Morphological And Some Ecological Researches On Leptotrombidium Rubellum

Objective The present paper is to clarify the morphological variations between differengeographical strains of Leptotrombidium rubellum(a species of chigger mites),and treveal the morphological differences between L.rubellum and its sibling species(Ldeliense).The morphological researches aim to provide a scientific guidance for thcorrect identification of L.rubellum.Based on the field investigation iXishuangbanna prefecture of Yunnnan province,the present paper also tries tillustrate the distribution patterns in different geographical areas and habitats,and odifferent species of hosts,together with the interspecific relationship between Lrubellum and some other dominant species of chigger mites.Materials and Methods: In the morphological researches on L.rubellum,the chigger larvae came from the accumulated specimens in some previous field investigations in Yunnan province.The clear larva specimens of determined chigger mite species(L.rubellum and L.deliense)with distinct structure were chosen as the target larvae in the study.In some ecological researches,the original data came from the field sampling investigations in Xishuangbanna between 2001 and 2015.Some conventional statistical methods were used to calculate the constituent ratio(Cr),prevalence(P),mean abundance(MA)and mean intensity(MI)of the chigger mites on rodents and some other small mammals,which is to reflect the general infestation of the mites.The distribution of L.rubellum in different geographical landscapes and habitats were compared and analyzed.Association coefficient(V)was used to analyze the interspecific relationship between L.rubellum and some other dominant species of chigger mites.The infestation of L.rubellum was compared among different ages and sexes of hosts.Results The morphological researches showed that there were several differences between L.rubellum in Yunnan province(Yunnan strain)and L.rubellum in Fujian province(Fujian strain).The value ranges of SD,SB,AP,ASB,PSB,AW,AL,AM and S,were wider in Yunnan strain than those in Fujian strain.The means of SD,SB,ASB,PSB,AW,AL,AM and S were also higher in Yunnan strain than those in Fujian strain(P<0.05).The value ranges of body length,body width,numbers of ventral setae and the length of three pairs of legs were wider in Yunnan strain than those in Fujian strains.Some specimens in Yunnan strain had 25 or 27 dorsal setae and their arrangement sequence was not 2-8-6-6-4-2.The present paper revealed some morphological differences between L.rubellum and its sibling species,L.deliense.It was revealed that L.rubellum had a quadrate-like scutum with a relatively smaller width/length ratio of SD,but L.deliense had a rectangle-like scutum with a relatively larger width/length ratio of SD.Both L.rubellum and L.deliense had the character of“AP>PS”,but more obvious in the former one.The obvious feature of “SB<AP”existed in L.rubellum,but “SB>AP” in L.deliense.Both L.rubellum and L.deliense had “ASB>2PSB”,but more prominent in L.rubellum.In the actual species identification,“SB<AP” is suggested as a key character of L.rubellum to differentiate from its sibling species,L.deliense with “SB>AP” or “SB=AP”.Some ecological researches showed that the captured 820 rodents and some other small mammals from7 investigation sites in Xishuangbanna were identified as 18 species and 10 genera in 5families of 3 orders.Rattus tanezumi reached 86.83% of total small mammals and it was determined as the dominant rodent species.From the body surface of total small mammal hosts,12150 individuals of chigger mites were collected and they were identified to comprise 64 species in 9 genera of 2 subfamilies.There were three dominant species of chigger mites.These dominant species of chigger mites are L.deliense(3924 individuals which account for 32.29% of the total),Ascoschoengastia indica(3461 individuals,28.49%)and Walchia micropelta(1501 individuals,12.35%).Of 64 species of chigger mites collected,only 654 individuals of L. rubellum were identified,which is not the main species of chigger mites in the investigated region.The 654 individuals of L.rubellum accounted for 5.38% of the total 64 species of chigger mites,and they were collected from 3 species,2 genera and2 families in 2 orders of hosts.The constituent ratios of hosts and L.rubellum in different landscapes and habitats were different.There were 531 individuals of hosts(64.76%)and 628 individuals of L.rubellum(96.02%)collected from the flatland areas.In the outdoor habitat,92.20% of L.rubellum were from shrub areas(bush woods),which may be related to the humid and shady soil environments in this kind of habitat.The humid and shady soil environments are suitable for the existence and survival of free-living phases of chigger mites.The results in the study suggested that L.rubellum might be mainly distributed in some hot and humid environments with low latitude and altitude in south coast or inland regions.A positive association existed between L.rubellum and L.deliense on their main host,R.tanezumi,and this suggested that these two mite species may have a preference to live on the same rodent hosts.Conclusions There are some morphological differences between different geographical strains of L.rubellum,Yunnan strain and Fujian strain.Yunnan strain has a wider range of SD,SB,AP,ASB,PSB,AW,AL,AM and S than Fujian strain.The morphology of L.rubellum is very similar to that of L.deliense and they are sibling species.The scutum shape of L.rubellum is like a quadrate with an obvious SB<AP while L.deliense has a rectangle-like scutum with SB>AP or SB=AP.There is the existence and distribution of L.rubellum in Xishuangbanna of Yunnan province,but this species of chigger mite is not the dominant species in the region.L.rubellum has a preference to live in the outdoor habitats in some hot and humid valley-flatlands with low latitude and altitude.