38 NEW YORK STATE MUSEUM 



weather enables wheat, baiie}- and rye to grow luxuriantly. Dur- 

 ing midsummer, as a rule, only a little volunteer wheat is in a con- 

 dition for the larvae to live on, though this was very different with 

 barley in 1901, when continued moist weather, after the spring 

 brood had developed to pupae, brought out hosts of flies. Eggs 

 were laid in large numbers in the barley, especially the late sown, 

 and in early July many fields in Genesee county were badly infested. 

 The maggots were near the groimd in the latest barley, and in that 

 early sown occurred 10 to 12 inches above the surface, showing 

 that the insect lives by preference in soft growth and inferentially 

 that it thrives only indifferently in the older, harder growth. The 

 relation between a rank, succulent growth and injury was further 

 shown ni a hilly patch of wheat. The grain on the gravelly, com- 

 paratively dry knolls was nearly immune, while in the more moist 

 gullies the stalks of wheat were very scattered. The resistance of 

 so-called '' fly proof " wheats depends in large measure upon the 

 relative hardness or maturity of the stalks at the time the flies 

 appear and deposit eggs. 



Emergence of flies. This is an exceedingly important matter 

 because successful methods of preventing injury depend upon a 

 correct understanding of the habits of the flies. The flight of the 

 Hessian fly is dependent on weather conditions. The following 

 rules will assist materially in forecasting probabilities : 



1 The flies may remain an indefinite period in the " flaxseed " 

 or pupal stage during dry weather. 



2 " Flaxseeds '' or pupae are very likely to develop flies in large 

 numbers during damp, warm weather. 



3 Adults are killed by heavy frosts though this is not true of 

 larvae and '* flaxseeds " or pupae, and hence flies may appear and 

 deposit eggs hetiveen killing frosts. 



4 L nder certain conditions some of these insects may spend 

 nearly a year in the flaxseed stage. 



5 Recentlv emerged flies must, in all probability, deposit eggs 

 shortly upon succulent grain. 



The above rules show that egg-depositing flies may appear at 

 any time during the growing season, provided weather conditions 

 are favorable, though naturally we would expect them to issue in 

 large numbers only at the first favorable period after a large brood 

 had attamed the '' flaxseed " or pupal stage. Thus, as our springs 

 are usually warm and moist, this means that ordinarily most of 

 the flies will emerge the latter part of April or early May. Then 



