﻿Nelson Association. 429 



1. " Oil the American Blight on Apple Trees," by T. Mackay, C.E. 



(abstract.) 



In the spring of the year a slight hoariness is oloserved upon the branches 

 of many of our apple trees. As the season advances this hoariness increases, 

 and towards the end of the summer the undersides of some of the b)'anches 

 are invested with a thick downy substance, so long as at times to be sensibly 

 agitated by the air. Upon examining this substance, it will be found that it 

 conceals a multitude of small wingless creatures which exude it from their 

 bodies, while at the same time they are busily employed in preying upon the 

 limb of the tree. This they are well enabled to do by means of a long beak, 

 or proboscis, terminating in a fine tubular bristle, which, being insinuated 

 through the bark and the sappy part of the wood, enables the creature to 

 extract, as with a syringe, the sweet vital liquor that circulates in the plant. 

 The sap-wood, being thus wounded, rises up in excrescences all over the 

 branch and deforms it ; the limb, deprived of its nutriment, grows sickly ; the 

 leaves turn yellow, and the tree perishes. The insect which is productive of 

 so much mischief is a species of the Coccidfe — order Homojjtera— Coccus (or 

 Pseudo-coccus) adoniduin, otherwise the Aphis lanigera, or woolly plant louse, 

 popularly called the American Blight. It was first observed in England in 

 1787, but it is n.ncertain if it was, as has been supposed, accidentally imported 

 there from America. Some entomologists say it came from France. At all 

 events, there is little doubt its original habitat was a warmer climate than that 

 of Britain. It has, however, found its way hence from the latter country. 



The wonderfully rapid development of the Ajjhis has thus been described 

 by a popular writer : — 



" It produces in the course of a season eleven broods of young. The first 

 ten are viviparous, or brought forth alive, and consist entirely of females. 

 These never attain their full development as perfect insects ; but being only in 

 the larval state (the larvae are active and resemble the perfect insect, but are 

 wingless) bring forth young, and the virgin aphides thus produced are 

 endowed with singular fecundity. But at the tenth brood this power ceases. 

 The eleventh does not consist of accive female larvge alone, but of males and 

 females. These acquire wings, rise into the air, sometimes migrate in countless 

 myriads, and produce eggs, which, glued to twigs and leaf-stalks, retain their 

 vitality through the winter. When the advance of spring again clothes the 

 plants with verdure the eggs are hatched, and the larva, without having to 

 wait for the acquisition of its mature and winged form, as in other insects, 

 forthwith begins to produce a brood as hungry, as insatiable, and as fertile as 

 itself. Supposing that one aphis produced 100 at each brood she would at the 

 tenth brood be the progenitor of one quintillion (1,000,000,000,000,000,000) 

 of descendants." — Paterson, "Science Gossip," 18G5. 



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