|Hammon D, Abner|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2001
Publication Date: N/A
Citation: N/A Interpretive Summary: The sweetpotato weevil is the most serious insect pest of sweetpotato worldwide, including the Southeastern and Southwestern United States. Sweetpotato commercial cultivars and other genetic sources differ greatly in their resistance to insects, and the causes are chemically based. These defense chemicals usually occur at very low levels, but increase after some eform of stress, including insect feeding. Stress was produced by cucumber beetles, which feed on the roots, and armyworms which feed on the leaves. Both types of damage resulted in increased feeding and egg laying by the sweetpotato weevils, but did not affect larval survival or weight of the pupae. Defoliation resulted in higher levels of resinglycosides and root damage resulted in higher levels of caffeic acid, both compounds occur in the stem of the potato. The levels of both compounds differed much between sweetpotato varieties but were not related to weevil resistance.
Technical Abstract: The effect of root and foliage feeding by other insects on sweetpotato resistance to sweetpotato weevil (SPW), Cylas Formicarius (Fab.), and on the levels of resin glycoside and caffeic acid in storage root periderm tissues was studied. In the field, banded cucumber beetle, Diabrotica balteata LeConte, adults and Spodoptera latifascia (Walker) larvae were introduced onto sweetpotato plants covered by saran cages (1.8x1.8x1.8m) t cause root damage and defoliation, respectively. Harvested storage roots were then evaluated for SPW adult feeding and oviposition under no-choice and choice conditions in the laboratory. Larval survival and pupal weight were also obtained. Genotype effects were examined by using genotypes ("Beauregard", "Excel", "W-244", "W250" and "Sumor") that possessed varying SPW susceptibility. Both types of damage were associated with increased SPW adult feeding and oviposition, but there was no association with larval lsurvival and pupal weight. Genotype had a significant effect on adult feeding, oviposition, and larval survival, suggesting both antixenosis and antibiosis as resistance mechanisms. Higher levels of resin glycoside were associated with defoliation, and higher levels of caffeic acid were associated with root damage. The levels of both compounds differed among genotypes, but showed no relationship to SPW resistance.