|Crop Knowledge Master|
Hellula undalis (Fabricius)
|Imported Cabbage Webworm|
Jayma L. Martin Kessing, Educational Specialist
Ronald F.L. Mau, Extension Entomologist
Department of Entomology
Updated by: J.M. Diez April 2007
Principal plant hosts are broccoli, cabbage and cauliflower. It also attacks Chinese cabbage, Chinese broccoli, Chinese mustard, daikon, eggplant flowering white cabbage, mustard cabbage and radish. In Hawaii it is a major pest of all Brassicaceae.
First identified in Italy, this insect has a widespread distribution throughout the Middle East, Asia and the Pacific. However, it is not known in North and South America or the West Indies. In Hawaii, it was first recorded Oahu in 1899 and is now present on all islands.
This caterpillar is an important pest on head cabbage, Chinese cabbage, and mustard cabbage. Major damage occurs on young plants but caterpillars also feed on older plants. Damage is most severe between transplanting and the heading stage of cabbage even though the larvae are present in the field throughout the crop (Sivapragasam and Abdul Aziz, 1990).
On cabbage seedlings, extensive damage can occur when the caterpillars feed on the growing points (apical meristem) and the developing leaves. Severe injury occurs when they tunnel into the main stem. Damage at this stage of plant growth results in stunting, and sometimes death of young plants. More often, however, damage to the growing point results in deformed plants and the formation of multiple growing points or heads. On older plants the larvae feed on leaves and by tunneling into leaf petioles.
Because of their secretive nature, symptoms of imported cabbage webworm infestations are often not detected until plants appear stunted or deformed. However, silk webbing and frass are easily found when infested seedlings are examined closely. As the common name of this pest suggests, silk webbing is often associated with their feeding especially when they feed on exposed parts of the plant. Sometimes the larvae tie leaves together with silk strands and feeds within. Other times, the larvae feed under a protective silk web. On loose heading cabbage plants, the larvae are often found without webs feeding on young leaves. This webbing and fecal frass are characteristic of webworm damage, although the intrained observer could easily mistake silk webbing for diamondback moth larvae for that of imported cabbage webworm.
Development of pest stages is greatly influenced by temperature. The upper threshold of development is about 98û F and the lower threshold for development is 68û F (Awai 1958). In Hawaii pest development is most rapid during July and August and slowest during December through February. The complete life cycle for the imported cabbage webworm varies from 17 to 52 days. Many generations occur in Hawaii throughout the year.
The ovoid eggs are about 1/50 inch long, rather variable in contour, being slightly flattened upon the surface of deposit. Pearly white when laid, they become pinkish the next day and then turn brownish-red with the dark head of the larvae visible at one end just before hatching (Harakly, 1968a). Eggs are laid singly, or in groups or chains of 2 or 3 on the leaves of cabbage near the bud. In Hawaii, eggs hatch in 2 to 3 days at mean temperatures of 82ûF (Awai, 1958; Sivapragasam and Abdul Aziz, 1990).
Caterpillars are greyish-yellow with five broad, irregular reddish-brown bands that extend the length of the body. There are five larval (caterpillar) stages. The first stage larva is about 1/25 inch in length and the mature larva is 1/2 inch long. Duration of larval stages varies with different hosts. On cabbage larval development is completed in 16 to 19 days, but on cauliflower it may require only 11-13 days. At 82.4ûF the duration's of the first, second, third and fourth larval stages are 3 days, 2 days, 3 days, 2 days, and 4 days, respectively.
Pupation occurs in a silk cocoon. Early stage pupae are soft and very pale yellowish-white in color with a bright red, dorsal blood. A few hours later, the pupae harden and turn a light brown. Pupae are 3/8 to 1/2 inch in length and 1/5 to 1/4 inch in width. Cocoons composed of silk threads are generally spun between leaves or at the entrance of the feeding tunnel. However, they have also been found under or beside secondary buds growing from old cabbage stems, inside the stem and bases of dropped leaves, or approximately 1/8 inch deep in the soil immediately surrounding the host plant. Adults emerge in 8 days at 82.4ûF (Sivapragasam and Abdul Aziz, 1990).
Adults are greyish-brown moths. Forewings have wavy gray markings, a curved pale patch subterminally, and a kidney shaped mark one third length from the tip. Hindwings are pale, with the tip being lightly colored. The wingspan ranges from 3/4 to 1/3 inch long. Adults live from 4 to 8 days, longevity increasing with a decrease in temperature.
Egg laying begins within 24 hours of adult emergence and continues for 3 to 10 days. At 82.4ûF each female lays an average of 27 eggs per day and 175 eggs during her life time (Sivapragasam and Abdul Aziz, 1990).
After hatching from the egg, the young larvae begin to feed on the leaves, especially the young tender leaves of the bud, and usually spin a web about themselves between two leaf surfaces (Fullaway & Krauss, 1945). It often mines into the stalk of the leaf.
Emergence of the adult moth generally occurs in the evening and rarely during the day time. Adults seek a mate 3 to 4 hours after emergence. Like other moths, the adults are primarily active at night. They fly readily, but are more or less obscure in their habits, and are not often seen in cabbage fields (Fullaway & Krauss, 1945).
Very little is known about parasitoids or predators of the imported cabbage webworm in Hawaii. Zimmerman (1958) reported that the parasitic wasp Chelonus blackburni Cameron oviposits into the cabbage webworm eggs, develops within the webworm caterpillar and emerges to spin its own cocoon within the webworm pupal cell. However, the importance of this parasitoid in managing webworm population densities is unknown.
Screening of seedling beds and clean culture are helpful in minimizing damage caused by the cabbage webworm down. Plants should be 5 or 6 inches high and have a vigorous growth before being set out (Fullaway & Krauss, 1945). It is important that "clean" seedlings are used, if not it may be necessary to apply 1 to 2 insecticide applications if infestations are found.
One of the most important considerations of choosing chemical pesticides is the complex of other pests in the cabbage ecosystem. Diamondback moth, imported cabbage worm, and cabbage looper are of equal or greater importance than the webworm. The assumed impact of insecticides on parasitoids of this and other pests is of prime importance in a pest management program. Another factor that may affect the effectiveness of chemical sprays is the difficulty of penetrating the webbing produced by the larvae.
Several insecticides are efficacious in other parts of the world. Carbaryl, methomyl, mevinphos, permethrin, and trichlorfon are effective in controlling larvae of this pest. Tests of bacterial insecticides (Bacillus thuringiensis) in Hawaii and elsewhere suggest that they are only partially effective, and certainly not recommended as standard treatments.
It is important to focus on controlling infestations in younger plants. Crops should be monitored for the presence of larvae and treatment decisions made based on the infestation density. There is no established treatment threshold so growers would want to establish their own arbitrary threshold. A threshold of 15% to 25% of plants infested in a random pattern monitoring program would be a good starting point.
There are no listings for carbaryl, methomyl, mevinphos, permethrin, and trichlorfon as of April 2007.
Awai, D. 1958. A Study of the Identity, Larval Stages, and Natural Enemies of Hellula undalis (Fabricius) (Lepidoptera: Pyralididae) in Hawaii. Thesis submitted to the Graduate School of the University of Hawaii in partial fulfillment of the requirements for the Degree of Master of Science. June 1958.
Fullaway, D. T. and N. L. H. Krauss. 1945. 179. Hellula undalis (Fabr.). In: Common Insects of Hawaii. Tongg Publishing Company, Honolulu, Hawaii. 228 pages.
Harakly, F. A. 1968. Biological Studies on the Cabbage Web-Worm, Hellula undalis FABR. Bull. Soc. Ent. Egypte. 52:191-211.
Harakly, F. A. 1968. The Egg and the Full-Grown Larval Stage of Hellula undalis FABR. Bull. Soc. Ent. Egypte. 52:183-190.
MARDI. 1981. Annual Report of the Miscellaneous Crops Division, Malaysian Agricultural Research and Development Institute Serdang, Selangor, Malaysia.
Marsden, D. A. 1979. No. 6 Cabbage Worm. Insect Pest Series. Cooperative Extension Service, University of Hawaii, College of Tropical Agriculture & Human Resources.
Sivapragasam, A. and A. M. Abdul Aziz. 1990. Chapter 8: Cabbage Webworm on Crucifers in Malaysia. pp. 75-80. In: Diamondback Moth and Other Crucifer Pests. N. S. Talekar (Ed.) Asian Vegetable Research and Development Center. 603 pages.
Waterhouse D. F. and K. R. Norris. 1989. Biological Control Pacific Prospects - Supplement 1. Australian Centre for International Agricultural Research. Canberra. pp. 77-81.
Zimmerman, E. C. 1958. Hellula undalis (Fabricius). pp. 35-38. In Insects of Hawaii, A Manual of the Insects of the Hawaiian Islands, including Enumeration of the Species and Notes on Their Origin, Distribution, Hosts, Parasites, etc. Volume 8: Lepidoptera: Pyralidae. University of Hawaii Press, Honolulu. 456 pages.
MAR/1991, revised MAY/1992.