Most recently reviewed by: Ed Bynum (2018)
Common Name(s): Corn earworm, Cotton Bollworm, Tomato Fruitworm
Pest LocationRow Crop
The corn earworm is also the pest known as the cotton bollworm and tomato fruitworm and can be found on many garden and farm crops and non-crop vegetation. Adults have buff-colored wings and rather stout bodies. The wingspan is approximately 1½ inches. They are good fliers and can easily move from field to field and often arrive in large numbers on storm fronts. The moths only feed on nectar and are not pests.
However, each female can lay 500 or more eggs. The eggs are laid singly and, when new, are pearly white. The color changes to a yellow/dull white tint over time before hatching. Small caterpillars look much like the small caterpillars of other species, and it is difficult to identify them without a microscope. Corn earworm caterpillars have many microspines on the back and sides of the body, and these are not found on most other common caterpillar pests. Larvae have a tan head and alternating dark and light stripes running lengthwise down the body, and they have numerous tubercles (dark spots) with long spines. Other pest species have stripes as well, but they do not have the abundance of microspines and tubercles, and a 10x hand lens will allow differentiation. There is no “typical” larval color, and it is common to find larvae that are either light green, dark green to grey green, or pink. Full grown larvae are approximately 1.5 inches long.
Origin and Distribution
The corn earworm is a New World insect (Western Hemisphere) and is present throughout this region. It overwinters only in areas with mild winters, but flies to other areas during the course of the spring, summer and fall.
Habitat & Hosts
Corn earworm has a very wide host range, and in Texas is usually the caterpillar found in ears of corn. Other cultivated hosts include tomato, sorghum, cotton, soybean, sunflower, squash, watermelon, potato, sweet potato, asparagus, artichoke, cowpea, snap pea, green bean, cabbage, cantaloupe, collard, cucumber eggplant, pepper, watermelon and others.
Adults are quite mobile and can lay eggs on any host that is at a susceptible stage. Eggs are often laid near or on fruiting structures, but they can be laid on leaves and stems as well. Moths prefer to lay eggs directly on the green silks of field corn and sweet corn, and the larvae then consume the silk and move toward the ear tip.
Eggs hatch in 3-5 days and there will be five to six larval instars, each separated by a molt to a larger caterpillar. The larval stage lasts from 13 to 31 days depending on temperature. Insects develop faster under higher temperatures. After the last larval stage, the larvae move to the soil and construct a burrow where they will remain while in the pupal stage, which lasts from 10 – 25 days depending on temperature. Adults then emerge and will live for an average of 10 days, some more and some less. Corn earworm overwinters in south Texas, and often flies north carried on storm fronts. There are several generations per year and the insect can be expected to be present for most of the growing season in the south, but only increases gradually in number in more northern parts of the state. However, the growing season starts later in the north, and corn earworm is usually quite abundant by the time vegetables and other crops are susceptible.
Corn earworm larvae are cannibalistic and, even though there may be several small larvae in an ear of corn, these will eventually be reduced to one, or less commonly two, per ear. As fruit feeders, even one larva can cause significant damage in vegetable crops, but in agricultural crops like field corn, corn earworm is rarely an economic worry
ManagementIf you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.
Home garden control options include:
- Spinosad (Rate varies by brand name)
- Synthetic pyrethroids
- Bacillus thuringiensis (Bt. subspecies Kurstaki)
See Understanding Common House and Garden Insecticides ( https://citybugs.tamu.edu/factsheets/ipm/ent-4002/ ) for more information on insecticides.