Effect of artificial sugar supply on ant-aphid interactions in protected horticulture

Ants tending aphid colonies may reduce the effectiveness of aphid natural enemies, which can result in additional plant damage. However, their mutualistic interaction is complex, and depending on the quantity and quality of the sugar that aphids produce, it may change to a predator–prey interaction. This study aims to test this hypothesis by providing ants with a high-quality sugar supply with the prediction that ants with an extra sugar source should more often prey on aphids and, therefore, the abundance of aphids on plants should decrease. We carried out an experiment on pepper plants infested with Aphis gossypii Glover (Hemiptera: Aphididae) in greenhouses with naturally occurring Tapinoma ibericum Santschi (Hymenoptera: Formicidae) in three different periods. Results showed a significant reduction in aphid abundance and greater aphid predation by ants in plants with an artificial sugar supply. However, the expected effects varied among greenhouses and seasons. A negative effect on aphid abundance was mainly detected in autumn, whereas the largest effect on aphid predation by ants was detected in summer when lower ant activity on the plants occurred. Although our results show that artificial sugar supply changes ant behavior from tending to preying on aphids, the large variation observed indicates that other unconsidered factors influence its effectiveness. Future research should focus on understanding factors driving variations across locations and seasons. Additionally, the effect of sugar feeders and their disruption of the ant-aphid mutualism may improve the access of biological control agents to aphid colonies, which is worth testing.