Geographic distribution of the sweet potato weevil, Cylas formicarius Fabricius (Coleoptera: Brentidae) and the small sweet potato weevil, Euscepes postfasciatus Fairmaire (Coleoptera: Curculionidae) in the Amami Islands.
The distribution of 2 weevil species, C. formicarius and E. postfasciatus, and their damage to sweet potato were investigated in the Amami Islands in 1997. The population density of C. formicarius male adults was determined using synthetic sex pheromone traps at 127 sites in November. The weevil density was higher in Amami-Ooshima Island and Kikai Island than in the other islands. The infestation of sweet potato by C. formicarius and E. postfasciatus was investigated at 148 fields from October 1997 to March 1998. An average of 18.8% sweet potato tuberous roots were infested with weevils. Tuberous root damage was more serious in Okierabu Island and Yoron Island. Both weevil species were found in all towns of the Amami Islands.