|Crop Knowledge Master|
Helicoverpa zea (Boddie)
|Corn Earworm, Tomato Fruitworm|
Ronald F.L. Mau, Extension Entomologist
Jayma L. Martin Kessing, Educational Specialist
Department of Entomology
The host range of the corn earworm includes over 100 plants; the most significant crops are corn, cotton and tomato. Occasional hosts include bean, broccoli, cabbage, chrysanthemum, eggplant, head cabbage, green bean, lettuce, okra, pea, pepper, soybean, strawberry and watermelon.
The corn earworm occurs throughout temperate and tropical regions of the world. Unintentionally introduced to Hawaii from North America in 1930, this moth has become a common species and a serious pest of agricultural crops on all major islands in the State.
On tomatoes, young larvae sometimes chew tiny holes into the blossom end of the tomato fruits. Older larvae chew holes in the sides of fruit and feed within. Both types of feeding activity produce unmarketable fruit. Young caterpillars rely on leaves and blossoms as their primary food source. Similar damage occurs on bell peppers.
In Hawaii, this pest has a distinct preference for sweet corn. Eggs are deposited on fresh silk and hatch on dried silk a few days later. The caterpillars crawl along the dried silk to fresh silk, feed, and enter the ear through the silk channel. Upon entering the ear, the caterpillars feed on the developing corn kernels usually near the tip of the ear. Mature caterpillars exit the ears by chewing holes in the husk. Caterpillars are cannibalistic and only one caterpillar reaches maturity. When eggs are laid in tassels, young caterpillars feed on developing flowers. Older caterpillars migrate to the developing ears, enter by chewing a hole in the husk, and feed on the kernels. The entry hole is usually away from the tip of the ear.
On lettuce, caterpillars can destroy seedlings and bore deeply into mature heads, rendering them unmarketable (Flint, 1985). Caterpillars feed within the crown of the plant leaving holes in the midrib and sometimes killing the growing point (Flint, 1985). When boring into the head of the lettuce plant they usually enter through the top half.
The entire life cycle occurs in 55-70 days. Generations are continuous in Hawaii.
The white to yellow, ribbed and spherical eggs are laid in the early evening hours. Eggs develop a dark red or brown ring around the top after 24 hours and completely darken before hatching. Eggs are not laid in clusters but instead are individually scattered on host tissue. They are distinguishable from looper eggs by deeper ridges and a more hemispherical shape (Flint, 1985). Eggs hatch in 3 days.
Caterpillars are 1 to 1-3/4 inches long when full grown. They vary in color from green, brown and red, to black and will have distinct, longitudinal stripes running down the body. The skin of the caterpillar is roughened by numerous minute spines (Zimmerman, 1958). The caterpillars usually feed on the fruiting parts of the plant. There are 4-6 larval stages, and development is completed in 28 to 35 weeks.
When mature, the larvae cease feeding and migrate to the soil where they pupate. The brown, relatively stout and smooth pupa is approximately 3/4 inch long. The pupal stage is completed in 12 to 16 days.
Adult moths have a wingspan of 1-1/2 inches and range in color from dark reddish brown to olive green. Wings are pale bordered by a dark band and about 1 3/5 to 1 4/5 inch in wingspan. They live for 12 to 16 days. Females have been reported to lay up to 2500 eggs (Hill, 1983).
If the caterpillars have bored into the head of the cabbage or lettuce plant they are protected and difficult to control with insecticides and by go unnoticed until harvesting (Flint, 1985).
Several natural enemies are present in Hawaii. Parasites include Eucelatoria armigera (Coquillet), Frontina archippivora (Williston), and Trichogramma minutum Riley. The corn earworm is prey to Pachodynerus nasidens (Latreille). Trichogramma minutum is an egg parasite. Populations are kept at tolerable levels by natural enemies if not disrupted by pesticide applications. Parasites and predators are particularly effective between thinning and heading of lettuce plants (Flint, 1985).
The summer crop of tomatoes in California often requires the use of broad spectrum insecticides, but the use of Bacillus thuringiensis and the release and encouragement of parasites assists in reducing damage (Lange and Bronson, 1981).
Cultural methods may be incorporated into a pest management plan to reduce pesticide use. Resistant corn varieties can be grown. Spray applications for this pest can be eliminated and ears marketed by removing the damaged tips.
The destruction of crop residues helps to control this pest by eliminating harboring areas between plantings.
At present there are no resistant tomato varieties. Resistance screening by Fery (1974) indicated that there is sufficient variability in the tomato cultivar germplasm to eventually develop resistant varieties. Although he found no immunity in the current tomato cultivar germplasm, the variety "Tiny Tim", a small-vined dwarf cultivar, exhibited the highest resistance Fery, 1974).
Chemical treatments should be applied if a significant number of eggs and young caterpillars are present on seedlings. Apply insecticides after eggs have attached since the chemicals are most effective on young caterpillars (Flint, 1985). Do not over spray. Repeated applications cause phytotoxicity and can cause yield losses greater than that caused by insects (Flint, 1985).
Treat lettuce heads if more than one corn earworm is found per 25 plants (Flint, 1985).
Fery, R. L. and F. P. Luthbert. 1973. Factors Affecting Evaluation of Fruitworm Resistance in the Tomato. J. Am. Soc. Hort. Sci. 98: 457-459.
Fery, R. L. and F. P. Luthbert. 1974. Resistance of Tomato Cultivars to the Fruitworm, Heliothis zea (Boddie). Hort. Science. 9(5): 469-470.
Flint, M. L. 1985. Corn Earworm, Heliothis zea. pp. 51-55. In: Integrated Pest Management for Cole Crops and Lettuce. University of California Publication 3307. 112 pages.
Hill, D. S. 1983. Heliothis zea (Boddie). pp. 367. In: Agricultural Insect Pests of the Tropics and Their Control. Cambridge University Press.
Lange, W. H. and L. Broson. Insect Pests of Tomatoes. Ann. Rev. Entomol. 26: 345-371.
Marsden, D. A. 1979. Insect Pest Series, No. 7: Corn Earworm. Cooperative Extension Service, University of Hawaii.
Vargas, R. I. 1979. Management of the corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), in sweet corn in Hawaii. Ph.D. Dissertation. University of Hawaii.
Zimmerman, E. C. 1958. Heliothis zea (Boddie). pp. 213-215. In: Insects of Hawaii A Manual of the Insects of the Hawaiian Islands, including Enumeration of the Species and Notes of the Origin, Distribution, Hosts, Parasites, etc. Volume 7: Macrolepidoptera. The University Press of Hawaii, Honolulu. 542 pages.
MAR/1991 revised MAY/1992.