1 The disruption of host-finding cues has been proposed as a key mechanism underlying the lower damage caused by phytophagous insects in mixed forests. We tested this hypothesis by investigating the distribution of pine processionary moth Thaumetopoea pityocampa (Denis & Schiffer-Müller) (Lepidoptera) infestation at the edges of pure stands of Pinus pinaster (Aïton) at some distance from nonhost trees (Experiment 1) or bordered in part by a broadleaved hedgerow (Experiment 2). 2 An 'edge effect' was demonstrated, with trees at the edge of the stand being more heavily infested than those at the interior of the stand. 3 The presence of a nonhost broadleaved hedgerow in front of the edge of the pine stand resulted in lower T. pityocampa infestation. There were significantly fewer T. pityocampa nests behind the hedgerow than on the exposed part of the edge. The presence of the hedgerow did not dilute or repel T. pityocampa infestation further into the pine stand, although it decreased the infestation of T. pityocampa throughout the pine stand. The decrease in T. pityocampa infestation behind the hedgerow was greater when the broadleaved hedgerow was taller than the pine trees. 4 These results highlight the benefits of using nonhost tree species on the edge of monospecific forest stands to reduce insect damage. This approach could be promoted as an innovative forest pest management method.

Species-rich plant communities may be more resistant to invasive herbivores because of reduced host-plant accessibility and increased natural enemy diversity and abundance. We tested these hypotheses in Corsica, a Mediterranean island recently invaded by the maritime pine bast scale, Matsucoccus feytaudi Duc., which causes widespread tree mortality in Pinus pinaster Ait. The endemic Matsucoccus pini Green infests Corsican pine, Pinus nigra laricio Poiret, where it is controlled by the native predatory bug Elatophilus nigricornis Zetterstedt. As revealed by kairomone trapping, E. nigricornis was most abundant in pure Corsican pine in areas not yet colonized by M. feytaudi, and in pure maritime pine its density decreased with the distance from the nearest Corsican pine forest. The abundance of M. feytaudi was compared in five pairs of pure maritime pine and mixed maritime and Corsican pine stands. It was consistently higher in pure than in mixed maritime pine stands, whereas E. nigricornis showed the opposite pattern, and relative differences were correlated with the proportion of Corsican pine in the mixture. The predation by E. nigricornis was manipulated in pure maritime pine stands using synthetic attractants of the predator. Matsucoccus feytaudi density was significantly reduced in maritime pines baited with kairomone dispensers.

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