Ecological Research Of Chigger Mites On Three Species Of House Rodents(Rattus Tanezumi, Etc.) In Yunnan Province

Objectives: This paper is to study the infestation, species diversity and communitystructure of chigger mites (trombiculid mites) on three species of house rodents(Rattus tanezumi, R. norvegicus and Mus musculus) in Yunnan Province. Besides, thepaper also tries to understand the dominant mite species, the spatial distribution patternsof the dominant mite species, the species abundance distribution and the fluctuation ofchigger mites in different geographical regions and altitudes.Materials and Methods: The field investigation was done in25counties ofYunnan Province between2001and2012. The whole province was divided into fivesub-regions according to the zoogeographical divisions. The five sub-regions areMiddle Sub-region of Hengduan Mountains, Southern Sub-region of HengduanMountains, Eastern Plateau Sub-region of Yunnan, Western Plateau Sub-region ofYunnan and Southern Mountainous Sub-region of Yunnan. Some conventional methodswere used to calculate the constituent ratio (Dr), prevalence or infestation rate (RM),mean abundance (MA), mean intensity (MI), species richness (S)and Shannon-Wiener’s diversity index (H′). The linear correlations between RM, MA and MI werealso analyzed in a conventional way. The dispersion coefficient (C), Cassie’s index(CA) and patchness index (m*/m) were adopted to measure the spatial distributionpattern of chigger mites among different individuals of their corresponding rodent hosts.According to the geographical stratification (latitude and longitude) and elevations ofthe investigation sites, a contrasted study was made to understand the fluctuations ofthe mite infestation and the dominant mite species on those house rodents along withgeographical regions and altitudes. The hierarchical cluster analysis under SPSS16.0 was used to compare the similarity of chigger mite communities on the main species ofhouse rodents. The model of Preston’s logarithmic normal distribution was used to fitthe theoretical distribution curve of species-abundance of chigger mite communities oneach species of the house rodents. The total species number of chigger mites on eachspecies of the house rodents was estimated based on the theoretical distribution curveof the species abundance.Results:(1)A total of3453individuals of three species of house rodents (Rattusflavipectus, Rattus norvegicus and Mus musculus) in2genera (Rattus and Mus) werecaptured, including2118individuals of R. flavipectus (61.34%),1110individuals ofR. norvegicus (32.14%) and225individuals of Mus musculus (6.25%). From the bodysurfaces of these three species of house rodents, a total of12570chigger mites werecollected and identified as3subfamilies,19genera and148species (including10unidentified species with79individuals). The overall RM, MA and MI of chigger miteson these three species of house rodents were16.91%(584/3453),3.64mites perexamined house rodent and21.52mites per infested house rodent respectively. Thespecies diversity of chigger mites was high with abundant mite species.(2) Two mainspecies of the house rodents (R. flavipectus and R. norvegicus) had a great potential toharbor many species of chigger mites, and for example R. flavipectus harbored120species of chigger mites. The infestation and the dominant mite species on the mainhouse rodents were not stable and fixed, which varied prominently in differentgeographical landscapes, habitats, altitudes, latitudes and zoogeographical subregions.The dominant species of chigger mite on R. flavipectus in the indoor and outdoorhabitats of flat-land areas was Leptotrombidium deliense, but were Ascoschoengastiaindica and Walchia micropelta in some other landscapes and habitats. In the altitudesbelow1000m and1001m-1500m, and in the latitudes in23°01＇N-23°59＇N and24°01＇N-24°59＇N, the dominant species of chigger mites on R. flavipectus was L.deliense, but were A. indica and W. micropelta, etc. in some other altitudes and latitudes.The dominant species of chigger mites on R. flavipectus was also prominently differentin different zoogeographical subregions. The similarity of chigger mite communities between the Plateau Subregion of Western Yunnan and the Mountainous Subregion ofSouthern Yunnan was the highest, and the dominant species of chigger mites was L.deliense. The dominant mite species, however, were A. indica and Schoengastiellaligula etc. in some other zoogeographical subregions. The dominant species of chiggermites on R. norvegicus was also different in the indoor and outdoor habitats of flat-landareas and mountainous areas, and they are W. ewingi and L. scutellare, etc. Thedominant species of chigger mites on R. norvegicus also varied in different altitudes,and they are A. indica and L. scutellare, etc. In the latitudes of23°01＇N-23°59＇Nand24°01＇N-~24°59＇N, the main dominant species of chigger mites on R.norvegicus was W. ewingi, but whereas were A. indica and W. koi in other latitudes.The dominant mite species on R. norvegicus varied obviously in differentzoogeographical subregions. In the Middle Sub-region of Hengduan Mountains and theEastern Plateau Sub-region of Yunnan, the dominant mite species on R. norvegicus wasW. ewingi, and L. scutellare coexisted in the Middle Sub-region of HengduanMountains and the Southern Subregion of Hengduan Mountains. In another subregions,the dominant mite species on R. norvegicus were A. yunnanensis and A. indica etc.(3)L. deliense was traditionally considered as the main dominant mite species and the maintransmitting vector of tsutsugamushi disease (scrub typhus) in Yunnan Province, butour investigation showed that L. deliense was not the dominant species of chigger mitein the whole Yunnan Province and it was only the dominant mite species in some localareas.（4）There was a linear positive correlation between the number of R. flavipectusand the species of chigger mites(r=0.954, P<0.05.A linear positive correlation alsoexisted between the overall RM and MA of chigger mites on R. flavipectus（r=0.901,P<0.05）. There was a linear positive correlation between the overall RM and MA, RMand MI, MI and MA of chigger mites on R. norvegicus （r=0.972, r=0.936, r=0.916,P<0.05）.（5）The dominant species of chigger mites on the three species of houserodents were all of aggregated distribution pattern with the coefficient (C)higher than1, Cassie index (CA) higher than0and patch index(m*/m) higher than1.（6）Thespecies-abundance distributions of chigger mites on R. flavipectus and R. norvegicuswere successfully fitted by semi-logarithmic normal distribution with the fitting goodness of R2=0.8922(when α=0.316) and R2=0.8958(when α=0.315) respectively.Based on the theoretical distribution curves of the species abundance distributions, thetotal species number of chigger mites on R. flavipectus was estimated as about208species, and the total species number of chigger mites on R. norvegicus was about90species. In Yunnan Province, the main species of house rodents have a great potentialto harbor abundant chigger mites. If the sampling number increases indefinitely, moreand more species of chigger mites would be found in the field investigation. A largesample is usually needed in the field investigation.Conclusions:（1）In Yunnan Province, Rattus flavipectus is the most abundantspecies of house rodents, and Rattus norvegicus comes next, and Mus musculus is theleast abundant. The infestation of chigger mites is usually common on the main speciesof house rodents with high prevalence or infestation rate (RM) and mean intensity(MI).Rattus flavipectus and Rattus norvegicus have a great potential to harbor abundantchigger mites. A large sample investigation is strongly recommended in the fieldinvestigation（.2）The dominant species of chigger mites tend to form aggregated groupson the body surface of the house rodents. The dominant mite species fluctuate indifferent geographical regions and habitats（.3）L. deliense was not the dominant speciesof chigger mite in the whole Yunnan Province. The dominant species of chigger mitesin the flat-land areas with low altitude and low latitude was L. deliense, but were theother mite species in the mountainous areas with high altitude and high latitude.