Sweet potato butterfly (Acraea acerata)
It is found in all sweet potato production areas in Eastern Africa, but is only considered an important pest in relatively dry areas. The adults are butterflies with orange wings with black margins. These butterflies are capable of flying distances of several kilometres. They lay small, pale yellow eggs in clusters on leaves. Caterpillars are greenish-black and are covered with short-branched spines. Fully-grown caterpillars are about 25 mm long. Caterpillars feed on leaves of sweet potato. Young caterpillars feed in groups on the upper leaf surface protected by a layer of webbing for the first two weeks.
Older caterpillars become solitary and nocturnal hiding on the ground during the day. They eat the whole leaf leaving only the midribs. Heavy attack may result on complete defoliation. Mature caterpillars crawl up supports such as tall grasses, leaves or walls near the sweet potato field in order to find a site to pupate in vertical position. The pupae are yellowish and hang singly on their support. The total lifecycle takes 27-50 days. Caterpillars are attacked by predatory ants, ladybird beetles, lacewings and dragonflies. The fungus Beauveria bassiana has been observed on caterpillars in the field during the rainy season.
- Look for sweet potato butterflies and damage early in the season and destroy caterpillars in webs.
- Use clean non-infested planting material.
- Plant and harvest early. This enables the crop to escape heavy attacks.
- Intercropping sweetpotato with onion/or the silver leaf desmodium (Desmodium uncinatum) might reduce the number of eggs laid by the females (CIP, the VITAA Partnership)