Measurements of aquatic populations on 

 stream bottoms are summarized in tables 4, 5, 

 6, 7, and 8 . Table 4 indicates that in the creek 

 at Conasauga Lake in 1959 the organisms per 

 square foot were reduced in numbers less in 

 the treated section than in the control sections, 

 except in the case of midges and blackflies. 

 Both midges and blackflies were quite prevalent 

 in Station 4, which lies below the dam. It is 

 possible that this particular area received a 

 heavier dose of DDT than the remainder of the 

 stream; however, GjuUin, et al (1949) found 

 that blackflies were highly susceptible to DDT. 

 The larval forms were partially paralyzed by 

 the insecticide. As a result, they lost their 

 ability to hold to the substrate and were carried 

 downstream by the current. Table 5, covering 

 1960, showed that reductions in numbers were 



greater in the treated areas than in the un- 

 treated, but that the reductions were only mod- 

 erate in extent. Midges were not as seriously 

 affected in 1960 as in 1959. 



Comparison of the data on drift samples 

 and bottom samples shows that the noterids were 

 the most heavily affected of all the larvae present, 

 but they constitute such a small part of the inver- 

 tebrate population that their loss may not be 

 serious from the fish standpoint. The stone- 

 flies cuid mayflies, on the other hand, made up 

 about 70 percent of the population and 75 percent 

 of the drift samples. Although the mayfUes out- 

 numbered the stone flies in the population, more 

 stoneflies appeared in the drift samples (fig. 2). 

 This is in contrast to the report by Hoffmann and 

 Surber (1949) indicating that mayflies were more 

 susceptible to DDT. 



Table h- — Number of organisms per square foot of bottom, before and 

 seventy-two hours after treatment in May, 1959- 



