Heliothis virescens

Scientific Name Heliothis virescens (Fabricius, 1777)
Common Names English: Tobacco budworm; German: Baumwolleule; Spanish: Gusano bellotero; French: Noctuelle verdoyante
Description The larvae are yellowish to dark green or reddish-brown, sometimes nearly black, and up to 45 mm (1.75 inch) long. They have several longitudinal bands on their backs and sides; the body also bears numerous tiny spines.

The wings of the adult moth span about 30-40 mm (1.18-1.57 inch), are of brownish color with a slight olive tinge, and are marked with three distinctive oblique bands on the forewings; the hindwings are light gray.

Biology

Damage

Newly-hatched larvae usually begin feeding on tender leaf surfaces and other tender vegetation before attacking fruiting forms. Smaller larvae feed on smaller fruits and generally move progressively to larger fruiting forms as they grow. They bore into buds or blossoms and destroy the fruiting structures. Loss of terminal buds can lead to growth distortions, and it interferes with plant development. Wounds caused by chewing on plant surfaces facilitate fungal infections. In cotton, bracts of the attacked squares flare out, and later yellow and are often shed. Young bolls will be hollowed out and soiled with frass. Older bolls may be damaged on the outside. On soybeans, the larvae also devour pods and the seeds within. In ornamentals, many of the attacked buds will not open, and those that do may have tattered petals; the flowers frequently wilt unusually quickly.

Lifecycle

During its lifetime of about 2 - 3 weeks, the moth lays about 500 - 1000, sometimes 2000, eggs singly on buds, blossoms or young foliage. After 2-5 days, the larvae hatch, and during a period of 2.5 - 4 weeks, they pass through five or six, sometimes seven instars. They are mostly active at dusk and will hide from daylight. Each of them may consume several buds or flowers. Older larvae are cannibalistic, though not as aggressively as those of H. zea, for example. The mature caterpillar drops to the ground and starts pupation. For this, it builds a cell from soil particles at a depth of about 5 - 12 cm (1.97 - 4.68 inch) . Two to three weeks later (if there is no diapause) the adult moth emerges. After a pre-oviposition period of about 2 days, the fertilized female starts laying eggs, normally in the early evening. Depending on climatic conditions, H. virescens can have several generations in each season.

The pupal stage is able to fall into diapause. This can happen during a period of extreme heat in summer, but it is more important for overwintering. As even diapausing pupae cannot withstand temperatures below -7° C (19.4°F), however, most of the insects die in hard winters. In cool regions, the moths often immigrate in spring. Although they probably have no regular migration patterns, they may fly long distances to escape unfavorable conditions. Therefore in some areas, infestations will vary considerably from year to year.

Occurrence

Additional Crop Information

Most important as a pest of tobacco, cotton, soybean and some ornamentals, but also causing serious damage on alfalfa, cabbage, lettuce, okra, pea, pepper, squash, tomato and many others crops.

Agricultural Importance

Heliothis virescens is found only in the Americas, from Canada to Argentina. It is very similar to the closely-related genus Helicoverpa, under which name both genera were formerly subsumed. Furthermore, it is still under discussion whether several populations of H. virescens that differ noticeably might actually be sibling species. Due to its high reproductive potential, H. virescens may cause considerable losses, especially in cotton, tobacco and soybean.

Control

Integrated Crop Management

Ploughing and destroying plant residues after harvest will significantly reduce the survival rate of overwintering pupae. Try to preserve active populations of natural enemies, as these will at least delay the build-up of damaging pest densities.
Growing early-maturing crops may help to forestall the peak of population development.

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