Nutrient composition of larval nectar secretions from three species of myrmecophilous butterflies.
A comparative chemical analysis of the larval nectar secretions and hemolymph from three unspecifically and facultatively ant-attended lycaenid species (Polyommatus coridon, P. icarus, and Zizeeria knysna) was performed by using high-performance liquid chromatography techniques. Sucrose was the main sugar component in all three species. In half of the samples of P. coridon, it was accompanied by glucose, whereas other sugars occurred only rarely. In P. icarus and Z. knysna, melezitose was the second-most important component, followed by fructose and glucose. Total sugar contents were 43.6 +/- 14.8 g/l (mean +/- SD) for P. coridon, 74.2 g/l for P. icarus, and 68.3 +/- 22.6 g/l for Z. knysna. Up to 14 different identified amino acids were found in P. coridon nectar, with a total content of 9.7 +/- 3.4 g/l. Leucine was always the major component (contributing 50% of overall amino acid content). Other important amino acids were tyrosine, proline, arginine, and phenylalanine. P. icarus nectar contained up to six amino acids with a total content of 1.2 g/l, dominated by tyrosine and phenylalanine. Z. knysna nectar contained alanine and proline, with only 0.3 +/- 0.17 g/l total content. In the hemolymph of all species, up to 16 different amino acids occurred relatively regularly, with histidine dominating, followed by serine and proline. The amino acid pattern in hemolymph was considerably different from that of the nectar secretions. Larval diet weakly influenced P. coridon nectar sugars, and with a semisynthetic diet, a more homogeneous amino acid pattern was detected. Comparison with reports from other lycaenid species shows that secretions rich in amino acids are related to intimate, often obligate ant associations, whereas facultative, unspecific myrmecophiles rely on carbohydrates.