Fruit borers (Helicoverpa armiguera, Spodoptera littoralis)
Fruit borers such as the African bollworm (Helicoverpa armigera) and leaf-eating caterpillars such as the cotton leafworm (Spodoptera littoralis) attack the developing and mature fruit of tomato. The African bollworm, also known as the tomato fruit worm, is one of the most destructive insect pests of tomato, causing yield losses as high as 70% due to fruit boring. They usually bore into the fruit from the stem end, and feed on the inner parts of the fruits, causing extensive fruit damage and promoting decay caused by secondary infections.
They prefer green fruit. Caterpillar of the cotton leaf worm feeds on the leaves of tomato and bores into the fruit, especially those growing down the plant near to the soil. They are olive-green, dark grey or brown in colour with large, black, triangular spots on their back. The fully-grown caterpillars are 3 to 5 cm long. The eggs are laid in batches in one or more layers, usually on the underside of the leaves and covered with hairs. Both caterpillars have many natural enemies such as predatory ants, spiders, damsel and robber flies, and parasitic wasps and flies
- Avoid planting tomato near maize or cotton to prevent heavy pest infestations.
- Monitor the crop regularly. Detection of eggs and small caterpillars before they enter into the fruit is very important. Once the caterpillars have entered the fruit they are protected from insecticidal sprays and will have caused damage. Check also for natural enemies and parasitised eggs. Healthy eggs are white with a reddish ring, but they turn black when parasitised. It has been recommended to randomly select 30 tomato plants and examine the leaves immediately below the topmost open flowers to look for eggs of African bollworm (AVRDC, 2000).
- Conserve natural enemies. A very rich variety of natural enemies of fruit borers have been recorded. The most important are parasitic wasps (egg and larval parasitoids) and predators such as anthocorid bugs, ants, lacewings and ladybird beetles. Although these natural enemies cannot always prevent economic damage, they play a significant role in controlling the pest populations. For more information on natural enemies click here.
- Spray selective biopesticides such as Bt or neem extracts. Pyrethrin and rotenone are also used for control of this pest, but they are harmful to natural enemies and not allowed in organic agriculture. Control measures should start when more than five healthy eggs are found or when large numbers of small caterpillars are found on leaves. For more information on Neem click here. For information on Bt click here.
- Hand pick and destroy eggs and caterpillars. This helps when their numbers are low and in small fields.