Articles
FOOD QUALITY OF SPRUCE NEEDLES AND THE PERFORMANCE OF THE LITTLE SPRUCE SAWFLY, PRISTIPHORA ABIETINA CHRIST (HYM., TENTHREDINIDAE). THE PROTEIN PRECIPITATING ABILITY OF THE YOUNG NEEDLES.
Results were compared with those obtained from trees on the same stands that remained unattacked.
Our investigation proved a significantly lower protein precipitating capacity of the affected trees than of the control trees.
Additional N-fertilization experiments demonstrated a clear negative correlation between the nitrogen content and the protein binding ability of the young needles.
As larval development highly depends on the optimal supply and quality of food we suppose that – besides other parameters – a low protein binding capacity could be a basic requirement for a mass attack of Pristiphora abietina. In view of selection those spruce populations should be favoured that are able to escape from larval feeding by a detrimental high content of phenolic compounds.
Due to the high atmospheric deposition of pollutants in European forest ecosystems nitrogen should also play an important role in the mass outbreak of Pristiphora abietina.
It seems possible that the ratio of nitrogen to protein precipitating compounds in the spruce needles might be of selective value as well: epidemic mass attack were only possible in spruce populations with a sufficient high quotient of total nitrogen to protein precipitation during the period of early larval feeding.