Potato Glycoalkaloids: Effect on Survival and Feeding Behaviour of the Potato Leafhopper

Total glycoalkaloid (TGA)fractions, extracted from foliage of 10 differentially-resistant Solanum species, were fed to nymphs of Empoascafabae (Harris)at concentrations equivalent to those of fresh foliage. The effects of TGA extracts on nymphal survival and on feeding behavior were assessed. Specific components of the feeding process were identified by use of an electronic recording system. Mean nymphal survival hours and salivation-ingestion periods ranged from a low of 2.7h and 5.3 min, respectively, on extracts of S. hougasii Corr. foliage to a high of 47.7 hand 18.1 min, respectively, on extracts from S. bulbocastanum Dun., corresponding to a 38-fold difference in TGA concentration. Nymphal survival and duration of settling, salivation-ingestion, and nonfeeding were significantly correlated with TGA concentration (r = -0.86, -0.79, -0.93, and 0.82). Although these findings provide further evidence of a causal role for potato glycoalkaloids in leafhopper resistance, TGA extracts from 2 species, S. berthaultii (PI 218215)and S. chacoense (WRF 888), were considerably less limiting to survival than expected on the basis of concentration alone. These discrepancies may be due to differences in levels of individual glycoalkaloids. The specific glycoalkaloid, tomatine, e.g., significantly limited the duration of salivation-ingestion at concentrations as low as 0.05 percent. Levels, types, and biological activity of individual glycoalkaloids in Solanum species need to be characterized before the full significance of these steroidal glycosides in leafhopper resistance can be understood.