Cowpea Aphid

Appearance

"Aphis craccivora" is a small species of aphid. The female has a glossy black or dark brown body with a prominent cauda, and legs in some shade of brown or yellow. The antennae have six segments and these and the limb segments, cauda and cornicles are pale proximally and dark distally. The adults do not have wax on their dorsal surface but the nymphs are lightly dusted with wax. Winged females are up to 2.2 mm long and have cross-barring on the abdomen. Wingless females are a little smaller.

Distribution

"Aphis craccivora" is believed to be Palearctic in origin but has expanded its range so that now it is near cosmopolitan. In recent years its range has extended further north in Siberia and Canada and further south in Chile and Argentina. It is abundant in the Mediterranean area and subtropics and in the tropics it is one of the most common aphid species. Infests cowpea in India, the Philippines, Thailand, the southern United States, tropical Africa, and Latin America.

Behavior

In the former USSR, "Aphis craccivora" overwinters as eggs, often at the base of young alfalfa plants, but is also reported to overwinter on "Acacia", camelthorn and perennial weeds. The eggs hatch in early spring and the first larvae are known as fundatrix and feed at first on alfalfa. These aphids are all female and reproduce by parthenogenesis, producing nymphs which moult four times over the course of eight to twelve days. By the end of April, winged females have migrated to other host plants, often "Acacia", and later to cotton, on which crop this pest does much damage. It may move back to alfalfa later in the year. In Belarus, lupine is an important host plant and in Ukraine, "Acacia" is most affected. A female aphid lives for 9 to 25 days and can produce from 25 to 125 young during its life. There may be up to twenty generations in the year. By November winged forms have developed and eggs are laid before winter sets in.

In warmer climates, parthenogenetic reproduction takes place throughout the year. The winged male insects are seldom encountered but have been observed in Germany, India and Argentina. The aphids tend to concentrate on the growing tips of plants, young leaves, shoots, flowers and developing seed pods. They are often tended by ants which feed on the secretions they produce and deter predators. Natural enemies include parasitic wasps, ladybirds, lacewing larvae and hoverfly larvae.