188 INSECTS INJURIOUS TO VEGETATION. 



the females only ; for winged individuals appear only at particular 

 seasons, usually in the autumn, but sometimes in the spring, and 

 these are small males and larger females. After pairing, the latter 

 lay their eggs upon or near the leaf-buds of the plant upon which 

 they live, and, together with the males, soon afterwards perish. 



The genus to which plant-hce belong is called Aphis^ from a 

 Greek word which signifies to exhaust. The following are the 

 principal characters by which they may be distinguished from 

 other insects. Their bodies are short, oval, and soft, and are 

 furnished at the hinder extremity with two little tubes, knobs, or 

 pores, from which exude almost constantly minute drops of a fluid 

 as sweet as honey ; their heads are small, their beaks are very 

 long and tubular, their eyes are globular, but they have not eye- 

 lets, their antennae are long, and usually taper towards the ex- 

 tremity, and their legs are also long and very slender, and there 

 are only two joints to their feet. Their upper are nearly twice 

 as large as the lower wings, are much longer than the body, are 

 gradually widened towards the extremity, and nearly triangular ; 

 they are almost vertical when at rest, and cover the body above 

 like a very sharp-ridged roof. 



The winged plant-hce provide for a succession of their race 

 by stocking the plants with eggs in the autumn, as before stated. 

 These are hatched in due time in the spring, and the young lice 

 immediately begin to pump up sap from the tender leaves and 

 shoots, increase rapidly in size, and in a short time come to ma- 

 turity. In this state, it is found that the brood, without a single 

 exception, consists v^'holly of females, which are wingless, but 

 are in a condition immediately to continue their kind. Their 

 young, however, are not hatched from eggs, but are produced 

 alive, and each female may be the mother of fifteen or twenty 

 young lice in the course of a single day. The plant-lice of this 

 second generation are also wingless females, which grow up and 

 have their young in due time ; and thus brood after brood is pro- 

 duced, even to the seventh generation or more, without the ap- 

 pearance or intervention, throughout the whole season, of a single 

 male. This extraordinary kind of propagation ends in the autumn 

 with the birth of a brood of males and females, which in due time 

 acquire wings and pair ; eggs are then laid by these females, and 



