Abstract: A laboratory test was conducted to determine the preference for host stage in the parasitic wasp Metaphycus parasaissetiae Zhang and Huang on its host Parasaissetia nigra at 25℃. The results indicated that the parasitic wasp M. parasaissetiae preferred to oviposit on the host adults in brown phase and with a few larvae beginning to crawl out from their hull. The P. nigra adults in the early phase could be parasitized only when wasp to host ratio was high. Fecundity ofM. parasaissetiae in a single host was the highest when P. nigra adults were in early oviposition stage, parasitism rate and selection coefficient reached the highest level when the hosts were in the brown phase. The developmental durations ofM. parasaissetiae were about 16 to 17 days whenM. parasaissetiae parasitized in P. nigra adults from the early stage to the stage with a few larvae crawling out from their hull. The wasp offspring number reached the highest (112.6 on average) when M. parasaissetiae parasitized in P. nigra adults in early oviposition stage. These results indicate that the most suitable phases of P. nigra adults for parasitization by M. parasaissetiae were the brown phase and the stage with a few larvae crawling out from their hull.