Abstract
The effect of submersed organic matter in decomposition on colonization of small water bodies
by insects (notably Culicidae and Chironomidae) was analysed. It was found that grass (Echinochloa polystacheo) is decomposed by bacteria, and that oviposition by Culicidae is correlated to bacterial
density. In containers with submerged forest litter (decomposing prevalently by fungi) bacterial densities remain roughly as low as in water controls, and oviposition by Culicidae is sporadic. Green leaves
of forest trees show an inconsistent pattern except for the correlation between bacterial density and
colonisation by Culicidae. Chironomidae are little affected by the substrate in decomposition during
the one month of the test series. Initial water quality (black, rain, pH, conductivity) has little or no
effect on decomposition and on colonization processes, and development of the aquatic insects is
normal under all regimes provided there is food for the larvae. Water quality, however, is the result of the decomposition process: specific pH-values are stabilised by the plant substrates. Decomposition
of forest litter by fungi inhibits growth of bacteria. The results are suggestive for possible interrelations
between chemical, biological and ecological factors in natural, Amazonian waters (Fig. 3).
