the similarities between the frequency and time 

 of occurrence of the various forms in the 1959 

 and 1960 drift samples . At the end of four hours, 

 very few organisms were appearing in the drift 

 samples . 



The first post- spray bottom samples 

 were taken seventy -two hours after treatment. 

 At this time the number of organisms in the 

 drift samples was back to pre -treatment levels. 

 These bottom samples indicated that the popula- 

 tions in the experimental stream on Brasstown 

 Bald had undergone a serious decline . Webb 

 (1959) in Canada, Cope and Park (1957) in Mon- 

 tana, Hoffmann and Drooz (1953) in Pennsyl- 

 vania, and Hoffmann and Surber (1945) in West 

 Virginia all recognize this severe immediate 

 reduction. Most workers seem to agree that 

 the caddisfly is one of the aquatic insects most 

 seriously affected by DDT. Caddisflies were 

 scarce in this particular stream, but the fact 

 that they were severely affected is evident by 

 their appearance in relatively large numbers 

 in the drift samples and their consequent reduc- 

 tion in bottom samples following the treatment. 

 Although the families Hydropsychidae and Limne- 

 philidae appeared in about equal numbers in the 

 pre -treatment samples, the limnephilids appear- 

 ed in much higher numbers in the drift samples; 

 this may imply that the burden of cases (the 

 hydropsychids are free living) made them more 

 susceptible to DDT poisoning. 



At the end of one month, population 

 levels in both the control and experimental 

 streams had declined still further; the declines 

 in the experimental stream were greater than 

 those in the control stream. If some of this de- 

 cline was caused by emergence, then it is pos- 

 sible that those immature forms which survived 

 the DDT poisoning did not suffer severe chronic 

 effects from the insecticide, and thus could com- 

 plete their life cycle and emerge . It is also 

 possible that some of the loss was due to a de- 

 layed effect of the DDT. The data from the 

 bottom samples indicate that none of the forms 

 present in these streams were immune to DDT 

 at the concentration reached in the Brasstown 

 Bald stream. However, only the Tendipedidae, 

 Tabanidae and Noteridae were entirely absent 

 from later samples. 



During the second month after treatment, 

 population levels in both streams began a grad- 

 ual increase, with the treated stream increasing 

 at a more rapid pace than the untreated. This 

 increase could come from several sources . The 

 fact that many of the forms present were mature 

 nymphs would suggest the possibility of an up- 

 stream migration from the unaffected lower 

 reaches of the stream. Roos (1957) mentioned 

 studies of positive rheotaxis and upstream mi- 

 grations as factors in invertebrate distribution 

 and Muller (1954) proposed a "Colonization 

 Cycle" . In this cycle the mature aquatic insects 

 migrated upstream to deposit eggs and then the 

 resulting immature forms floated downstream . 

 Both of these could be responsible for the general 

 increase shown. 



The last set of samples, taken four 

 months after treatment, indicate a complete re- 

 covery of the bottom fauna at all stations, in 

 terms of total numbers of organisms . 



Larrimore, et al (1959) state that the 

 rate of reinvasion of a stream habitat depends 

 on (1) extent of the area affected, (2) source of 

 the new organisms, (3) degree of damage and 

 the recovery of habitat, (4) water levels, and 

 (5) season of the year. The rapid reinvasion of 

 the aquatic insects in this study was favored by 

 each of these factors: (1) only a small section 

 of the stream was treated; thus, there could be 

 an upstream migration of insects; (2) there were 

 several streams in close proximity of the treated 

 stream which could act as hatcheries or reserves 

 for the treated area; (3) most of the aquatic forms 

 were not completely eliminated from the stream; 

 thus, they themselves could help repopulate the 

 stream; (4) no detrimental change in water level 

 occurred; and (5) the stream was treated at that 

 time of the year when only a short time would 

 elapse before mature forms would be laying their 

 eggs for the new brood. TTiis date coincides 

 closely with those shown in studies by Anderson 

 and Hooper (1956) and Ball and Hayne (1952). 



SUMMARY 



The watersheds of sections of two small 

 mountain streams in Georgia were treated with 

 0,5 pound per acre of EOT in a one -gallon oil 

 solution in both 1959 and 1960. In the Conasauga 



