Baetis, was the only kind of insect collected be- 

 fore the spray; four drift samples contained an 

 average of 6 per sample. After the spray was 

 appUed, one drift sample was taken each time 

 water samples were collected. The numbers 

 and kinds of insects contained in each sample 

 are presented in table 1 . The greatest number 

 of affected insects were drifting in the stream 

 1 hour after the spray was applied. The total 

 number dropped sharply after 2 hours and 

 leveled off 7 hours after the spray. 



in the drift samples were not separated taxo- 

 nomically; the analyses reflect the level of 

 toxicant in the whole sample. The results sug- 

 gest that aquatic insects can concentrate rela- 

 tively large amounts of DDT in their tissues in 

 a short time . Only a trace of DDT was found 

 in the 0.5 hour sample. The 1.0 and 3.0 hour 

 samples contained 3.4 ppm and 11.0 ppm of 

 DDT, respectively. The 3.0 hour sample also 

 contained 14.2 ppm of the derivative, DDE. 



Table 1 — Numbers f^f aquatic Insects per drift sample from Swan Creek after aerial spray of DDT 



Figure 2 shows, graphically, the time- 

 frequency occurrence of drift -sample insects 

 of each of the four orders that were most com- 

 mon. The largest collection of affected insects 

 of each order occurred at a different time: 

 Plecoptera, 1/2 hour; Ephemeroptera, 1 hour; 

 Trichoptera, 1-1/2 hours; and Diptera, 3 hours 

 after the spraying. This situation probably re- 

 flects varying degrees of susceptibility to the 

 toxicant rather than differences in distribution 

 of insects in the stream, since the stream was 

 flowing at a rate that would have carried insects 

 from the uppermost spray area to the mouth in 

 less than an hour and since its ecological fea- 

 tures were relatively uniform within the spray 

 plot. 



Acute effects on fish 



Live-cars containing 4-5 inch rainbow 

 trout from the Bozeman National Fish Hatchery 

 were placed in the stream 1 day before the spray . 

 Initially, 90 fish were exposed. Samples, each 

 containing 15 fish, were taken from the live -cars 

 for residue analysis 6, 12, 24, 48, 72, and 96 

 hours after the spray. No mortality occurred 

 in the live -cars and the fish did not exhibit any 

 unusual reactions. Apparently, the resident 

 fish population did not suffer acute effects, since 

 observations of the stream did not reveal any 

 dead or morbid fish . 



DDT residues in fish 



DDT residues in aquatic insects 



Drift samples collected 0.5, 1.0, and 

 3 .0 hours after the spray was applied were fro- 

 zen for chemical analysis . Insects contained 



As indicated above, fish from the live- 

 cars were collected for chemical analysis after 

 varying periods of exposure in Swan Creek . The 

 results of the residue analysis of fish tissues 

 appear in table 2 . All measurable amounts of 



