Host-Plant Mediation of Insect Mutualisms: Variable Outcomes in Herbivore-Ant Interactions

I present and evaluate the hypothesis that host plants indirectly affect the fitness of many homopterans and lepidopterans by mediating the outcome of their interactions with ants. Two conditions must be met to support this contention. First, the attractiveness of herbivores to ants must vary predictably with intra- and/or interspecific changes in host-plant quality. Such variation will occur if a) the chemical compositions and/or quantity of ant attractants (excretions and secretions) produced by herbivores varies with changes in host quality and b) ants preferentially tend those herbivores that produce the most nutritionally rewarding attractants.Second, the number of tending ants must have a significant effect on the fitness of herbivores.While there is abundant evidence to support these individual conditions, few studies have examined both conditions for a single herbivore / ant association