Effects of Previous Insect Feeding Injury to Sweet Potato on Resistance to Sweet Potato Weevil (Coleoptera: Curculionidae) and Storage Root Chemistry

The effects of root and foliage feeding on sweet potato resistance to sweet potato weevil, Cylas formicarius (F.), and on the levels of resin glycoside and caffeic acid in sweet potato storage root periderm tissues were studied. Genotypes (“Beauregard,” “Excel,” “W-244,” “W250,” and “Sumor”) with varying levels of sweet potato weevil resistance were evaluated. Adult banded cucumber beetle, Diabrotica balteata LeConte, and larval Spodoptera latifascia (Walker) were introduced onto caged sweet potato plants in the field to elicit root feeding and defoliation on plants. Storage roots were evaluated for sweet potato weevil resistance by quantifying sweet potato weevil adult feeding, oviposition, larval survival, and pupal weight. Both root and foliage injuries were associated with an increase in oviposition (significant in 1998 but not in 1997), but there was no association with adult feeding, larval survival and pupal weight. Genotype had a significant effect on adult feeding, oviposition, and larval survival but not on pupal weight. Root and foliage injuries did not have a significant effect on the levels of resin glycoside and caffeic acid in storage roots. The levels of these compounds differed significantly among genotypes, but there was no apparent relationship between sweet potato weevil resistance (antibiosis) and the levels of these compounds.