378 



AN ECONOMIC ENTOMOLOGY. 



Fig. 435. 



any evidence at present, there is a continuous breeding by female 

 individuals only. 



There are only a very few injurious species among these gall- 

 flies. Occasionally we find on blackberry stems an irregular, 



warty swelling, and if 

 this be cut into, it will 

 be found full of cells 

 occupied by these little 

 Cynipid larvae. This 

 kind of gall is known 

 as " multicellular," be- 

 cause inhabited by nu- 

 m e r o u s specimens. 

 Similar galls are found 

 on the roots of rose 

 and plants of the same 

 natural family, and in 

 a few other cases cul- 

 tivated plants become 

 subject to gall growths. 

 As a matter of fact 

 these galls are scarcely 

 injurious, because in 

 most cases the plant 

 continues growing be- 

 yond them, or even if 

 a shoot is lost, perma- 

 nent injury is rarely 

 done. Certain species 

 of oak-galls produce a 

 black stain, and these 

 were at one time al- 

 most universally employed in making an ink of remarkable per- 

 manence. Even yet the law in some States requires for certain 

 records an ink of which oak-galls is one of the ingredients. 



It is a small step from parasitism upon vegetation to parasit- 

 ism upon animals, and hence it is not surprising to find that some 

 species of this family are parasitic on other insects. The differ- 

 ences between these forms and the true gall-makers are not easily 



c, Pithy gall on blackbern 

 7iebulosus ; b, section to show cells 

 pupa. 



made by Diastrophus 



larva 



