Impact of Linepithema humile and Tapinoma sessile (Hymenoptera: Formicidae) on three natural enemies of Aphis gossypii (Hemiptera: Aphididae)

Ants frequently protect honeydew-excreting hemipterans from their natural enemies in exchange for food, and these interactions can have a negative impact on biological control. Invasive ant species, such as the Argentine ant, Linepithema humile (Mayr), enter into mutualisms with some hemipteran species and are generally regarded as more aggressive than native ants. Consequently, they may be more effective at protecting honeydew-producing hemipterans from natural enemy attack. We compared changes in populations of Aphis gossypii (Glover) tended by equal numbers of invasive L. humile, and the North America native Tapinoma sessile (Say), when exposed to the natural enemies Chrysoperla carnea (Stephens), Hippodamia convergens (Guer.) and Aphidius colemani (Viereck). While more L. humile than T. sessile workers foraged on plants with A. gossypii, both ants were equally effective at protecting A. gossypii from their natural enemies when aphid populations were relatively low. Using larger starting populations, A. gossypii were less negatively impacted by C. carnea or H. convergens when tended by L. humile than T. sessile. In a field experiment, the number of Aphis gossypii on plants with L. humile or T. sessile were greater than on plants without ants. We conclude that due to its higher foraging tempo L. humile may more effectively patrol plant surfaces supporting honeydew-producing hemipterans than T. sessile, which may, in part, underlie the success of this invasive ant.