diversity and abundance of birds [153], an important consideration in any 

 impact review of mosquito control plans. 



4.16.4 Temporary Control with Pesticides 



Limited use of decomposable pesticides for mosquito control may be 

 justified in urgent situations, but the use of pesticides should be 

 limited. Fortunately, between 80 and 90 percent of the salt marshes in 

 the U.S. have not been systematically treated with pesticides for mos- 

 quito control [139]. 



Adult mosquito pesticides are effective for one day, larval mosquito 

 pesticides for several days [154]. Adulticides are applied shortly after 

 emergence, when adult mosquitoes are still concentrated near their breed- 

 ing areas and before they have dispersed. Ground-level application, typi- 

 cally from truck-mounted foggers, may confine the pesticides closer to the 

 application area than is possible with aerial fogging. Adulticides, how- 

 ever, are the least desirable pest control technique [155]. Larvaciding 

 is generally considered to be more efficient than spraying adult mos- 

 quitoes, but caution is required in applying pesticides directly to 

 water because other organisms may be killed. 



Products such as Abate (for larvae) and malathion and dibron (for 

 adult mosquitoes) are in common use today. They are believed to be rela- 

 tively benign and short-lived in the ecosystem [156]. Nevertheless, the 

 misapplication of organophosphate chemicals has been shown to have poten- 

 tially lethal effects on fishes, shrimp [148], and warm-blooded animals. 

 Oil and surfactant combinations, instead of pesticides, are also commonly 

 used as control agents [157]. 



Sensitivities of typical estuarine organisms to three major groups 

 of pesticides are shown below (higher numbers reflect greater 

 sensitivity) [158]: 



It is clear that "sensitivities" vary greatly between types of pesticide 

 and groups of fauna [159]. 



In a toxicity test that included 12 insecticides and seven species 

 of estuarine fish, the descending order of toxicity was as follows: 

 endrin, DDT, dieldrin, aldrin, dioxathion, heptachlor, lindane, 

 methoxychlor, Phosdrin, malathion, DDVP, and methyl parathion [160]. 



180 



