Effects of mosquito control insecticides on nitrogen fixation and growth of blue green algae in natural plankton associations

The effects of temephos, propoxur, methoxychlor, Dimilin and methoprene insecticides on blue-green algae have been investigated. After 3-6 days , temephos, methoxychlor and high doses of methoprene and propoxur stimulated nitrogen-fixation rates of blue-green algae, and, in some cases, a small increase in chlorophyll a. Nitrogen-fixation rates were strongly correlated with Aphanizomenon heterocyst concentrations. Dimilin and low methoprene doses caused slight decreases in nitrogen-fixation rates . The results show that normally used doses of pesticides can markedly affect nitrogen fixation and growth of blue-green algae and consequently the nitrogen flow in aquatic systems.