Aphids and other hemipteran insects secrete a sweet liquid called honeydew, when they feed on plant sap. The sugars in honeydew are a high-energy food source, which many ant species collect. In some cases, the aphids secrete the honeydew in response to ants tapping them with their antennae. The ants in turn keep predators away from the aphids and will move them from one feeding location to another. (source: wiki: Ant)
Does a presence of a large amount of ants on a plant in my garden (especially fruit trees, willow trees, flowers, vegetables) mean that the plant has been infested by aphids?
It's easier to spot the ants rather than the relatively smaller aphids so I am wondering if I may use this as a trigger for using an anti-aphid pesticide before the aphids start causing visible damage to the plants.