Although sometimes called ‘blackfly’, the black bean aphid is actually a true bug (a member of the order Hemiptera). All true bugs are united by the possession of specialised piercing and sucking mouthparts, which are used in this species to obtain plant juices (3). It is this characteristic, coupled with its prolific reproductive capabilities that has made the species a notorious enemy of farmers and gardeners alike (3). This widespread aphid is a minute species with a small head and bulbous abdomen(4). The body is blackish or dark green in colour (2) and the membranous wings are held angled over the body (like a roof) when at rest. Not all individuals possess wings, and the wingless forms have squatter bodies than winged specimens (2). Two tube-like protrusions at the rear of the abdomen, known as cornicles, are the openings of wax glands. This wax protects the aphid from certain predators (4).
Aphids have fascinating and complex life-cycles, comprising of several different forms and numerous generations each year (4). The eggs overwinter on certain host plants, which in the black bean aphid are the spindle tree (Eunomys europaeus), or on Viburnum or Philadelphius plants. The aphids that hatch from these eggs in spring are all special wingless females, known as ‘stem mothers’. These stem mothers are able to reproduce asexually through a process known as ‘parthenogenesis’ that does not involve mating. Furthermore, they do not lay eggs but give birth to live offspring, which are also females and able to reproduce without mating. The next generation to be produced are typically winged forms, and these undertake migrations to new plants. These summer hosts include a range of species such as beans, docks and spinach. Further bursts of asexual reproduction and live births on these hosts allow large populations to build up quickly on these plants. Winged and wingless forms are produced throughout the summer, with the winged forms allowing dispersal to new plants. Towards autumn, migration back to the primary hosts occurs. Sexual females are produced on the winter hosts and males mate with the females. It is on these plants that the mated females lay eggs which will overwinter, allowing the whole cycle to start once more the following year (4).
In arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree (but not visibly in most spiders). In crustacea (e.g. crabs) some of the limbs attach to the abdomen; in insects the limbs are attached to the thorax (the part of the body nearest to the head) and not the abdomen. In vertebrates the abdomen is the part of the body that contains the internal organs (except the heart and lungs).
Of asexual reproduction- reproduction that does not involve the formation of sex cells (‘gametes’). In many species, asexual reproduction can occur by fission (or in plants ‘vegetative reproduction’); part of the organism breaks away and develops into a separate individual. Some animals, including vertebrates can develop from unfertilised eggs, this process, known as parthenogenesis gives rise to offspring that are genetically identical to the parent.
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