Rough Sweetpotato Weevil (Blosyrus asellus) Damage to Sweetpotato (Ipomoea batatas) Cultivars in Hawaii

Sweetpotato, Ipomoea batatas (L.) Lam., production has increased in recent years in Hawaii and, based on 2011 data, was the 10^th highest value crop in Hawaii.  Production constraints have included three insect pests of quarantine significance as well as several diseases.  In 2008 a new insect pest of quarantine significance, the rough sweetpotato weevil, Blosyrus asellus (Olivier) (Coleoptera: Curculionidae), was found on a commercial sweetpotato farm on the island of Oahu, with subsequent detection on the island of Hawaii in 2014.  In contrast to other weevil pests of sweetpotato in Hawaii where the immature stage (grubs) feed inside the root, rough sweetpotato weevil grubs form grooves or channels on the root surface as they feed.  At present, this pest is not known to occur on the U. S. Mainland.  Ten sweet potato cultivars were evaluated for yield, and resistance to pests and diseases found along the Hamakua Coast of Hawaii Island.  These cultivars included three from Hawaii (‘Okinawan’, ‘Mokuau’, and ‘Kona B’) and seven from the USDA Germplasm Repository in Griffin, Georgia  (‘Beauregard’, ‘Darby’, ‘Pelican Processor’, ‘Picadito’, ‘392’, ‘L329’, and ‘ACC208’).  Cuttings of these cultivars were planted in plots at a spacing of 1.5 m between rows and 0.3 m within rows, with 30 cuttings per plot.  Due to limited number of cuttings, treatments of cultivars were replicated over time, with the first planting on 8 May 2014 and the second planting on 1 October 2014.  Root damage by rough sweetpotato weevils was first observed at the harvest of the first planting.  Traps designed to monitor the presence of rough sweetpotato weevil adults in each sweetpotato cultivar were deployed near the time of harvest of the second planting.  Average trap catch across all ten varieties was 1.4 weevils/trap/day (range: 0.62 – 2.5 weevils/trap/day).   Plants were harvested at 5 months and 4.5 months after planting, respectively.   Marketable yields differed significantly among cultivars, ranging from 263 to 15,132 kg/ha.  There were also significant differences among cultivars in root damage by rough sweetpotato weevil, with injury ranging from 23 to 100% of marketable yields.  Root damage results suggest that resistance to damage by rough sweetpotato weevils may vary among sweetpotato cultivars.