Cotton boll drills
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Cotton Boll Drill ( Helicoverpa zea ) |
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| Helicoverpa zea | ||||||||||||
| ( Boddie , 1850) |
The cotton bollworm ( Helicoverpa zea ) is a butterfly ( moth ) from the owl butterfly family (Noctuidae). The species is an important pest in maize , cotton and vegetable cultivation .
features
butterfly
Adult moths reach a wingspan of 32 to 45 mm. Like the caterpillars, the moths are very variable in color. The forewings are usually yellowish-brown in color and often have a small, dark spot in the center, which can be seen particularly clearly from below. The forewings can show a broad, dark transverse ligament distally , but the edge of the wings is light. The hind wings are cream-colored towards the body, blackish distally and usually with a small dark spot in the center of the hind wing.
Egg, caterpillar
The egg is pale green immediately after being laid, later yellowish and then gray. It is dome-shaped or flattened spherical, the diameter is between 0.5 and 0.6 millimeters and it is about 0.5 millimeters high.
The color of the caterpillars is variable. There is a light greenish and a dark brown form. The caterpillar head is orange to light brown and has a net-like pattern. The thoracic plate is black. The color of the caterpillar ranges from brown, green, pink and yellow to almost black. A dark side line runs over the stigmas and a light yellow to white band underneath. There is often a pair of dark narrow stripes on the center of the back. Microscopic examinations have shown that the caterpillar body is provided with thorn-like spikes. Based on the spines and the color of the caterpillar's head, Helicoverpa zea can be distinguished from similar species such as Spodoptera frugiperda and Ostrinia nubilalis . The similar species Heliothis virescens also has thorn-like spines, but the caterpillars never live on maize plants.
distribution
Helicoverpa zea is common in America between Canada and Argentina . In the eastern United States, the species cannot winter successfully in the northern states. Successful wintering is possible up to about 40 degrees north latitude.
The cotton boll drill does not occur outside of America. The cotton boll owl ( Helicoverpa armigera ) is a close relative that is found in the ancient world.
biology
The females lay between 500 and 3000 eggs individually on leaf hairs or the stigmas of maize. The caterpillars hatch after three to four days . Immediately after hatching, the young caterpillars look for a suitable feeding site on the host plant. In the first caterpillar stage they are not yet cannibalized, so that several young caterpillars feed together. Later stages are aggressive, so that only a small number of caterpillars develop in a corn cob. The number of caterpillar stages is variable. Usually six stages are passed through, only five stages are not uncommon, seven to eight stages have also been detected.
In tropical and subtropical regions, Helicoverpa zea continuously forms new generations; with increasing geographical latitude, the number of generations per year decreases. In the north of the distribution area, which includes large parts of Canada, Minnesota and western New York State , only one generation emerges per year. There are two to three generations in Maryland , three generations in the Great Plains and northern California , four to five in Louisiana and southern California, and possibly seven generations in southern Florida and Texas . The generation time is strongly dependent on the temperature. It is 31.8, 28.9, 22.4, 15.3, 13.6 and 12.6 days at 20, 22.5, 25; 30 and 34 degrees Celsius.
American researchers at Southern Illinois University found that bats can significantly reduce the worldwide feeding damage in agriculture by the moths.
Plant protection
The cotton bollworm is one of the most important cotton and corn pests in America. In North America, it is considered to be the second most important pest after the codling moth . Reasons lie in the high fertility, the broad food spectrum of the larvae, the high mobility, and the ability to diapause .
There are various ways to combat it:
- Insecticides : Insecticides are applied to the leaves as liquids when the crops are infested. Insecticide applications are scheduled every 2 to 6 days, and daily in Florida. Due to the frequent and geographically widespread use of cotton bollworm is already against some insecticides resistant .
- Growing method: Using trapping plants can help direct pests to a more attractive crop. For example, the cotton boll drill prefers the lima bean over the tomato. However, it is difficult to keep catch plants in an attractive stage for a long time. If populations first develop on weeds, as in the southern United States, then these weeds can be mowed down or treated with herbicides to control them. In the north, it is sometimes possible to sow or harvest early to avoid damage, as population density and damage are highest towards the end of the growing season. Plowing can reduce the pupae's chances of overwintering, especially in autumn.
- Biological pest control : The use of Bacillus thuringiensis preparations or stone nematid nematodes can help in the control. Trichogrammatidae can be used as parasites of the eggs; in California and Florida, parasite rates of 40 to 80% have been achieved.
- Resistance of the crop: several crop varieties have been developed that offer a certain tolerance to the cotton boll borer. With the help of green genetic engineering , varieties were also bred that produce Bt toxins, e.g. B. Bt maize or Bt cotton .
Individual evidence
- ↑ a b John L. Capinera: corn earworm. University of Florida.
- ↑ GD Butler: Bollworm: development in relation to temperature and larval food. Environmental Entomology (1976): 520-522.
- ↑ Roland Knauer: Agriculture - Bats prevent billions in losses , on stuttgarter-zeitung.de, accessed on September 14, 2015
- ↑ Josiah J. Maine, Justin G. Boyles: Bats initiate vital agroecological interactions in corn , published on pnas.org, accessed September 14, 2015
