The effect of secondary needle compounds on the development of phytophagous insects

Compounds in spruce needles (Picea abies Karst) were evaluated for their capacity to promote or inhibit the development of the European spruce sawfly, Gilpinia hercyniae Htg., (Hymenoptera, Diprionidae). Correlations were calculated between patterns of compounds in needles and developmental characters of the sawflies, such as mortality, development period, weight gain, egg number, and cocoon weight. The most satisfactory correlations were obtained (P < 1%) when the particular patterns of compounds included both nutrients and inhibitory compounds. Two classes of inhibitory compounds can be distinguished, each in a close, antagonistic relation to a specific group of nutrients: 1. (1) low-molecular-weight phenols (p-hydroxyacetophenone, catechin, gallocatechin), shikimic acid, quinic acid ↔ soluble carbohydrates; 2. (2) fraction of the soluble phenols ↔ proteins. The intestinal protein digestion of the sawfly is inhibited by catechin, shikimic acid and quinic acid. But the inhibiting effect can be compensated by the action of a detoxification metabolism which requires carbohydrates. Catechin is stored as a catechinglucoside in the silk glands of the larvae, shikimic acid and quinic acid are degraded by intestinal bacteria and the gut is deacidified by a postulated proton excretion system.