PAKASITES IN CEREAL AND FORAGE CROP PRODUCTION. 95 



him if he had noticed any insects on the heads of his wheat, and he 

 gave me most conchisive proof to the contrary by stating that he had 

 never looked to see if there were any there, but he thought not. 



Another case in point will be appreciated by those who are familiar 

 with the actions of the Hessian fly and its parasites. A field of wheat 

 in northern Indiana back in the 80's was so seriously affected by the 

 fly in the fall as to render the outlook for the owner getting even his 

 seed back at harvest exceedingly dubious. With the coming of spring 

 the wheat plants, or rather the belated tillers thereof, sprang up and 

 the owner harvested a crop of 20 bushels per acre. There was almost 

 no infestation of fly in spring. Now for the reason for this seemingly 

 superuatural phenomenon. In fall I had taken the precaution to 

 collect a quantit}' of dead wheat plants from this field aud placed 

 them in breeding in a warm room. Very few flies were reared, but 

 swarms of PoJyf/notus hiemalis Forbes emerged from the '* flaxseeds " 

 ensconced among the dead wheat plants. I now^ know that of that 

 yield of 20 bushels per acre secured from this field not less than 18 

 l)ushels per acre should go to the credit of Polygnotus. This was 

 the year following Doctor Forbes's description of his P. hiemalis^ and 

 none of us at that time knew much about it. More than ten years 

 after, in another State, almost a parallel case was presented. This 

 time, however, a most perplexing matter developed. The infested 

 wlieat was of a variety that persons with seed to sell were endeavor- 

 ing to boom, and one of the virtues claimed Avas immunity to attack 

 of the Hessian fly. Although I reared fully 100 Polj^gnotus to one 

 fly from the dead plants in the fall and knew^ absolutely that the 

 parasite saved the croj) by sweeping the fly almost out of existence, 

 yet I found both myself and the Polygnotus alike discredited and 

 the claim set up and sustained that the whole thing was due to certain 

 virtues possessed by this particular variety of seed wheat, for which 

 a fancy price was demanded and obtained. 



Within the last two years, in a section where spring wheat only is 

 grown, we have found a similar condition existing, and all facts so 

 far obtainable go to show that but for the efficient aid offered by Poly- 

 gnotus spring-Avheat growing in the Northwest would cease to be 

 profitable. These minute insect parasites save the country millions 

 of dollars, yet they are unknown except among entomologists. 



Again, Dr. Paul Marchal, who studied the development of Poly- 

 gnotus minutns in France, but did not witness oviposition, states that 

 there is every evidence of polyembrj'^onic development, the egg being 

 deposited in that of the Hessian fly and hatching in the body of the 

 maggot of the latter after it has left the egg. That is to say, there 

 may be several germ cells within a single ovum, and consequently sev- 

 eral larvfe may develop from a single Qgg. We have not by any 

 means cleared \\^ the obscurity relative to an American species, 



