568 



BIOLOGY AND HUMAN LIFE 



In this country various species of native ladybirds serve as effective 

 checks upon plant lice of many kinds. It has been possible to control 

 the destructive Hessian fly by means of the parasitic insect Polygnotus. 



Shipments of 

 such parasitic in- 

 sects from one part 

 of the country to 

 another are fre- 

 quently made to 

 meet the outbreaks 

 of injurious in- 

 sects. ;\ further 

 step was taken 

 when specialists 

 were sent abroad 

 by the government 

 to look for natural 

 enemies of inju- 

 rious insects in the 

 regions from which 

 these insects orig- 

 inally came. 



The United States 

 probably suffers more 

 from injurious insects 

 than any other coun- 

 try, because there 

 have come here with 

 the migrations of 

 peoples a large num- 

 ber of foreign in- 

 sects, without their natural enemies. This country has also done more 

 than any other in the scientific and practical study of insects and of 

 methods of control. 



Ladybird beetles have been imported from Austraha and Asia to 

 keep down the San Jose scale. Calosoma beetles and several parasitic, 

 waspHke insects have been imported to fight the gypsy moth and the 



Fig. 237. Gypsy and brown-tailed moths (1924) 



Dotted area generally infested and ruled area lightly in- 

 fested with the gypsy moth. Area between heavy line 

 and the ocean also infested with the brown-tailed moth 



