Abstract:The plateau pika (Ochotona curzoniae)has been recorded as one of the serious pests in alpine meadows on the Qinghai-Tibet Plateau. However,biological control,recognized as a primary way in pest control,generally does not display visible effectiveness in the short term. Coccidian parasites are intestinal protozoans,and are currently recognized as the main parasite infecting plateau pika populations. Infection with coccidia seriously impairs the survival of hosts. In order to test whether coccidia could be used for control pikas,we incorporated coccidia into bait and tested its efficacies in both laboratory and field. Our results showed that the bait (containing 300 ×104 oocysts and synergist)led 63. 6% adults to die in the laboratory, and 54. 9% and 71. 0% decreases in numbers of adults and juveniles in field,respectively. In addition,embryo weight was significant lower in the treatment group than that in the control group. Infection rate and infection intensity were significantly higher in treatment plots than those in control plots. Our results suggest that coccidian parasites have good effectiveness in pika control,and it may also influence embryo development of pregnant female infected in the field.