The black bean aphid, Aphis fabae, is widespread in temperate regions, where it is a serious economic pest of beans. It is highly polyphagous, and attacks a wide range of other crops.
Life cycle and appearance of Black bean aphid
Aphids have a complex life cycle, with both winged and wingless forms of adults and a great variety in colour. In greenhouses, reproduction takes place by parthenogenesis, with unfertilized viviparous females continuing to produce new generations of females. Aphids moult four times before reaching adulthood. With each moult they shed white skin, betraying their presence in the crop.
The black bean aphid is dark olive green to black with black bands across the back. The two cornicles (or siphunculi) are short and usually darker than the body. The legs are light yellow with darker tips. Adult wingless aphids are 1.5-3.1 mm long.
Economic damage by black bean aphid is mainly due to direct feeding damage. Indirect damage is caused through the transmission of plant viruses. Infestations start usually at the younger parts of the plant but can spread all over the plant.
Nymphs and adults extract nutrients from the plant and disturb the balance of growth hormones. As a result, the plant’s growth is retarded giving rise to deformed leaves or, if the infestation occurs early enough in the season, the death of young plants. Retarded growth and defoliation reduce yield.
Plant sap is rich in sugars, but has a low protein content. Aphids therefore need to extract large quantities of sap to get sufficient protein. The excess sugar is secreted in the form of honeydew, making the crop and its fruit sticky. Black moulds grow on this honeydew, contaminating fruit and ornamental crops. At the same time, photosynthesis in the leaves is reduced, affecting production.