The Gall-Gnats 



the larval state, in stems of wheat, and annually damages 



the wheat crop of the 

 United States to the ex- 

 tent of many millions 

 of dollars. It is sup- 

 posed to have been in- 

 troduced into the United 

 States in the straw 

 brought over for bedding 

 by the Hessian troops 

 during the War of the 

 Revolution. Hence the 

 popular name. Other 



Fig. 64. Diplosis resinicola, 

 (After Comstock.) 



resembling a pine 

 cone. Another spe- 

 cies lives on the sur- 

 face of the maple 

 leaves. Still another 

 forms a gall in the 

 stem of Chrysopsis. 

 There are also several 

 Cecidomyiid galls on 

 golden rod, sun- 

 flowers and Aster. 

 The species of two 

 genera have been 

 found in Europe to 

 give birth to young 

 while in the larval 

 state. This phenom- 

 enon is known as 

 paedogenesis, but has 

 not been observed in 

 any American forms. 



American species form 

 curious galls on willow, 

 one of them for example 



Fig. 65. Diplosis pyrivora. 

 (From United States Department Agriculture.) 



114 



