174 INDIRECT INJURIES CAUSED EY INSECTS, 



from which in this country both these plants suffer most 

 are the Aphides, commonly called leaf-lice, but which pro- 

 perly should be denominated plant-lice. — As almost every 

 animal has its peculiar louse, so has almost every plant its 

 peculiar plant-louse ■ and, next to locusts, these are the 

 greatest enemies of the vegetable world, and like them are 

 sometimes so numerous as to darken the air a . The mul- 

 tiplication of these little creatures is infinite and almost 

 incredible. Providence has endued them with privileges 

 promoting fecundity, which no other insects possess : at 

 one time of the year they are viviparous, at another ovipa- 

 rous; and, what is most remarkable and without parallel, 

 the sexual intercourse of one original pair serves for all 

 the generations which proceed from the female for a whole 

 succeeding year. Reaumur has proved that in five gene- 

 rations one Aphis may be the progenitor of 5,904,900,000 

 descendants; and it is supposed that in one year there 

 may be twenty generations 5 . This astonishing fecundity 

 exceeds that of any known animal; and we cannot wonder 

 that a creature so prolific should be proportionably inju- 

 rious : some species, however, seem more so than others. 

 Those that attack wheat, oats, and barley, of which there 

 are more kinds than one, seldom multiply so fast as to be 

 very noxious to those plants ; while those which attack 

 pulse spread so rapidly, and take such entire possession, 

 that the crop is greatly injured, and sometimes destroyed 

 by them. This was the case with respect to peas in the 

 year 1810, when the produce was not much more than the 



a I say this upon the authority of Mr. Wohiough of Hoi lesley (late 

 of Boyton) in Suffolk, an intelligent agriculturist, and 3 most acute 

 and accurate observer of nature. 



b Reaum. vi. 566, 



