Aphids are small(about 1mm), soft-bodied, sap-sucking insects and members of the superfamily Aphidoidea, family – Aphididae.
Some species feed on only one type of plant(monophagous) , while others are generalists, colonising many plant groups (Polyphagous) .
Aphids are among the most destructive insect pests on cultivated plants and cause huge loss in agricultural productivity . In addition to weakening the plant by sucking sap, they act as vectors for plant viruses and disfigure plants with deposits of honeydew and the subsequent growth of sooty moulds.
About 5,000 species of aphid have been described, all included in the family Aphididae. Around 400 of these are found on food and fibre crops, and many are serious pests of agriculture and forestry, as well as an annoyance for gardeners.
Some of the different species of aphids observed under foldscope –
1) Aphis gossypii (Cotton aphid) –
These are greenish in colour( varying shades, yellow-green to darkish green) .
It is a widely distributed pest of a variety of agricultural crops in the families Cucurbitaceae, Rutaceae and Malvaceae. Among cucurbit vegetables, it can seriously affect watermelons, cucumbers, cantaloupes,squash and pumpkin. Other vegetable crops attacked include pepper, eggplant, okra and asparagus. It also affects citrus, cotton and hibiscus.
Aphis gossypii sucking sap by piercing its proboscis into the vascular tissues of the leaf of host plant.
2) Rhopalosiphum padi –
It attacks all major cereals and pasture grasses and particularly barley, oatsand wheat and other Gramineae members. It can also be found in maize. It has a worldwide distribution.
3) Rhopalosiphum maidis (maize or corn aphid) –
These are yellow-green to dark bluish green in colour.
Rhopalosiphum maidis, commonly named as corn leaf aphid and corn aphid, is an insect, and a pest of maize and other crops. It has a nearly worldwide distribution. Other host plants include Barley, Green beans, Millets, Papaya, Potato, sugarcane, wheat and several gramineae species.
4) Aphis craccivora (cowpea aphid) –
Adults have glossy black or dark brown body. The nymphs are dusted with wax.
Aphis craccivora is polyphagous, meaning it feeds on a large number of different species of plant, but it seems to have a preference for members of the bean family. Crops attacked by this aphid include brassicas, cucurbits, beetroot, peanut, cotton,cowpeas, chickpeas and cardamom.
Nymph stage of Aphis craccivora.