Taste-enhancing effects of glycine on the sweetness of glucose: a gustatory aspect of symbiosis between the ant, Camponotus japonicus, and the larvaeof the lycaenid butterfly, Niphanda fusca

The lycaenid butterfly, Niphanda fusca, has a parasitic relationship with i ts host ant, Camponotus japonicus: the caterpillars may use chemical mimicr y to enter the ant nest where they are fed mouth-to-mouth by the adult ants until pupation. Nevertheless, larvae offer their host ants a nutritious se cretion that contains 160 mM glucose and 43 mM glycine. Using glucose and g lycine mixture as artificial secretions, we investigated the gustatory effe ct of glucose and/or glycine on the arts. Glycine induced neither feeding b ehavior nor gustatory response in the ants if its concentration was < 500 m M. In the presence of glycine at the concentration in the secretion, howeve r, the ants improved their preference to glucose, and the sugar receptor ce ll exhibited electrophysiological enhancement of response to glucose in a g lycine-concentration-dependent manner By adding glycine to glucose in their secretions, therefore, the butterfly larvae can manipulate the gustatory s ense of the ants. The alluring taste of 'glycine-flavored glucose' could mo tivate the host ants to feed the larvae and thereby receive the secretions as a reward. The taste enhancement created by the combination of sugar and amino acid may play a role in the evolution of the parasitic relationships of these insects. The taste-enhancing effect appears to be analogous to tas te enhancement by 'umami' substances in humans.