RAVAGERS OF CROPS 243 



night through ; the crop of hops was immense, 

 scarcely a fly was to be found, and the betted 

 (estimated) duty, which began in May at 120,000, 

 rose to 265,000 ; the gross duty actually paid 

 was 468,401 i6s. \d., being the largest amount 

 ever known. From this it will appear that, in 

 duty alone, a little insignificant fly has control 

 over 450,000 annual income to the British 

 Treasury ; and, supposing the hop grounds of 

 England capable of paying this duty annually, 

 which they certainly are, it is manifest that in 

 1825 these creatures were the means of robbing 

 the Treasury of 426,000. This seems a large 

 sum, but it is not one-twentieth part of the 

 sums gained and lost by dealers during the 

 two years in question." Although since those 

 memorable years considerable advancement has 

 been made in the artificial means of combating 

 the ravages of the Hop Aphis, the cost still 

 remains very high, and it is the natural enemies 

 of the Aphides, such as the ladybirds, hawk- 

 flies, lace-wing flies, parasitic ichneumon flies, 

 and insectivorous birds, which are the only 

 really successful agents in preventing their 

 excessive increase. 



In like manner, our cereal crops in some 

 seasons suffer very serious damage from the 

 depredations of Aphides; the Corn Aphis 

 (Siphonophora granaria), to be found feeding upon 

 wild grasses, at times ravaging the cornfields 

 to such an extent as to seriously impoverish if 

 not altogether destroy the crop. But this Aphis 

 has a deadly natural foe in the shape of a 

 parasitic ichneumon fly which deposits its eggs 



