Differential rate of parasitism of the pine beauty moth (Panolis flammea) depends on host tree species

Edinburgh

2007

S. 5-10

1 Abb., 3 Tab., 41 Lit. Ang.

Bandaufführung

161286

Trees have a variety of mechanisms to reduce herbivory by insects including physical and chemical defences, but occasionally some insects can take advantage of these defences to escape the effects of their natural enemies. The architecture of the shoots and leaves can provide a refuge for some herbivores from their natural enemies allowing them an enemy-reduced space and less natural population control. The pine beauty moth, Panolis flammea, exhibits differing population dynamics on its natural hostScots pine compared with the introduced lodgepole pine in Scotland. We tested the hypothesis that the architecture (shoot morphology) and position in the canopy affects the level of parasitism of P. flammea and this effect is different between the two host trees. A scaffolding experiment set up in the different forest types, showed not only that the rates of parasitism by hymenopterous parasitoids were significantly greater for larvae occurring on Scots pine when compared with lodgepole pine but also adifference in parasitism according to the height at which the larvae were located. Field sampling of natural populations provided additional evidence that parasitoids attack their hosts in the upper canopy. Laboratory experiments confirmed that one majorP. flammea parasitoid attacks host larvae on Scots pine at twice the rate as those on lodgepole pine. The morphology of shoots (needle length and density) was significantly different between Scots pine and lodgepole pine. Panolis flammea larvae on lodgepole pine have reduced parasitism due to the longer and more densely packed needles. The present results along with evidence from other natural enemies, suggest that lodgepole pine trees provide enemy-reduced space for colonizing P. flammea and have contributed to the differential population dynamics observed between insects on that host and on Scots pine.