416 AN INTRODUCTION TO ENTOMOLOGY 



The winged agamic form. — After a variable number of generations 

 of the wingless agamic form have been developed and the food-plant 

 has become overstocked by them, there appears a generation which 

 becomes winged and which migrates to the secondary host. These 

 are all parthenogenetic, viviparous females. They are known as the 

 winged agamic form or spuricB alatce or migrants or migrantes. In some 

 species, the second generation, the offspring of the stem -mother, are 

 winged migrants. 



When the migrating winged agamic form becomes established on 

 the secondary host, it produces young which are all females of the 

 wingless agamic form. After a variable number of generations of 

 this form have been developed, there is produced a generation of 

 winged agamic females which migrate from the secondary host to 

 the primary host. The two forms developed on the secondary host, 

 the wingless and the winged agamic forms, may closely resemble the 

 corresponding forms previously developed on the primary host or 

 may differ markedly from them. 



The members of the last generation of the series of partheno- 

 genetic forms, which produce the males and the oviparous females, 

 are termed the sexuparcB. In some non-migrating species this genera- 

 tion is wingless. 



The males and the oviparous females. — The winged agamic females 

 that have migrated from the secondary host to the primary one, 

 here give birth to true sexual forms, male and female. These pair, 

 and each female produces one or more eggs. These are sometimes 

 designated as gamogenetic eggs to distinguish them from the so-called 

 pseudova developed in agamic females. See note on page igi. 



The males and the oviparous females are termed collectively the 

 sexuales; and some writers refer to the oviparous females as the 

 ovipara. (Note that ovipara is a plural noun.) 



The sexuales differ greatly in form and habits in the different tribes 

 of aphids. In the more generalized aphids the ovipara of some species 

 are winged, and the males are very commonly winged; both sexes 

 have beaks and feed in the same way as do the other forms; and each 

 female produces several eggs. In some of the more specialized aphids 

 the sexuales are small, wingless, and beakless; consequently they can 

 take no food. Each female produces a single egg, which in some cases 

 is not deposited but remains throughout the winter within the 

 shriveled body of the female. 



In some cases the young produced by the agamic females are 

 each enclosed in a pellicle when born ; this is soon ruptured and the 

 young aphid escapes from it. The young thus enclosed are termed 

 pseudova by many writers. 



The foregoing account, omitting exceptions and variations, can be 

 summarized as follows : 



A. DIFFERENT TYPES OF INDIVIDUALS IN THE APHIDID^ 



First type. — ^The stem-mother or fundatrix, which is hatched from a fertilized 

 egg, is usually wingless, and reproduces parthenogenetically. 



Second type. — The parthenogenetically produced wingless agamic females. 



