LEVELS OF DAMAGE OF SCOTS PINE AND NORWAY SPRUCE CAUSED BY NEEDLE MINERS ALONG A SO2 GRADIENT

Needle damages caused by mining insects on Scots pine and Norway spruc e were studied in the vicinity of a pulp mill. The abundance of needle s mined by the pine bud moth Exoteleia dodecella (Lepidoptera: Gelechi idae) on Scots pine Pinus sylvestris, and the spruce needle miner Epin otia tedella (Lepidoptera: Tortricidae) on Norway spruce Pic en abies had a significantly peaked response curve on logarithmic distance scal e. For pine bud moth, the maximum expected population density was esti mated to be at the distance of 1.35 km from the factory. The maximum e xpected population density for the spruce needle miner was at the dist ance of 1.53 km from the factory. However, for both species the curves were significantly different among transects. Both species had a peak ed and significant response to sulphur level in needles as well. The m aximum expected density in pine was at 1270 ppm, and in spruce at 1070 ppm sulphur concentration in pine needles. The results are consistent with earlier reports demonstrating that these mining insects frequent ly attack trees suffering from air pollution. The nonlinear response o f both species to distance from the pulp mill suggests that E. dodecel la on pine and E. tedella on spruce are rather indicators of the zone of intermediate air pollution than of strongly polluted or nearly unpo lluted sites. This also agrees with the plant stress-insect performanc e hypothesis indicating that insect response varies with the magnitude of stress, and at very high stress levels a tree no longer provides t he insects with relevant food.