424 THE INVERTEBRATA 



Order ANOPLURA (Sucking lice) 



Ectoparasites of mammals, with mouth parts adapted for piercing the 

 skin and sucking the blood of their hosts. The eyes are ill-developed 

 or absent. The single-jointed tarsus carries a large curved claw ad- 

 mirably adapted for clinging to the host. The thoracic segments are 

 fused, and a flattened abdomen of nine segments possesses large 

 pleural areas allowing the body to swell on feeding. 



The mouth parts are tubular and capable of withdrawal into the 

 ventral side of the head. Their homologies are obscure. 



Pediculus humanus., the body louse (Fig. 314), is associated with the 

 spread of many diseases, such as typhus and relapsing fever. The 

 disease known as trench fever, prevalent in all war areas during the 

 Great War, has also been shown to be transmitted by this insect. 



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 three hundred. Temperature plays a big part in controlling 

 the development of these animals. Under average conditions, the life 

 cycle is completed in about three or four weeks. 



Order THYSANOPTERA (Thrips) 



Minute insects with asymmetrical piercing mouth parts; prothorax 

 large and free ; tarsus two- or three-jointed with terminal protrusible 

 vesicle ; two pairs of similar wings, provided with a fringe of pro- 

 minent long hairs, veins few or absent; metamorphosis slight, 

 including an incipient pupal instar. 



These insects are for the most part plant feeders, a few being 

 carnivorous. They are regarded as serious pests in that they rob the 

 plant of sap. They also often cause malformations and in some cases 

 inhibit the development of fruit. Parthenogenesis is of frequent 

 occurrence. In the case of the pea thrips, Kakothrips robustus, the 

 eggs are inserted in the stamen sheath of the flower and the nymphs 

 emerging feed on the young fruit, inhibiting its growth. Later they 

 feed on the soft tissues of pea pods, causing scar-like markings. The 

 nymphs leave the plant and bury themselves deeply in the ground, 

 where they remain till the following spring, w^hen they pupate. 

 Common thrips of importance are Taeniothrips inconsequens of pears 

 and Anaphothrips striatus of grasses and cereals. 



