African bollworm (Berries)

Authors: B.N. Barnes, A.T. Burger, K.L. Pringle, E. Allsopp. 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.

African bollworm, Helicoverpa armigera. damage to immature blueberry fruit.
African bollworm, Helicoverpa armigera. damage to immature blueberry fruit. - A.T Burger

Helicoverpa armigera

Other common names: American bollworm, cotton bollworm, Old World bollworm, tomato caterpillar; Afrikabolwurm, Amerikaanse bolwurm, katoenbolwurm (A); lagarta americana; lagarta-do-tomate (P).

Host plants

This pest has an extremely wide host range, including most vegetables, fruits and berries, many ornamental plants, as well as many wild host plants.

Damage

Larvae feed on young growth, including blossoms, young leaves and young fruit, immediately after hatching. On raspberries and blackberries, damage is found on closed buds, blossoms, fruitlets and growing tips. Younger larvae feed in developing leaf buds; the larvae tunnel into the tightly folded young leaves, leaving perforations along the veins when the leaves unfold. Entire portions of leaves can be eaten away by older larvae. First instar larvae eat through the drupelets in and can then feed, often unnoticed, inside the fruit. Early colouring of the damaged drupelets gives away their presence. Older instars also feed on blossoms, young leaves and immature or mature berries. Blossoms and immature fruit can be almost totally devoured. Malformed berries result from partial feeding. Deep circular holes are eaten into older fruit. Berries tend to fall apart when more drupelets are eaten. On blueberries, the larvae feed on both leaves and fruit; on the latter, deep circular holes are eaten into the immature and mature fruit, as illustrated. Infestation by micro-organisms can occur in the damaged area, which can lead to extensive rotting.

African bollworm is a sporadic pest. The severity of the damage varies between crops and regions, and between seasons. The causes of outbreaks are not properly understood. In the Western Cape, African bollworm has reached pest status on raspberries in the Hemel and Aarde Valley near Hermanus and on Porterville Mountain. On blueberry, serious damage by this pest has been recorded in the Vyeboom area and on Portervill Mountain.

Management

Management is best achieved by implementing a monitoring system based on the inspection of shoot tips and drupelets of selected bushes for eggs, larvae, or larval damage symptoms. Young larvae are the most susceptible to chemicals, but when they are large enough to easily be seen with the naked eye, they have passed their sensitive stage. The necessity for and timing of chemical treatments should therefore be based on egg counts.