52 



CALIFORNIA STATE COMMISSION OF HORTICULTURE. 



FIG. 52. Aphids or plant lice. Winged and wing- 

 less forms. 1 and 3 natural size. 2 and 4 greatly 

 enlarged. 



many species, some of which attack most forms of vegetation. In this 

 family we have the phylloxera and the woolly-aphis, and many other 

 well-known forms, all exceedingly destructive to vegetation. The larg- 

 est species is about a quarter of an inch in length, and from this they 

 range down until it requires a good eye, sometimes assisted by a mag- 

 nifying glass, to see the smaller members. Some are subterranean, 



living wholly underground; some 

 are aerial, living on the tops of 

 plants; while some are both, and 

 pass one stage of their existence 

 underground and another above. 

 Insects belonging to this fam- 

 ily are soft-bodied, gregarious, 

 and most numerous in the wing- 

 less form. They have absolutely 

 no means of defense, being de- 

 stroyed by thousands by every 

 change in the weather, blown to destruction by the winds and washed 

 off by the rains. They have more enemies among predaceous insects 

 than has any other family, being preyed upon in all stages by the lady- 

 birds, which devour them externally, and by Braconids, which devour 

 them from the inside. Many birds eat them, and, being utterly 

 defenseless, they are beset by enemies on every hand. Why, then, 

 are they not exterminated? For the reason that nature has made them 

 so j enormously prolific that 

 they are enabled to withstand 

 all the destructive forces 

 which are at work against 

 them, and still leave enough 

 for a new start, for if but a 

 single one is left, that is 

 enough to stock the country 

 with a new brood. 



The aphis furnishes the 

 most interesting study in the 



entomological world. It is a contradiction of all known laws 

 relation to propagation. The first brood, which appears very early in 

 the spring, as soon as there is sufficient plant life to sustain it, is hatched 

 from eggs which have been previously deposited in the crevices of the 

 bark. These are all females. They commence the active work of their 

 lives at once, and suck the plant juices and grow, casting their skin, as 

 they become too large for it, about four times, by which time they have 

 reached adult size and are ready to begin the second great object of 

 their life that of propagation. 



Woolly aphis of apple (Schizoneura lanigeroJ). 

 Enlarged. 



Ill 



