Experimental Population Ecology Studies Of Aleurolyphus Ovatus??(Troupeau)(Acarina:Acaridae)under The Stress Of The Heavy Mental Lead

With the rapid development of industrialization and urbanization,the increasing heavy metal pollution in the ecosystems causes serious air pollution,water pollution and soil pollution.Aleurolyphus ovatus with characteristics such as small in size,short life-cycle,short generation times,easy to experimental manipulation and non-specialist living requirements,which provide an ideal model for the study of the relationship between lead stress and Acari species.In this study,A.ovatus were fed with artificial feed of five different concentrations of lead?Pb?NO₃?₂?were used as research materials.A.ovatus developmental period,sex ratio and fecundity of each developmental stages of the treated short-term?the first generation?and long-term?8-10 month?were measureed.With life table established,the net reproductive rate?R₀?,intrinsic rate of natural increase?r_m?,finite rate of increase???,average generation cycle?T?and population doubling time?D?of different groups were calculated.Main results were as follows:1.The effect of lead on A.ovatus developmental period:A.ovatus were fed on artificial diet made by a mixture of flour and yeast extract?4:1?,and cultured under 28°C,85%relative humidity.The developmental period of A.ovatus under the short-term stress of five lead concentrations?0,12.5,25,50 and 100 mg/kg?were14.014?16.846?16.486?16.727 and 17.258 d,respectively.The developmental period of all lead concentrations were increased in contrast to the control group.Under25-100 mg/kg lead concentrations,A.ovatus developmental period was increased while the developmental rate was slowed with the increase of Pb concentration.During long-term lead stress,total immature stage of A.ovatus under five lead concentrations were 14.014?17.421?15.917?15.833 and 16.225 d,respectively.The developmental period of all lead concentrations were increased in contrast to the control group.Under 25-100 mg/kg lead concentrations,the total immature periods of the short-term were more constant than that of long-term stress.During short-term lead stress,the length of the developmental period under 12.5 mg/kg was only less than that of the 100 mg/kg group.During long-term lead stress,the maximum value of the length of the A.ovatus developmental period was detected under lead concentration of 12.5 mg/kg.2.Effect of lead on fecundity of A.ovatus:During short-term stress,the total egg production per female of five lead concentrations?0,12.5,25,50 and 100 mg/kg?were 236.333,257.074,371.667,168.818 and 284.654,respectively.Total egg production per female was significantly increased in the 25 mg/kg group,and significantly decreased in the 50 mg/kg group.No significant changes of total egg production per female were detected in 12.5 and 100 mg/kg groups.During long-term stress,the total egg production per female under five lead concentrations?0,12.5,25,50 and 100 mg/kg?were 236.333,176.652,301.542,281.913 and 285.667,respectively.No significant changes were detected between the control group and the treated groups on total egg production per female.Compared with short-term stress,the control group and the treated groups of long-term stress were more constant on pre-oviposition period,oviposition period,post-spawning stage,adult life expectancy and per female fecundity.3.Effect of lead on life table parameters of A.ovatus:During short-term stress,the population doubling time?D?showed an increasing trend as lead concentrations increased under 12.5-100 mg/kg,and were shorter compared with the control group.But the population doubling time was longer than that of the control group under lead concentration of 100 mg/kg.Our results showed that low lead concentrations promoted population growth,while high concentration inhibited population growth.The intrinsic rate of natural increase?r_m?and finite rate of increase???decreases with the increase of lead concentration.The intrinsic rate of natural increase?r_m?and finite rate of increase???were larger than that of the control group in 12.5 and 25 mg/kg and lower than that of the control group in 100 mg/kg.This indicates that low lead concentrations promoted population growth,while high concentration inhibited the potential of population growth.During long-term stress,the maximum value of the intrinsic rate of natural increase?r_m?and finite rate of increase???,and the minimum value of the population doubling time?D?were appeared in the control group.The control group has the greatest reproductive potential and the fastest growth rate.The net reproductive rate?R₀?,average generation cycle?T?,intrinsic rate of natural increase?r_m?and finite rate of increase???of A.ovatus under 12.5 mg/kg reached the highest values.The population doubling time was the shortest at 12.5 mg/kg.This suggests that female adult A.ovatus possessed the greatest reproductive potential and the longest life span during short-term stress under lead concentration of 12.5 mg/kg.On the contrary,the minimum reproductive potential and population expansion rate were appeared under 12.5 mg/kg in long-term stress.4.Effect of lead on sex ratio of A.ovatus:The sex ratio of the short-term stress under five lead concentrations?0,12.5,25,50 and 100 mg/kg?were 0.849,1.176,1.056,0.675 and 0.895,respectively.Females account for a largest proportion of the population at 12.5 and 25 mg/kg,and a lowest at 50 mg/kg.During long-time lead stress,the sex ratio of A.ovatus under five lead concentrations?0,12.5,25,50 and100 mg/kg?were 0.849,0.839,0.919,0.583 and 0.646,respectively.The male A.ovatus taked up a dominant position in all treated lead concentrations.The highest sex ratio was at 25 mg/kg while lowest at 50 mg/kg.