Interactions between the willow beetle Phratora vulgatissima and different genotypes of Salix viminalis

1 Planting of species mixtures is a strategy for the non-chemical management of willow beetles in short-rotation coppice willows. However, the relatively susceptible Salix viminalis genotypes and their hybrids dominate current high-yielding willows. Interactions between Phratora vulgatissima and different genotypes of S. viminalis were examined under laboratory conditions to determine if these genotypes exhibit genetic differences in susceptibility to willow beetle damage. 2 Seven S. viminalis genotypes and four hybrids were tested for the feeding preference of adult P. vulgatissima, larval performance and within-season plant response to manual defoliation (50% and 75%). 3 The feeding preference of adult beetles, the growth rate of larvae, and the weight at 33 days of larvae and pupae differed significantly between genotypes. Genotypes also differed significantly in their height and weight responses to mechanical defoliation. Two genotypes were taller, with longer internodes, after defoliation than were undamaged plants. Two hybrids and their S. viminalis parent showed no significant reduction in final dry weight between 0% and 50% defoliation treatments. 4 Susceptibility of genotypes to adult feeding was not correlated with their tolerance to defoliation in terms of weight or height responses; however, larval growth rate on genotypes was negatively correlated both with final height and number of leaves after 75% defoliation and with the susceptibility of genotype to adult feeding. 5 Salix viminalis showed genetic differences for all parameters tested. This suggests that the planting of a mixture of these genotypes would contain genetic differences with respect to host susceptibility to P. vulgatissima. Some parameters showed similarities between a hybrid and its parent, whereas others showed differences between siblings. This offers potential for effective breeding of desirable traits.