Effects of symbiotic coccid on the plant-ant colony growth in the myrmecophyte Macaranga bancana

Abstract

Macaranga (Euphorbiaceae) myrmecophytes provide their partner ants (plant-ants) with hollow stems used as nesting spaces, as well as food bodies as food rewards. In return, they benefit from the anti-herbivore defense of the ants. The plants harbor not only ants but also specific honeydew-producing coccids, which live inside the ant nests in the hollow stems. Although the honeydews are fed by the plant-ants, their effect on the growth of plant-ant colonies is undetermined. In this study, we investigated how such myrmecophilous coccids, Coccus spp. affect the colony growth of plant-ants, Crematogaster spp. on the myrmecophytic species M. bancana. We compared the growth of plant-ant colonies on seedlings from which coccids were experimentally excluded with that on seedlings into which specific myrmecophilous coccids were experimentally introduced. Foundress queens in 14 of 16 coccid-excluded seedlings died by the time we dissected the seedlings 235-637 days after the seedlings were transplanted in a meshed nursery. In contrast, those on 12 of 17 coccid-introduced seedlings survived during that period, with the survival rate of queens differing significantly between treatments. This result suggests that the symbiotic coccids provide nutrients that facilitate the colony growth of plant-ants inhabiting Macaranga myrmecophytes.