The Role of Nutrients in the Interactions between a Herbivorous Beetle and Some Competing Plant Species in Heathlands

The role of nutrients, especially of nitrogen, in the interactions between an insect herbivore and some competing plant species in a heathland system has been studied by removal and fertilization experiments in the plant community and by rearing experiments with the beetles. Opening up of the canopy, in combination with increased nutrient availability, as can result from a heavy infestation of Calluna vulgaris by the beetle Lochmaea suturalis, stimulates the growth of grasses and leads to a shift of dominance. Increased nutrient availability in the soil and a subsequent increased nutrient content of the leaves of Calluna result in better growth of the larvae of L. suturalis. As a consequence the population may increase and more severe and frequent outbreaks of the herbivore may occur. It is suggested that eutrophication of the Dutch heathlands resulting from a change in management practices and increased rates of dry and wet deposition of nutrients, especially of nitrogen, is responsible for these effects.