ARS | Publication request: Harvester ants (Hymenoptera: Formicidae) discriminate among artificial seeds with different protein contents

Submitted to: Sociobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2009
Publication Date: March 18, 2009
Citation: Whitford, W.G., Steinberger, Y. 2009. Harvester ants (Hymenoptera: Formicidae) discriminate among artificial seeds with different protein contents. Sociobiology. 53:549-558.

Interpretive Summary: Ants are some of the most important animals in native ecosystems. They are responsible for a number of key processes that contribute to the proper function of native systems. One of these processes is the harvesting and distribution of seeds. There are numerous seed-harvesting species of ants, and this study was designed to understand if one species common in the United States, the western harvester ants, was sensitive to the quality of seeds in its selection and storage of food items in its ant colonies. Harvester ants showed preference for collecting seeds of high protein content, even when these seeds were artificially provided and did not represent a native (or known) seed source. This preference for quality implies that ants would harvest seeds of introduced plant species, if those seeds were of high protein quality, and may provide one explanation for the incorporation of introduced species into native environments.

Technical Abstract: Workers of colonies of the western harvester ant, Pogonomyrmex occidentalis, were recruited to patches of artificial seed of the same caloric value but different protein content. Rates of forager returns with artificial seeds containing five percent protein were nearly twice those of zero percent protein. Differences in foraging rates on artificial seeds of ten and twenty percent protein compared to foraging rates on zero percent protein seeds were not different from the comparison of foraging rates on five percent and zero percent protein seeds. There were no differences in foraging rates on zero percent protein seeds, 0.5 percent and one percent protein seeds. P. occidentalis presented with patches containing equal amounts of zero, five, ten, and twenty percent protein seeds returned equal amounts of each protein content seed type to the colonies. When presented with high quality seed patches in the same location for four successive days, the rates of forager returns increased over time. When seed patch locations were switched, P. occidentalis' rate of return of zero protein content seeds was the same as for the five percent protein seeds at that location the previous day. Seeds with protein content between one and two percent represent a threshold for seed quality that affects the foraging rate of P. occidentalis workers.