Euscepes postfasciatus (West Indian sweet potato weevil)

Under heavy infestation, the entire root is riddled and filled with faecal matter. It becomes dark in colour, light in weight and spongy in appearance (Sherman and Tamashiro, 1954). An unpleasant smell is characteristic of this damage and the affected roots taste bitter (Alleyne, 1982a). Larval damage is similar to that of Cylas formicarius and both cause the roots to produce furano-terpenoids and coumarins, making them unpalatable (Uritani et al., 1975). Larvae bore into the root just below the epidermis; the feeding tunnels are defined as sunken areas on the surface of the sweet potato (Sherman and Tamashiro, 1954). Heavily infested vines become enlarged, malformed and cracked (Sherman and Tamashiro, 1954). Adults emerge by chewing exit holes, so emergence holes are visible on the surface of roots or stems (Raman and Alleyne, 1991).

E. postfasciatus is a major pest of sweet potato in the Pacific, Caribbean basin and some countries of South America (Raman and Alleyne, 1991). Even low-level infestations of this weevil reduce marketable yield because sweet potato roots produce furano-terpenoids in response to weevil feeding that make even slightly damaged roots unpalatable (Uritani et al., 1975). In the Caribbean, the weevil has caused extensive damage to roots both in the field and in storage for as long as sweet potato has been grown (Tucker, 1937; Parasram, 1970; Alleyne, 1982b).In Japan, the weevil is the most serious pest of sweet potato in the Ryukyu Islands (Kohama, 1990). Japanese phytosanitary regulations prohibit the transport of sweet potatoes from these islands to markets in mainland Japan.