INTRODUCTIDN 



Field observations along streams have shown that large numbers 

 of terrestrial and aquatic insects are killed when forested areas 

 are sprayed by airplane with DDT at the rate of 1 pound per acre, 

 ■nie immediate loss in bottom organisms ordinarily amounts to aoout 

 90 percent (Hoffmann and Iferkel 1948) . As tne affected insects 

 alight on tlie water or come to the surface, fish gorge on them. Ob- 

 servations (Surber 19A6) made shortly after the spraying of a trout 

 stream in Pennsylvania showed that 30 brook trout in a livebox made 

 54 rises for insects in a 5-minute period. 



As a result of these field observations, questions arose as to 

 whether the consumption of poisoned insects might not kill fish 

 directly, or whether the insects and a dearth of food after the gorg- 

 ing affected the fish. Information on this general problem was ob- 

 tained through controlled outdoor and laboratory tests, Ginsburg 

 (1947) found that mosquito larvae killed by DDT at concentrations 

 from 1 to 0,05 p.p»m., and subsequently fed to goldfish at the average 

 daily rate of approximately 25 larvae per fish over a 4-day period, 

 did not poison the goldfish ( Carassius aura t us ) . As our preliminary 

 work indicated that the condition of the fish at the time of treatment 

 greatly influences susceptibility to poisoning, some experiments were 

 conducted along this line. Typical symptoms of DDT poisoning are 

 nervousness exhibited by the quivering of tne body and rapid move- 

 ment of the fins, and, in the later stages, by wild aimiess dashing 

 about. Fish often succumb with their gill-flaps extended as in suf- 

 focation; occasionally they have been observed to exhibit the nei-vous 

 symptOiUS and recover. 



Methods 



laboratory-reared adults and larvae of the housefly ( Musca 

 doraestica Linnalus) and field-collected tendipedid (midge-fly) larvae 

 were sprayed with a DDT suspension or a DDT-oil solution at a rate 

 equivalent to 1 pound of DDT per acre. These insects were then fed 

 to smallmouth black bass ( Micro pterus dolomieu ) . largemouth black 

 bass ( Micropterus salnpides ) , bluegill CLepomis macrochirus ) . and 

 black crappie ( Pomoxis nigro-maculatus ) . The adult flies were anaesthe- 

 tized with carbon tetracnloride and scattered on paper in the bottom 

 of a 0,1-niilliacre chamber into which the insecticide was applied 



Note — The authors are indebted to D. D, Friddle, Fish and Wildlife 

 Service, and to E. P. Merkel, Bureau of Entomology and Plant 

 Quarantine, for technical assistance. The Division of Control 

 Investigations, Bureau of Entomology and Plant Quarantine, 

 furnished cultures of houseflies. 



