THE SORGHUM MIDGE. 



57 





and the predominant parasite is not found, these parasites may be seen 

 actively ovipositing through the outer glume of the sorghum seed in 

 precisely the same manner as has been described with reference to 

 Aprostocetus diplosidis. At the same time the writer has reared this 

 parasite from Setaria glauca infested by another species of midge. 



The pupae of Aprostocetus diplosidis and Tetrastichus sp. are found 

 occupying the same position within the spikelets as is taken by the 

 pupae of the sorghum midge, viz, directly against the ovary within 

 the delicate palet, the head directed toward the apex of the seed. 

 These pupae are not enveloped in the larval skin of the midge, but 

 are naked. While microscopic examinations of sectioned midge 

 larvae have not been made for the purpose of studying the develop- 

 ment of these 

 parasites, it is 

 evident that 

 these parasites 

 oviposit within 

 midge larvae in 

 all stages of de- 

 velopment. Ex- 

 amination of seed 

 observed to have 

 been visited by 

 parasites has re- 

 vealed, in some 

 instances, newly 

 hatched larvae, 



while in other cases half-grown or even full-grown larvae were 

 present. 



PREDACEOUS ENEMIES. 



By far the most important predaceous enemy of the midge is the 

 Argentine ant (Iridomyrmex humilis Mayr) occurring in Louisiana. 

 These ants swarm over the sorghum stalks and heads in the fields and 

 whenever they find midge pupae projecting from the apex of the glumes 

 they seize the latter in their mandibles and carry them off to their nests. 



The fly Psilopodinus jlaviceps Aldrich has been observed by the 

 writer to prey upon the adults of the midge. These flies rest upon a 

 sorghum blade conveniently near a head and dart out frequently, 

 seizing an adult and devouring it immediately. 



On July 15 the writer saw a hummingbird (probably Trochilus 

 alexandri, according to Prof. F. E. L. Beal, of the. Bureau of Bio- 

 logical Survey) hovering about the heads of sorghum, which were 

 at the time swarming with midges. To all appearances it was feeding 

 upon the sorghum midge. Professor Beal states that small spiders 

 and minute insects are often found in the stomachs of hummingbirds. 



Fig. 31.— Tetrastichus sp.: Female. Greatly enlarged. (Original.) 



