|Scientific Name||Helicoverpa zea (Boddie)|
Heliothis zea (Boddie)
Originally, the species now in the genus Helicoverpa were included under Heliothis, together with numerous others. Their classification as a distinct group is, however, generally accepted by now.
|Common Names||English: Corn earworm, tomato fruitworm, cotton bollworm; German: Amerikanischer Baumwollkapselwurm; Spanish: Isoca del maíz, Oruga del tomate; French: Chenille des épis du maïs|
The caterpillar's body can reach 30 to 40 mm (1.18-1.57 inch) in length, and is very variable in color. Several stripes run along the body, and minute spines cover its surface.
Adult moths have a wingspan of 35-40 mm (1.36-1.57 inch) and a body length of 20-30 mm (0.78-1.18 inch). Their color ranges from green-gray to orange-brown.
Helicoverpa zea can be a pest on a variety of crops, as is reflected by the different regional common names. The larvae preferentially attack blossoms, buds and fruits. On corn, the young caterpillars initially feed on silks (thus interfering with pollination) or on developing flowers. When they are older, they feed inside the ear, often near to its tip, sometimes consuming half of its developing kernels. When they mature, the larvae leave the ears by chewing holes in the husk, thereby leaving noticeable, round holes.
On tomatoes and bell peppers, young caterpillars start feeding on leaves and blossoms. They later chew holes in the fruits and start feeding within, making them unmarketable. They will often damage several fruits in succession. Other vegetables such as cucumbers or beans are injured in a similar way. When feeding on cotton, the larvae bore holes into the sides of buds and bolls, enter them, and hollow them out. If buds or bolls are not available, leaves and shoots are attacked. Lettuce can be completely destroyed when larvae kill-off the growing point. Otherwise, the larvae often burrow deep into the lettuce heads, rendering them unmarketable. In all hosts, secondary damage may occur due to infection by plant pathogenic fungi, leading to rotting and fruit or leaf drop.
In seasonal climates, the number of generations varies from 1 to 7 per season; depending on temperature, the life cycle can be completed in about 30 days.
Up to 3,000 eggs per female are deposited singly, mostly at night. The larvae hatch in 2-5 days and wander over the plant until they find a suitable feeding site, usually the reproductive structures of the plant. Several larvae may feed together initially, but older instars become very aggressive and cannibalistic. Once they have become fully grown (a process involving 5-7 instars and lasting about 3-4 weeks) the caterpillars burrow several cm into the ground, where they pupate in a silk-lined chamber. In temperate regions, the last generation overwinters in this stage.
Additional Crop Information
Over 100 crop plants, the most important of which are corn, cotton and tomato. Other hosts include bean, broccoli, cabbage, eggplant, lettuce, okra, pea, pepper, soybean and watermelon.
Corn earworm is found throughout the temperate and (sub)tropical parts of the Americas. It cannot overwinter successfully farther north than about 40°C (104°F); but being highly dispersive, it will immigrate into the northern USA and southern Canada each spring. Due to its high multiplication rate, H. zea can rapidly build up large populations, so the feeding caterpillars can sometimes cause devastating crop losses.
Useful non-chemical contribution to Integrated Weed Management
Tillage in autumn can significantly reduce the overwintering success of the pupae.
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