|Crop Knowledge Master|
Pieris rapae (Linnaeus)
|Imported cabbage worm|
Ronald F.L. Mau, Extension Entomologist
Jayma L. Martin Kessing, Educational Specialist
Department of Entomology
Updated by: J.M. Diez April 2007
All the vegetables of the cabbage and mustard families are hosts of the imported cabbageworm. Some of these host plants include: broccoli, Brussels sprouts, cabbage, cauliflower, Chinese broccoli, Chinese cabbage, choy sum, collards, daikon, horseradish, kale, kohlrabi, mustard, mustard cabbage (kaichoy), pak choy, radish and turnip. They also occasionally feed on other plants such as nasturtium, lettuce and sweet alyssum. Shepherd's purse is a weed host of this pest.
Imported cabbageworms are very common to all parts of the United States and Canada. Introduced into the New World in 1860 from Europe, within 20 years it spread throughout the entire eastern United States. This pest was first recorded in the State on Oahu in 1897 and is now common throughout all islands.
Damage consists of large, irregular sized holes throughout the leaf. Worms are usually found on exposed positions on the leaves, which they eat through or gnaw from the edges, giving the outer leaves a very ragged appearance (Fullaway and Krauss, 1945). Young larvae feed on the first formed outer leaves of their host plants. As the worms become mature, they feed on succulent leaves beneath older, fibrous outer leaves. Masses of greenish to brown excrement may be found in the crevices of the plant when the leaves are parted. Extensive feeding can affect plant growth.
Muggeridge (1942) presents extensive life cycle data at varying temperatures. The life span from egg to adult takes from 4 1/2 to 7 weeks depending on temperature. In temperate regions there are three to five overlapping generations per year. In Hawaii this pest is found throughout the year. Eggs and larvae of this insect do not develop at temperatures below 50û F and larvae do not develop at temperatures above 90û F (Muggeridge, 1942).
The yellow, bullet-shaped egg has surface ridges running lengthwise and crosswise. The egg is laid on end, usually on the under surface of the leaves. They occur singly, never in clusters. Eggs hatch in 3 to 7 days.
The green caterpillar has a slender yellow stripe along the middle of the back, and another intermittent yellow stripe along each side of the body. The larva has a velvet-like appearance formed by the presence of numerous, close-set, short, white and black hairs on its body. Detailed descriptions of the larval stages are given by Muggeridge (1942). Larvae increase in size from approximately 1/15 inch long to about an inch in 2 weeks. Throughout their development the larvae are slow crawlers and feed voraciously on leaves.
The pupa is called a chrysalis. It is usually green, but gray or tan colored pupae occur often. The chrysalis is distinctly shaped. It has sharp angular projections over the back and front. Pupae are attached to the under surface of leaves by silk at the tail and a silk rope near the midsection. Pupae are about 3/4 inch long and are found on the plant or in a sheltered area up to 15 yards away from the host plant. Pupal development is completed in 1 to 2 weeks.
The adult white butterfly has a wingspan of 1-1/2 inches. The forewings are black-tipped. A female has two black spots on top of each of her forewings; a male has only one spot. Hindwings are all white on the surface except for a black spot on the outer front margin. There is a slight yellowish hue on the undersides of the wings. Each adult female lays hundreds of eggs.
This butterfly has a slow and lumbering flight (Fullaway and Krauss, 1945). The adult female is quite active during the day. They are easily seen flying in an erratic pattern into the fields to lay eggs, and out of the field to feed on the nectar of wild flowers throughout the day. The males fly in a straight line manner and remain in the field.
High temperatures can inhibit larval development (Muggeridge, 1942) and heavy rainfall can cause high mortality in early instars (Harcourt, 1966). Therefore, larval populations are small during hot and wet seasons, and large in dry and cool seasons.
Harcourt (1966) showed three preadult periods where extensive mortality may occur: 1) between hatching and the second molt, 2) larval stages three to five and 3) during the pupal stage. Control is most effective when it is directed towards the young to half-grown worms (Fullaway and Krauss, 1945; Harcourt, 1966). During these stages the worms are more susceptible to control measures and damage is still relatively low. Rainfall is a major mortality factor on the first two larval stages and parasites are more significant on the more developed larvae (Harcourt, 1966).
After harvest, crop plants should be destroyed and the field plowed. Weeds such as wild mustard and shepherd's purse should be destroyed in nearby areas since the first larval stage of the imported cabbageworm may develop on these alternative weed hosts.
A number of natural enemies prey on and parasitize the imported cabbageworm in Hawaii. The tachnid fly Frontina glomeratus does much to reduce cabbageworm populations (Fullaway and Krauss, 1945). In 1934, the parasitic wasp Apanteles glomeraus was introduced from Japan and also helps to control this pest (Fullaway and Krauss, 1945).
The microsporidian pathogen, Nosema mesilini, is an internal parasite that causes chronic infections with long debilitating effects, sometimes fatal, and reduces the fecundity of female adults. In Hawaii, this pathogen is present throughout the year and has a depressive effect on cabbageworm populations (Haji-Mamat and Tamashiro, 1988). This pathogen is most effective on larvae and has moderate control on adults (Haji-Mamat, 1984). Bacterial diseases, such as Chalcis obscurata, are common amongst these worms (Fullaway and Krauss, 1945). Diseases are more effected in controlling the last three larval stages (Harcourt, 1966). The effects of bacterial and virus diseases are most prevalent when densities of the pest are high.
This pest can easily be controlled using chemical insecticides and certain Bacillus thuringiensis products. Growers greatly benefit from applying sprays when larvae are in early developmental stages.
Because many chemical insecticides have harmful residues, larvae can be controlled with Bacillus thuringiensis products. This application controls larvae without leaving hazardous residues.
Antonelli, Arthur L. 1987. Insect Answers EB1414: Caterpillar Pests of the Cabbage Family. Cooperative Extension, College of Agriculture and Home Economics, Washington State University, Pullman.
Fullaway, D. T. and N. L. H. Krauss. 1945. Pieris rapae (L.). pp. 139-139. In: Common Insects of Hawaii. Tongg Publishing Company, Honolulu, Hawaii. 228 pages.
Haji-Mamat, H. Some Pathological Manifestations in Adult Artogeia rapae (L.) (Lepidoptera: Pieridae) Developing from Larvae Infected with Nosema sp. Master's Thesis. University of Hawaii, Department of Entomology. 75 pp.
Haji-Mamat, H and M. Tamashiro. 1988. The Prevalence of Infections of Nosema mesilini (Microsporida: Nosematidae) in Field Populations of Artogeia rapae (Lepidoptera: Pieridae) Adults in Hawaii. Proc. Hawaiian Entomol. Soc. 28: 191-196.
Harcourt, D. G. 1966. Major Factors in the Survival of the Immature Stages of Pieris rapae (L.). Can. Entomologist. 98(6): 653-662.
Heu, Ronald A. 1990 Revision. Distribution and Host Records of Agricultural Pests and Other Organisms in Hawaii. Original format prepared by G. Funasaki, February 1966. Revised June 1969, October 1971, October 1974, October 1975, March 1978. State of Hawaii, Department of Agriculture, Honolulu, Hawaii.
Metcalf, C. L., and W. P. Flint. 1962. 114. Imported Cabbageworm. pp. 662-664. In Destructive and Useful Insects Their Habits and Control, Fourth Edition. Revised by: R.L. Metcalf. McGraw-Hill Book Company, Inc. New York, San Francisco, Toronto, London. 1087 pages.
Muggeridge, J. 1942. The White Butterfly (Pieris rapae L.). New Zeal. J. Sci. & Tech. 24: 107-129.
Richardson, T. E. 1970. The Histopathological Effects of Bacillus thuringiensis var. thuringiensis (Berliner) on Pieris rapae (L.). Master's Thesis. University of Hawaii, Department of Entomology. 75 pages.
MAR/1991 revised MAY/1992.