54 CEREAL AND FORAGE INSECTS. 



the adults in considerable numbers, and as long as there are any heads 

 in which to oviposit they will continue to breed, although without the 

 regularity of the warm season, their development being entirely 

 dependent upon a sufficiently high temperature. On November 25, 

 1908, the writer % discovered, in a field near Grand Prairie, Tex., 

 several stalks of sorghum which had been allowed to stand after the 

 last crop had been harvested. Examination of seed in these heads 

 revealed a number of midge pupae, which, after remainingin the warm 

 office at Dallas for 24 hours, yielded a number of adults. Later these 

 heads were sent to Washington, where they were kept throughout the 

 winter at outdoor temperature, which was very low, and a careful 

 dissection of these seed during the month of January showed that all 

 the pupae had transformed into adults during the time the heads were 

 in the heated room at Dallas, leaving nothing but the true hibernating 

 "cocooned larvae" to carry the species over winter. It appears from 

 this that artificial heat w T ill not develop " cocooned larvae" that have 

 been found late in the season. 



HIBERNATION. 



As previously stated, the true hibernating form of the midge is the 

 11 cocooned larva." Although naked pupa? derived from normal 

 larvae can be found during the winter months, this " cocooned larva" 

 is the one form which, if the seed heads are subjected to extreme cold, 

 will perpetuate the species. Normal pupae will stand considerable 

 cold, and later, upon being exposed to sufficiently high temperature, 

 will emerge, but the " cocooned larvae," when once they have been sub- 

 jected to cold, will remain over winter until spring and produce 

 cocooned pupae and, later, adults. Therefore we can only say that 

 the sorghum midge hibernates as " cocooned larvae" and naked pupae, 

 though the preponderance of the former during the winter is very 

 marked. In addition to the instance cited by the writer at Grand 

 Prairie, Tex., Pr.of. Glenn W. Herrick records an instance in which, 

 after a freeze sufficient to kill the sorghum and Kafir corn, he brought 

 in infested heads of the latter, from which, after they had been exposed 

 to the temperature of a heated room, adult midges emerged in large 

 numbers. Professor Herrick found that the normal pupae and larvae 

 in these heads had not been killed by the freeze. 



The occurrence of larvae within seed during the winter months does 

 not indicate the wintering of the midge in this stage, but is attribu- 

 table to the habit w T hich the sorghum has of continuing to put out a 

 number of branch heads during recurring w^arm days when the temper- 

 ature does not become sufficiently low to kill the plant itself. As 

 already pointed out, the midge likewise will emerge irregularly during 

 the winter months, and as these heads present the opportunity, ovi- 

 position takes place. The normal larvae are then formed and during 



