Weevils

Adult weevils are recognisable by their elongated snout and elbowed antennae, with body size and colour varying enormously by species. Larvae are typically legless, C-shaped grubs found inside plant tissue, soil, or stored grain, depending on species habit.

Field signs include distinctive notched or scalloped leaf margins from adult feeding and internal tunnels in roots or tubers, while stored-grain species leave small round exit holes and fine dust in infested kernels.

Females use their snout to chew a small cavity in plant tissue or a grain kernel before depositing an egg inside. Larvae develop within this protected site, feeding until pupation, and for species affecting root and tuber crops, larvae often complete development in the soil near the host plant.

In the field, larval tunnelling into roots and tubers causes internal damage and scarring that reduces marketability, while adult feeding on foliage and stems can reduce vigour. In storage, internal grain feeders reduce weight, germination, and quality, and can render grain unmarketable if infestations are heavy.

Host crops include sweet potato and cotton in the field, and stored rice and other cereal grain, reflecting the range of habits across this large family.

Pheromone traps are available for several economically important weevil species and help track field or storage populations. Inspecting roots, tubers, and stems for tunnelling, and sampling stored grain for internal feeding and exit holes, complete a monitoring programme.

Because weevil species range from field pests to stored-product pests, management combines field sanitation, timing, and storage hygiene as appropriate to the species involved.

• Use clean, weevil-free planting material and rotate away from known high-risk sequences
• Harvest promptly and handle roots and tubers carefully to limit entry points for infestation
• Store grain clean, dry, and in sealed conditions to limit stored-grain weevil populations
• Conserve parasitoid wasps and other natural enemies where relevant