Tending and defending: Comparing ant-aphid mutualisms involving native and invasive ants

Ants consume sugar-rich honeydew produced by some Hemipterans, including many aphid species.  In return, ants defend these aphids from predators such as green lacewing larvae.  We compared the recruitment of an invasive ant and a native ant to aphids and their efficacy as aphid defenders to test the hypothesis that invasive ants are “better” mutualists.  We found that the red imported fire ants (Solenopsis invicta) were more attracted to and better defended cotton aphids (Aphis gossypii) from green lacewing larvae than native pyramid ants (Dorymyrmex bureni), even when we controlled for differences in ant abundance.  In the field, we observed several native ant species recruiting to cotton aphids, but S. invicta recruited to the aphids in proportionally larger numbers.  These results suggest that invasive ants may have disproportionately large effects on the abundance and distribution of some honeydew-producing Hemipterans.