260 ORDER DIPTERA 



autumn. The eggs deposited in the autumn give rise to larvae 

 whicli de\elop and pass into the flaxseed stage to hibernate. 

 If tliey are accelerated in their development and are provided 

 with food material — volunteer wheat — there may be one or 

 more extra broods in the summer. As high as five or six 

 extra broods were observed by Marchal. There are ordi- 

 narily two broods adjusted to the occurrence of young wheat 

 plants. One important thing is the distribution of the 

 species by means of the shipping of infested straw. This 

 must be the main or only means by which the species is 

 taken from one country to another. It has been introduced 

 into most wheat-growing countries of the world. The 

 natural distribution of the species is limited to about 20 

 miles a year. Flight aided by the wind might carry it some 

 little distance. For local measures attention to the stubble 

 is one of the most important things. If it is thick and dry 

 enough to burn over diu'ing midsummer, it can be destroyed 

 in this manner. Plowing under very deeply is another 

 method but must be done early enough to bury the stubble 

 before the flies have issued. T]je most generally practised 

 method, and most highly recommended, is to adjust the time 

 of planting so as to avoid the period of egg deposition. If 

 the time of planting wheat can be deferred for a week or two 

 after the appearance of the flies, it will escape. Flies will 

 not deposit eggs on the bare plowed field. If the wheat comes 

 up after the flies have issued and passed the egg-laying period, 

 it escapes attack. F'or the Central States the time of aj)pear- 

 ance has been pretty definitely determined, and it has been 

 shown at what time wheat can be planted with the greatest 

 security. For the latitude of Columbus, Ohio, it is about 

 the first of October. It is possible to plant trap crops so as 

 to catch the flies as they appear and the whole crop can be 

 plowed under after the eggs are deposited on it. This is not 

 particularly popular. If planting is done with reference 

 to temperature and to dift'erent seasons, results will be better. 

 Hot, dry weather seems to prevent the issuing of the flies. 

 Family Simuliidae. — The family Swudiidw includes the 

 black flies and buft'alo gnats. These constitute extremely 



