Scientific name: Helicoverpa armigera (Hubner)
Common names: American Bollworm; African Bollworm
Synonyms: Heliothis armigera (Hubner)
Heliothis obsoleta F.
Main hosts: Cotton, Beans, Maize, Sorghum
Alternative hosts: Tobacco, Tomato, Many pulses, Wheat
IMPORTANCE IN ETHIOPIA:
Major pest of: Several pulses, tomato, cotton
Minor pest of: Maize, Sorghum, Wheat
In sorghum the caterpillars feed on the head when the grains are in the milky stage. They are especially damaging to sorghum varieties with tight compact heads. Varieties with loose open panicles are rarely damaged.
In maize the developing cobs are attacked.
In pulses, large clean holes are eaten in the pod where the seed is forming.
INSECT BIOLOGY & RECOGNITION:
Egg: The spherical eggs are 0.5 mm in diameter. They are first yellow, later turning brown. The egg stage takes 2-7 days according to the temperature. Each female moth may lay 1000 or more eggs.
Larva: The colour of the larvae is greenish or brown, but colouration is very variable. The body has longitudinal dark and pale bands. Head, prothoracic plate, and legs are brownish. Spiracles are black. The length of a fully grown caterpillar is 40 mm. There are 6 larval instars. The total larval period is usually 14 24 days, but up to 50 days at low temperatures. Excreta may be seen on the plant or under it. On maize the caterpillars are feeding with the forepart of the body inside the ear while the hind part remains outside. A similar behaviour is observed on pulses.
Pupa: The shiny brown pupa is about 16 mm long. Pupation takes place in the soil. The pupal period takes 2-4 weeks according to the temperature.
Adult: A stout bodied light brown nocturnal moth with a wingspan of 32-40 mm. The body length is 16-18 mm. The forewings are yellowish brown or greyish to brown, with a broad slightly darker band and a small dark spot. The hind wings are pale with a broad dark grey or brown marginal band with two lighter spots on it.
For sorghum the use of varieties with open panicles is recommended.
Ploughing the field will exterminate the pupae in the ground.
Clear up the weeds around the field, because large numbers of caterpillars can migrate from weeds into the field.
Plant the crop within a limited period of time (2 3 weeks).