| Objectives:(1) To understand the species composition, species diversity, community structure and species abundance distribution of chigger mites on their rodent hosts in family Muridae (Rodentia).(2) To study the spatial distribution patterns of dominant chigger mites on some hosts’body surface.(3) To study the host specificity and host selection of some main chigger species associated with the transmission of scrub typhus in Yunnan Province.Materials and Methods:(1) The original data came from the field investigation in20locations of Yunnan Province from2001to2010. The field investigations were chosen according to different landscapes, geographical orientations, climate and environment, etc.(2) The community structure was illustrated by a series of parameters, including the constituent ratio (Dr), species richness (S), Simpson’s dominance index (D), Shannon-Wiener’s diversity index (H’),evenness (J’), mite infected rate (Rm) and mite index (IM).(3) The patch index (m*/m) was used to measure the spatial distribution pattern of dominant chigger mites on some hosts’ body surface.(4) Niche breadth (Shannon-Wiener index and Simpon index) and Pianka niche overlap index were used to study the niche overlaps between some main chigger mite species and hiearchical cluster analysis was used to classify the overlapping groups.(5) Preston’s logarithmic normal distribution was used to describe the theoretical distribution curve of species-abundance of chigger mites, and then estimated the total species number of chigger mites on small Rodents in Muridae (Rodentia) in Yunnan Province based on the distribution curve.Results:(1) A total of7757individuals of rodents (rats) in Muridae were captured in Yunnan Province and identified as22species in9genera.27042individuals of chigger mites were collected from the body surface of these rodent hosts and identified as191species,20genera in3subfamilies (not including unidentified species). Of these191species, there were142species (19179individuals) and14genera, which belong to subfamily Trombiculinae. Of subfamily Trombiculinae, there were82species (13802individuals) in genus Leptotrombidium and60species (5377individuals) in other13genera. In subfamily Gahrliepiinae, there were 45species (7813individuals) and4genera. In subfamily Leeuwenhoekiinae, there were4species (50individuals) and2genera. Of191chigger species, the constituent ratios of three dominant mite species, Leptotrombidium scutellare, Walchia ewingi and Walchia micropelta, were much higher than other species.7708individuals of Apodemus chevrieri were captured and they were considered as one dominant species of rodent hosts in this paper.(2) The altitude of the investigation areas had some influences on the distribution of rodent hosts and their ectoparasitic chigger mites in Yunnan province. In the areas below2000meters, the dominant rodent hosts was Rattus tanezumi (R. flavipectus) and the dominant chigger mites were Ascoschoengastia indica, Walchia ewingi, W. micropelta and Leptotrombidium deliense. In the areas above2000meters, however, the dominant hosts were Apodemus chevrieri, Rattus norvegicus while the dominant chigger species was Leptotrombidium scutellare.(3) Chigger mites of rodents in Yunnan Province have high species diversity but low host specificity.Not only one chigger mite can parasite one more hosts, but also one host can be found one more chigger mites.(4) The distribution of Leptotrombidium scutellare and L. deliense, which are the two main vector species in China, fluctuated in different latitude regions and habitats. Both these two mite species had a wide host range. Apart from some other rodent species, however, the main host of Leptotrombidium deliense was Raltus tanezumi.(5)The widest niche breadth is L. densipunctatum,the narrowest is Microtrombicula munda among total21main chigger mites species. Most chigger mites can parasite several rodents,so niche breadth is low. Most chigger mites have different niche overlap. The result of Hierachical analysis revealed that all21mite species be clusted into3categories.(6) The species abundance distribution of the chigger mite community was successfully fitted by a lognormal distribution model. Based on the theoretical curve of species abundance distribution, the total number species of the chigger mites was roughly estimated as365species, the same as Niviventer confucianus, the total number species was roughly estimated as170species.Conclusions:(1) The species diversity of chigger mites on rodent hosts in Yunnan Province is very high with a complicated structure.(2) Leptotrombidium scutellare, Walchia ewingi and Walchia micropelta are the dominant chigger species in Yunnan Province on hosts of Muridae.(3) Two main vector species of chigger mites, Leptotrombidium scutellare and Leptotrombidium deliense, coexist in Yunnan Province. The former (L. scutellare) mainly distributes in high altitude regions while the later (L. deliense) mainly in low altitude regions.(4) The distribution of chigger mites on main hosts of Muridae is assembled.(5) The host specifity of most chigger mites of hosts on Muridae is quite low with a wide host range. There is a high niche overlap,but low co-evolution on chigger mites.(6) The species abundance of chigger mite community conforms to lognormal distribution and the total species number of chigger mites is roughly estimated as365species. The same as Niviventer confucianus, the total number species is roughly estimated as170species. |
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