PREFACE 



As economic biology and pathology are subjects worthy 

 of the deepest study on the part of farmers, market-gar- 

 deners, and others interested in the cultivation of crops, — 

 my aim has been -to make this little volume a useful 

 companion to those who are interested in the diseases of 

 crops caused by the attacks of parasitic insects and fungi. 



The annual loss from the ravages of insects and fungi 

 upon growing crops is beyond calculation ; but it may be 

 estimated that on the average at least " one-sixth " of the 

 entire yield of farm-crops, hop-gardens, etc., is sacrificed 

 through the ravages of insect and fungoid pests. 



"As actual instances of the enormous losses which 

 farmers sustain through the ravages of insects, it may be 

 mentioned that Miss Ormerod estimated, for the season of 

 1881 alone, the financial loss represented by the cost of 

 seed and the expenses of sowing and re-sowing the turnip 

 crop destroyed by the ' turnip-fly ' in twenty-two English 

 and eleven Scotch counties, amounted to over half a 

 million pounds sterling." In Mr. Whitehead's Official 

 Reports for 1886 and 1887 it is stated, " that the ' diamond- 

 back turnip moth ' is the cause of losses estimated at 

 from £4 to £6 per acre ; that the ' dart moth ' occasioited 

 to a market-gardener in Essex losses to the extent of more 

 than £100 ; that through the ' mangel-wurzel fly ' farmers 



