Abstract:Studies on the synergism of rotenone mixed with fipronil against the striped flea beetle, Phyllotreta striolata (Fab.), were carried out after the investigation of the contact poisoning to the adults of P. striolata with 16 kinds of insecticides, including organophosphorus, pyrethroid, heterocyclic and botanical insecticides. The results in dip tests showed that the value of LC50 was 9.60 μg/mL and the co-toxicity coefficient was 230.14 after treatment 24 h when ratio of rotenone: fipronil was 3 ∶ 2. Based on these results, 6% rotenone-fipronil EC was formulated and all of its technical indexes accorded with quality level of pesticide. The adjust mortalities were 83.70% and 98.70% when the treatment dosages were 0.45 μg/cm2 and 0.75 μg/cm2 in toxic membrane test after treatment 48 h, respectively. The value of LT50 was only 10.12 min when the adults of P. striolata is treated with 50 μg/mL in topical application test. The rotenone-fipronil EC could significantly enhanced the breath inhibition to tested adults, which may be the main synergism mechanism. The results of field plot test demonstrated that the amount of adults of P.striolata was reduced by 72% -96% and effectiveness was over 90% when the rotenone-fipronil EC was sprayed with 450 mL/hm2. The rotenone-fipronil EC was worthy to be popularized.