Eradication of the sweetpotato weevil, Cylas formicarius elegantulus (Coleoptera: Curculionidae), from Kume Island, Okinawa, Japan by using a combination of the sterile insect technique and the male annihilation technique

The sweetpotato weevil, Cylas formicarius elegantulus (Summers), is a serious pest of sweet potato in tropical and subtropical regions of the world. The Japanese Plant Protection Law has prohibited the transport of the weevil and its host plants (e.g., sweet potato) from the infested areas to uninfested areas. To solve this problem, an eradication program for C. formicarius elegantulus, using the sterile insect technique (SIT) was initiated on Kume Island (approx. 6,000ha) in Okinawa Prefecture in 1994. After the suppression of the wild population by the male annihilation technique (MAT) using a synthetic sex pheromone and insecticide from November 1994 to January 1999, we have regularly released sterile weevils, which were irradiated with gamma rays at a dose of 100 or 200Gy, at one-week intervals in the targeted areas (approx. 2,000 ha in the early stages) since February 1999. Although we were able to control most of the infested areas until 2000, host plant or pheromone trap surveys have detected some “hot spots”. We have then been conducting additional MAT and/or host plant removal along with the SIT in these areas for almost 10 years, and no wild weevils were observed for thirteen months (from November 2011 to December 2012) regardless of the intensive and extensive survey conducted around the island. These findings thus indicate that the eradication program was successful. This is the first case of the area-wide eradication of a Coleopteran insect using the SIT in combination with the MAT.