Comparative study of the composition of hornet larval saliva, its effect on behaviour and role of trophallaxis

Abstract

1. The physiological and hydrolyzed amino acid compositions and carbohydrate contents of hornet larval saliva were analyzed in five species: Vespa mandarinia, V. crabro, V. tropica, V. analis and V. xanthoptera. 2. D-Glucose or trehalose was found in the larval saliva from five hornet species, but trehalose was not detected in V. tropica. d-Glucose contents (1.0–5.6 mg/ml) were higher than those of trehalose (1.2–9.0 mg/ml) except V. xanthoptera. The sum of d-glucose and trehalose was consistently 11–12% of the total carbohydrate. 3. The physiological amino acid compositions showed a common pattern among all five hornet species: the amounts of cystine and cysteine were very low or non-detectable; there were low contents of glutamic acid (0.5–3.0 mol %) and aspartic acid (0.10–0.15 mol %), against the contrarily high contents of proline, threonine and glycine; the molar ratios of essential amino acids (30–55 mol %) were similar. 4. The contents of the major physiological amino acids in fresh saliva fluctuated slightly among the species. Proline was abundant in V. analis (28.5 mol %), V. xanthoptera (21.7 mol %) and V. mandarinia (17.1 mol %), while threonine was dominant in V. crabro (10.4 mol %) and V. tropica (13.0 mol %). High amounts of glycine were found in V. mandarinia (18.2 mol %), V. crabro (12.1 mol %) and V. tropica (17.3 mol %). 5. The physiological amino acids accounted for over 76% of the total amount of hydrolyzed amino acids in larval saliva except in V. mandarinia (36%). 6. In experiments on the aggressive behaviour of V. analis and V. xanthoptera, the feeding of salival amino acid mixtures brought on a calmness in the worker hornets. 7. It is strongly suggested that the larval saliva is indispensable to hornet life, and also ecological or instinctive behaviour, especially the foundation of the social family, by virtue of the fact that the hornet has no stock foods.