The cotton crop is hit by many pests but pink bollworm is a major pest of cotton, which not only causes reduction in yield but also affects the lint quality by causing yellow spots in its fibre. The economic loss it causes is heavier than the impact of other worms. Depending on the degree of infestation and weather conditions, it can cause about 20 – 30 % loss. It is a serious pest of cotton throughout the world. In 2001, Pakistan faced difficulty in exporting its lint in the international market and this problem has occurred many times.
Description of Pink Bollworm
Female pink bollworm lay eggs singly or, more commonly, in small groups and normally hatches in about three to four days. Eggs of the first field generation in the spring are often laid on vegetative cotton plants. Second and later generation eggs are generally laid under the calyx of cotton bolls.
Larva causes damage by cutting through the lint with its mouthparts. Larvae are white after they have hatched and they have four stages of growth and begin to turn pink in the fourth stage. They generally need 12–15 days to complete their development after that they go into pupation.
It is the developmental stage that makes the transformation from a larva to an adult moth. And it mostly occurs in the top layer of soil beneath cotton plants. It is brown n colour and about one-half inch long. It does not feed or move during this period of about seven to eight days.
Adult pink bollworms are brown to grey moths and are approximately one-half inch long. They emerge from pupae in 1:1 male to female ratio. There is a time period of two to three days. After development the female prepares to lay eggs and lays most of her eggs in nearly ten days. Both male and female adults feed mainly on nectarines located on the bottom of cotton leaves and may live for about one to two months.
Nature of Damage:
Larva when attacks on the flower buds of less than 10 days old then shedding of bud occur and larva dies. But with older buds, larvae can complete its development. Larva in flower bud spins webbing that prevents proper flower opening and thus lead to rosette-bloom (improper opening of petals) and it is mostly common of bollworm attack. These feed on the developing seeds. While in younger bolls the entire content may be destroyed. Several larvae can invade a single boll. Small exit holes are seen on developing green bolls. Stained lint around feeding areas is observed in open bolls. Improper boll opening with damaged seeds are obvious. Attacked bolls are of inferior quality.
During active season, pink bollworm completes four generations on cotton and the larvae of the fifth generation remains inactive for months when temperatures start falling. Most of the remaining bolls on cotton sticks have inactive larvae at the end of the season. Such bolls do not open and remain on cotton sticks. They are the main source of this harmful pest from one season to another. Larvae hatched from the eggs normally take 30-60 minutes to enter the flower buds. Most of it enters through the base of buds, leaving no mark of entry. Larvae do not persist if an infested buds sheds at an early stage. These continues to feed on internal parts of buds and petals together, preventing the flower from opening.
In green cotton bolls, larvae usually enter through the tip of 14-28-days old bolls and leave a yellow spot on the lint at entry point. It nourishes on lint, seed coat and kernel completely before attacking the second seed. Two seeds are enough to complete larval development but some also feeds on more seeds within the same boll. One week old infested boll remains attached to the plant and dries up. Some bolls does not shed but exhibits partial damage and leads to earlier opening. The rate of infestation varies considerably and depends mainly on climatic factors. Frequent rains during August and September provide favourable conditions for pink bollworm infestation.