On the food quality of spruce needles for forest damaging insects. Pt. 11

Twigs of Picea abies with 1-3 year old needles were radioactively labeled by photosynthesis two hours long in atmosphere of 14CO2. The 14C-activity of the components investigates remains nearly constant between the 6th and 23rd hour after the pulse. During this period the labeled needles were fed to 20 days old larve of Gilpinia hercyaniae. The 14C-distribution of soluble neutral and acidic compounds, hydrolyzable neutral and acidic compounds, lipids, amino acids, and proteins in needles, bodies of the larve without guts, and faeces was investigated. In addition to the total intake of soluble needle sugars by the larvae there are indications of a limited digestive decomposition of starch. The carbohydrates absorbed are mainly directed to the synthesis of one fraction of the larvae lipids. As to the molar composition in the larvae the protein bound amino acids serine, alanine, glycine, and glutamic acid were found in greater quantities than in the needles. Their carbon back-bone is partially synthesized from the absorbed needle sugars. For these transaminations proline, aspartic acid, valine, isoleucine, leucine, and lysine seem to be possible amino donors. The remaining α-keto acids were considered to be involved in the fuel supply of the larvae. (orig.)