160 



ZOOLOGY. 



generations appearing within the year, vary accord- 

 ing to the species. There are species in which 

 each female bears from eighty to one hundred young, 

 and nine to sixteen generations succeed one another 

 in the year. In autumn males and egg-laying 

 females once more appear. As a rule the eggs live 

 through the winter, but the insects themselves may 

 also do this. I must add that there are constant 

 differences within the boundaries of the same species 

 according to the habitat, and especially in the species 

 which regularly wander, either from one plant to 

 another, or from the leaves to the roots. But since 

 the species injurious to agri- 

 culture do not migrate in this 

 way, nothing further need be 

 said on the point. As aphides 

 suck plant juices during the 

 whole of their lives, and have 

 enormous reproductive powers, 

 they are very destructive. They 

 suck from stems and leaves the 

 juices which would otherwise 

 be used by the plants them- 

 selves for growth or for the 

 production of flowers and fruit, 

 and bear young, which bore 

 their beaks into the same part 

 in the immediate neighbour- 

 hood of their mother, and 

 quickly begin to multiply in 

 their turn. In this way, colo- 

 nies consisting of a hundred 

 more individuals are regularly formed {e.g. on 

 peas, beans, roses). A plant part attacked in this 

 way shrivels for want of nourishment, and the 

 aphides upon it would die if they did not wander 

 elsewhere. The third generation usually contains, 

 not only wingless individuals, but also others 



Fig. 108.— The Bean Aphis (Aphis 

 papaveris)-^ a larva of the same 

 below. 



or 



