File: <anoplura

Phthiraptera (= Anoplura) are the sucking or true lice that are ectoparasitic on mammals (primates, ungulates, canines and rodents). Most important on humans are the Head louse (Pediculus capitis), Body louse (Pediculus humanus) and Crab louse (Phithirus pubis).

Body louse

Head louse

Crab louse

The evolution of these lice with their hosts is closely paralleled. They are small wingless insects. Their mouthparts are adapted for piercing the skin and sucking the blood of their hosts. The eyes are poorly developed or absent. The legs are very short and the single-jointed tarsus carries a large curved claw that is well adapted for clinging to the host. The thoracic segments are fused, and a flattened abdomen of nine segments has large pleural areas allowing the body to swell on feeding. There is no metamorphosis.

Blood Sucking Habit

The tiny mouthparts are held at their bases in a stylet sac or buccal cavity, that is a diverticulum ventral to the pharynx. Buccal teeth grip the host while stylets penetrate. There are two stylets of which the dorsal is a paired structure, the halves of which maintain contact with each other distally to form a half-tube that is completed by the ventral stylet. This also consists of two parts. Between the dorsal and ventral stylets lies the salivary duct, which distally may be a modification of the hypopharynx.

The stylet complex can be extended so as to make contact with the skin. Into the wound is poured the salivary fluid that keeps blood from coagulating, and the mouth funnel is plunged in to enable the blood to be sucked up by the pharyngeal pump. During development the 1st maxillae unite to form the dorsal stylet, the ventral being formed by the labium. A pair of mandibles is also present but these are undeveloped.

Reproduction & Life Cycle

Eggs are laid attached to hairs of the body or clothing, and the three instars, passed through before attainment of the mature state, closely resemble the adult. The louse has been found to lay about ten eggs daily, depositing in all about 300. Temperature plays a big part in controlling the development of these animals. Under average conditions the life cycle is completed in 3-4 weeks.

Economic Importance

Humans develop a rash from the salivary secretions. They are also vectors of Rickets and Relapsing Fever. Pediculus humanus, the body louse is associated with the spread of many diseases, such as typhus and relapsing fever. This insect also transmitted the disease known as Trench Fever, which reduced Napoleon's Army and was prevalent in all war areas during World War I (see ent79):

Body louse

The group as a whole includes the most important vectors of Typhus Fever. During World War II, DDT treatment of the Italian population was required to rid it of a louse epidemic. Although the crab louse is not a disease vector, it can be contacted either through bodily contact or indirectly from bedding, etc. It is known to attack only humans and wild gorillas in Africa.

Crab louse

Sucking lice rank number one in livestock pests with three different species attacking cattle, two species goats and one species hogs.

Please also view Medical Importance

Control of Sucking Lice

Cleanliness is of the utmost importance in keeping down infestations of sucking lice. For livestock it is important to maintain the animals in a healthy state. DDT and Rotenone applied twice a year in autumn and spring has been effective for the control of both adults and eggs.

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Details of Insect Taxonomic Groups

Examples of beneficial species occur in almost every insect order, and considerable information on morphology and habits has been assembled. Therefore, the principal groups of insect parasitoids and predators provide details that refer to the entire class Insecta. These details are available at <taxnames.htm>.

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References

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