Fig, 88. — Turnip aphis, magnified, (i) 

 wingless viviparous female; (2) Immature 

 winged form, with wing-rudiments. After 

 Buck ton. 



154 INJURIOUS AND USEFUL INSECTS 



long, flexible boring organ works its way through the cells of a 

 leaf or shoot, often taking a sinuous course to avoid impene- 

 trable structures, and at last, it may be, tapping the vessels of 



the soft bast. Other species, 

 however, drive the proboscis 

 straight in. Each is adapted 

 to pierce its customary food- 

 plant in the most effective 

 way. The fifth segment of 

 the abdomen bears a pair of 

 long tubes, directed back- 

 wards and upwards, which 

 discharge a viscid fluid, 

 secreted by a gland at the 

 base of each. The fluid is 

 quite distinct from the sugary 

 excretion discharged from the 

 intestine, and known as honey- 

 dew. There are three thoracic and seven abdominal spiracles. 

 This form of aphis is exclusively female. It lays no eggs, 

 but brings forth its young alive, and is therefore a wingless 

 viviparous female. 



In the height of summer we find among the wingless aphids 

 just described winged forms, which, like the others, are exclus- 

 ively female and viviparous. The winged viviparous female is 

 of slighter build than the wingless kind ; it has a narrower 

 thorax, larger com- 

 pound eyes, and 

 three simple eyes 

 between them. The 

 wings are four, and 

 membranous, the 

 front pair twice as 

 long as the body, 

 and greatly surpass- 

 ing the hind ones 

 in size. These winged forms are particularly fitted for dis- 

 persing the species, and are produced just at those times when 

 the food-plants are most crowded with sedentary aphids. Now 

 and then the winged females appear in swarms which cover the 

 whole country. Such a visitation was observed in July 1865, 



Fig. 89.- 



-Tiirnip aphis, winged viviparous female. 

 After Buclcton. 



