Abstract: Through a monthly observation of the parasitic load of the imagoes, the output of parasite eggs from sheep’s feces and the survival rate of ectogenetic parasites of Marshallagta, which was a typical dominant species among the parasitic nematodes parasitic on the sheep living on Bayanbulak grassland,which was a subalpinealpine meadow grassland, with the addition of the observing records of air temperature,relative humidity,evaporation capacity,the paper obtained the seasonal dynamics of Marshallagta in sheep and on grassland in different developmental stages as well as its relationship with the changes of air temperature and humidity. Both the parasitic load in sheep and the incubation amount in vitro on grassland were the lowest from July to August of 2006.But they reached their peak period in November of 2006 for the first time, and then an obvious decrease in February of 2007 before another peak period again in April of 2007. In addition, the amount of the parasitic larva was also the lowest from July to August of 2006, but its peak period appeared in September of 2006 for the first time, and afterwards an obvious rise came again in February of 2007. The peak period of the parasitic larva of Marshallagta corresponded to the peak period of the adult. It turned out that the peak period of the adult came with the peak period of larva, while the peak value of the parasite eggs in feces would often come along with the peak period of the adult.The in vitro survival rate was obviously affected by air temperature and humidity. When the average humidity was lower than 50%, no peak would come.When the temperature was lower than 5.6 ℃, the survival rate was zero. When the humidity was lower than 79%, the survival rate was very low. The test made a study on the seasonal dynamic regularity of Marshallagta in sheep and on grassland, which supplied theoretical foundations for the formulation of proper prevention measures.

Key words: Marshallagta; in sheep; on grassland; developmental stage; seasonal dynamics