TRANSFORMATIONS OF BUFFALO GNATS. 25 



DESCRIPTION OF PUPA OF SIMULIUM RRACTEATUM. 



The pupa of S. bractcatum (PI. IV, fig. 3) measures about 4 mm. in length and 

 is of a golden yellow color when first formed. 



The respiratory filaments are composed of a single main trunk on either 

 side of the thorax, each of which divides in the following manner : Two long 

 branches arise from the base of the main trunk, which again divides a short dis- 

 tance farther up, making four long branches on each side, counting the 

 branches at the distal ends. The hooks on the abdomen are arranged as usual. 



The pupae were reared from larvae and determined from adults 

 reared from them and compared with the type. 



DURATION OF PUPAL STAGE. 



The duration of the pupal stage of S. venustuTn, according to 

 Mrs. Sarah J. McBride, at Mumford, N. Y., is three weeks. The 

 maximum period in the pupal stage of the same species observed by 

 the writer was nine days at Havana, 111., late in the fall, the average 

 temperature during that period being 36° F. 



The minimum period in the pupal stage of S. venustum was a little 

 over 84 hours at Spartanburg, S. C, during the month of June, with 

 a temperature from 70° to 90° F. The average length of the pupal 

 period for the five species under consideration, during the summer, 

 is from five to seven days. 



The general effect of low temperature seems to be to retard, and 

 of rising temperature up to 90° F. to hasten the emergence of the 

 adult from the pupa. The effect that low air temperature has on the 

 pupa in retarding development is much less in proportion than the 

 effect that a rising temperature between 60° and 80° F. has in 

 hastening emergence. Though their structure is normally adapted 

 for aquatic life, yet when they are exposed to the air, as sometimes 

 happens when the water falls, they will often emerge even after 24 

 hours spent out of water if the adult is sufficiently developed within 

 the pupal skin. This was especially noticeable at Havana, 111., in 

 1912, when the river began to fall. 



The respiratory system of the pupa is a modification of the general 

 tracheal system of the larva. The rectal gills having been cast off, their 

 function appears to be assumed by the tubelike filaments arising on each 

 side of the thorax. There are two long main trunks extending down 

 each side of the abdomen. These give off branch tracheae, connected 

 by commissures, which lead to the abdominal spiracular chambers, 

 from which arise the initial threads leading to the spiracles. The 

 spiracles are cuticular invaginations and become closed, according to 

 Taylor, 1 on the withdrawal of the old tracheae at the time of the 



1 Taylor, T. H. On the tracheal system of Siniulium. In Trans. Ent. Soc. London, f, 

 1902, p. 701-716 (p. 703), 8 fig., 1902. 



