Host plants and damage
The following details will refer mainly to the cotton aphid, Aphis gossypii, the green peach aphid, Myzus persicae and the tobacco aphid, Myzus nicotianae, all cosmopolitan and extremely polyphagous pests. They attack different species of the cucurbitaceae (e.g. cucumber, melon, watermelon), solanaceae (e.g. sweet pepper, eggplant), citrus, cotton and many ornamental plants.
Located chiefly on the underside of the leaves and sucking sap from the plant's vascular system, the aphids inflict both direct and indirect damage. They weaken the plant by draining its resources and cause severe distortion of growth. They secrete sugary liquid - honeydew - which not only clogs the stomata of the leaves, but also encourages the growth of sooty mould, which prevents light from reaching the photosynthetic tissues. In addition, aphids are common means of transmitting plant viruses from infected to healthy plants. 

Morphology and biology
The aphids are small (2 mm long) soft-bodied insects that live on plants in dense colonies. The body is generally pear-shaped, green, yellow and sometimes black and red in color. The legs and antennae are slender and the hind end of the abdomen bears a pair of tubular wax-secreting glands, the cornicles. Two forms of adults exist: the aptera, which are wingless, and the alate, which are winged. The latter form appears particularly in crowded conditions.

      adult of  Aphis gossypii and her  offspring
             

The reproduction of aphids is highly adapted to exploit a new temporary habitat by rapid population increase. Under most circumstances, all individuals are females which reproduce parthenogenetically (fertilization is not needed). The young are born fully formed and able to feed immediately. They grow rapidly, moulting 4 times before they mature. This process takes 5-6 days at 26°C and 13 days at 16°C. Young are produced at a rate of 3-6 a day for several weeks. The highest rate of increase is achieved at temperatures around 23°C.