PHENOLIC GLUCOSIDES AS FEEDING CUES FOR WILLOW-FEEDING LEAF BEETLES

The effects of individual phenolic glucosides and total glucoside frac tions on the feeding behaviour of three willow-feeding leaf beetles (C oleoptera: Chrysomelidae) were tested in the laboratory. Feeding prefe rences of the tested leaf beetles were strongly influenced by certain phenolic glucosides which are typical secondary compounds of willows ( Salicaceae: Salix). Two of the tested leaf beetles, Galerucella lineol a and Lochmaea capreae showed rather similar responses to glucoside tr eatments. Both of them were strongly stimulated by total glucoside fra ctions from Salix triandra and by its major glucoside salidroside. The third species, Phatora vitellinae, was attracted most by the fraction s from S. myrsinifolia and S. pentandra, and by two related salicylate glucosides, tremulacin and salicortin. Food selection pattern of the tested beetles in the laboratory concords fairly well with their distr ibutions in the field and with the occurrence of phenolic glucosides i n their host willows. Phenolic glucoside extracts stimulated more feed ing than individual pure glucosides. This indicates that different com pounds have synergistic effects in the feeding behaviour of leaf beetl es. Our results clearly show that willow leaf beetles select their foo d based on phenolic glucosides of their host plants.