Rural School Leaflet 



901 



Fig. 2. — Sprouts on a cabbage stump in spring 



the weather is favorable. By taking this cabbage aphis into the warm 

 greenhouse during the winter we have bred as many as thirty 

 generations in one year. 

 In Fig. 3 is shown a mother 

 aphis with a small brood 

 of young ones on a cab- 

 bage leaf. The mother 

 aphis is just starting the 

 colony, but it will increase 

 until perhaps the whole leaf 

 is covered with aphids so 

 closely packed together that 

 one could not put a finger 

 on the leaf without touch- 

 ing several of them. 



Finally, late in the 

 autumn, the true shining 

 black eggs (Fig. i) are 

 again laid on the leaves, 

 thus completing a very in- 

 teresting life history. 



One interesting phase of the life of these aphids, and also of other species 



of plant lice, is the sudden 

 appearance of individuals 

 with wings. The first gen- 

 eration of lice hatched from 

 the eggs on the cabbage 

 sprouts in the spring are all 

 without wings. Indeed, the 

 individuals of the second 

 generation are wingless, so 

 far as has been observed; but 

 in the third and following 

 generations there appear many 

 individuals that possess wings. 

 This is really a very remark- 

 able thing, and scientists have 

 been wondering and guessing 

 for many years as to why these 

 winged lice appear and what 

 causes them to appear. Certain it is, that these winged aphids fly away 

 to other cabbages or other food plants and there start new colonies. Per- 



FiG. 3. — Mother aphis with colony of young aphids 



