Infestation and distribution of chigger mites on Brown rat (Rattus norvegicus) in Yunnan Province, Southwest China

Abstract

Chigger mites is a group of arthropods and some of them are vectors of scrub typhus. As a common synanthropic rodent species, the Brown rat (Rattus norvegicus) often harbors lots of ectoparasites including chigger mites. According to some "data mining" strategies, the present study took the advantage of the abundant original data from a long-term field ecological investigation between 2001 and 2015 to make a detailed analysis of chigger mites on R. norvegicus in Yunnan Province, Southwest of China. From 18 of 33 investigated counties, only 1414 chigger mites were collected from 1113 Brown rats with relatively low infestations. The 1414 individual chigger mites were identified as comprising 61 species, 11 genera and 2 subfamilies of the family Trombiculidae with a high species diversity (S=61, H'=3.13). Of 61 mite species, there were four main species, Walchia ewingi, Ascoschoengastia indica, W. koi and A. rattinorvegici, which accounted for 44.41% of the total mites. All the chigger mites were of aggregated distribution among different individuals of R. norvegicus. The Brown rats in the outdoor habitats harbored much more individuals and species of chigger mites with a higher mean abundance (MA=1.46) and mean intensity (MI=12.53) than in the indoor habitats (P<0.05). The overall infestation of the rats was significantly higher in the mountainous landscapes than in the flatland landscapes (P<0.001). The species similarity (C ss) of the mites on the male and female rats reached 64.44% with sex biased infestations. The male rats harbored more species and individuals of the mites than the female rats. The adult rats harbored more species and individuals of the mites than the juvenile rats. The species abundance distribution of the mites was successfully fitted by Preston's lognormal model with Ŝ(R)=15e-[0.31(R-1)] 2 (α=0.31, R 2 =0.95). On the basis of fitting the theoretical curve by Preston's model, the total mite species on R. norvegicus was estimated to be 86 species, and 25 rare mite species were missed in the sampling field investigation. The curve tendency of the species-plot relationship indicates that R. norvegicus have a great potential to harbor many species of chigger mites, and more species of the mites would be collected if more rats are sampled.

Infestation and distribution of chigger mites on Chevrieri's field mouse (Apodemus chevrieri) in Southwest China

“…The constituent ratio ( C r ), prevalence ( P M ), mean abundance ( MA ) and mean intensity ( MI ) were used to calculate the infestation of A. chevrieri with chigger mites ( Ding et al, 2021a ; Liu, 2020a ), in which C r represents the percentage of a certain chigger species on A. chevrieri mice, P M the percentage of the infested mice with chiggers, MA the average number of chiggers per examined mouse and MI the average number of chiggers per infested mouse. The richness index (richness, S ), Shannon-Wiener's diversity index (H′ ), Pielou's evenness ( E ) and Simpson's dominance index (D) were used to describe the chigger community structure on the mice ( Magurran, 1998 ; Ding et al, 2021a ; Lv et al, 2021 ). …”

“…Preston's lognormal model was used to fit the theoretical curve of species abundance distribution as the following formula ( Preston, 1948 ; Peng et al, 2016 ). Based on the species abundance distribution, the expected total species of chigger mites ( S T ) on A. chevrieri were estimated by the method based on Preston's lognormal model ( Ding et al, 2021a ; Preston, 1948 ; Peng et al, 2017 ).…”

“…Chigger mites (trombiculid mites) are a group of tiny arthropods and they belong to families Trombiculidae and Leeuwenhoekiidae in the subclass Acari ( Li et al, 1997 ; Ren et al, 2014 ; Ding et al, 2021a ). Some literatures claim that there are over 3000 species of chigger mites recorded in the world and more than 400 species in China ( Li et al, 1997 ; Zhan et al, 2013 ; Lv et al, 2021 ).…”

“…Some literatures claim that there are over 3000 species of chigger mites recorded in the world and more than 400 species in China ( Li et al, 1997 ; Zhan et al, 2013 ; Lv et al, 2021 ). Some other literatures, however, indicate that over 3700 species of chigger mites have been documented throughout the world and more than 510 species in China ( Ding et al, 2020 , 2021a , 2021b ). Of many chigger mite species documented in various literatures, some species are actually synonyms or invalid species, and therefore it has been a long time to obtain an exact number of chigger mite species ( Nielsen et al, 2021 ; Li et al, 1997 ; Vercammen-Grandjean and Langston, 1976 ).…”

“…Rodents and some other small mammals (e.g. insectivores and tree shrews) usually harbor lots of chiggers on their body surface and chiggers are common ectoparasites of rodents ( Peng et al, 2016 ; Ding et al, 2021a ). The Chevrieri's field mouse, Apodemus chevrieri (Miline-Edwards, 1868), is a common species of rodent in China and it is widely distributed in many parts of China such as Yunnan, Guizhou, Sichuan and Chongqing, etc.…”