INSECTA 



485 



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, when they pupate. Common 

 thrips of importance are Taeniothrips 

 inconsequens of pears and Anapho- 

 thrips striatus of grasses and cereals. 



Subclass ENDOPTERYGOTA 



Order NEUROPTERA 

 (Alder flies, lacewings, antlions) 



Rather soft-bodied insects with biting 

 mouth parts; two similar pairs of 

 membranous wings held in a roof- 

 like manner over the body when at 

 rest. The wings have a primitive type 

 of venation, a distinguishing feature 

 being the ladder-like arrangement of 

 veins along the anterior border. The 

 abdomen is without cerci. The larvae 

 are invariably carnivorous — campo- 

 deiform, with biting or suctorial 

 mouth parts. Aquatic larvae usually 

 possess abdominal gills. 



The alder fly, Sialis, may be taken 

 as an example with an aquatic larva. 

 In June and July the adults fly rather 

 sluggishly in the neighbourhood of 

 water. They lay eggs in clusters on 

 grass blades and leaves overhanging water, and the larvae on hatching 



Fig. 336. Larva of Sialis lutaria. 

 From Inims, after Lestage. 



