Aphid protection by a native and exotic ant

Ant-hemipteran mutualisms are thought to be key to the success of many ant species and invasive ants may better utilize these mutualisms to fuel population growth and thereby outcompete native ants. We compared the relative protection provided to Aphis gossypii against three natural enemies by the invasive Argentine ant, Linepithema humile, and native odorous house ant, Tapinoma sessile in laboratory and field experiments. We used three different predator guilds to assess ant protection: crawling predators (Chrysoperla carnea larvae), flying predators (Hippodamia convergens adults) and parasitoids (Aphidius colemani adults). Both ant species provided equally effective protection against C. carnea and A. colemani, though L. humile outperformed T. sessile in trials with H. convergens. L. humile also had much higher foraging tempo. Higher foraging rate combined with better protective ability may facilitate increased honeydew acquisition and colony expansion in L. humile and perhaps other invasive ants.