The growth and survival of Panolis flammea larvae in the absence of predators on Scots pine and lodgepole pine

Abstract. 1. The survival, growth and development of larvae of the pine beauty moth, Panolis flammea (D & S) (Lepidoptera: Noctuidae) were examined as part of a study to determine (i) why damaging outbreaks of this insect in Scotland are frequent on lodgepole pine but do not occur on Scots pine, and (ii) why outbreaks are associated with areas of deep un-flushed peat.
2. Larvae were studied inside predator exclusion cages on mature pine trees in Elchies forest where a major infestation occurred in 1978–79.
3. Surprisingly, larval survival was generally greatest on Scots pine and lowest on lodgepole growing in deep peat. Also, larval growth and development were greater on Scots than lodgepole pine and were unaffected by the type of soil in which the lodgepole pine was growing.
4. Larval performance was generally better on lodgepole pine that had been thinned and received fertilizer.
5. Larval survival was affected by pine shoot stage during egg hatch in one of the two years in which this was examined.
6. Observations on P.flammea pupae were confused by disease, parasitism and probably by differences in weight loss caused by differences in larval development. Parasitism by ichneumonid parasitoids was recorded on Scots pine but not on lodgepole pine.
7. It was concluded that (i) the absence of pine beauty moth outbreaks on Scots pine, and (ii) the occurrence of outbreaks on lodgepole pine growing in deep unflushed peat were not the result of lodgepole pine growing in deep peat being a more suitable host plant than lodgepole pine and Scots pine growing elsewhere. It seems more likely that the observed outbreak behaviour of P.flammea in Scotland is associated with differences in predation and parasitism in plantations of difference host plants and in plantations of lodgepole pine growing in different soils.