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Hosts

One of the most important pest of crop plants in the crucifer family, the cabbage looper often attacks broccoli, cabbage, cauliflower, Chinese broccoli, Chinese cabbage, daikon, flowering white cabbage, head cabbage and mustard cabbage. This species also attacks several other crops including lettuce, beet, peas, celery, tomato, certain ornamental plants, and many weed plants.

Distribution

The cabbage looper is a native American species distributed throughout North America from Canada to Mexico. In Hawaii, this pest was first recorded in 1939 on cauliflower on Molokai and has subsequently been reported on all major islands except Lanai.

Damage

It is primarily the larval stages that damage the crop. The first two larval stages feed on the lower side of the leaf, eating through the upper epidermis, leaving "windows" in the leaf. Older larvae chew larger holes in the leaves. They often do extensive damage to leaves. Although this pest usually damages leaves, occasional damage has been reported on watermelon rinds and on flowers of various host plants.

Biology

Generations of this insect are continuous throughout the year in Hawaii. The life cycle duration (egg to adult) ranges from 24-33 days.

EGGS

Eggs are hemispherical, pale green or white with shallow ridges that meet at the center of the egg. They are usually deposited singly on the lower leaf surface near the leaf margin. Occasionally they may also be found on the upper side of the leaf. Eggs hatch in 3-4 days.

LARVAE

The newly emerged caterpillars are translucent white. Once feeding starts the larvae become pale green, with a thin white line running lengthwise down each side of the body and two white lines along the middle of the back. The caterpillar stage lasts for 12 to 20 days.

PUPAE

Pupae are yellow green with a few brown patches when newly formed and gradually darken to dark brown before adult emergence. They are 3/4 inch in length. The pupal stage lasts for 9 days.

ADULTS

Adult moths are dark, smoky, gray variegated with light grayish brown. Characteristic small silvery oval spots and U-shaped silvery white marks are on the middle of the forewings. Hindwings are pale brown with the veins conspicuously visible. Males have tufts of gold hair at the tip of the abdomen. Adults live for about 24 days and feed on nectars.

Behavior

Deposition of eggs occurs around dusk. Kishaba et al. (1976) reported greater egg laying preference on lettuce; cabbage and spinach was neutral.

Caterpillars walk in a "looping" manner. They move by holding on with their front legs, arching the middle portion of their body to bring the hind legs forward, and then extending the front of the body holding on with the hind legs.

Pupation usually takes place in leaf litter and crop debris.

Adults are nocturnal.

Management

NON-CHEMICAL CONTROL

Generally used more as a diagnostic tool rather than a control method, ultra-violet traps used with sex pheromone, have controlled populations of the cabbage looper in some localities in the mainland US.

Biological Control

Many natural predators and parasites have been reported for this pest and may be responsible for high field mortality of cabbage loopers. The encyrtid wasp, Coptisoma truncatellum, develops polyembryenically (several wasps develop from a single laid egg -- like identical twins) and emerges from young pupae. This wasp has been reasonably effective in controlling the cabbage looper in some situations.

The nuclear polyhedrosis virus that occurs naturally in the field is also effective against this pest. Loopers killed by this virus are dark, soft and shapeless with their body contents often spilling onto leaves.

Bacillus thuringiensis is most effective on small larvae. This treatment does not adversely affect beneficial insects and is also effective against some other lepidopterous pest.

CHEMICAL CONTROL

Historically, chemical control has been difficult because this species has established resistance to many insecticides including DDT, carbaryl, parathion, methomyl, and others. This pest is readily controlled by applications of bacterial and pyrethroid insecticides. Cabbage loopers are best controlled during the early larval stages.

References

Adlerz, W. C. 1971. Cabbage Looper Control on Watermelon at Leesburg, 1968-1970. Florida State Horticulture Soc. Proc. Ann. Meeting. 8:145-146.

Flint, M. L. 1985. Loopers, Trichoplusia ni and Autographa californica. pp. 44-47. In Integrated pest Management for Cole Crops and Lettuce. University of California Publication 3307. 112 pages. 

Kishaba, A. N., T. W. Whitaker, Berry, W., and H. H. Toba. 1976. Cabbage Looper Oviposition and Survival of Progeny on Leafy Vegetables. Hortscience. 11(3):216-217.

Marsden, D. A. 1979. Insect Pest Series No. 6 Cabbage Worm. Cooperative Extension Service, University of Hawaii, College of Tropical Agriculture and Human Resources.

Tanabe, A. M. 1961. The Biology and Pathogenicity of a Microsporodian Parasite of the Cabbage Looper, Trichoplusia ni (Hubner). MS Thesis, University of Hawaii.

Zimmerman, E. C. 1958. Plusia Trichoplusia ni brassicae (Riley). pp. 366. In Insects of Hawaii. A Manual of the Insects of the Hawaiian Islands, including Enumeration of the Species and notes on the Origin, Distribution, Hosts, Parasites, etc. volume. 7: Macrolepidoptera. The University Press of Hawaii, Honolulu. 542 pages.

SEP/1991 revised MAY/1992.

T-NI

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