Ecological Researches On Gamasid Mites On Three Species Of Domestic Rodents(Rattus Tanezumi,Rattus Norvegicus And Mus Musculus) In Yunnan Province,Southwest China

Objectives:The present study is to investigate the species composition and infestations of gamasid mites on the body surface of three domestic rodents or house rodents(Rattus tanezumi,R.norvegicus and Mus musculus)under different ecological circumstances such as habitats and altitudes.Besides the studies on the spatial distribution patterns and seasonal fluctuations of dominant species of gamasid mites,this paper is also an attempt to explore the related risk factors of gamasid mite infestations on three domestic rodent species and the species abundance distribution of the mites.Methods:The original data of the present study include two parts:one from a long-term accumulated field investigation in 39 investigation counties of Yunnan province in southwest China between 1990 and 2015,and the other from a monthly investigation at Jingha site of south Yunnan between April 2016 and March 2017,which was for studying the seasonal fluctuation of two dominant species of gamasid mites.The constituent ratio(Cr),prevalence(P_M),mean abundance(MA)and mean intensity(MI)were used to analyze the infestations of gamasid mites on the body surface of three species of domestic rodents(house rodents)under the different circumstances such as different habitats,altitudes,sexes and ages.The multivariate unconditioned logistic regression was used to analyze the risk factors of gamasid mite infestations on three species of domestic rodents.Some commonly used indices were introduced in the analysis of the spatial distribution patterns dominant gamasid mites on two main species of domestic rodents.The theoretical sampling model was established according to the principle of Iwao’s linear regression.Preston’s model was used to fit the distribution curve of species abundance of gamasid mites on the domestic rodents,and then to estimate the overall species of the mites on the rodents roughly.Furthermore,Chao 1 and Chao 2 formulae were also used to predict the total species of gamasid mites on two species of domestic rats,R.tanezumi and R.norvegicus.Results:A total of 6956 rats and mice,including R.tanezumi,R.norvegicus and M.musculus,were captured from the 39 investigation counties of Yunnan Province,southwest China.And 42384 individuals of gamasid mites were collected from the body surface of these rodent hosts and identified as 79 species,23 genera in 10 families(not including unidentified species).There were 378 individuals of gamasid mites remained unidentified.Of the three species of house rodents,R.tanezumi rats were the most abundant with the highest constituent ratio(Cr=75.52%)and prevalence(P_M=58.05%)of gamasid mites on their body surface.The dominant gamasid mites on the body surface of two rat species(R.tanezumi and R.norvegicus)were Laelaps nuttalli,L.echidninus,and Ornithonyssus bacoti.Besides these three dominant mite species,L.guizhouensis was also the dominant gamasid mites on M.musculus mice.The prevalence(P_M)and mean abundance(MA)of gamasid mites on three species of domestic rodents in the outdoors were higher than in the indoors.The prevalence(P_M)and mean abundance(MA)of gamasid mites on two rat species(R.tanezumi and R.norvegicus)were the highest below the altitude of 999 meters,but the P_M and MA of gamasid mites on M.musculus mice were the highest between 2000-2999 meters.The male adult rats(R.tanezumi and R.norvegicus)showed a higher infestation of gamasid mites than the female juvenile rats,but the female juvenile M.musculus mice had a higher mite infestation than the male adult mice.Using the multivariate unconditional logistic regression analysis,the risk factors for the infestation of gamasid mites on R.tanezumi rats were determined to be habitats and sexes.The risk factors for the infestation of gamasid mites on R.norvegicus rats were habitats,but the risk factors for the infestation of gamasid mites on M.musculus mice were altitude gradients.The dominant gamasid mites on two main species of house rats(R.tanezumi and R.norvegicus)showed an aggregated pattern of distribution.The Iwao’s linear regression equations of two dominant gamasid mites(L.nuttalli and L.echidninus)on R.tanezumi rats were M~*=21.527+8.7076m for L.nuttalli and M~*=7.5882+3.9941m for L.echidninus.According to the principle of Iwao’s linear regression,the theoretical sampling models were established.The theoretical sampling model for L.nuttalli was N=(22.527/m+7.7076)t~2/D~2,and the theoretical sampling model for L.echidninus was N=(8.5882/m+2.9941)t~2/D~2.The species abundance relationship of gamasid mites on R.tanezumi conformed to the lognormal distribution withα=0.28 and R~2=0.96(the best fittnes),and the overall species of gamasid mites on this rat species were then estimated to be 127.However the total species number of gamasid mites on R.tanezumi was predicted to be 98 by Chao 1 method,which is different from the former estimation.The species abundance of gamasid mites on R.norvegicus was also of the lognormal distribution withα=0.66 and R~2=0.83(the best fittnes).Based on Chao 2 formula,the total species number of gamasid mites on both R.tanezumi and R.norvegicus were estimated to be 105,which also shows an obvious difference.The seasonal fluctuations of L nuttalli and L.echidninus did not show an obvious regularity.The prevalence was higher in November,December and January for L.nuttalli while it was higher in December and March for L.echidninus.Conclusions:Two species of house rats(R.tanezumi and R.norvegicus)have a great potential to harbor abundant gamasid mites.The dominant gamasid mites on the body surface of R.tanezumi and R.norvegicus are L.nuttalli,L.echidninus,and O.bacoti,and besides L.guizhouensis is also the dominant mite species on M.musculus as well.The three species of house rodents have different infestations under different habitats and altitudes.Most gamasid mites have a preference to infesting the male adult house rats.The habitats,sexes and altitude gradients are the three risk factors for the infestation of gamasid mites on three species of house rodents.The estimated total species of gamasid mites vary with different methods.The prevalence was higher in November,December and January for L.nuttalli while it was higher in December and March for L.echidninus.