Sweet potato weevil

The sweet potato weevil (Cylas formicarius) is arguably the most destructive pest of sweet potato crops worldwide. It belongs to the Brentidae family within the order Coleoptera. Due to its high reproductive rate and the difficulty of controlling it once inside the plant tissue, it is strictly monitored as a quarantine pest in many agricultural regions.

This beetle primarily attacks sweet potato (Ipomoea batatas). However, it is also known to infest various wild morning glory species (Convolvulaceae). These wild hosts serve as critical reservoirs, allowing the pest population to survive when commercial fields are left fallow or during off-seasons.

The biological development of the weevil consists of four distinct stages: egg, larva, pupa, and adult. Females bore small holes in the vines or roots to deposit eggs. Larvae hatch and tunnel through the plant, consuming the interior. The entire life cycle can be completed within the plant, shielding the developing stages from external environmental factors and many contact insecticides.

Economic damage is severe because the infested roots develop a bitter taste due to the production of sesquiterpenes, which the plant produces in response to larval feeding. This renders the produce inedible and unmarketable. Furthermore, secondary bacterial and fungal rots often follow the internal tunneling, leading to complete degradation of the root quality.

Effective management requires an Integrated Pest Management (IPM) approach. Strategies include:

• The use of clean, weevil-free cuttings for propagation.
• Crop rotation with non-host crops to break the life cycle.
• Frequent earthing up (hilling) of soil to cover exposed tubers and prevent female access.
• Implementation of pheromone traps to disrupt mating and monitor population densities.
• Sanitation, including the removal and destruction of crop residues post-harvest.