Biological control of the black bean aphid, Aphis fabae
How to control the black bean aphid in an environmentally friendly way
The black bean aphid, Aphis fabae (Order: Hemiptera; Family: Aphididae), also called blackfly, bean aphid or beet leaf aphid, is a damaging aphid that lives preferably on broad bean, but also on many other plants, such as beetroot and carnation.
The aphids are dark brown or black and often occur in dense colonies. In many instances these colonies are protected by ants.
Biology of aphis fabae
The black bean aphid overwinters as an egg on spindle tree (Euonymus europaeus) as well as on Vibernum and Philadelphus. In spring wingless, asexual females hatch from the eggs. These give birth, parthenogenetically (i.e without the need to mate) to daughters that are also wingless and asexual, and which in turn give birth to wingless duaghters.
After several generations of wingless females, winged females are born in early June. These fly to the summer host plats (such as broad bean or beet). Once settled, they produce wingless daughters. When too many aphids appear on a plant, the mothers produce, under the influence of this population pressure, winged daughters, which fly off in search of new food plants, after which they again produce wingless offspring.
Early september, when the day shorten, winged females and males are born. These fly back to the winter host, for example Euonymus. There the winged females produce wingless, sexual daugters, who mate with the males and lay the overwintering eggs.
Damage of the black bean aphid
On the summer host plant, large, dense colonies of Aphis fabae can occur, usually in the growing tips. These colonies are able to withdraw so much nutrition from the plants, that entire shoots may wilt.
Moreover, the honeydew that the aphids produce is a good nutricional source for sooty mould, causing the leaves to blacken and weaken.
The aphids can also transmit certain viral plant diseases.
Example of a dense colony of blackfly
Natural enemies of Aphis fabae
The aphids are eaten by ladybirds and the larvae of lacewings, syrphids and gall midges, that is to say if the colony is not protected by ants, which happens often!
The only enemies of the aphid that are not attacked by ants, are parasitoid wasps (Braconidae) that lay their eggs in the aphid bodies. These wasps excrete a scent that makes the ants think that the wasps are ants, too.
A braconid wasp lays an egg in an aphid - The aphids are not Aphis fabae
Right away you see a small wasp laying an egg in the tiny aphid, while the ants tap the big aphid, without being aware of the presence of the wasp. Later on the wasp tries to lay an egg in the big aphid.
Treatment of the black bean aphid
- Remove the large colonies by rubbing them off by hand
- Water and spray the plants well, so that they remain strong. That way they will be able to withstand the effects of the sucking aphids better and longer.
- Do not grow spindle trees, Vibernum or Phidelohus in your garden, as the aphids overwinter on these trees!
- Keep ants off the plants by banding the stems with a horticular glue. Take care that the ants cannot use an alternative route to the aphids, such as branches that reach to the groud, or grass stems nearby.
- Buy lacewing eggs from garden centres or Amazon.
Why you should NOT remove aphids from your fava beans or broad beans - They attract beneficial insects to your garden
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