The Old World bollworm, scientifically known as Helicoverpa armigera, is a significant agricultural pest that affects over 180 plant species. It is also known as the cotton bollworm, corn earworm, or scarce bordered straw.
Helicoverpa armigera eating tomato.
This highly polyphagous and cosmopolitan pest species is native to Africa, Asia, Australia, and Europe. This article delves into the characteristics, habitat, diet, and control measures associated with the African bull worm.
Origin and Spread
The Old World bollworm is native to Africa, Asia, Australia, and Europe. It was first discovered in Brazil in 2012 and is now also present in South America and the Caribbean.
In 2014, the pest was found in Puerto Rico, and in 2015, specimens were captured in Florida; however, no Old World bollworm have occurred in Florida in subsequent years, despite continuous survey. In 2019, APHIS detected adults in areas adjacent to Chicago’s O’Hare International Airport and is eradicating the isolated population.
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Subspecies
This species comprises two sub-species:
- Helicoverpa armigera armigera: native and widespread in central and southern Europe, temperate Asia and Africa.
- Helicoverpa armigera conferta: native to Australia, and Oceania.
The former sub-species has also recently been confirmed to have successfully invaded Brazil and has since spread across much of South America and reached the Caribbean.
Physical Characteristics
The cotton bollworm is very variable in both size and colour. Fully developed larvae can be up to 2 inches long and can range in color from bluish green to brownish red. Adult moths have a wingspan of about 1.4 inches and vary in color from light yellow to greenish brown to orangish brown. Adults are active in the late afternoon and at night.
Signs of Larval Damage
Signs of larval damage includes:
- Holes bored into the base of flower buds, fruit, or bolls
- Feeding damage to leaves and shoots
- Young fruit or bolls that fall prematurely
- Internal feeding damage to fruit
All Old World bollworm life stages are nearly identical to those of the native corn earworm (Helicoverpa zea), and both species feed on the same plants. The two species can only be distinguished from each other by a trained professional.
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Corn Earworm.
Life Cycle and Reproduction
The female cotton bollworm can lay several hundred eggs, distributed on various parts of the plant. The eggs are spherical and 0.4 to 0.6 millimetres (1⁄64 to 3⁄128 in) in diameter, and have a ribbed surface.
The larvae take 13 to 22 days to develop, reaching up to 40 millimetres (1+1⁄2 in) long in the sixth instar. Their colouring is variable, but mostly greenish and yellow to red-brown. The head is yellow with several spots. Three dark stripes extend along the dorsal side and one yellow light stripe is situated under the spiracles on the lateral side. The ventral parts of the larvae are pale.
They are rather aggressive, occasionally carnivorous and may even cannibalise each other.
Diet and Host Plants
The cotton bollworm is a highly polyphagous species. The most important crop hosts are tomato, cotton, pigeon pea, chickpea, rice, sorghum, and cowpea. The greatest damage is caused to cotton, tomatoes, maize, chick peas, alfalfa, and tobacco.
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The caterpillars feed on buds, flowers, grains, fruits, pods; sometimes leaves and stems. In cotton they are found on the vegetative part and reproductive structures. In corn, millet at sorghum they attack the grain.
Economic Impact
The economic threshold of harmfulness in central Asia is three to five larvae per hundred plants of long-staple cotton and eight to twelve larvae per hundred plants on medium-staple cotton.
In cotton crops, blooms that have been attacked may open prematurely and stay fruitless. When the bolls are damaged, some will fall off and others will fail to produce lint or produce lint of an inferior quality. Secondary infections by fungi and bacteria are common and may lead to rotting of fruits.
Injury to the growing tips of plants may disturb their development, maturity may be delayed, and the fruits may be dropped.
Control Measures
How to control pink bollworm in cotton - strategy to control pink bollworm in cotton (Gulabi Sundi)
Corn earworm is found throughout most of North America, and there is a long history of pest management for this species. Old World bollworm adults can fly long distances to lay eggs. They are also migratory and can be carried by wind. Larvae (caterpillars) can hitchhike on fruits, vegetables, plants, and other commodities.
Control measures include:
- The use of NOCTOVI adulticide attract and kill formulation
- Growing of resistant varieties
- Weeding
- Inter-row cultivation
- Removing crop residues
- Deep autumn ploughing
- Winter watering to destroy the pupae
- The use of insecticides or biological control through the release of entomophages such as Trichogramma spp. and Habrobracon hebetor.
Commercially available insecticide sprays and genetically modified crops that contain a naturally occurring microorganism called Bacillus thuringiensis (Bt) may control Old World bollworm. The protein produced by Bt is lethal to caterpillars. Both Bt cotton and Bt corn are widely grown in the United States.
An active eradication of Old World bollworm is currently underway at Chicago O’Hare International Airport. Spot treatments using a combination of chlorantraniliprole and Helicoverpa armigera nucleopolyhedrovirus have targeted areas immediately around the airport where suitable habitat exists, including industrial corridors, vacant lots, and rail/automobile rights-of-way.
The CABI-led programme, Plantwise and their partners suggest planting trap crops and intercropping with crops including cowpea, sunflower, maize, marigold. Plantwise and partners have suggested the release of natural enemies, including the parasitoid Trichogramma brassilences or T.
Genomic Studies
The genomes of Helicoverpa armigera conferta and Helicoverpa zea were published in July 2017. Significant differences have been identified between Chinese and Greek populations, and between those tending toward short migration and long migration. H. armigera populations already had widespread resistance to the Bt toxins Cry1Ab, Cry1Ac, Cry2Ab, and Vip3A before the multiple recent invasions of South America.
| Characteristic | Description |
|---|---|
| Scientific Name | Helicoverpa armigera |
| Common Names | Old World bollworm, cotton bollworm, corn earworm |
| Native Range | Africa, Asia, Australia, Europe |
| Host Plants | Tomato, cotton, maize, chickpea, alfalfa, tobacco, and more |
| Larval Length | Up to 2 inches |
| Adult Wingspan | About 1.4 inches |
| Control Measures | Insecticides, Bt crops, biological control, cultural practices |
