INSECTS INJURIOUS TO WHEAT. 115 



it is sufficient to merit consideration, and only a knowledge 

 of their life-history can give a key to their successful 

 control. 



IXJURIXG THE LEAVES AND HEAD. 



The Wheat-louse {Nectar o pi mr a avenm^2^.^. 



History and Distrihution. — At comparatively long inter- 

 vals the wheat crop is extensively injured by the Wheat- 

 louse or Grain-aphis. In 1861 and 1862 serious damage 

 was done throughout New York and New England, which 

 seems to have been the first serious outbreak of the jDest 

 in this country, it being a native of England. Since then 

 the crop of 1889 throughout Kentucky, Ohio, Indiana, 

 Illinois, Wisconsin, and Michigan was the worst damaged, 

 sometimes to the extent of 60 per cent. The follow^ing 

 year the lice appeared on the eastern shore of Maryland in 

 large numbers, causing a total failure of the crop in some 

 sections, and in 1894 they did serious damage in Washing- 

 ton and northern Idaho, wdiere they had been known for 

 some years. Though no record of its distribution is to be 

 found, it would seem probable from the above that the 

 Wheat-louse occurs throughout the northern half of the 

 United States, as no mention of its occurrence in the South 

 is found. 



Like many aphids it rarely becomes excessively injurious, 

 being usually held in check by internal parasites, ^Dre- 

 daceous insects, diseases, and weather conditions. Just 

 how far the weather is directly responsible for their 

 increase or decrease is unknown; but it has been observed 

 that an outbreak is usually preceded by several dry seasons, 

 and that cold, damp weather during late sjoring and early 

 summer seems to favor their development. Parasitic 



