DIPTERA 



819 



the larvag that they produce but Httle if any seed, and often bend or 

 even break off at the weakened spot. 



There is no method by which a crop of wheat can be saved from 

 the ravages of this pest after it is infested by it; the only means of 

 control are those that prevent infestation. Where practicable all in- 

 fested stubble should be plowed under immediately after harvest and 

 the soil rolled or lightly harrowed , thus preventing the emergence of 

 the fall brood of gnats; but this can not be done where clover or 

 grasses are sown with the wheat. The most available means of con- 

 trol is to sow wheat moderately late, that is, after the fall generation 

 of gnats has disappeared, but early enough to secure the maximum 

 yield of grain. This safe date varies with the latitude, longitude, and 

 elevation above sea level. This date has been carefully determined 

 for the different parts of the country and can be ascertained for any 

 locality by application to a State or Federal Entomologist. Dr. A. D. 

 Hopkins, who has made a very extended investigation of this subject 

 states that the first general coloring of the foliage, especially on the 

 hickories, dogwood, birch, ash, etc., is, as a rule, coincident with the 

 safest and best time to begin sowing wheat on any farm within the 

 range of winter wheat culture. 



The wheat -midge, Thecodiplosis nioselldna. — This gnat is also a 

 very serious enemy of wheat. It deposits its eggs in the opening 

 fiowers of wheat. The larvas feed on the pollen and the milky juice 

 of the immature seeds, causing them to shrivel up and become com- 

 paratively 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. No effective method of control of this 

 pest has been devised. 



Until recently our common wheat-midge was supposed to be the 

 same as the European species the specific name of which is tritici, and 

 which has been placed successively in the following genera; Tipula, 



Cecidowiyia, Di ptosis , and 

 Contarinia. But it has 

 been found to be another 

 European species the 

 Thecodiplosis mosellana. 

 The resin-gnat, Re- 

 tinodiplosis resimcola. — 

 This species infests the 

 branches of various 

 species of pine. I have 

 found it throughout the 

 Atlantic region from New 

 York to Florida. The 

 larvse live together in 

 _. r> ,r>, - considerable numbers 



F:g. io38.-The resm-gnat. ^^^^in a lump of resin. 



They derive their nourishment from the abraded bark of the twig; 

 and the resin exuding from the wound completely surrounds and 



