Black bean aphid
The adult wingless form is 1.5 - 3.1mm long, usually sooty black or very dark olive green, with some individuals having distinct white waxy stripes on the upper surface of the abdomen. The two tubes (siphunculi) at the rear end are black, short and tapering slightly towards the tip. The tail (cauda) is black, blunt finger shaped and short. The antennae are about half the length of the body. The winged form is 1.3 - 2.6mm long, also very dark, with some barely discernible black cross-bars on the upper surface of the abdomen.
Host plants/Life cycle
This species overwinters mainly as eggs on spindle, Euonymus europaeus, and occasionally in the south in the mobile stages on leguminous weeds or winter beans. The eggs hatch from late February to early April and colonies develop on young leaves and shoots. The winged forms are produced in May/June, and these migrate to an enormous range of summer hosts. This species has been recorded on almost 300 plant species. The principal commercial crops involved are field beans, broad beans and sugar beet, as well as most forms of garden bean. Some common summer wild hosts include docks, poppies, goosefoot and fat hen. Breeding continues throughout the summer, and further winged forms are produced in response to crowding, and these spread within crops and invade new crops. The populations usually peak in July/August, and are often noticeably attended by ants. In autumn A. fabae migrates back to E. europaeus and winter eggs are laid.
This species is a major pest on beans and sugar beet, occasionally at an epidemic scale, principally by causing direct feeding damage. The plants lose vigour, flowers are damaged and pod development in beans may be retarded or even prevented. Spring sown field beans can be damaged severely with considerable loss of yield. However, winter and early sown spring crops are less likely to be seriously affected, because plants are well established and flowering has finished before the aphid attack starts. In sugar beet very dense colonies can develop during the summer, causing significant wilting and poor growth. This species is known to transmit more than 30 viruses, mainly of the non-persistent variety. Large populations can cause significant secondary spread, even when it did not provide the initial primary infection. A by-product of such large colonies of aphid is contamination of the plant surface with sticky secretions, which promote the growth of sooty moulds. This superficial damage can reduce the sales value of the horticultural bean crops.
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