It has long been debated whether populations of phytophagous insects are regulated by density-dependent processes acting to return their densities to equilibrium levels, or whether they are characterized instead by non-equilibrium processes such as local extinction and recolonization. This question will be addressed by performing density-perturbation experiments on Microrhopala vittata, a leaf-mining beetle that feeds on goldenrod (Solidago spp.). Work will commence with assessments of density, mortality and fecundity of this beetle in several small (<1000 stems) stands of goldenrod. Populations will then have their density experimentally supplemented (to levels 10-20% below the minimum observed), and the effect of these manipulations on predation, parasitism, fecundity and dispersal will be quantified. All samples for mortality and fecundity will be done non-destructively (no Microrhopala or enemies will be killed) so that quantification of these processes will not affect population density. A return of Microrhopala density to more moderate levels following perturbations will support the equilibrium viewpoint. Alternatively, supplemented populations may irrupt and reduced populations may become locally extinct; this would constitute evidence for the non-equilibrium viewpoint. Funding is being awarded for two years of postdoctoral fellowship research at The University of Quebec in Montreal, Canada.
