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Authors: B.N. Barnes. Text extracted with permission from the editors from: Prinsloo, G.L. & Uys, V.M (Eds) 2015. Insects of Cultivated Plants and Natural Pastures in Southern Africa. Entomological Society of Southern Africa. Buy the book.
Other common names: American bollworm, cotton bollworm, Old World bollworm, tomato caterpillar; Afrikabolwurm, Amerikaanse bolwurm, katoenbolwurm (A); lagarta-americana, lagarta-do-tomate (P)
The eggs are pearly white and ribbed, about half the size of a pinhead, and are laid singly; they turn almost black just prior to hatching. Larval colour varies considerably, making them difficult to describe. Young larvae are generally yellowish to almost blackish, usually darker than older larvae, their backs with numerous black bumps with short hairs, lending them a spotted appearance. Older larvae sometimes retain these spots and often have dark stripes along the sides of their bodies. All instars are characterized by a longitudinal white or beige stripe that extends along each side of the body. They can grow to 30-40 mm in length.
African bollworm is highly polyphagous. Larvae start feeding on blossoms, young leaves and young fruit immediately after hatching. They eat circular holes into the fruit, the size depending on the age of the larva. Infestation by micro-organisms can occur in the damaged area, which can lead to extensive internal rotting.
African bollworm is a sporadic pest; the severity of the damage varies between crops and regions and between seasons. In epidemic years, extensive damage and resultant crop loss can occur.
Management is best achieved by implementing a monitoring system based on the inspection of shoot tips of selected trees for eggs, larvae or larval damage symptoms. Young larvae are the most sensitive to chemicals, but they become increasingly more difficult to control as they get older. The necessity for and timing of chemical treatments should therefore be based on egg counts.
