Abstract: To study influences of host larvae treated with sublethal pesticides on host selection and progeny performances of koinobiont parasitoids, Meteorus pulchricornis-Spodoptera exigua larvae system was studied in non-choice and choice experiments. The host larvae were treated by Cypermethrine at the sub-lethal concentration. The results showed that more successful parasitism was accomplished in heavier host larvae treated with the sublethal pesticide, which was attributed to higher probability of survival to pupation in these hosts. Treated hosts were attacked much less than the control as much as 2.5 fold, produced progeny parasitoids with longer development time and larger body size. Compared with those emerged from attacking control host larvae, the progeny parasitoids from treated hosts were not affected in parasitism rate, and produced progeny parasitoids with lower pupation rate, shorter development time and larger body size, which indicated that progeny parasitoids that emerged successfully were improved in fitness parameters. Inconsistent results were obtained from the choice experiment. While control and treated hosts were equally susceptible to parasitism based on selection ratio, the former hosts were more prone to parasitism than the later at the second time of oviposition, based on failure-time analysis on the recognition time to attacks. Our study suggests that M. pulchricornis could be alleviated from indirect impacts of sublethal pesticides on parasitized host larvae through favor for heavier hosts at oviposition, and might be able to discriminate against host larvae that are exposed to parasitism instantly after receiving sublethal pesticides.