In light of the remarkable ability of certain insects to harbor and transport pathogens, coliforms, and other organisms of interest to man, it might be worthwhile to exploit more efficiently the use of these in
sects as biological indicators of pollution, as suggested for flies by Lind
say and Scudder (1956). T h e flora of aquatic insects might be more indicative of water conditions than the free-living flora. T h e parasites of mosquito larvae can be used as an index of habitat pollution. Laird (1959) reported that the species of bacteria, algae, and protozoa found as external and internal associates of mosquito larvae proved to be referable to a system of classification of degrees of water pollution in which the end products of oxidation provide the nutritive substrate.
There was a correlation between the presence of microorganisms known to be good indicators of pollution with particular species of mosquitoes.
Certain organisms with wide limits of tolerance to pollution could not be used as indicators. Laird emphasized that none of the epibionts ex
hibited a marked preference for mosquito larvae over other available substrates, and if they had been collected without reference to the ecol
ogy of the habitat, they might well have been regarded as bona fide mosquito parasites. T h e variety of microorganisms was limited and the epibionts particularly rare on larvae taken from artificial containers such as drums, tires, and cans. Natural conditions of advanced pollu
tion and decomposition could be simulated in laboratory breeding pans by adding excessive food. This produced conditions favorable for the development of particular microorganisms harmful to the mosquito culture. T h i s study corroborates other indications that nonsymbiotic microorganisms reflect the immediate past history of the insect.
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