SWEETPOTATO LATEX: EFFECT ON SWEETPOTATO WEEVIL FEEDING AND OVIPOSITION

Abstract

Latex is known to act as a natural defense system in some laticiferous plants against certain herbivores. The importance of latex produced by the sweetpotato, Ipomoea batatas, Lam., as a defense mechanism against the sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae), was tested. Distinct genetic and environmental differences were found in latex production in a broad cross-section of sweetpotato germplasm (96 lines). Most lines produced 2.6 to 10 mg fwt-vine-1 of latex when the second internode from the apex was severed. Some lines, however, produced substantially more, the highest being 48.3 mg·vine-1. The percent dwt of the latex exudate ranged from 2.5 to 54, with most lines falling within the 10 to 22.5% range. The amount of latex (fwt) released varied (1.9X) with differing environmental conditions (primarily light intensity). Young vine material produced more latex and had less feeding by the weevil than in older more mature portions of the vine. Application of latex to the surface of root cores markedly reduced feeding (67%) and oviposition (92%) after 24 hours in choice and oviposition in no choice experiments. Addition of latex to a semi-artificial media also significantly reduced feeding. Leaf feeding location (veins) and direction (basipetal), however, were not indicative of a deterrent role for latex. Collectively, existing evidence does not support a significant deterrent role for latex with regard to the sweetpotato weevil, however, additional information is needed on latex chemistry and quantitative and qualitative variation in latex within the sweetpotato genepool.