142 JTOIEECT INJURIES CAUSED BY INSECTS. 



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 oviparous ; and, what is most remark- 

 able 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 generations 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.^ This astonishing 

 fecundity exceeds that of any known animal ; and we cannot 

 wonder that a creature so prolific should be proportionably 

 injurious : 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 seed sown ; 

 and many farmers turned their swine into their pea-fields, 

 not thinking them worth harvesting. The damage in this 

 instance was caused solely by the Aphis, and was universal 

 throughout the kingdom, so that a sufficient supply for the 

 navy could not be obtained. The earlier peas are sown the 

 better chance they stand of escaping, at least in part, the 

 effects of this vegetable Phthiriasis. Beans are also often 

 great sufferers from another species of plant-louse, in some 

 districts, from its black colour, called the Collier, in others 

 the Dolphin, which begins at the top of the plant, and so 

 keeps multiplying downwards. The best remedy in this 

 case, which also tends to set the beans well, and improves 

 both their quality and quantity, is to top them as soon as the 

 Aphides begin to appear, and carrying away the tops to burn 

 or bury them. In a late stage of growth great havoc is often 

 made in peas by the grub of a small beetle {Bruehus gra- 

 narius), which will sometimes lay an egg in every pea of a 



Reaum. vi. 566. 



