Taole 5. — Number of insects and other organisms per square foot (0.092 m.^) collected in Iron 

 River before chemical treatment and 1 week and 1 year after treatment, Laie Superior, 

 1962-63 



Organism 



Riffle area 



Pretreatment 



1 year 



Sand and detritus area 



Pretreatment 



Insects : 

 Plecoptera 



Perlidae 



Other 



Qjhemeroptera 



JJjhemeridae. ... 



Caenidae 



Baetiscidae. ... 



Heptageniidae. . 



Leptophlebiidae 



Baetidae 



Other 



Odonata 



Gomphidae 



Other 



Hemiptera 



Corixidae 



Trichoptera 



Philopotamidae. 



Psychoiicriidae. . 



^ydropsychidae. 



Phryganeidae. . . 



Other 



Coleoptera 



ELmidae 



Dytiscidae 



Diptera 



Chironoraidae. . . 



Heleidae 



Other 



Other invertebrates 



Bryozoa 



Annelida 



Crustacea 



Cladocera 



Amphipoda 



Decapoda 



Ifydracarina 



Mollusca 



Gastropoda 



Pelecjrpoda 



Total ,. 



Percentage of 

 pretreatment 

 number 



7 

 2 





 30 





 57 



1 



Number per square foot 



7 2 



110 



16 



6 3 195 



2 



138 19 2 



13 1 



77 201 <; 



63 3 



4 16 



2 



1 

 1 



13 

 24 



20 

 8 

 2 



16 



1 



11 

 4 





 

 3 

 

 5 



9 

 



57 

 1 

 2 



2 

 2 



26 



74 







4 



1 

 1 



748 



100 



64 



108 



100 



51 



pretreatment number (table 8) was similar to 

 the 65 percent reduction in the riffle area of 

 the Sturgeon River. The percentage of pre- 

 treatment numbers 5 weeks later, however, 

 was only 39 percent. Elmidae and Chironom- 

 idae, which were abundant before and 1 week 

 after treatment, were sharply reduced 6 weeks 



after treatment. The reduction of Chironomidae 

 may have resulted from emergence, but the 

 cause of the decline in Elmidae is uncertain. 

 Some larval forms of Elmidae leave the 

 streams to pupate (Sanderson, 1938); this 

 egress nnay explain the reduction, as the time 

 of year was appropriate for this movement. 



