Helicoverpa zea

Helicoverpa zea

Helicoverpa zea, also known as cotton bollworm, is a butterfly (moth ) from the family of cutworms. In maize, cotton and vegetable cultivation, the species is a serious pest.

Features

Butterfly

Adult moths reach a wingspan of 32-45 mm. Like the caterpillar, and the butterfly are colored very variable. The front wings are usually of yellowish- brown in color and often wear a small central dark, bottom particularly clearly recognized spot. The front wings can distally show a broad, dark lateral band, the edge of the wings, however, are bright The hind wings towards cream to the body, blackish distally and usually with a small dark spot in the middle of the hind wings.

Egg, caterpillar

The egg is pale green immediately after deposition, later yellowish and gray. It is dome-shaped or flattened spherical in shape, the diameter is between 0.5 and 0.6 millimeters and about 0.5 millimeters high.

The color of the beads is variable. There is a bright and a dark greenish brown mold. The tracked head is orange to light brown and provided with a reticulated pattern. The Thorakalplatte is black. The coloring of the crawler body ranges from brown, green over pink and yellow to almost black. About the stigmata runs a dark side line and including a light yellow to white ribbon. In the middle of the back is often a pair of dark narrow strip. Microscopic studies have shown that the caterpillars body is provided with thorn-like spines. By means of the barbs and the color of the tracked head Helicoverpa zea can be distinguished from similar types such as Spodoptera frugiperda, and Ostrinia nubilalis. The similar kind of Heliothis virescens also has thorn-like sting, the caterpillars but never live on corn plants.

Dissemination

Helicoverpa zea is used in America between Canada and Argentina. In the eastern U.S. can not successfully overwinter the kind in the northern states. A successful overwintering succeeds to about 40 degrees north latitude.

Outside the Americas of the cotton bollworm does not occur. The cotton Kapseleule ( Helicoverpa armigera ) is a close relative, which is found in the ancient world.

Biology

Females lay 500-3000 eggs singly on leaf hairs or from the stigmas of the corn. After three to four days, the larvae hatch. The young caterpillars search Immediately after hatching on the host plant, a suitable feeding site. In the first caterpillar stage they live not cannibalistic, so that more young caterpillars feed together. Later stages are aggressive, so that developed into a corn cob only a small number of caterpillars. The number of stages is variable tracked. Normally six stages are run through, only five stages are not uncommon, even seven to eight stages were detected.

In tropical and subtropical regions of Helicoverpa zea continuously forms new generations; with increasing latitude decreases the number of generations per year. In the north of its range, to which large parts of Canada Minnesota and the western part of the State of New York include, produced only one generation per year. Two to three generations there are in Maryland, three generations in the Great Plains and in Northern California, four to five in Louisiana and in southern California, and possibly seven generations in southern Florida and Texas. The generation time is strongly dependent on the temperature. It amounts to 31.8, 28.9, 22.4, 15.3, 13.6 and 12.6 days at 20, 22.5, 25; 30 and 34 degrees Celsius.

Plant protection

The cotton bollworm is a major cotton pests in America. In North America it is considered as a whole and the second most important pest after the codling moth. Reasons are the high fertility, the broad food spectrum of the larvae, the high mobility, and the ability to diapause.

To fight different possibilities exist:

• Insecticides: Insecticides are applied in case of infestation of crops as liquids on the leaves. Insecticide applications are provided every 2 to 6 days in Florida daily. Due to the frequent and geographically broad application of the cotton bollworm is already resistant to some insecticides.

• Cultivation Method: The use of trap crops can help to steer a more attractive crop pests. For example, the cotton bollworm pulls the Lima Bean before over the tomato. However, it is difficult to obtain trap plants in an attractive state for a long time. When initially developing populations such as the southern United States on weeds, then you can mow to combat these weeds or treat with herbicides. In the north, it is sometimes possible to bring forward the sowing or harvest, in order to avoid damage, as the population density and the damage towards the end of the growing season is at its highest. Plowing can reduce the chances of overwintering pupae especially in the fall.

• Biological Pest Control: The use of Bacillus thuringiensis preparations or Steinernematid nematodes can help in the fight. Trichogrammatidae can be used as parasites of the eggs; in California and Florida parasite rates were sometimes from 40 to 80 % are achieved.

• Resistance of the Crop: Multiple crops varieties have been developed that provide a certain tolerance to the cotton bollworm. Use of green genetic engineering were also bred varieties that make Bt toxins such as Bt corn or Bt cotton.