Similarity of Amino Acids in Nectar and Larval Saliva: the Nutritional Basis for Trophallaxis in Social Wasps.

Larvae of social wasps of the family Vespidae produce an oral exudate that is imbibed by attendant adults. Passage of this liquid from larvae to adults is the key feature of trophallaxis behavior (Wheeler, 1918), which has recently been reviewed by Wilson (1971), Spradbery (1973), and Jeanne (1980). Exchange of alimentary liquid among adults is also generally viewed as a component of trophallaxis, but this exchange is distinct from the larva-adult exchange (Hunt, 1982), and we will not consider it here. Maschwitz (1966) showed that the larval exudate in Vespula vulgaris is chemically identical to the labial gland secretion. Morimoto (1960) fed larvae of Polistes chinensis antennalis a radioactively labeled solution, and he noted that no label appeared in the trophallactic liquid after 30 min, but at 3 h and thereafter label did appear. In another experiment Morimoto (1960) used radiotracers to confirm the uptake of larval liquid by the adults. Nutritive value of the liquid has been demonstrated by several studies (Table 1). Attractiveness of the liquid for the attendant adult wasps has been widely reported. Roubaud (1916) proposed, in fact, that adult attraction to the larval secretion was the raison d'etre of wasp sociality. This extreme position has been challenged by West-Eberhard (1978), who argues that polygynous social groupings of wasps antedate the monogynous ocial species, and so the attraction to larval secretions is not necessary to explain group living in wasps. While we feel that this may be true, it does not fully dismiss the potential importance of the larval secretions in the evolution of wasp sociality. Hunt (1982) has specified larva-adult trophallaxis as one of five varied feeding behaviors that may have affected social evolution in Hymenoptera. In this paper we will present new data on the nutritive value of the larval trophallactic secretion, propose an hypothesis on the origin of larva-adult trophallaxis, and briefly discuss the significance of such trophallaxis in the social evolution of wasps.