Effects of aphids on foliar foraging by Argentine ants and the resulting effects on other arthropods

1. Although interactions between ants and honeydew‐producing insects have received considerable study, relatively little is known about how these interactions alter the behaviour of ants in ways that affect other arthropods. In this study, field and greenhouse experiments were performed that examined how the presence of aphids ( Aphis fabae solanella ) on Solanum nigrum influenced the foraging behaviour of Argentine ants ( Linepithema humile ) and, in turn, modified the extent to which ants deter larval lacewings ( Chrysoperla rufilabris ), which are known aphid predators. 2. A field experiment demonstrated that the level of foliar foraging by ants increased linearly with aphid abundance, whereas no relationship existed between the level of ground foraging by ants and aphid abundance. 3. In the greenhouse, as in the field, foliar foraging by ants greatly increased when aphids were present. Higher levels of foliar foraging led to a twofold increase in the likelihood that ants contacted aphid predators. As a result of these increased encounters with ants, lacewing larvae were twice as likely to be removed from plants with aphids compared with plants without aphids. Once contact was made, however, the behaviour of ants towards lacewing larvae appeared similar between the two experimental groups. 4. Argentine ants drive away or prey upon a diversity of arthropod predators and parasitoids, but they also exhibit aggression towards certain herbivores. Future work should attempt to quantify how the ecological effects that result from interactions between honeydew‐producing insects and invasive ants, such as L. humile , differ from those that result from interactions between honeydew‐producing insects and native ants.