DIPTERA. 



447 



infest the young wheat-plants near the surface of the ground. 

 When full-grown each changes to a pupa within a brown 

 puparium, which resembles a flax-seed. Here they remain 

 throughout the winter. In the spring the adult gnats 

 emerge and lay their eggs in the sheaths of leaves some dis- 

 tance above the ground. The infested plants are so weak- 

 ened by the larva that they produce but little if any seed. 



The Wheat-midge, Diplosis tritici (Di-plo'sis trit'i-ci). 

 This gnat is also a very serious enemy of wheat. It deposits 

 its eggs in the opening flowers of wheat. The larvae feed 

 on the pollen and the milky juice of the immature seeds, 

 causing them to shrivel up and become comparatively 

 worthless. When full-grown the larvae drop to the ground, 

 where the transformations are undergone near the surface. 

 The adults appear in May or June. 



The Resin-gnat, Diplosis resinicola (D. res-i-nic'o-la). - 

 This species infests the branches of various species of pine. 



FIG. 526. Diplosis resinicola. (From the Author's Report for 1879.) 



We have found it throughout the Atlantic region from New 

 York to Florida. The larvae live together in considerable 

 numbers within a lump of resin. They derive their nourish- 

 ment from the abraded bark of the twig; and the resin 

 exuding from the wound completely surrounds and protects 



