Matrix habitat and plant damage influence colonization of purple loosestrife patches by specialist leaf-beetles.

The characteristics of the matrix, that is, the unsuitable habitat connecting host-plant patches may facilitate or limit herbivore movement thus affecting their population dynamics. We evaluated the effect of matrix habitat, distance between patches, and plant damage on movement of two leaf-beetles (Galerucella calmariensis Linnaeus and G. pusilla Duft) introduced to North America as biocontrol agents of the invasive purple loosestrife (Lythrum salicaria Linnaeus). Mark-recapture/resight experiments indicated (1) that leaf-beetles are more likely to colonize purple loosestrife patches surrounded by meadow than forest; (2) that previously attacked purple loosestrife plants are more likely to be colonized by Galerucella spp. than unattacked plants, especially in the forest habitat; and (3) that leaf beetle colonization of purple loosestrife decreased with distance from release point. Low colonization rates of purple loosestrife patches embedded in forests suggest either insufficient detection or active avoidance of such habitats. Biological control programs intend to manage dispersal of specialized insect herbivores for the purpose of sufficient and sustained control of their host plants. Such management needs to be informed by knowledge of interactions of habitat structure, plant damage, and dispersal capabilities of herbivores to facilitate release programs and control at the local and regional level.