16 



F. Aquatic Pest Control 



Treatment of aquatic areas to control nuisance or biting insects is 

 usually at low dosages; however, such compounds as dieldrin sometimes are used 

 at 1 pound per acre. In the latter cases, immediate mortality of aquatic forms 

 (except adult mollusks and annelids which are relatively resistant) is es- 

 sentially complete for the higher invertebrate and vertebrate forms [30]. 

 These treatments annually involve millions of acres of the most valuable fish 

 and wildlife marsh habitats. A recent survey of this problem by Bureau person- 

 nel is in press [25]. It concludes that knowledge of the full import of low 

 dosage rates is still lacking. Indirect effects may be quite important. 



V. INDIRECT EFFECTS OF PESTICIDES ON WILDLIFE 



Direct mortality, however serious and spectacular, is not the only danger 

 to wildlife from pesticides. Indirect mortality or loss of reproductive 

 potential may result from consumption of minute amounts of poisonous chemicals 

 over a period of time. In laboratory studies certain compounds are found to be 

 additive, while others are synergistic. Some food organisms are relatively 

 resistant and may store toxicants [3], [29], [59]. Others are very susceptible 

 and there may be changes in numbers or relations of food-chain organisms. Even 

 dying insects may be toxic [l7], [28], 



Adult quail and pheasants seemingly unaffected by minute amounts of toxi- 

 cant in their feed may become deficient in reproductive potential [l4], [l5j. 

 Penned quail whose diets contained DDT at the rate of 3 ounces per ton of food 

 produced eggs whose fertility was reduced 305^ [l6]. They produced 3^ fewer 

 chicks per hen and 800/^ more cripples than did quail on diets uncontaminated by 

 DDT. More than 903^ of the chicks from treated birds died within 6 weeks - even 

 though pesticides were not fed to the chicks themselves. In other pen tests, 

 woodcock, which had first been fed DDT with littl'e apparent effect, were more 

 susceptible to dieldrin than uncontaminated birds (Dodge and Sheldon, unpubl.). 



A. Earthworm Studies 



Earthworms have been shown to be relatively resistant to pesticides, to be 

 able to store toxicant in tissues, and to be able to poison vertebrates feeding 

 on them. Earthworm studies in connection with the fire ant program have already 

 been reviewed. Studies of the effects of feeding contaminated earthworms to 

 captive birds are in progress. 



B. Aquatic Pest Control 



To control a bothersome gnat. Clear Lake, California, was treated in 1949 

 with DDD at 0.01 to 0.02 parts per million [9], [4l], [Sl]. Treatment was 

 repeated in 1954 and 1957. The suraner breeding colony of western grebes dis- 

 appeared soon after the first treatment. In November, 1957, hundreds of 

 wintering grebes died. Both the breeding and wintering populations have been 



