Effects of stress-induced changes in plant quality and host-plant species on the population dynamics of the pine beauty moth in Scotland: partial life tables of natural and manipulated populations.
Abstract
The population behaviour of Panolis flammea was observed to determine whether the association between outbreaks and trees growing in deep peat sites is due to the foliage of these trees providing a better source of food for larvae, resulting in better insect survival, than trees growing in other soils, and to ascertain why outbreaks are common on lodgepole pine [Pinus contorta] but do not occur on Scots pine [P. sylvestris] in Scotland. In 1983 and 1984, the population size of Panolis flammea was manipulated by infesting with eggs 25-tree plots of lodgepole pine, growing in different soils within the Elchies block of Speyside Forest. The subsequent survival of larvae and pre-pupae was monitored. In 1985 and 1986, natural populations were studied in larger plots. The population survival of P. flammea on trees growing in deep peat was not higher than on other trees at any time during the study. Larval mortality was higher on Scots pine than on lodgepole pine during the early instars when P. flammea numbers were high (in 1984) but was similar or lower during the later larval instars and the pre-pupal stage. These results refute the hypothesis that lodgepole pine trees growing in deep peat provide a better food source for P. flammea than lodgepole pine growing elsewhere, or Scots pine. Alternative hypotheses are discussed to explain the observed outbreak of P. flammea in Scotland.