Battle black bean aphids in your garden this summer

The shortage of sap now affecting the survival of the aphids causes the colony to produce winged females (alates), which disperse from the shrubs to find new tender-leaved plants that they can establish new colonies. These will include dahlias, poppies, and various legumes, which soon become heavily infested with hundreds of aphids as they voraciously feed on the sap and reproduce.

When these new aphid colonies become overpopulated and cause harm to their host plants, they won’t need to produce winged females to disperse to new hosts again, as black bean aphids establish a mutualistic relationship with the Black Garden ant Lasius niger who will carry and transfer the aphids to new host plants when required, whilst protecting them from predators such as ladybirds. The ants farm the aphids throughout the growing season to harvest and consume the rich sugary honeydew that the aphids excrete.

By the end of summer, when tender-leafed plants begin to wither, the black bean aphid colonies start to decline, and the ants depart. Toward the end of the summer season, colonies produce another batch of winged aphids, which include males amongst the females. These then disperse from the colony and complete the black bean aphids annual lifecycle by mating and laying overwintering eggs on the shrubs again.

For gardeners and growers who wish to control black bean aphids during the growing season, but not harm the ants, a thorough and direct application of SB Plant Invigorator a non-toxic surfactant-based product can be used.