| Objectives:Apart from describing the normal morphology and aberrant individuals,the present study is an attempt to sum up the taxonomic identification result,species composition and diversity of chiggers(chigger mites)on three species of wild small mammals,Anourosorex squamipes,Eothenomys miletus and Suncus murinus,in Southwest China.The study is also to illustrate the infestation,community structure,spatial distribution of dominant mite species and their mutual association,species-abundance distribution,expected total species estimation,and the variation and heterogeneity of chigger species composition and infestation along different gradients of landscapes and altitudes.The results will enrich the taxonomy,fauna and ecology of chigger mites,and provide more scientific information for the surveillance and control of vector chiggers and related mite-borne diseases.Methods:Based on the original data and specimens of chiggers collected from the field investigation in 91 survey sites of Southwest China between 2001 and 2019,the taxonomic result of chiggers was summed up after the re-identification and measurement under the high power and oil lens of microscope.On the basis of morphological illustration with drawing software,the normal morphology and some aberrant individuals were described.The constituent ratio(C_r),prevalence(P_m),mean abundance(MA)and mean intensity(MI)were used to analyze the infestation of chiggers on three species of wild small mammals,A.squamipes,E.miletus and S.murinus.Margalef index(M_f),Shannon diversity index(H’),Pielou’s evenness(E)and Simpson’s dominance index(D)were used to illustrate the species diversity and community structure of chiggers on three species of wild small mammals.The patch index(m*/m),clumping index(I)and Cassie index(C_A)were used to measure the spatial distribution pattern of dominant chigger species.The mutual association between different dominant species was qualitatively and quantitatively analyzed by using x~2value and Pearson correlation coefficient(PCC).Preston’s log-normal distribution model was used to fit the species abundance theoretical curve of chigger community on the three species of wild small mammals.The i Chao’s method was used to estimate the number of expected total chigger species.Results:Of total 91 survey sites in Southwest China between 2001 and 2019,there were 49 sites with 1694 A.squamipes shrews captured,32 sites with 2661 E.miletus voles captured and 23 sites with 293 S.murinus shrews captured.A total of 56072chiggers were collected from all the three species of wild small mammals and they were identified as 200 species,16 genera and 2 families of the mites,including 3169 mite individuals and 72 mite species from A.squamipes shrews,52261 mite individuals and185 mite species from E.miletus voles,and 642 mite individuals and 54 mite species from S.murinus shrews.The normal morphology and six types of aberration of the chigger Herpetacarus callosciuri were described.The chigger species,individuals and infestation indices on E.miletus were higher than those on A.squamipes and S.murinus(P<0.05).The overall prevalence(P_m),overall mean abundance(MA)and overall mean intensity(MI)of chiggers on E.miletus were P_m=53.96%,MA=19.64 mites/vole and MI=36.39 mites/infected vole respectively.The overall infestation indices of chiggers on A.squamipes were P_m=11.10%,MA=1.87 mites/shrew and MI=16.86 mites/infected shrew,and those on S.murinus were P_m=16.72%,MA=2.19 mites/shrew and MI=13.10mites/infected shrew.The vole E.miletus harbored abundant chiggers with highest species richness of the mites(M_f=16.94),and the dominant chigger species were Leptotrombidium scutellare(C_r=19.17%)and L.sinicum(C_r=11.06%).The dominant chigger species on A.squamipes was L.densipunctatum(C_r=22.12%),and the dominant mite species on S.murinus were L.deliense(C_r=28.50%)and L.scutellare(C_r=12.77%).The dominant mite species showed an aggregated distribution pattern among different individuals of the three species of wild small mammals(m*/m>1,I>0,C_A>0).There was a significant positive association between the dominant chigger species on E.miletus(x~2=857.46,PCC=0.57)and S.murinus(x~2=24.20,PCC=0.32)(P<0.001),and the association degree of the dominant mite species on E.miletus was higher than that on S.murinus.The chigger infestations on the three species of wild small mammals varied along different gradients of geographical landscapes and latitudes with an obvious heterogeneity.The chigger species,individuals,P_mand MA on the same species of small mammal hosts were higher in the mountainous landscape than in the flatland landscape(P<0.001).The chigger species and individuals on A.squamipes and E.miletus showed the highest peak with the heaviest infestation at the middle latitude gradient of 24-26°N,while those on S.murinus showed the highest peak with the heaviest infestation at the low latitude gradient of<24°N(P<0.05).The species abundance distribution of chigger communities on the three species of wild small mammals conformed to the log-normal distribution.The number of expected total chigger species on A.squamipes,E.miletus and S.murinus were 80,231 and 63 species respectively.Conclusions:In Southwest China,the chigger infestation is common on A.squamipes,E.miletus and S.murinus with abundant mite species and diversity.Some chigger species in the region have normal variations and a few types of aberrant individuals.An enough number of specimens are usually needed for the nomenclature and description of new mite species.Anourosorex squamipes,E.miletus and S.murinus have different composition of dominant chigger species and the dominant chigger species are of aggregated distribution among different individuals of their corresponding hosts.A positive association exists among some dominant chigger species.There is an obvious heterogeneity of chigger species composition and infestation at different landscapes and latitudes.The species abundance distribution of chigger community conforms to the log-normal distribution. |
