THE SOEGHUM MIDGE. 



43 



tory methods were employed to get at the more obscure phases of the 

 problem. 



In Louisiana it was found that, owing to the excessive humidity, 

 infested sorghum heads when brought into the laboratory from the 

 field almost invariably molded and rotted before observations upon 

 the emergence of the adults could be made, and, furthermore, such 

 conditions would not yield true 

 results. For this reason, then — 

 and the same applies to Texas — 

 all records of life history were 

 made in the field upon growing 

 heads and subject to absolutely 

 normal conditions. 



In brief, the method employed 

 in the study of the various forms 

 of the midge was to select a num- 

 ber of sorghum stalks in the field 

 whose heads had not broken the 

 boot or protecting sheath and 

 which were therefore not in- 

 fested by the midge. Over these 

 unbroken heads were placed 

 waterproof paper bags, the tops 

 of which were gathered securely 

 about the stalks well below the 

 head and securely tied with 

 string, to which tags were at- 

 tached . These bags were allowed 

 to remain over the unopened 

 heads until by observation the 

 latter had broken the sheath 

 and the spikelets were in a con- 

 dition to receive an infestation 

 by the midge. Then they were 

 removed from the heads, and 

 these were watched until females 

 were actually seen to oviposit 

 within the glumes. When the 

 natural infestation was well un- 

 der way a note was made upon the small tag attached to the stalk 

 below the head, giving the date and the hour of the first egg deposi- 

 tion. (See fig. 22.) 



At various times these heads were cut and dissected in the labo- 

 ratory and the oldest form of the midge found therein recorded, 

 79536°— Bull. 85, pt 4—11 2 



Fig. 22.— Growing sorghum head, bagged and 

 after natural infestation by the sorghum midge. 

 This method is also practical for protecting seed in 

 the field from damage by the midge. (Original.) 



