African bollworm (Helicoverpa armigera) is an important pest belonging to the family Noctuidae which attacks the vegetative growing, flowering and fruiting stages of the host plants. Due to its aggressive behaviour of feeding, this insect pest creates a great impact on a wide range of host plants.
It is sometimes referred to as American Bollworm.
Host Range
African Bollworm is polyphagus and thus attacks and damages a wide range of plants. These include;
- Legumes e.g. beans, cowpeas
- Cereals e.g. maize, sorghum
- Vegetables e.g. peppers, tomato
Life Cycle
Eggs are laid on the plant parts which hatch after about 2-5 days into larvae. The larval stage lasts up to approximately 16-30 days as the caterpillars feed. A fully grown caterpillar drops off the plant and burrows into the soil in order to pupate. Pupation takes place in the soil and lasts for about 15-20days.
A complete cycle takes 25-60days depending on environmental factors like temperature.
Identification
- Adult– it is about 18-25mm long with a wingspan of 35-40mm, yellowish brown in colour with a dark speck, grey irregular lines and a black mark on the forewings. Hind wings are whitish with a black patch along the outer margin.
- Egg– initially, it is tiny, round and yellowish-white in colour. However, it darkens before hatching and usually laid singly on the tender parts of the plant.
- Larva– initially it appears yellowish- white to reddish brown in colour with a dark brown to black head and several rows of black bumps with short hairs along the back, which gives it a spotted appearance. Mature larvae vary in colour from brown, green or black to pale yellow with dark grey stripes along their bodies and are about 40mm long.
- Pupa– it is about 16-20mm long, shiny brown with a smooth surface which has two parallel spines at the posterior tip of its body.
Feeding & Damage
The larva (caterpillar) is the most destructive stage of the pest. It feeds on leaves, growing points, buds, flowers as well as fruits, causing heavy losses. Damages on leaves reduces the photosynthetic area which directly affects the general performance of the plant. Feeding on the flowers prevents formation of fruits.
These caterpillars bore circular holes through pods or fruits and feed on their internal contents. They feed with their heads and foreparts inside and the rest of the body outside. These holes also serve as entry venues for pathogens.
A single caterpillar can attack several fruits/pods.
Management & Control
African Bollworm can be controlled through several methods. The most popular and effective method is by use of chemicals (insecticides)
The following insecticides are effective for the control of this pest.
- LEXUS 247SC 8ml/20l
- PENTAGON 50EC 10ml/20l
- KING CODE ELITE 50EC 10ml/20l
- LEGACY5% EC 10ml/20l
Note; -Always mix the insecticide with INTEGRA 3ml/20l whenever spraying. This is a sticker, spreader and penetrator thus it helps in improving the effectiveness of the respective chemical.
In order to avoid build up resistant to any of the insecticides by the pest, it is advisable that chemicals be alternated, and not spraying one for the whole season. If the pest has attacked the crop at fruiting and harvesting stage, it is advisable to use the insecticide with a short post-harvest interval.
Other methods which can be used to manage African Bollworm include the following;
- Introduction of predators
- Practicing crop rotation with non-host plants
- Maintaining field hygiene
- Proper weed management in order to ensure the insect cannot hide in the weeds
