Interactions between ants and the coccid Icerya seychellarum on Aldabra atoll.

Abstract

Infestations of the phloem feeding coccid Icerya seychellarum on the natural vegetation of Aldabra atoll are attended at night by large numbers of the large ant Componotus maculatus and, during the day, by small numbers of other ant species.Large ant species preferentially tended larger coccids. The efficiency of C. maculatus worker spacing among the patchily distributed Icerya resource on a plant, was dependent upon the overall ant/Icerya biomass ratio. At high ratios (i.e. low resource availability per ant) they were more evenly dispersed.Size of honeydew loads carried by C. maculatus workers declined as the night progressed, although ant numbers remained constant. From this, and the observations of more even dispersion at higher ant/Icerya biomass ratios, it is concluded that the ants are probably stimulating the coccids to produce more honeydew.The results of an ant exlusion experiment were inconclusive, but suggested that I. seychellarum can exist at reasonably high densities in the absence of ants and that numbers of Chilocorus nigritus, a diaspid scale predator, are reduced by ants.The implication of these results for the biological control of I. seychellarum on Aldabra are discussed, together with the processes involved in honeydew collection in a patchily distributed Icerya population.