Plant lice aka “aphids” : Aphids are small sap-sucking insects. A typical life cycle involves flightless females giving living birth to female nymphs without the involvement of males. Maturing rapidly, females breed profusely so that the number of these insects multiplies quickly. Winged females may develop later in the season, allowing the insects to colonise new plants.
Some species feed on only one type of plant, while others are generalists, colonising many plant groups. About 5,000 species of aphid have been described. 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.
Aphids are among the most destructive insect pests on cultivated plants. Not only do they weaken the plant by sucking sap, but they act as vectors for plant viruses and disfigure ornamental plants with deposits of honeydew and the subsequent growth of sooty moulds. Because of their ability to rapidly increase in numbers by asexual reproduction, they are a highly successful group of organisms.
Control of aphids is not easy. Insecticides do not always produce reliable results, given resistance to several classes of insecticide and the fact that aphids often feed on the undersides of leaves. Biological pest control as part of an integrated pest management strategy is possible but difficult to achieve except in enclosed environments such as glasshouses.
There are also other types of lice detailed below. Lice are parasitic insects which feed off of skin and debris while sucking lice feed on blood and other secretions. They will lay eggs and take up permanent residence until treated. The claws of these three species are adapted to attach to specific hair diameters.
Body lice are vectors for the transmission of the human diseases epidemic typhus, trench fever, and relapsing fever. There are three stages: Nits, nymph and adult. Nits are louse eggs. They are generally easy to see in the seams of an infested person's clothing, particularly around the waistline, under armpits or even in body hair. They are oval and usually yellow to white in color. Body lice nits may take 1–2 weeks to hatch. A nymph is an immature louse that hatches from the nit (egg). A nymph looks like an adult body louse but is smaller. Nymphs mature into adults about 9–12 days after hatching. To live, it must feed on blood. The adult body louse is about the size of a sesame seed (2.5–3.5 mm), has six legs, and is tan to greyish-white. Females lay eggs. To live, lice must feed on blood. If separated from their hosts, lice die.
Head lice are wingless insects spending their entire lives on the human scalp and feeding exclusively on human blood. Humans are the only known hosts of this specific parasite. Unlike body lice, head lice are not the vectors of any known diseases. Except for rare secondary infections that result from scratching at bites, head lice are harmless, and they have been regarded by some as essentially a cosmetic rather than a medical problem.
Pubic aka crab lice:
This insect feeds exclusively on blood. The crab louse usually is found in the person's pubic hair. Although the louse cannot jump, it can also live in other areas of the body that are covered with coarse hair, such as the eyelashes. Humans are the only known hosts of the crab louse.The eggs of the crab louse are laid usually on the coarse hairs of the genital regions of the human body. Crab lice may also be found on other areas of the body that have coarse and relatively sparse coverings of hair, such as the beard, mustache, eyelashes, and underneath the arms. They do not generally occur on the finer hair of the scalp. The main symptom of infestation with crab lice is itching, usually in the pubic-hair area, resulting from hypersensitivity to louse saliva, which can become stronger over two or more weeks following initial infestation.