Taxonomy And Ecology Of Chiggers On Rats Niviventer Confucianus And N.fulvescens In Southwest China

Objectives:The present paper is an attempt to systematically study the species composition and species diversity of chigger mites on two common rat species（Niviventer confucianus and N.fulvescens）in Southwest China,to name and describe some new species,and to describe some individual variations of the mites.The paper is also to reveal the infestation status,community structure,dominant species,spatial distribution,species abundance distribution,and total species estimation of chigger mites on the rats.The heterogeneity of infestation and community structure will be illustrated along different gradients of altitudes,latitudes,and longitudes.The results will enrich the knowledge of the taxonomy,fauna,and ecology of chigger mites,and provide more scientific information for the surveillance and control of vector mites and related mite-borne diseases.Methods:Based on the original data and specimens from the field investigations in 91 sites in Southwest China,chiggers（chigger mites）collected from the rats N.confucianus and N.fulvescens were re-examined and re-identified,and the final identified results were then summed up according to the taxonomic system of the mites.Some"unidentified"chigger specimens from Southwest China were re-identified and measured under the high power and oil lens of the microscope.Together with some aberrated individuals,some new species of chiggers were named and described,and their morphological structures were drawn with the related mapping software.The constituent ratio（C_r）,prevalence（P_M）,mean abundance（M_A）,and mean intensity（M_I）were used to analyze the infestation of chiggers on N.confucianus and N.fulvescens.The richness index（S）,Margalef index（R）,Shannon-Wiener’s diversity index（H）,Simpson’s index（D）,and Pielou’s evenness（E）were used to analyze the community structure of chiggers on the two rat species.Jaccard’s index（J）and Sorensen’s similarity index（IS）were used to compare the species similarity between two chigger communities on the two rat species.The C_Aindex（C_A）,I index（I）,patchiness index（m*/m）,and index of K value（K）were used to determine the spatial distribution patterns of dominant chigger species among different individuals of their corresponding rat hosts.The species abundance distribution of chiggers on the two rat species was fitted by Preston’s log-normal model,and the s₄h（62）index was used to estimate the total number of chigger species on the two rodent species.Results:A total of 911 N.confucianus rats were captured from the 53investigated sites of the total of 91 sites in Southwest China between 2001 and 2019,and 342 N.fulvescens rats were from 25 sites of the total 91 sites.The species names and their taxonomic status of chiggers on the two rat species were systematically studied and summed up according to the results of taxonomic identification.A total of11017 individuals of chiggers were collected from 911 N.confucianus,and they were identified as 2 families,16 genera,and 166 species.And 6557 individual mites collected from 342 N.fulvescens were identified as 2 families,13 genera,and 100species.Two new species（Trombiculindus yanyuanensis n.sp.and T.luhuoensis n.sp.）were named and described for the first time.The aberrated T.luhuoensis（one of the two new species）and Neotrombicula tongtianhensis were also described.Although the number of chigger species and individuals on N.confucianus exceeded that of N.fulvescens,the overall prevalence（P_M=37.43%）,overall mean abundance（M_A=12.09chiggers/rat）,and mean intensity（M_I=32.31 chiggers/rat）of chiggers on N.confucianus were lower than those on N.fulvescens（P_M=39.77%,M_A=19.17chiggers/rat,and M_I=48.21 chiggers/rat,P<0.05）.The dominant chigger species on N.confucianus were Ascoschoengastia sifanga（C_r=25.59%）,Walchia ewingi（C_r=13.20%）,and Leptotrombidium rupestre（C_r=8.56%）.The dominant mite species on N.fulvescens were L.cangjiangense（C_r=16.76%）,Neotrombicula japonica（C_r=15.46%）,and A.sifanga（C_r=10.64%）.The dominant chigger species were of aggregated distribution among different individuals of their rodent hosts,N.confucianus and N.fulvescens.The overall infestations（P_M,M_A,M_I）of N.confucianus and N.fulvescens with chiggers varied along the gradients of altitudes,longitudes,and latitudes with obvious heterogeneity.The species abundance distribution of chigger communities on N.confucianus and N.fulvescens conformed to a log-normal distribution.Based on the s₄h（62）index,the predicted total chigger species of N.confucianus and N.fulvescens were estimated to be 211 and 126 species respectively.Conclusions:There are some new chigger species（e.g.T.yanyuanensis n.sp.and T.luhuoensis n.sp.）and some aberrated individual mites in Southwest China.The infestation of N.confucianus and N.fulvescens with chiggers are common with high species diversity.The dominant chigger species are different from the two rat species,and they are of aggregated distribution among different host individuals.There is an obvious heterogeneity of chigger infestation and community structure at different gradients of altitudes,latitudes,and longitudes.The species abundance distribution of the chigger community conforms to a log-normal distribution.