973) and Sivapragasam and Aziz (1992), and is virtually identical to that of H. rogatalis.

Damage

Larvae initially mine the leaves, eventually webbing and rolling the foliage. They may cause enough damage to destroy the growing tip of plants. Thus, the problem is most severe with young plants (Smith and Brubaker, 1938). Webworms also sometimes burrows into veins, causing death of the leaf beyond the point of feeding.

Cabbage webworm is normally a minor component of the lepidopterous defoliator complex of crucifers. However, Latheef and Irwin (1983) suggested that it had the potential to become one of the most serious pests in Virginia, especially of autumn-grown crops. Kok and McAvoy (1989) reported that webworm com-

Hellula Phidilealis
Adult cabbage webworm.

prising 43% of the larvae affected broccoli during a 1987 study in Virginia, making it the most abundant defoliator.

Management

Insecticidal control can be difficult owing to the cryptic feeding behavior of the larvae, and the tendency to feed on the rapidly expanding terminal growth. To keep the terminal tissue protected with chemical insecticides or Bacillus thuringiensis, frequent applications are required, at least once in a week. Evaluation of trap crops in India (Srinivasan and Moorthy, 1992), using early planted mustard to attract insects and thereby to reduce damage to cabbage, was effective for both diamondback moth, Plutella xylostella (Linnaeus) and oriental cabbage webworm, H. undalis; this is likely effective for H. rogatalis, also. In Virginia, late-maturing cultivars tend to be more heavily infested than early maturing varieties (Vail et al., 1991).

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