Sweet potato weevil

Cylas formicarius

List of symptoms/signs
Leaves  -  external feeding
Roots  -  external feeding
Roots  -  internal feeding
Roots  -  soft rot of cortex
Stems  -  distortion
Stems  -  external feeding
Stems  -  internal feeding
Stems  -  rot

C. formicarius adults feed on the epidermis of vines, scraping oval patches off young vines and petioles. Adults also feed on external surfaces of storage roots resulting in round feeding punctures. These punctures are deeper than oviposition punctures. The developing larvae tunnel the vines and tuberous roots resulting in significant damage. Frass is deposited in tunnels. In response to the damage, tuberous roots produce terpene-like chemicals which render the damaged root inedible, even at low concentration and low levels of insect damage. Feeding inside the vines causes malformation, thickening and cracking of the vine (Sherman and Tamashiro, 1954). Leaves may become pale green, and growth and overall vigour of the plant is adversely affected. Occasionally adult weevils feed on leaves chewing away portions of leaf lamina or scraping small patches of major veins and petioles.

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