474 ANNUAL REPORT OF THE Off. Doc. 



DRY SEASON DESTRUCTIVE 



Eutumologists who Lave investigated the (ly tell us that a dry sea- 

 son, especially during July and August, is very destructive of the 

 pupa or the quiescent stage in the life history of this fly and, there- 

 fore, we would conclude that very fcAv of the pupa of this insect 

 M'ould have escaped one of the longest, most extensive and destructive 

 periods of dry weather (that of 1910) that has been experienced in 

 the State for a long time, and yet the following season the Hessian 

 fly was the most abundant and destructive for many years. The 

 question naturally comes up, why is this if dry weather is such a 

 menace to the development of tJiis fly, and in so far as possible we 

 shall endeavor to answer this question. In looking up the tempera- 

 tures for July, August and September, 1910, we And that the weather 

 was comparatively cool, in fact so much so that the farm crops did 

 not suff'er such extreme desiccation as they would had the tempera- 

 ture been higher. The same is true of the Hessian fly, for we hud 

 that the desiccating ©fit'ects of the hot sun when the ground is dry 

 have, in many instances that have been thoroughly investigated, 

 destroyed well nigh the entire brood lying dormant in the wheat 

 stubble and on the ground. Here we have two climatic conditions 

 that will destroy the Hessian fly, hot and dry weather, therefore, if 

 immediately after harvest the ground is dry, the weather hot and 

 plowing difficult, and a wheat stubble field is known to have quite 

 a brood of dormant Hessian fly in its stubble and on the ground it 

 is not necessary to plow the field early to destroy the fly because heat 

 and dry weather will do this just as well. 



BOTH SOWINGS INFESTED 



But, if a drought prevails, as it did in the summer of 1910, and the 

 weather is cool, the pupa of the Hessian fly Avill lie in the stubble 

 until there is moisture sufficient for the fly to change from the dor- 

 mant to the adult stage, or the full-fledged fly, which, on account 

 of there being a little rain in 1910 until very late in the fall, may 

 not have taken place until, perhaps October, so that both early and 

 late sowing were equally badly infested. Another thing. In some 

 places where there was sutificient moisture together with the prevail- 

 ing cool weather there may have been more than the supposed usual 

 two broods of fly and the likelihood is there were more than the two 

 broods in some places. 



PARISAN EXPERIMENT 



Dr. Paul Marchal, of the Institute Agronomique, in Paris, France, 

 in order to determine how many broods of Hessian fly could be 

 produced under the most favorable conditions, began a series of ex- 

 periments in April, 1894. His plots of wheat were enclosed so that 

 there would be no infestation from without. From puparia which 

 had been collected March 12, of that same year, imagos issued April 

 5. These proceeded to lay eggs on the wheat growing in the plot 

 in which they were inclosed. These eggs hatched .larvae that fed 

 on the wheat as they would in Nature's realm and changed into 

 puparia from which flies issued May 30. These flies were put intq 

 another plot of wheat, especially prepared for them, and the third 

 generation of flies was flying in these cases July I. In like manner 



