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

Abstract

Ant tending aphid colonies reduce the effectiveness of biological control on aphids which is detrimental to the crop plants. 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. The objective of this study is to test this hypothesis by providing ants with a high-quality sugar supply with the predictions that ants with an extra-sugar source should more often predate on aphids and, therefore, the abundance of aphids on the experimental plants should be reduced. We carried out an experiment on pepper plants, inoculated with the aphid Aphis gossypii in greenhouses with naturally occurring Tapinoma ibericum colonies in three different periods. Our results showed a significant reduction in aphid colonies abundance and greater aphid predation by the ants in plants with an artificial sugar supply. However, the expected effects greatly varied among greenhouses and seasons. A negative effect on aphid abundance was mainly detected in autumn, while a positive effect on ants predating aphids were mainly detected in summer, when a lower ant activity on the plants occurred. Although our experimental results show that the artificial sugar supply changes ant behavior from tending aphids to preying on them, the large variation in the expected effects suggests that some other unconsidered factors influence their strength. Consequently, future advances should focus on detecting factors driving observed variations among study areas and year seasons, to continue research on using biological control for aphids in horticultural protected crops.