Plant -Lice 



practical extermination of the hosts of lice which are frequently 

 found in the wheat fields in the spring. The lady-birds and the 

 larvae of the syrphus flies and the golden-eyed lace-wing tlies as 

 well as the maggots of certain midges of the genus Diplosis and 

 others breed upon plant-lice and in fact derive the greater part of 

 their food from these creatures. Extreme prolificacy is the means 

 which nature adopts to continue the existence of many other- 

 wise unprotected :md much harassed species. In this instance, 

 however, it has taken the form of extreme rapidity of develop- 

 ment instead of great prolificacy. 



The relationship between plant-lice and ants has often been 

 described and is one of the most fascinating topics in the whole 

 field of nature study. The honey dew which is secreted by 

 plant-lice both from the anus and from two tubes upon the back 

 of the abdomen is greatly enjoyed by ants which in a surprisingly 

 intelligent way care for the plant-lice, drive away their natural 

 enemies, carry them bodily to better feeding grounds, recognize 

 the necessity for migrations at times and assist in these migra- 

 tions and actually prepare locations in advance of transportation. 

 The term which is frequently applied to Aphids, viz, "the milch 

 cows of the ants," is a very appropriate one. 



Probably the most famous of the plant-lice in the economic 

 sense are the grape-vine Phylloxera (Phylloxera vastatrix), a 

 species which is said to have cost the French nation more than 

 the indemnity paid to the Germans after the Franco-Prussian 

 war, the woolly root-louse of the apple ( Shi:{onetira lanigera) 

 erroneously known in most parts of the world as the American 

 blight, and the hop-plant louse (Phorodon humuli Schrank^, a 

 species which is fast becoming cosmopolitan and which for years 

 has been the greatest enemy to the hop-growing industry in 

 England and parts of this country. 



Life History of the Hop-Plant Louse 



(Pliorodon humuli Schrank.) 



This insect which we have just mentioned as an extremely 

 injurious species is commonly known as the hop-plant louse and 

 sometimes as the hop blight insect. It is a native of Europe, is a 

 great drawback to the success of hop-growing in England, was 



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