Sweet potato hornworm or the hawk moth (Agrius convolvuli)
Adults are large grey hawk moths with black lines on the wings and broad incomplete pink bands on the abdomen. The female lays small spherical greenish eggs singly on either surface of the leaves. Caterpillars have a conspicuous posterior horn. They are variable in colour, usually greenish or brownish. Fully-grown caterpillars are large (up to 9.5 cm long and 1.4 cm broad). They pupate in the soil.
Caterpillars feed on leaves, causing irregular holes. They may eat the entire leaf, leaving only the petiole. Insect frass can often be found near the infested plant part. One large caterpillar can defoliate a plant on its own. When older caterpillars are present in large numbers they can defoliate a field overnight. Yield losses can occur if heavy defoliation takes place when the crop is young. But, if the young plants are healthy and growing well, they can recover. However, damage to the leaves may delay harvest, increasing the likelihood of attack by the sweet potato weevil.
- Hand-pick caterpillars from leaves. This is usually feasible in small areas.
- Turning the soil over between crops exposes the pupae to predators and desiccation..
- Light traps can be used to monitor the population of moths.
- Manual removal of small caterpillars can prevent the build-up of a large population of older caterpillars.