Stephen Nottingham

Attraction of adult sweet potato weevils, Cylas formicarius elegantulus (Summers), (Coleoptera: Curculionidae), to sweet potato leaf and root volatiles.

A dual-choice olfactometer was developed to study the responses of sweet potato weevils,Cylas formicarius elegantulus (Summers), to volatiles from the sweet potato,Ipomoea batatas (L.) Lam. Both males and females were attracted by volatiles from sweet potato leaves and a methylene chloride leaf extract. Females, but not males, responded to volatiles from storage roots and a methylene chloride root extract. Leaves and storage roots from four sweet potato cultivars (Centennial, Jewel, Resisto, and Regal) were attractive to female weevils; however, the attractant response varied with cultivar. GC profiles from leaf and root extracts, and GC-MS analysis of leaf extract, for Jewel cultivar enabled the volatile peaks to be identified as sesquiterpenes.

Feeding and oviposition preferences of the Sweet Potato Weevil, Cylas formicarius elegantulus, on the outer periderm and exposed inner core of storage roots of selected Sweet Potato cultivars

Cores from sweet potato (Ipomoea batatas L.) storage roots, with either the outer periderm or inner core exposed, were presented to female sweet potato weevils, Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae) in cage preference tests. Tests with weevils of different ages showed that feeding was constant 21 to 76 days after emergence, while oviposition showed a slight peak between 21 and 45 days. Differences in the levels of feeding and oviposition were noted for the periderms of four sweet potato cultivars, but these differences were not evident for the inner cores. Oviposition was reduced to low levels on the inner core and, therefore, the oviposition stimulant appears to reside in the root periderm. Feeding did occur on the inner cores, but at a reduced level compared to the root periderm in preference tests where both were available. Inner root cores have a potential use in the elucidation of the oviposition stimulant of the sweet potato weevil.

Feeding and oviposition preferences of sweet potato weevil,Cylas formicarius elegantulus (Summers), on storage roots of sweet potato cultivars with differing surface chemistries

Cores from sweet potato [Ipomoea batatas (L.) Lam.] storage roots (Centennial, Jewel, Resisto, and Regal cultivars) were presented to sweet potato weevils [Cylas formicarius elegantulus (Summers) (Coleoptera; Curculionidae)] in multiple-choice, limited-choice, and no-choice bioassays. Centennial, a susceptible cultivar in field-plot experiments, was preferred for feeding and oviposition by female weevils in choice bioassays, and for ovi-position in no-choice bioassays, compared to three other cultivars. Analysis of root surface chemistry showed a tentatively identified triterpenol acetate in Centennial, which was not found in the more resistant cultivars; another root surface component was found in higher concentrations in the more resistant cultivars.

Characterization of an oviposition stimulant from the surface of sweet potato Ipomoea batatas storage roots for the sweet potato weevil, Cylas formicarius elegantulus

An improved laboratory bioassay was used to characterize an oviposition stimulant from the surface of sweet potato Ipomoea batatas (L.) Lam. storage roots for the sweetpotato weevil, Cylas formicarius elegantulus (Summers). Filter paper discs impregnated with a methylene chloride surface extract of sweet potato storage roots induced significantly (p < 0.05) higher oviposition on root cores than those treated with solvent only. Significantly higher oviposition was also observed in the nonpolar fractions, especially one that contains a tentatively identified triterpenoid present in susceptible cultivars.

Feeding by adult sweet potato weevils, Cylas formicarius elegantulus, on sweet potato leaves

A bioassay was developed to quantify the feeding of adult sweet potato weevils, Cylas formicarius elegantulus (Summers) (Coleoptera; Curculionidae) on the foliage of four cultivars (Centennial, Jewel, Resisto and Regal) of sweet potato (Ipomoea batatas (L.) Lam.) (Convolvulaceae). Weevils fed along the leaf veins, preferring the lower to the upper leaf surface. Males and females had similar levels of feeding. Different levels of feeding by female weevils were observed between cultivars in dual‐choice bioassays with Centennial, a susceptible cultivar in field‐plot experiments, being most preferred and Resisto least preferred. However, these feeding differences were not observed in no‐choice bioassays. Little difference was observed in the leaf surface chemistry of the four cultivars.