Experiments on colonization of small water bodies by Culicidae and Chironomidae as a function of decomposing plant substrates and their implications for natural Amazonian ecosystems

Abstract

The effect of submersed organic matter in decomposition on colonization of smaii water bodies by insects (notably Culicidae and Chironornidae) was analysed. It was found that grass (Echinochloa polystachea) is decomposed by bacteria, and that oviposition by Culicidae is correlated to bactenal density. In containers with submerged forest litter (decomposing prevalently by fungi) bactenal 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 bactenal 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 ail 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, Arnazonian waters