438 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



The eggs are usually laid in the fall on the twigs or other parts 

 of the plant on which the insect is feeding. These eggs go over 

 the winter. The young aphids that hatch from these eggs in 

 the spring immediately begin feeding upon the host plant. 

 Usually this is a generation of females. When about two 

 weeks old they begin giving birth to living young which in turn 

 give birth to other young and so through the summer. Thus 

 there is a series of generations of wingless females that give 

 birth parthenogenetically to living young. In the fall there 

 appears a generation that is composed of both males and 

 females which are usually winged. After mating, the females 

 lay the winter eggs. At any time during the summer when food 

 becomes scarce or when conditions are otherwise unfavorable, 

 there may appear winged generations of females that fly to 

 other plants and thus provide for the distribution of the species. 

 This method of reproduction and distribution makes possible 

 a very rapid increase of the number of individuals. The off- 

 spring from a single female, if all the members of the summer 

 generations lived, would amount to hundreds of millions. 

 Fortunately, they do not all live. They have many natural 

 enemies, chief among which are the ladybird-beetles, the 

 syrphus-fly larvae, the lace-wing-fly larvae, the braconid-flies, 

 etc. 



Certain secretions from the body of the aphids play an 

 important part in their life. Through small pores or openings 

 scattered over the body, many kinds, as the woolly aphis and 

 others like it, secrete a waxy substance that forms a mat of 

 felted or woolly threads which afford the insects considerable 

 protection. Nearly all of the aphids also secrete a sweet, 

 sticky substance known as honey-dew. Formerly it was sup- 

 posed that this honey-dew came from the two little tubercles 

 that occur on the posterior end of the body of many of them, 

 but it is now known that it issues in drops from the alimentary 

 canal. Sometimes so much is produced that the plants and 

 the ground below are quite covered with the sticky, honey-like 

 secretion. Many insects are very fond of this honey-dew, 

 the ants being especially partial to it. On page 492 is given 

 an account of a particular way in which the ants care forcer- 



