Black bean aphid

The black bean aphid (Aphis fabae) is a small black insect in the genus Aphis, with a broad, soft body, a member of the order Hemiptera. Other common names include blackfly, bean aphid, and beet leaf aphid. In the warmer months of the year, it is found in large numbers on the undersides of leaves and on the growing tips of host plants, including various agricultural crops and many wild and ornamental plants. Both winged and wingless forms exist, and at this time of year, they are all females. They suck sap from stems and leaves and cause distortion of the shoots, stunted plants, reduced yield, and spoiled crops. This aphid also acts as a vector for viruses that cause plant disease, and the honeydew it secretes may encourage the growth of sooty mould. It breeds profusely by live birth, but its numbers are kept in check, especially in the later part of the summer, by various predatory and parasitic insects. Ants feed on the honeydew it produces, and take active steps to remove the aphid's enemies. It is a widely distributed pest of agricultural crops and can be controlled by chemical or biological means. In the autumn, winged forms move to different host plants, where both males and females are produced. These mate and the females lay eggs which overwinter. The specific name of the black bean aphid, fabae comes from the Latin faba meaning a 'bean', a plant on which this aphid often feeds. Aphis fabae is in the superfamily Aphidoidea and the subgenus Aphis. Some taxonomists consider it a group of related species, or possibly biotypes. Fauna Europaea lists six subspecies: The black bean aphid is a small, soft-bodied (meaning that the exocuticle part of the exoskeleton is greatly reduced) insect that has specialised piercing and sucking mouthparts which are used to suck the juice from plants. This aphid is usually seen in large numbers and is a tiny, plump insect about two millimetres long with a small head and bulbous abdomen. The body is blackish or dark green in colour. Many adults are devoid of wings, a state known as aptery. Winged forms, known as alates, are longer and more slender than aptates and have shiny black heads and thoraxes. The membranous wings of the alates are held angled over the body. The antennae are less than two-thirds of the length of the body and both they and the legs are pale yellow in colour with black tips. The tibiae of the hind legs are swollen in egg-laying females. Near the rear of the abdomen is a pair of slender, elongated tubes known as cornicles or siphunculi. Their function is the production of a defensive waxy secretion. They are twice as long as the finger-like tail and both are brownish-black. The black bean aphid has both sexual and asexual generations in its life cycle. It also alternates hosts at different times of year. The primary host plants are woody shrubs, and eggs are laid on these by winged females in the autumn. The adults then die and the eggs overwinter. The aphids that hatch from these eggs in the spring are wingless females known as stem mothers. These are able to reproduce asexually, giving birth to live offspring, nymphs, through parthenogenesis. The lifespan of a parthenogenetic female is about 50 days and during this period, each can produce as many as 30 young. The offspring are also females and able to reproduce without mating, but further generations are usually winged forms. These migrate to their secondary host plants, completely different species that are typically herbaceous plants with soft, young growth. Further parthenogenesis takes place on these new hosts on the undersides of leaves and on the growing tips. All the offspring are female at this time of year and large populations of aphids develop rapidly with both winged and wingless forms produced throughout the summer. Winged individuals develop as a response to overcrowding and they disperse to new host plants and other crops. By midsummer, the number of predators and parasites has built up and aphid populations cease to expand. As autumn approaches, the winged forms migrate back to the primary host plants. Here, both males and sexual females are produced parthogenetically, mating takes place, and these females lay eggs in crevices and under lichens to complete the lifecycle. Each female can lay six to ten black eggs which can survive temperatures as low as −32 °C (−26 °F). More than 40% of the eggs probably survive the winter, but some are eaten by birds or flower bugs, and others fail to hatch in the spring. The black bean aphid can feed on a wide variety of host plants. Its primary hosts on which the eggs overwinter are shrubs such as the spindle tree (Euonymus europaeus), Viburnum species, or the mock-orange (Philadelphus species). Its secondary hosts, on which it spends the summer, include a number of crops including sugar beets, spinach, beans, runner beans, celery, potatoes, sunflowers, carrots, artichokes, tobacco, and tomatoes. It colonises more than 200 different species of cultivated and wild plants. Among the latter, it shows a preference for poppies (Papaver species), burdock (Arctium tomentonum), fat-hen (Chenopodium album), saltbush (Atriplex rosea), chamomile (Matricaria chamomilla), thistles (Cirsium arvense), and docks (Rumex spp.).