51 



there is no chance of recovery. At this time, and in this condition, the stench 

 from the hop plantation is most offensive. * * * * 



" The propfress and usual termination of the Aphis blight maj' be thna 

 described : The flies, as before remarked, on their first arrival, immediatelj' 

 suck the underside of the upper small leaves of the vine, and thus they 

 there deposit their young, upon the most succulent part of the plant. The 

 multiplication of the lice is so rapid, that the leaves become so thickly 

 covered as scarcely to allow a pin to be thrust between them. They 

 quickly abstract the juices of the vine, so that the leaves assume a sickly, 

 brown hue, and curl up, and the vine itself ceases to grow, and falls from 

 the pole, the lice continuing till they perish for want of food ; and thus tiie 

 crop is destroyed, and the grower may often consider himself fortunate if 

 the plant recovers a due amount of vitality to produce a crop in the follow- 

 ing year, for occasionally the hills are killed by the severity of the attack. 

 This description, of course, applies only to the most severe and unusual 

 blights." 



The Aphides are the most evanescent of all insects. They spring up 

 suddenly, in such immense numbers as to threaten the utter destruction of 

 the vegetation on which they subsist, and ere long they vanish with equal 

 suddenness — sometimes continuing but a few weeks, and rarely remaining 

 in force longer than through one year. It thus appears, that, so long as 

 the atmospherical or other influence which favors their increase, continues 

 to operate upon them, they thrive and prosper, and when this influence 

 passes away they rapidly decline. The writer in the Gardener's Chronicle, 

 cited above, remarks of this Aphis on the hops, " These insects are remark- 

 ably susceptible of atmospherical and electrical changes, and on a sudden 

 alteration of the weather we have known them perish by myriads in a 

 night. Tills was specially exemplified in the Farnham district, about the 

 middle of June, 1846, which suddenly recovered from a most severe attack, 

 and afterwards produced the largest crop ever known in that quarter. We 

 know, also, several instances in East Kent, which occurred in the same 

 year, when the planters sold their growths on the poles at a few shillings 

 per acre, and these same plantations so far recovered that many of them 

 afterwards produced a crop worth from 30^. to 50i. per acre." 



The decline and disappearance of these plant lice is greatly expedited by 

 other insects which destroy them ; and in many instances it is to these de- 

 stroyers rather than to any atmospherical change, that the vegetation on 

 which they abound becomes so suddenly released from them. No other 

 tribe of insects has so many enemies of its own class as the plant lice. The 

 different species of Coccinella or lady-bugs which are everywhere so com- 

 mon, live exclusively upon the aphides, as do also the larvaj of the two- 

 winged Syrphus flies and the four-winged Golden-eyed flies. Superadded 

 to these destroyers the plant lice also have their internal parasites — ex- 

 ceedingly minute worms or maggots residing within their bodies and 

 feeding upon till they kill them. Thus, whenever a tree or shrub becomes 

 thronged with plant lice, these destroyers gather among and around them, 

 in rapidly augmenting numbers, and subsist upon them until they have 

 wholly exterminated them. Kirby and Spence (page 181) state that in the 



