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.
Fertility control has been identified by studies in the laboratory and the field as a more appropriate and long-term control strategy for rodent pests than lethal control.In this study,we investigated the effects of quinestrol on mass of reproductive organs and on social behaviors in female and male Himalayan field rats(Rattus nitidus).A total of 16 adult females and 16 adult males were randomly assigned to 4 groups.One male and one female group were fed rice with 0.005%quinestrol by weight for 7 days,and another 2 groups were fed rice only.After 7 days,rats were assigned to 10 min dyadic encounters between groups,and investigation,aggression,defense and attack latency were quantified.All animals were killed on day 10,and reproductive organs were dissected and weighed.Dyadic encounter data showed that there were obvious changes in social behaviors of quinestrol-treated rats.Quinestrol significantly inhibited the investigative behavior of quinestrol-treated males toward control females in Rattus nitidus,but seldom affected investigation between control males and quinestrol-treated females.Aggression of control females toward quinestrol-treated males was higher than that of quinestrol-treated females,and defense of quinestrol-treated males toward control females was more remarkable than that of control males.Quinestrol remarkably decreased wet masses of epididymis and spermotophore in males and ovaries in females,but had no effect on wet masses of testes and uteri after quinestrol treatment.These results indicate that the anti-fertility effects of quinestrol on R.nitidus are attributed to not only suppressing reproductive organs but also impacting social behaviors associated with territory defense and mate choice.
