Effect of nitrogen on resistance of sweet potato to sweetpotato weevil (Coleoptera : Curculionidae) and on storage root chemistry

The effects of nitrogen fertilizer on sweet potato, Ipomoea batatas (L.) Po ir., resistance to the sweetpotato weevil, Cylas formicarius elegantulus (S ummers), was studied. Adult weevil feeding and oviposition preference, larv al survival, and pupal weight were used as measures of sweet potato resista nce. Sweet potato resin glycosides and caffeic acid concentrations in the p eriderm tissue of storage roots also were measured. Sweet potato genotypes (Beauregard, Excel, W-244, W-250, and Sumor) with varying levels of resista nce to sweetpotato weevil were grown in the field under three nitrogen regi mes (0, 45, and 135 kg N/ha). Harvested storage roots were evaluated in the laboratory for feeding and oviposition activity of sweetpotato weevil fema le adults under no-choice and choice test conditions. Larval survival rate and pupal weight were determined by rearing the insects individually on sto rage root sections. Nitrogen level had a significant effect on the number o f eggs deposited, but not on the number of feeding punctures. Sweetpotato, weevils laid fewer eggs on plants with the highest level of nitrogen. Nitro gen levels did not significantly affect larval survival and pupal weight. G enotype had a significant effect on feeding, oviposition, and larval surviv al Beauregard had higher levels of feeding, oviposition, and larval surviva l compared with the other genotypes. No interaction effects between nitroge n and genotype were significant. Resin glycosides and caffeic acid concentr ations were significantly different among genotypes and between years. Nitr ogen levels significantly affected the concentrations of caffeic acid in 19 97.