68 



APHIS VASTATOR. 



(267.) The Aphis vastator comes upon the potatoe plant 

 in the winged state, and there brings forth its young alive. 

 These generally prefer at first a large and rather debili- 

 tated leaf. After a short time the insect brings forth other 

 young, which young themselves reproduce without any 

 connexion with individuals of the other sex ; and thus from 

 a single specimen a plant may speedily become covered 

 with the insects. 



(268.) It has been proved by Reamur, that in five genera- 

 tions 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. I know no reason why the vastator 

 should be less prolific than its congeners ; and the rapid 

 rate at which I have seen them produced would in some 

 degree justify the conclusion that they are not at all 

 behind-hand in this respect. 



(269.) 1 have repeatedly seen both winged and apterous 

 specimens produce their young alive, though up to the 

 present time I believe that 1 am conversant only with 

 females. I do not certainly know the males of the vasta- 

 tor. It is stated, however, that the males of all Aphides 

 may be either winged or apterous, and that the females may 

 produce young for nine generations without any union with 

 the males. 



(270.) As far as my own observations are concerned the 

 vastator always appears as a viviparous creature ; but I do 

 not as yet know how it is propagated throughout the year. 



(271.) Entomologists state that in autumn the females 

 lay eggs, instead of bringing forth their young alive j but 

 this I have not yet myself had an opportunity of observing. 

 It is, however, a very important circumstance, and I hope 



