The influence of needle physiology of Scots pine (Pinus sylvestris L.) on mass outbreak needle feeding insects

Rant constituents utilized as nutrients by phytophagous insects vary qualitatively and quantitatively, both among and within plants and through time. Of these, protein is generally recognized as the nutrient most limiting to insect growth under natural conditions. 20-year old Scots pines with different social rankings and previous silvicultural treatments were artficially infested with Lymantria monacha L.(Lepidoptera, Lymantriidae). It caterpillars of this moth showed different preferences for certain amino acids depending jointly on the particular larval stage of the caterpillar and the composition of the food source. The successful development of the caterpillars was partially affected by an inhibition of protein digestion caused by proanthocyanidine. The importance of the proteins as a source of nitrogen for phyllophagous insects and the influence of needle physiology on the rate of mass population growth of pine needle-eating insects are discussed.