MASS OUTBREAK OF THE SMALL SPRUCE SAWFLY PRISTIPHORA-ABIETINA (CHRIST) (HYM, THENTRINIDAE) IN HAUSRUCK .2. INFLUENCE OF AIR-POLLUTION

The mass outbreak of the small spurce sawfly Pristiphora abietina (Christ) in Hausruck (Upper Austria) was the basis for the examination of the relationship between air pollution and epidemics of this insect pest. Measurements of the deposition of total nitrogen, NO3, SO4, Ca, Mg, K, Na and H+ at three experimental sites generally show a high impact of air pollutants on the forest ecosystem in the whole research area. BERGER (1992) found no ecological factors to explain the striking differences in the pattern of the insect impact within the research area. A correlation was, however, apparent between the deposition of nitrogen and sulphur and the degree of insect infestation. The impact of pollution is reflected in the chemical compounds of the needles. The increased nitrogen and thiol content of the spurce needles seems to improve the food quality for Pristiphora abietina.