Delayed effects of mosquito-larvicidal Bacillus sphaericus on Culex quinquefasciatus

The toxicity and the delayed effects of Bacillus sphaericus C3-41 to \%Culex quinquefasciatus\% larvae has been studied.The bioassay results indicated that the C3-41 acetone powder has a considerable toxicity against target under the laboratory condition, with a fifty percent lethal concentration (LC 50 ) of 6 92±0 22 μg/L against 3 rd ～4 th instar larvae at 48 h. The significant continued mortalities and abnormal development were observed in larval, pupal and emergence stages after the initial 48 h exposure of larvae were terminated, and the cumulative preadult corrected mortality of LC 30 , LC 50 , LC 70 , LC 90 , LC 98 dosage treatment were 84%, 91%, 95%, 98% and 100% respectively. In comparison, only 5% cumulative preadult corrected mortality was observed in control. Moreover, the delayed pupation, abnormal emergence and delayed oviposition were also noticed in surviving treated individuals. These long-term effects of C3-41 to mosquito larvae may be resulted from the damage of the midgut epithelium caused by binary toxins in initial treatment and would be contributed a great deal to the efficacy of B. sphaericus in field application for mosquito control.