The cotton bollworm (Helicoverpa armigera) occurs in the tropics and sub-tropics of all continents except for North America. Larvae of the cotton bollworm (Helicoverpa armigera) are highly polyphagous, feeding on crops such as cotton, sorghum, tomato, sweet corn, beans, soybeans, tobacco, sunflowers and various fruit crops. Among greenhouse crops, tomato is particularly affected.
Life cycle and appearance of Cotton bollworm
Eggs are deposited individually on young shoots near buds, flowers, fruits or on leaves. They are almost spherical with a flattened base and a diameter of about 0.5 mm. They are at first a shiny yellowish white, with their colour changing to brown just before the larvae emerge.
The cotton bollworm (Helicoverpa armigera) normally goes through six larval stages, although under certain circumstances five or seven stages may occur. Young caterpillars are yellowish-white to reddish-brown with dark spots. In later instars the head is mottled, and the body is marked with three prominent longitudinal dark bands with numerous lighter coloured wavy lines. The colour of the older caterpillar is extremely variable, and may be green, straw yellow, black, or pinkish / reddish brown. Full grown larvae are 30 to 40 mm long. The first instars are the most mobile, and move like loopers. The caterpillars are often aggressive and cannibalistic. Pupation occurs in the soil, with pupae of 14 to 18 mm long, with a brown, smooth body surface.
Adult female cotton bollworms (Helicoverpa armigera) are brownish orange moths approximately 18 to 19 mm in length and have a wingspan of about 40 mm. The grey-green males are smaller. The forewings are edged with a line of black spots, and the hindwings in both sexes are cream with a dark brown band around their outer margin.
First instar larvae feed on soft leaves, creating small holes. When they reach the second instar, they can penetrate fruit through a small hole, often bored near the stalk. During development, the caterpillars damage most fruits by mining. All fruits can be damaged, although the preference is for smaller specimens. The fruits stop growing, mature rapidly, and drop off. In legumes, flowers are attacked, and seed pods may be pierced.