African sweet potato weevil

The African sweet potato weevil (Cylas brunneus) is a specialized insect pest that causes severe damage to sweet potato crops, particularly in sub-Saharan Africa. Taxonomically, this insect belongs to the order Coleoptera and the family Brentidae. It is considered one of the primary limiting factors in commercial sweet potato production due to its destructive feeding habits.

Both adults and larvae are responsible for damage, though the larval stage is the most destructive. Adults feed on foliage and exposed tubers, creating small punctures. However, the larvae bore extensively into the tubers and stems, creating internal tunnels filled with frass. This not only destroys the market value of the crop but also facilitates the entry of secondary pathogens that cause soft rot.

The life cycle of Cylas brunneus is closely linked to the host plant. Female weevils lay eggs individually in small cavities excavated in stems or tubers. The larvae complete their development inside the plant tissue and pupate there before emerging as adults. This cryptic lifestyle makes the pest difficult to control with traditional surface-applied insecticides once the larvae are established.

Economic damage is often underestimated until harvest time. Infested tubers show small emergence holes and internal decay. Furthermore, the plants respond to larval feeding by producing secondary metabolites, such as terpenes, which impart an intensely bitter flavor to the tubers. This rendered the crop completely unpalatable, making it unusable for both human consumption and livestock feed.

Integrated Pest Management (IPM) is essential for controlling this beetle. Key strategies include the use of clean, weevil-free vine cuttings for planting and strict adherence to crop rotation cycles.

• Timely harvesting to minimize the duration of tuber exposure to weevils.
• Deep hilling of plants to prevent female weevils from reaching the tubers to lay eggs.
• Elimination of volunteer sweet potato plants and weed hosts.
• Application of pheromone traps to reduce the adult male population and monitor activity.