174 SIXTEENTH ANNUAL REPORT 



The Apple Leaf-hopper, which was so abundant in 1901 

 and scarce in 1902, continued scarce in 1903. The insect 

 will probably not become again destructive for several 

 years. 



As usual the Plum Curculio was destructive to plums 

 and cherries, and also did considerable damage to apples, 

 causing much of the gruit to be deformed. The Codling 

 Moth was about as injurious as in other recent years. 



The various saw-fly larvae, especially the Imported Cur- 

 rant Worm, the Pear Slug and the Rose Slug, did about 

 the usual damage. 



These pests are very easily killed by the use of hellebore, 

 or any of the arsenical insecticides. 



Vegetable Insects. 



It has been long acknowledged that one of the most per- 

 plexing problems in economic entomology is that of the 

 sudden and often apparently unaccountable increase or 

 decrease in the numbers of a large proportion of our insect 

 pests. Reasons for these fluctuations have often been 

 suggested : weather conditions, parasitic and predaceous 

 enemies, birds, and fungous diseases doubtless at times are 

 potent factors in the mysterious changes. 



During the season of 1903 there was a very extraordinary 

 attack throughout a large part of New England of the 

 various root-maggots of the genus Anthomyia. Cabbages, 

 cauliflowers and onions were infested to an extent that 

 completely ruined the crop for hundreds of growers. In 

 other years these insects have been vexatious, and occasion- 

 ally very destructive, but there was a general agreement 

 that the damage this past season was greater than had before 

 been known. 



In thinking over possible reasons for this unusual attack, 

 which in my own garden cleaned out rows of onions as 

 fully as could be done with fire, I happened one day to 

 pull up a wild mustard plant and found its roots completely 



