Summary1. Phratora vulgatissima is the most serious pest of willow grown as short-rotation coppice in Britain. The eects of genetically diverse plantations of willow on beetle density, damage and oviposition were studied in a ®eld trial containing monocultures of willow varieties with dierent willow beetle susceptibility, and mixtures which diered in number and spatial con®guration of varieties. In addition, P. vulgatissima adults were introduced to potted willows in cages in a glasshouse as either a monoculture or a mixture of three varieties, and damage and oviposition were recorded. 2. Beetle density, damage and oviposition in the ®eld were generally lower in mixtures than in monocultures, especially with ®ve varieties rather than three and random structural composition rather than regular. In the caged experiment, where beetles could not migrate, there were no signi®cant dierences between the monoculture and the mixture for mean damage or oviposition on the two susceptible varieties. 3. Over time, the average beetle density per tree in the ®eld increased in the monocultures of susceptible varieties, yet decreased in the mixtures. The behavioural response of P. vulgatissima to vegetational diversity was consistent with the resource concentration hypothesis, with lower colonization in, and increased emigration from, mixtures compared with monocultures. 4. Genetically and spatially diverse willow mixtures provide a sound basis for pest management due to the propensity for movement by the beetles. As each movement necessitates the location of a new host plant, it is more dicult for beetles to ®nd favourable varieties in a genetically diverse mixture than in a monoculture. 5. Adult P. vulgatissima occur in mobile aggregations, so pest and damage surveys must be intensive and cover a wide time interval. An option for pest management is a mixture of ®ve willow varieties, at least one of which has low susceptibility to the willow beetle, grown in a random planting of varieties. The choice of variety is important, especially the susceptibility to the rust disease, as are physiological interactions between varieties that might aect beetle ecology.

1 Phratora vulgatissima (Chrysomelidae) is the major pest of short-rotation coppice willows in the U.K., capable of causing severe defoliation in monoculture plantations. As this beetle shows feeding preferences between willow clones, knowledge of the spatio-temporal dynamics of P. vulgatissima is needed in order to assess the effects of mixed clonal plantings on the management of this pest. 2 Distribution patterns of adult P. vulgatissima were monitored over a season at a spatial scale of every tree or every other tree in single clone plantings (monocultures) of three willow clones and in a regular row mixture of these clones. 3 Distribution indices (deviation from Complete Spatial Randomness) demonstrated that P. vulgatissima adults were spatially aggregated on favourable clones in the monocultures and the mixture. The degree of aggregation (measured by the k-parameter of the negative binomial) differed between willow clones. Beetles were highly aggregated at the start of the season, but less so later. 4 Dispersal studies of P. vulgatissima adults over time showed a pattern of beetle infestation along rows of the preferred clones in a regularly structured mixture. In the monocultures, movement was less directional. 5 Plantation design offers some potential for more effective non-chemical pest management for P. vulgatissima. Monitoring of the pest must take account of our ®ndings that adults occur in mobile aggregations.

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.

Factors influencing the aggregative response of the blue willow beetle, Phratora vulgatissima (L.) (Coleoptera: Chrysomelidae), on potted plants of Salix dasyclados (Wimm) were investigated in the field. A significantly higher female beetle density was recorded on plants that had a combination of beetle‐feeding damage and conspecific beetles present as compared with control plants and plants having only damage or beetles. Volatile chemicals emitted from undamaged S. dasyclados (Wimm) leaves were found to be benzaldehyde and the green leaf volatiles (GLVs) cis‐3‐hexenyl acetate and cis‐3‐hexenol. Upon beetle‐feeding damage, there was a higher concentration of these compounds and an increase in the number of different volatile chemicals emitted. These results are discussed in relation to the behavioural ecology of the willow beetle.