Effects of Crop Rotation on Wireworm (Coleoptera: Elateridae) Populations in North Carolina Sweetpotato Fields

Abstract

Studies were conducted to determine the wireworm (Coleoptera: Elateridae) species present in the Coastal Plain agricultural region of North Carolina, effects of crop rotations on the abundance of wireworms, and effects of both crop rotations and wireworm abundance on damage to harvested sweetpotato roots. Wireworm larvae were sampled in the soil using oat baits. Adult wireworms were sampled using yellow sticky traps. In 2005 and 2006, 2,857 total oat baits and 521 total sticky traps were retrieved from insecticide-free portions of 60 total sweet potato fields located throughout the Coastal Plain. Two thousand one hundred twenty-four total larvae and 3,482 total adults were obtained, belonging to eight species. The proportion of total wireworm larvae and adults captured represented by each species, respectively, were: Conoderus amplicollis (0.051, 0.002), C. bellus (0.043, 0.022), C. falli (0.046, 0.020), C. lividus (0.047, 0.033), C. scissus (0.057, 0.056), C. vespertinus (0.627, 0.629), Glyphonyx sp. (0.049, 0.176), and Melanotus communis (0.066, 0.010). Three studies were conducted to determine the effect of preceding crop on the abundance of overwintering wireworms present in fields which may damage any subsequent crop planted. Treatments were defined by the previous year’s crop and were chosen to reflect common crop rotations in the region. A small-plot study was conducted wherein baiting was conducted in spring and early summer with the following treatments: corn, cotton, fallow, soybean, sweet potato, and tobacco. The second was an overwintering study, and involved baiting commercial fields in late fall and early spring. Treatments were: corn, cotton, peanut, soybean, sweetpotato, and tobacco. In the third study, a commercial field survey, baiting was conducted in commercial fields in late spring and early summer. Treatments were: corn, cotton, cucurbit, peanut, soybean, sweetpotato, and tobacco. In the small-plot study, M. communis was the predominant species, and was found in significantly higher numbers following soybean and corn. Mean total numbers of wireworms per bait (all species) were highest following soybean. In the overwintering study, C. lividus was the predominant species, and mean total numbers of wireworms were highest following corn and soybean. In the commercial field survey, C. vespertinus was the predominant species, and mean total numbers of wireworms per bait were highest following corn. The small-plot study and commercial field survey continued into early autumn. Sweetpotatoes were planted in each field used in these studies, and data were analyzed to examine wireworm populations in sweetpotato through the growing season, whether wireworm abundance differed during the growing season or by previous crop, and whether wireworm damage to sweetpotato was related to wireworm abundance during a particular time period or previous crop. The most abundant wireworm species across these studies was C. vespertinus. C. vespertinus larvae were smaller and more abundant after 15 July than earlier in the season, indicating an early-summer generation turnover, and that adults oviposit in sweet potato. C. vespertinus larval abundance was not affected by previous crop. Incidence of wireworm damage to sweet potato was positively correlated with late-season abundance of C. vespertinus.