TUBER VEGETABLES :: MAJOR PESTS :: SWEET POTATO WEEVIL

1. Sweet potato weevil: Cylas formicarius (Apionidae: Coleoptera)
Distribution and status
It is a specific pest of sweet potato. Seen in Pantropical, Tropical Africa, India, South East Asia, Australia, Hawaii, South USA, West Indies and South America.
Host range
            Ipomoea litoralis, I learii, I.purpurea, I.prescaprae, I trifida and I.sepiaria
Damage symptoms
Grubs bore into stems, cause tunneling inside and feed on soft tissues. Grubs and adults bore into tubers both in field and storage godowns. Affected tubers develop dark patches, which later start rotting. Pest is disseminated from field to field through infested vines and is carried over from season to season by breeding in damaged tubers left in the fields after harvest.

Bionomics
Adult weevils are ant-like, slender bodied having elongated snout-like bluish-brown head with non-geniculate antenna, bright red thorax and legs and brownish-red abdomen. Females make small cavities on the tubers or stems and lay eggs singly. Each female lays 100-200 eggs. Grubs are apodus, pale-yellowish white in colour. Pupation takes place in larval burrows. Incubation, grub and pupal stages last for 5 to 10, 16 to 20 and 4 to 8 days respectively. Life cycle is completed in 4-5 weeks.

IPM

• Remove previous sweet potato crop residues and alternate host, Ipomoea sp. and destroy them. Discourage growing sweet potato in the same field year after year.
• Use pest free planting materials
• Mulch with leaves of Chromolaena doormats, Clerodendron infortunatum at 3 tonnes/ha at 30 days after planting (DAP)
• Use cut sweet potato tubers (100 g) as trap during 50-80 DAP at 10 days intervals. Set the traps at 5 m apart at 4 pm and collect and destroy adult weevils at 6  am next day
• Dip planting materials in monocrotophos 36 WSC  15 ml per L of water.
• Rake up soil and earth up at 50 days after planting
• Drench soil with endosulfan 35 EC @ 4 ml /L. Spray endosulfan 35 EC 1.5 L in 750 L of water per ha any of these, if needed from 30 DAP

1. Harvest immediately after maturity and destroy the crop residues
2. Install yellow sticky trap @12/ha
3. In godowns, treat the bag surface with malathion 5% or carbaryl 5 % dust.