Influence of quaternary ammonium and organic silicon adjuvant on insecticidal activity of acetamiprid and environmental toxicity against aquatic organisms

To evaluate combined effects of quaternary ammonium and organic silicon adjuvant to the activity of acetamiprid, their independent and joint toxicities against Aphis citricola von der Goot and two aquatic organisms, Daphnia magna and Brachydanio rerio, were determined following the immersion test for insecticide activity and the additive index method. All the tested surfactants showed obvious synergistic effect on the activity of acetamiprid for the control of A. citricola, among which the maximum synergistic ratio was 210.2 induced by silwet 618. Acetamiprid exhibited low toxicity to D. magna and B. rerio, while all three organic silicon adjuvant and five quaternary ammonium surfactants showed the extremely high toxicities to D. magna. In terms of toxicity to B. rerio, organic silicon adjuvants showed moderate toxicities and quaternary ammonium surfactants exhibited high toxicities. Mixtures of organic silicon adjuvant+acetamiprid exhibited increased combined toxicity for D. magna and B. rerio. However, four of the five quaternary ammonium surfactants except tetradecyl dimethyl benzyl ammonium chloride (1427) were antagonism to two non-target aquatic organisms when combined with acetamiprid. Besides, all the tested surfactants can significantly reduce the surface tension of distilled water (from 74.37 mN/m to 20.50-40.07 mN/m) and increase its maximum retention on leaves (from 1.54 μg/cm² to 2.39-4.34 μg/cm²). When quaternary ammonium surfactants and organic silicon adjuvant were used as synergists, their toxicity to aquatic organisms should also be emphasized. Among them, quaternary ammonium surfactants were safer to D. magna and B. rerio.