Evaluation of insecticides for the management of rough sweetpotato weevil, Blosyrus asellus (Coleoptera: Curculionidae) in Hawai'i island

Sweetpotato is an important staple food crop in Hawai'i, both for local consumption and export. Insect damage, especially from weevils, is a major production constraint of sweetpotato in the state of Hawai'i. Rough sweetpotato weevil, Blosyrus asellus (Olivier) is an invasive pest recently detected in the Hawaiian Islands. The immature stages of the weevil gouge shallow grooves on surfaces of storage roots that adversely affect their appearance, reduce their marketability, and result in wounds that could allow secondary microbial infections. Sustainable pest management practices are limited for this pest, due to its recent introduction in Hawai'i. As an interim approach, the efficacy of four insecticides including one bio-insecticide were compared against a control to manage this pest in the field. Results from two replicated trials indicate that broad spectrum insecticides such as Belay 16 WSG (Clothianidin) and Sevin XLR Plus (Carbaryl) are effective in managing this pest. Bio-insecticide BotaniGard (Beauveria bassiana strain GHA) was not very effective at the tested rate. Planting sweetpotatoes continuously in the same area would likely increase pest pressure in subsequent crop cycles because of the buildup of populations in the field. Cultural practices such as crop rotation and use of clean planting materials should help to reduce the incidence of pests in the field.