Richard N. Story

EFFECT OF SWEETPOTATO GENOTYPE, STORAGE TIME AND PRODUCTION SITE ON FEEDING AND OVIPOSITION BEHAVIOR OF THE SWEETPOTATO WEEVIL, CYLAS FORMICARIUS (COLEOPTERA: APOINIDAE)

The effect of sweetpotato genotype, storage time and production site on Cylas formicarius (Fab.) feeding and oviposition was investigated. Sweetpotato genotype had a significant effect on feeding and oviposition rates in both no-choice and choice arenas. Beauregard and Centennial were uniformly susceptible across all age groups. W-250 had the least number of feeding punctures and eggs at 7 and 25 days after harvest. At 85 days after harvest, W-244 had the least number of feeding punctures and eggs, while W-250 was not significantly different from Beauregard and Centennial. Roots of the same genotype grown in different locations differed in the number of feeding punctures and eggs. These results suggest that antixenosis is responsible for at least part of the sweetpotato weevil resistance. Storage time and production sites appeared to affect the expression of the resistance, but the outcomes depended on the genotypes.

Effect of Nitrogen on Resistance of Sweet Potato to Sweetpotato Weevil (Coleoptera: Curculionidae) and on Storage Root Chemistry

Abstract The effects of nitrogen fertilizer on sweet potato, Ipomoea batatas (L.) Poir., resistance to the sweetpotato weevil, Cylas formicarius elegantulus (Summers), was studied. Adult weevil feeding and oviposition preference, larval survival, and pupal weight were used as measures of sweet potato resistance. Sweet potato resin glycosides and caffeic acid concentrations in the periderm tissue of storage roots also were measured. Sweet potato genotypes (Beauregard, Excel, W-244, W-250, and Sumor) with varying levels of resistance to sweetpotato weevil were grown in the field under three nitrogen regimes (0, 45, and 135 kg N/ha). Harvested storage roots were evaluated in the laboratory for feeding and oviposition activity of sweetpotato weevil female adults under no-choice and choice test conditions. Larval survival rate and pupal weight were determined by rearing the insects individually on storage root sections. Nitrogen level had a significant effect on the number of eggs deposited, but not on the number of feeding punctures. Sweetpotato weevils laid fewer eggs on plants with the highest level of nitrogen. Nitrogen levels did not significantly affect larval survival and pupal weight. Genotype had a significant effect on feeding, oviposition, and larval survival. Beauregard had higher levels of feeding, oviposition, and larval survival compared with the other genotypes. No interaction effects between nitrogen and genotype were significant. Resin glycosides and caffeic acid concentrations were significantly different among genotypes and between years. Nitrogen levels significantly affected the concentrations of caffeic acid in 1997.