Responses of the willow beetle Phratora vulgatissima to genetically and spatially diverse Salix spp. plantations

Abstract

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.

Does host genotype diversity affect the distribution of insect and disease damage in willow cropping systems?

“…Because the willow beetle is very mobile and discriminates between host-plants within a mixture (Peacock, Herrick & Brain 1999), time would be lost looking for suitable plants, especially in plots with several different willow genotypes and less regular spatial configurations (Peacock & Herrick 2000). These mobile aggregations of adults would result in a distribution of damaged plants throughout the plots.…”

“…There are differences in beetle-feeding preferences between these genotypes, with S. × dasyclados and S. viminalis 'Mullatin' the most, and S. burjatica 'Korso' the least, preferred by P. vulgatissima (Kendall et al . 1996), the major willow beetle identified within this willow plantation (Peacock & Herrick 2000).…”

“…1996) indicating that beetles actively select their preferred willow food source. A study of the responses of the willow beetle to mixed willow genotype plantations shows a reduction in the overall density, damage and oviposition in the mixtures compared with the monocultures (Peacock & Herrick 2000). Beetles overwinter mainly outside plantations (Kendall & Wiltshire 1998), enter the plantation during April, feed, mate and lay eggs.…”

How far away is the next basket of eggs? Spatial memory and perceived cues shape aggregation patterns in a leaf beetle

“…), and these beetles are the most common specialist herbivore of willow in Europe (Peacock and Herrick 2000). Adults overwinter in reeds or under the bark of trees (Bjo¨rkman and Eklund 2006), emerge in April, feed for about two weeks, mate, and subsequently lay hundreds of eggs on the undersides of leaves in clutches of 1-50 eggs.…”

Spillover of tent caterpillar (Malacosoma americanum) herbivory onto willow bioenergy crops in an agricultural landscape

“…Also, there is wide variation in susceptibility to herbivory among cultivars; cultivars other than Millbrook may be more or less susceptible to tent caterpillars (Kendall et al, 1996). To address this potential pest problem, less palatable cultivars could be identified and integrated into genetically diverse stands of willow to confer associational resistance to willow stands and deter large scale herbivory (Kendall et al, 1996;Peacock & Herrick, 2000;Barbosa et al, 2009). In extreme cases of damage, insecticide treatments may be necessary.…”