3 o2 THE STUDY OE INSECTS 



tips of twigs of the heart-leaved willow, Salix cordata. The gnat that 

 causes the growth of this gall is Rhabdophaga strobiloides. The larva 

 remains in the heart of the gall throughout the summer and winter, 

 changing to a pupa early in the spring. The adult emerges soon after- 

 ward, and lays its eggs in the newly-started buds of the willow. 



The clover-flower midge. Dasyneura legumimcola, is a very serious 

 pest. The larvae live in the heads of clover and destroy the immature 

 seed. Different kinds of clover are infested by this pest; but red clover 

 is its chief food plant. 



The larva of the clover-flower midge passes the winter on or slightly 

 below the surface of the ground, usually but not always, in a cocoon; 

 it changes to a pupa early in the spring, and emerges an adult in late 

 April or early May. The eggs are laid in the small green clover heads, 

 many eggs in a single head, as each larva infests a single floret. The 

 larvae mature in about four weeks, and then drop to the ground to trans- 

 form. Two or three weeks later a second generation of midges appear 

 and lay their eggs. 



The Hessian-fly, Phytophaga destructor, is the most serious pest in- 

 festing wheat in this country. The larvae live at the base of a leaf be- 

 tween it and the main stalk, where they draw their nourishment from 

 the plant. There are two or three broods of this insect in the course of 

 the year. The larva? of the fall brood 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 flaxseed. Here they re- 

 main throughout the winter. In the spring the adult gnats emerge and 

 lay their eggs in the sheaths of leaves some distance above the ground. 

 The infested plants are so weakened by the larvae that they produce but 

 little if any seed, and often bend or even break off at the weakened spot. 



The wheat-midge, Thecodiplosis mosellana, 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 pear-midge, Contartnia pyrivora, deposits its eggs by means of a 

 long ovipositor, in the interior of the unopened blossoms of pear. The 

 young fruit is destroyed by the larvae. There is a single annual genera- 

 tion. The winter is passed in the ground, usually as pupae but sometimes 

 as larvae. 



The chrysanthemum gall-midge, Diarthronomyia hypogcea, causes the 

 growth of galls on the leaf, stem, and flower-head of the chrysanthemum 

 plant, and is sometimes a serious pest in greenhouses. 



There are a few species of gall-gnats that are remarkable for their 

 mode of reproduction. The larvae of these gnats which live beneath the 

 bark of decaying trees give birth to living larvae. Such a type of repro- 

 duction is known as pedogenesis. 



Family Bibionid^e 



The March-flies 



In this family the abdomen is often comparatively robust, and the 

 legs shorter and stouter than in most of the families with thread-like 



