Deltatrap
General
The European corn borer (Ostrinia nubilalis), is a severe pest of maize and has also been reported to attack apple, strawberries, peppers and other plants. It is present in Europe, North Africa and North America, where it was introduced.
Life cycle and appearance of European corn borer
The adults have a wingspan of 22-32 mm and pale yellowish to olive brown forewings with irregular purplish grey markings. The hindwings are light grey with darker markings.
The eggs are nearly flat, ca 1 mm in diameter and white when first laid but later turn yellow. The black head of the larva can be seen just before hatching. The eggs are laid in a mass and overlap like tiles on a roof. The average number of eggs per egg mass is 30.
The larvae are up to 25 mm long; body pale purplish brown to brownish and dark spots with a pale centre at the base of the hairs. The head is brown to brownish black. The pupae are up to 2 cm long and light to dark reddish brown.
In Europe, adults appear in June. The eggs are laid mainly on the underside of leaves. The larvae initially feed on the leaves and then bore into the upper part of the maize plants. Later, second generation larvae tunnel into stem internodes and produce extensive galleries. The larvae pupate in situ in the galleries or in the soil. Fully grown larvae overwinter inside their tunnels in stubble, stalks and maize ears, or in wild plants.
Damage symptoms
Horizontal rows of holes in the young leaves, caused by larval feeding, provide an early indication of European corn borer attack. Later, frass and holes are easily visible on stems, or on the apical part of maize ears. Larval tunnelling weakens the stalks and causes them to break during windy weather.
Larval feeding inside the maize stem destroys vascular tissue. As a result, heavily attacked plants are smaller and produce fewer kernels per ear.