156 Annals Entomological Society of America [Vol. XIII, 



4. THE LIFE CYCLE OF APHIDS AND COCCIDS.* 



Edith M. Patch, 

 Maine Agricultural Experiment Station. 



APHIDS. 



To attempt to .epitomize the life cycle of the aphid is like 

 trying to draw an orderly sketch of Chaos. But after all, the 

 confusion may be more seeming than real and certain rules, 

 beset though they may be with exceptions, govern the life of 

 even the aphid. 



The gamogenetic egg is an outstanding argument for the 

 conclusion that the aphid of the North is holding more closely 

 to its prehistoric past than are those that spend their lives 

 where the successive seasons of the year offer a constant source 

 of food. For in the region of real winters there is no member of 

 the family Aphididse (in its restricted sense) whose total life 

 history has been worked out, that is known to pass its annual 

 cycle without exhibiting a concluding generation comprising 

 both sexes. The aphid, then, starts its life cycle like a typical 

 insect — in the fertilized egg. 



The overwintering egg is thus true to the traditions of the 

 Hexapods, but with it ends all conventional observances, for 

 between one such egg and the next in sequence there are crowded 

 such phenomena as a succession of parthenogenetic viviparous 

 generations; extreme examples of polymorphism; alternation 

 of generations in a series where a duplication may not occur for 

 seven or more generations; parallel series in which certain 

 fetnales give birth to true sexes without beaks while others of 

 the same generation give rise to normal young which hibernate 

 in the first instar without feeding; and a system of seasonal 

 migration which is not surpassed by any other in the animal 

 kingdom. That all these divergences from the ordinary life 

 cycle for insects take place within the limits of the family 

 Aphididas would seem remarkable indeed; but it is no less than 

 appalling to realize that the total range of phenomena just 

 indicated may be exhibited by a single species. 



*These groups share with other Hemiptera the general heterometabolic or 

 "gradual" metamorphosis, but present a bewildering array of specializations 

 and adaptations. 



Papers from the Maine Agricultural Experiment Station: Entomology No. 106. 



