Most recently reviewed by: (1970)
Common Name(s): Corn earworm, Cotton Bollworm, Sorghum headworm, Soybean Podworm, Tomato Fruitworm
The soybean podworm is also known as the corn earworm, cotton bollworm, sorghum headworm and tomato fruitworm and can be found on many garden and farm crops and non-crop vegetation. In most soybean production, soybean podworm is referred to as corn earworm. 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. Soybean podworm 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.
A very similar pest that may be found infesting soybean is the tobacco budworm. Eggs and larvae of soybean podworm and tobacco budworm indistinguishable without fine magnification. Tobacco budworm larvae have a tooth-like projection, called a retinaculum, on the inside surface of the mandibles and fine short hairs on the first, second and eighth abdominal projection (tubercle) which bear a single, prominent spine. If the projection and hairs are absent, this indicates a podworm. Damage and management of these two pests are the same in soybean. Soybean podworm may be distinguished from other soybean infesting caterpillars primarily based on the number of pairs of abdominal prolegs.
Origin and Distribution
The soybean podworm 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
Soybean podworm 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, sunflower, squash, watermelon, potato, sweet potato, asparagus, artichoke, cowpea, snap pea, green bean, cabbage, cantaloupe, collard, cucumber eggplant, pepper, watermelon and others. The first generation of soybean podworm primarily develops on wild hosts, principally clovers. The second generation develops primarily on corn. Among soybean podworm hosts, corn is the most suitable of all hosts. The third and fourth generations generally occur in other agronomic host crops such as soybean, cotton, and grain sorghum with the fifth generation occurring primarily on volunteer crop plants after harvest and on other non-crop wild hosts.
Host preference of soybean podworm is positively correlated to plant maturity and it strongly prefers plants in the flowering stage. Thus, egg lay in soybean most often occurs during flowering or the R1-R2 stages. Later infestations may occur but are much less common. High infestations of soybean podworm often follow pyrethroid applications during bloom, due to destruction of natural enemies.
Although a less common pest of soybean in Texas, in other parts of the southern U.S. soybean podworm is often the most economically important insect pest of soybean. Soybean podworm causes damage to soybean through defoliation and from consuming pods. Early instars typically feed on blooms and and leaves. Feeding on blooms is not considered economical and defoliation by podworms alone is usually not severe enough to warrant control. Most damage is associated with 3rd-6th instar larvae which will feed upon leaves, but more importantly soybean pods. One larva can consume 15-20 flat pods or 6-10 older pods.
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. 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. Soybean podworm 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 northern parts of the state. However, the growing season starts later in the north, and soybean podworm is usually quite abundant by the time vegetables and other crops reach susceptible stages.
Soybean podworm larvae are cannibalistic but in soybean they are usually not confined to groups in small areas so this behavior is inconsequential.
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.
Most states have well defined action threshold to aid in management decision making. Sampling for soybean podworm usually involves sweep net or drop cloth. In much of the southern U.S., pyrethroid resistance is common in soybean podworm populations so caution should be used if using a pyrethroid for podworm control. Commonly used insecticides for soybean podworm and tobacco budworm include products containing chlorantraniliprole, spinetoram or spinosad. Additionally, the nucleaopolyhedrovirus, i.e. Heligen, has proven to be an effective alternative to chemical insecticides.
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