Ecological Study Of Ectoparasitic Mites On Two Species Of House Rats And Morphological Study Of The Chigger Mite Ascoschoengastia Indica In Yunnan

Objectives:The present study was to analyze the species composition,species diversity,community structure and species abundance distribution of ectoparasitic mites(chigger mites and gamasid mites)on two species of house rats(Rattus tanezumi and Rattus norvegicus)in Yunnan Province.It was to compare the species composition and infestations of mites on two rat species in different landscapes and altitudes and on different sexes of the rats,and to analyze the spatial distribution patterns of dominant mite species and their mutual ecological relationship.Ascoschoengastia indica was one of the dominant species mites on two species of house rats.The study was also to compare the morphological variations between different geographical strains of the chigger mite Ascoschoengastia indica,and to illustrate the geographical differentiation of A.indica.Methods:The present study included two parts.The original data of the first part came from the field investigations in 30 counties of Yunnan Province,in which both gamasid mites and chigger mites were collected at the same time,and a retrospective analysis was made.The constituent ratio(C_r),prevalence(P_m),mean abundance(MA)and mean intensity(MI)were used to analyze the the infestations of mites on two rat species.The richness(S),Shannon-Wiener's diversity index(H'),Pielou's evenness(E),Simpson's dominance index(D)and Cody index(?_C)were adopted to analyze the community structure and species diversity.Jaccard index(C_J)was used to analyze the species similarity of different mite communities.By using common indices(C,I,m*/m and K),the spatial distribution patterns of dominant mites were determined.The association coefficient(V)was used to analyze the mutual relationships between chigger mites and gamasid mites,and between different dominant species.Preston's model was used to fit the theoretical distribution curve of species-abundance of mite communities on R.tanezumi and R.norvegicus,and then the total number of mite species was estimated.In the second part of the study,100 larval specimens of the chigger mite A.indica were chosen as the target and their morphological structures were observed and measured under a microscope.The different geographical strains of A.indica were compared to analyze the variations of different geographical populations of the mites.Results:The present study included two parts.The first part is“the ecological study on ectoparasitic mites on two species of house rats in Yunnan Province”.The second part is“the morphological study on the chigger mite Ascoschoengastia indica in Yunnan Province”.In the first part,a total of 43015 individuals of mites belonging to197 species,were collected from two rat species,R.tanezumi and R.norvegicus,in 30counties of Yunnan Province where chigger mites and gamasid mites were simultaneously investigated and collected.Of the 197 species of mites collected,there were 129 species of chigger mites and 68 species of gamasid mites.A total of 166species and 32781 individuals of mites were identified from 1750 R.tanezumi rats,and101 species and 10234 individuals of mites were from 991 R.norvegicus rats.The dominant species of chigger mites on R.tanezumi rats were Leptotrombidium deliense(C_r=34.63%),A.indica(C_r=14.69%)and Walchia ewingi(C_r=11.26%),and the dominant species of gamasid mites were Laelaps nuttalli(C_r=64.43%),L.echidninus(C_r=25.06%)and Ornithonyssus bacoti(C_r=5.92%).The dominant species of chigger mites on R.norvegicus rats were W.ewingi(C_r=16.12%),A.indica(C_r=11.02%)and A.rattinorvegici(C_r=9.52%),and the dominant species of gamasid mites were also L.nuttalli(C_r=45.46%),L.echidninus(C_r=28.10%)and O.bacoti(C_r=15.91%).The dominant mites species were of aggregated distribution among different individuals of their corresponding hosts.The dominant mite species showed some positive association(V:0.12?0.30)or negative association(V:-0.12?-0.29)between any two of them.Most mites were collected in the flatland landscapes.The overall mean abundance and overall mean intensity of mites on the house rats in flatland landscapes were higher than those in mountainous landscapes(MA:P>0.05,MI:P<0.05).The infestations of mites on different sexes of hosts were different and male rat hosts were more susceptible to mite infestations than female ones.The species composition of chigger mites showed a moderate dissimilarity on male and female rats with species similarity index C_J=0.467on R.tanezumi and C_J=0.459 on R.norvegicus.The species composition of gamasid mites,however,was a moderate similarity on male and female rats(R.tanezumi:C_J=0.576,R.norvegicus:C_J=0.625).The overall infestations(P_m,MA and MI)of mites on two species of house rats were significantly different at different altitudes(P<0.05),and the infestations were the heaviest at lower altitudes(<1500 meters).The species richness and individuals number of mites on R.tanezumi reached the maximum values at 500-999 meters,while those on R.norvegicus reached the maximum values at2000-2499 meters.The species similarity of mites on the house rats was very low at the adjacent altitude gradients(C_J<0.31).The theoretical curve of species abundance distribution of mites communities on R.tanezumi and R.norvegicus conformed to logarithmic normal distribution,and the total mite species on R.tanezumi and R.norvegicus were estimated as 295 species and 129 species based on the theoretical curve.In the second part of the study,the results showed that Yunnan strains of A.indica showed a narrow range of PW,SB,ASB,AP,AM,AL,PL and S with lower values of mean in comparison with Guangdong strains,the mean of AW was also smaller in Yunnan strains than that in Guangdong strains(P<0.05).The mean of body length,body width and the lengths of three pairs of legs in Yunnan strains were smaller than those in Guangdong strains(P<0.01).In Yunnan strains,the means of AM,AL and S were larger than the means of A.indica from Guam of USA.The means of ASB,PSB,AL and S were larger than those of A.indica from Australia.Conclusions:The two species of house rats(R.tanezumi and R.norvegicus)in Yunnan has a great potential to harbor abundant mites.The dominant species of chigger mites on R.tanezumi are L.deliense,A.indica and W.ewingi,and the dominant mite species on R.norvegicus are W.ewingi,A.indica and A.rattinorvegici.The three dominant species of gamasid mites on two species of house rats are the same,and they are L.nuttalli,L.echidninus and O.bacoti.The dominant mite species are of aggregated distribution among different individuals of their corresponding hosts.Different landscapes,host sexes and altitudes can influence the composition and infestations of mites on R.tanezumi and R.norvegicus.There are some morphological variations among different geographical strains of A.indica,including Yunnan strains,Guangdong strains and the strains from USA and Australia.Population differentiation may exist in different geographical strains of A.indica.