OUTBREAKS OF THE PINE BEAUTY MOTH ON PINE IN SCOTLAND - INFLUENCE OF HOST PLANT-SPECIES AND SITE FACTORS

In Scotland, outbreaks of the pine beauty moth (Panolis flammea Denis and Schiffermuller (Lepidoptera, Noctuidae)), do not occur on its native host, Scots pine (Pinus sylvestris L.), but are associated with lodgepole pine (P. contorta Douglas) growing in deep unflushed peat. A number of different approaches have been adopted to test the hypothesis that pine-beauty-moth outbreaks are caused by an increase in the nutritive quality of the foliage of the host plant due in some way to the 'stress' imposed by being grown in deep peat relative to the quality of trees growing more vigorously in better soils. These approaches were: the monitoring of natural and manipulated populations; studies of the growth and survival of larval cohorts from which predators were excluded; analysis of the chemical content of pine foliage; the manipulation of plant quality by thinning and fertilizer application; and subsequent observations of foliar chemistry and population development. No evidence was found to support the 'stress' hypothesis; neither was any evidence found to support the view that Scots pine is a poorer host plant than lodgepole pine. Alternative hypotheses are discussed, and it is concluded that predation and parasitism may be responsible for the observed outbreak behaviour of pine-beauty-moth populations in Scotland.