Abstract: In order to increase the control effects, reduce the use of insecticides, enhance the safety of agricultural products, the synergism of two cationic adjuvants (1277 and C_8-10) and one silicone adjuvant (Breakthru S240) to three insecticides beta-cypermethrin, chlorpyrifos and chlorfenapyr against 3rd-instar larvae of the Spodoptera exigua (Hübner) and Helicoverpa armigera (Hübner) were studied by dipping method, and the influence of the three adjuvants on physical properties of water was determined. The results showed that: (1) all of the tested adjuvants showed significant synergism to those insecticides, and the synergism ratio was significantly correlated to the concentration of adjuvant. The synergism ability of tested adjuvants to those insecticides against S. exigua and H. armigera was C_8-10＞1227＞Breakthru S240 under the same concentration, except that Breakthru S240 showed higher synergism ability to 1227 against H. armigera. The optimum synergistic concentration of tested adjuvants to those insecticides against S. exigua was 900 mg/L, while against H. armigera it changed into 900 mg/L (1227), 300 mg/L (C_8-10) and 900 mg/L (Breakthru S240), respectively. (2) All of the tested adjuvants showed significant influence on the physical properties of water. Reducing ability of surface tension, as well as the increasing ability of expanded diameter and the maximum retention of tested adjuvants to water were Breakthru S240＞1227＞C_8-10under the same concentration. In conclusion, the synergism of tested cationic adjuvants (1277 and C_8-10) to three insecticides against both S. exigua and H. armigera was significantly higher than that of silicone adjuvant (Breakthru S240), while the latter showed better ability to enhance insecticide deposition on plant leaves than the former. These results provide theoretical proofs for the application of the tested adjuvants.

Key words: Insecticide, cationic adjuvant, silicone adjuvant Breakthru S240, Spodoptera exigua, Helicoverpa armigera, synergism, synergism ratio