Rodent pest population outbreaks occur frequently in grassland ecosystems in northern China.The Mongolian gerbil(Meriones unguiculatus)is a dominant pest rodent which is distributed across the semi-desert grasslands of Inner Mongolia,China.In 2009,we studied the contraceptive effect of levonorgestrel-quinestrol(EP-1),concentration 50 ppm,on a wild Mongolian gerbil population.The one-off contraceptive treatment was compared with a control group using a semi-monthly live trapping method in the Ordos Semi-desert Grassland Region of Inner Mongolia.The results show that juveniles were not recruited in spring in the treatment group.Ratios of juveniles in the control and treatment groups showed significant semi-monthly differences from spring to summer(one-way ANOVA,F_(2,14)=7.53,P<0.05).Between both groups,annual fluctuations of juvenile and total population densities were significantly different respectively(F_(2,14)=4.64,P<0.05;F_(2,18)=7.72,P<0.05).The contraceptive EP-1 delayed the normal reproductive pattern of Mongolian gerbil populations.This suppressed birth rates of gerbil populations,reduced their densities,and changed their age structures.The period of EP-1 baiting should be extended but it could be an ideal method for controlling Mongolian gerbil populations during each breeding season.
