Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2001
Publication Date: N/A
Interpretive Summary: The sweetpotato weevil is the major pest on sweetpotatoes worldwide, including the southern USA. If not combated aggressively the entire crop may be lost for the fresh market. Breeding for plant resistance to the weevil is the most preferred strategy. Conventional evaluation of plant resistance to the weevil is a laborious and multi year endeavor, plagued by ya number of variables, such as the size of the insect population and weather. In field and laboratory studies we found that the weevil prefers intermediate levels of applied nitrogen fertilizer. Furthermore, egg- laying (inside the potato), but not the amount of feeding was a good indicator of sweetpotato resistance, allowing a more quantitative evaluation of our germplasm. We found significant differences in resistance among the evaluated cultivars.
Technical Abstract: The effect of nitrogen fertilizer on sweetpotato, Ipomoea batatas (L.) Lam., resistance to the sweetpotato weevil (SPW), Cylas formicarius (Fab.) was studied. Adult weevil feeding and oviposition preference and larval survival and pupal weight were used as measures of sweetpotato resistance. Resin glycoside and caffeic acid contents in the periderm tissue of storage eroots were also measured. Sweetpotato genotypes (Beauregard, Excel, W-244 W-250 and Sumor) with varying levels of resistance to SPW were grown in the field under 3 nitrogen regimes (0,45 and 135 kg N/ha). Harvested storage roots were evaluated in the laboratory for feeding and oviposition activity of SPW 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. Significant nitrogen effects were found on the number of eggs deposited, but not on the number of feeding punctures. SPW preferred plants with the intermediate level of nitrogen for oviposition. Nitrogen levels did not significantly affect larval survival and pupal weight. Genotype effect was significant on SPW 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 glycoside and caffeic acid contents were significantly different among genotypes and between years. Nitrogen levels significantly affected the content of caffeic acid in 1997.