Eradication of sweetpotato weevil, Cylas formicarius, from Tsuken Island, Okinawa, Japan, under transient invasion of males

Abstract

AbstractAn eradication project against the sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae), one of the most important pests of sweet potato in the world, was initiated in Oct. 2007 on Tsuken Island, Okinawa Prefecture, Japan. The sterile insect technique (SIT) and male annihilation technique (MAT) were employed as the main control measures to suppress and ultimately eradicate wild populations by impeding normal mating. In addition, two monitoring methods (host plant survey and trap survey) were used to evaluate the progress of the control actions. However, several years after the start of the project, wild male weevils were regularly captured by male‐attractant traps in seasonal patterns, although infestation was scarcely detected by host plant surveys. Evidently, the males flew to Tsuken Island from uncontrolled areas that were farther away than the weevils were previously expected to travel. Although the transient invasion of only males did not cause new colonization, it created a challenge for the progress of the project and the confirmation of the eradication of the weevil on Tsuken Island. To solve this problem, suppressive control measures in the uncontrolled area (Okinawa Island) to reduce transient invaders were implemented. In addition, to assess if control actions needed after eradication, a system was introduced to detect recolonization of the weevil based on trap catches of transient invading males. After the successive collection of 142,257 m of stem of host plants and 158.45 kg of root tubers of sweet potato without infestation (from February 2019 to November 2020), the eradication of C. formicarius from Tsuken Island was ultimately confirmed in November 2020.