An indirect mutualism: ants deter seed predators from ovipositing in yucca fruit

An indirect mutualism arises when the beneficial effect of two species on each other depends upon the presence of a third species. Surveys, fruit dissections, and behavioural observations on yucca (Yucca glauca Nutt.) indicate that wood ants (species of Formica L., 1758) deter oviposition by non-pollinating, seed-predating moths (Tegeticula corruptrix Pellmyr, 1999) but not by pollinating moths (Tegeticula yuccasella (Riley, 1872)). Wood ants also have a direct negative effect on yuccas owing to flower bud feeding damage; however, damage is minor and variable. As wood ants decrease seed-predator oviposition by 38%, there is a net benefit of wood ants on yuccas. Thus, we suggest that an indirect mutualism can occur between wood ants and yuccas when non-pollinating yucca moths are present.