2 MANUAL OF VEGETABLE-GARDEN INSECTS 



restricted to a single family or other closely related group of 

 plants, both wild and cultivated. Thus many l)eet insects 

 also feed on weeds belonging to the goosefoot family, cabbage 

 insects on weeds of the mustard family, potato insects on wald 

 solanaceous plants and sw^eet potato insects on wild morning- 

 glories. This fact, that certain insects form more or less 

 definite associations wath certain groups of plants, is of great 

 practical importance and must be kept in mind when considering 

 methods of preventing injury. It also explains why clean farm- 

 ing is one of the most important factors in preventing insect 

 injuries to vegetable crops. In fact, clean farming together 

 with proper cultural practices often makes it unnecessary to re- 

 sort to special remedial measures, or at least renders it possible 

 to obtain more effective results from the use of insecticides. 



About 250 species of insects have been recorded as serious 

 enemies of vegetable crops in the United States and Canada but 

 a much larger number may occasionally become injurious. 

 Only the more important species are treated in the following 

 chapters, arranged under the crops to which they are most 

 injurious. Flea-beetles, blister-beetles, cutw^orms and other 

 general feeders are discussed in separate chapters. 



