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Table of Contents
SHORT RESEARCH COMMUNICATION
Year : 2020  |  Volume : 57  |  Issue : 1  |  Page : 96-100

Species composition of mosquito breeding in bamboo stumps in Sikkim, India


Department of Zoology, School of life Sciences, Sikkim University, Sikkim, India

Date of Submission13-Jul-2018
Date of Acceptance13-Dec-2018
Date of Web Publication05-Feb-2021

Correspondence Address:
Dr B Singh
Department of Zoology, Sikkim University, Gangtok–737101, East Sikkim
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-9062.308808

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  Abstract 

Background & objectives: Sikkim is a part of Eastern Himalayan biodiversity hotspot of India rich in bamboo flora harbouring over 30 different bamboo species. The present study was aimed to investigate the larval mosquito diversity in the bamboo stumps of Gangtok, Sikkim. Besides, efforts were also made to evaluate the propensity of particular species of mosquito towards specific bamboo species (if any).
Methods: A total of 75 bamboo stumps of four genera were surveyed and screened at five different sampling sites of Gangtok from July to October 2017. Mosquito species similarity between the five sampling sites and the four varieties of bamboo species was calculated using the Bray-Curtis similarity index.
Results: A total of 216 larvae were collected from 25 different bamboo stumps studied. The species identified were Aedes albopictus, Ae. atlanticus, Ae. aegypti, Orthopodomyia signifera, Oclerotatus japonicus, Oc. taeniorhynchus, Armigeres subalbatus, and Toxorhynchites splendens. The Oc. japonicus (34.5%) was found to be the most abundant species having distribution in Phyllostachys assamica, Dendrocalamus hamiltonii and Bambusa nutans. On the other hand, genus Armigeres subalbatus and Tx. splendens were found to breed only in the stumps of P. assamica. Based on Bray-Curtis similarity index highest species similarity was recorded between D. hamiltonii and P. assamica bamboo species.
Interpretation & conclusion: The study may help to understand the bioecology of the mosquito larvae which may help to devise suitable mosquito control programmes. Future studies including the survey of large number of bamboo stumps both in urban and rural areas of Sikkim may provide better insight into the mosquito diversity in the bamboo stumps of Sikkim.

Keywords: Bamboo stumps; eastern Himalaya, mosquitoes; Sikkim


How to cite this article:
Singh B, Baruah C, Saikia D, Gurung J. Species composition of mosquito breeding in bamboo stumps in Sikkim, India. J Vector Borne Dis 2020;57:96-100

How to cite this URL:
Singh B, Baruah C, Saikia D, Gurung J. Species composition of mosquito breeding in bamboo stumps in Sikkim, India. J Vector Borne Dis [serial online] 2020 [cited 2021 Apr 18];57:96-100. Available from: https://www.jvbd.org/text.asp?2020/57/1/96/308808


  Introduction Top


Sikkim is a part of the Eastern Himalayan biodiversity hotspot of India, covering an area of 7096 km2 and lies at 27° 00’ 46’' and 28° 07’ 48’' N latitude and 88° 00’ 58’' and 88° 55’ 25’' E longitude. The topography of the state is quite diverse and the altitude ranges from 200–8598 m[1]. Sikkim is rich in bamboo flora harbouring over 30 different bamboo species[2]. Its capital city Gangtok is one of the famous holiday destinations for its unique ambience and attracts many tourists every year. The city experiences heavy rainfall during the months of May to September with the average annual rainfall being 2739 mm. The rainfall accumulates in natural and artificial habitats which create a varied environment favouring mosquito breeding. The temporal changes in the number of habitats and the heterogeneity are important factors that affect habitat use of species and community organization[3]. Such a situation can be seen in the bamboo stumps, that hold small aquatic pools which harbour communities of aquatic organisms consisting of several taxa including mosquito larval breeding[3].

Studies have found that bamboo stumps provide ideal breeding habitat for mosquitoes under Diptera: Culicidae, comprising the genus Wyeomyia, Toxorhynchites[4], Trichoprosopon spp.[5], Anopheles vagus[6], Culex pseudovishnui, Cx. whitmorei[7], Armigeres[8], Cx. quinquefasciatus, Aedes aegypti[9], Ae. albopictus[10], An. barbirostris, and An. vagus[11]. As far as the literature review is concerned, only one study has been conducted in Sikkim to study the mosquito diversity in the water samples of roadside seepage pools and channels[12]. Despite the fact that the region is rich in bamboo fauna, till date no study has been conducted to investigate the diversity of mosquitoes in the bamboo stumps of Sikkim. Therefore, the present study was carried out to investigate the larval mosquito diversity in the bamboo stumps in and around the city of Gangtok, Sikkim with the objectives: (i) to study the distribution and species composition of mosquitoes in the bamboo stumps; (ii) to evaluate the preference of specific species of mosquito for breeding; and (iii) to study the similarity of mosquito species breeding various bamboo species.


  Material & Methods Top


Study area

The present study was carried out in and around the hills of Gangtok from July to October 2017. The study area was divided into five different sites based on the availability of the bamboo stumps. The elevation of the study area varied within the range of 870–1447 m. The five different study sites were Ranipool (870 m) where samples were collected from six stumps, 5th Mile (1161 m) where samples were collected from seven stumps, Tadong (1389 m) where samples were collected from five bamboo stumps, Indira By-pass Road (1409 m) where samples were collected from four bamboo stumps, and Sichey (1447 m) samples were collected from three bamboo stumps. In some of the sites, the bamboo was of the same species, whereas in others there were two to three different species of bamboo.

Sampling

Around 75 bamboo stumps were screened at five different sampling sites of Gangtok, East Sikkim. Out of these searched stumps, 25 were found to have rainwater harbouring larval immatures of mosquitoes. The volume of water present was estimated which varied depending on the depth and thickness of bamboo stumps. The water along with mosquito larvae was drawn out from the selected stumps with the help of a 5 ml pipette and collected in the plastic containers (150 ml) and processed in the laboratory of the Department of Zoology, Sikkim University, Sikkim for identification and further analysis. In the laboratory, the number of species of mosquito larvae and the volume of water samples per bamboo stumps were estimated. The larvae of mosquitoes were identified on the basis of identification keys of Tyagi et al[13], Cutwa and O’Miara[14], Dehgan et al[15], Andreadis et al[16] and Barraud[17]. To identify the larval species of mosquitoes, the IV instar larvae were selected since these larvae have fully developed morphological features such as antennae of varied sizes present on the head region, clusters of hairs which may be branched or unbranched, head setae, etc. The species of bamboo were identified by a plant taxonomist from the Department of Botany, Sikkim University.

Statistical analysis

The statistical analysis was performed using SPSS software version 23, IBM Corp. Mosquito species similarity between the five sampling sites and the four varieties of bamboo species was calculated using Bray-Curtis similarity index[18] which is an abundance-based similarity index in EstimateS software. The formula for the Bray-Curtis similarity index is as follows:



where BCij is the sum of the lesser values for only the species common between two sites and nik and njk are the total number of specimens counted at both the sites. The mosquito diversity at different sampling sites was estimated by the Shannon-Weiner diversity index (H).


  Results Top


A total of 216 larvae were collected from 25 different bamboo stumps studied [Table 1]. The volume of the water in different bamboo stumps ranged from 20 to 210 ml. From the collected larvae, eight species of mosquitoes were identified which included, Ae. aegypti Linnaeus, 1762; Ae. albopictus Skuse, 1894; Ae. atlanticus Dyar and Knab, 1906; Orthopodomyia signifera Coquillett, 1896; Ar. subalbatus Coquillett, 1898; Oclerotatus taeniorhynchus Wiedemann, 1821; Toxorhynchites splendens Wiedemann, 1819; and Oc. japonicus Theobald 1901, all under Diptera : Culicidae. Of all the species identified, Oc. japonicus (34.3%) was the most abundant species followed by Ae. albopictus (25%), O. signifera (15.7%), Ae. atlanticus (14.3%), Ae. aegypti (6%) and Oc. taeniorhynchus (1.9%). The least prevalent species were Ar. subalbatus (1.4%) and Tx. splendens (1.4%). The bamboo stumps belonged to Dendorocalanus sikkimensis, Bambusa nutans, D. hamiltonii and Phyllostachys assamica species.
Table 1: Distribution and species diversity of mosquito larvae in bamboo stumps of Gangtok, Sikkim

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Further, it was observed that the genus Ar. subalbatus and Tx. splendens each (1.4%) were found to breed only in the stumps of bamboo P. assamica, while O. signifera (15.7%) was found to breed in the stumps of two species of bamboo, viz. D. sikkimensis and D. hamiltonii. On the other hand, the immatures of Ae. albopictus (25%) and Ae. aegypti (6%) were found to breed in the stumps of two bamboo species, P. assamica and D. hamiltonii whereas, Ae. atlanticus (14.3%) was found only in the stumps of D. hamiltonii species. The study also revealed that Oc. japonicus (34.3%) had wide range of distribution in three species of bamboo stumps, i.e. P. assamica, D. hamiltonii, and B. nutans while, Oc. taeniorhynchus (1.9%) was found breeding only in the stumps of bamboo species, P. assamica. Maximum similarity was recorded between the two species of bamboo, namely D. hamiltonii and P. assamica (0.374) [Table 2]. The χ2 test for the preference of mosquitoes for specific bamboo species revealed significant value (χ2 = 250.36; df = 24; p < 0.01). Of all the mosquito species observed in the present investigation Ae. albopictus showed preference for bamboo species of D. hamiltonii2 = 10; df = 1; p <0.01) and P. assamica2 = 17; df = 1; p <0.01). The analysis of mosquito diversity by Shannon-Weiner diversity index (H) showed the highest diversity at the Ranipool [Table 3].
Table 2: Mosquito species similarity among different bamboo species of Gangtok, Sikkim. Mosquito genera shared (above diagonal) and species similarity based on Bray-Curtis similarity index, an abundance-based index (below diagonal)

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Table 3: Analysis of mosquito diversity by Shannon-Weiner diversity index (H) at different sampling sites

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  Discussion Top


The present study is the first of its kind to investigate the diversity of immatures of mosquitoes in the bamboo stumps of Sikkim. From the results of the study, it is apparent that the bamboo species prevalent in Gangtok, Sikkim act as suitable habitat for the mosquito larvae to breed. These habitats, however, are temporary in nature and are mostly dependent on the accumulation of rainwater. Though there are many other congenial habitats present in and around Gangtok, the preference shown by mosquito larvae to bamboo for breeding may be due to the undisturbed nature of bamboo stumps in terms of human interference[9].

In the present investigation, Oc. japonicus larvae were found to be the most abundant species (34.26%) occupying bamboo stumps of P. assamica, D. hamiltonii and B. nutans. The larvae of this species are highly effective competitors and can significantly reduce populations of other species of mosquito through interspecific competition for limited resources which may be the reason for their higher abundance. Moreover, Oc. japonicus produces desiccation resistant eggs that can tolerate a wide range of temperatures[19]. In addition, the adult species show a longer active period during the warm season and high fecundity[20]. However, the species do not survive in the places where summer temperature goes beyond 30°C[19]. This may be the reason, for a greater abundance of Oc. japonicus larvae in the higher elevation (Tadong, 1389 m onwards) where the temperature is less than 30°C.

The presence of the genus Aedes and Armigeres in the bamboo stumps of Gangtok was in accordance with the previous study by Bhat[12] in Sikkim. However, unlike the study by Bhat[12] mosquito species belonging to the genus Anopheles and Culex were not observed in the present investigation. This may be due to the fact that only bamboo stumps were considered for sampling in the present study, whereas, in the study by Bhat[12], sampling was done from roadside seepage pools and channels. However, unlike the previous study, new species of mosquito, namely O. signifera, Oc. japonicus, Oc. taeniorhyncus, Ae. albopictus, Ae. aegypti, Ae. atlanticus, and Tx. splendens were observed in the present study. This may be due to expansion of the geographical boundaries of the different mosquito species in the hilly areas[21]. However, in the present study, the number of individuals of a species recorded in each of the bamboo stumps was low, and there was no coexistence of species in the same stumps which may be due to the structurally simple habitat, and limited resource to support large mosquito population[22]. The number of individuals in each of the stumps ranged from 1–18. The highest number of species in a single bamboo stump, as well as highest density was recorded for Ae. albopictus which may be due to high resistance to desiccation in the egg stage for this species, and immediate hatching ability of the larvae after the eggs are submerged[23]. On the other hand, the lowest number of species were recorded for Tx. splendens in a single stump which may be due to high predatory nature of the species in the container habitat[24].

In comparison to the study of Aditya et al[9] where two species, Cx. quinquefasciatus and Ae. aegypti were described, in the present study, eight species of mosquito immatures were observed. The possible reason for this may be due to the consideration of more species of bamboo. In addition, in the present study Ae. aegypti was recorded from two species of bamboo stumps, namely D. hamiltonii and P. assamica which is in contrast to the study by Aditya et al[9]. However, the genus Culex was not observed from any of the stumps in the present study. This may be due to the survey of less number of bamboo stumps in the present study. The results of the current study also showed prevalence of two more species, i.e. O. signifera and Oc. japonicus within the stumps of D. hamiltonii which was not reported by Aditya et al[9]. Unlike the results of Aditya et al[9], the current study also shows the occurrence of genus Ar. subalbatus and Tx. splendens in bamboo stumps of P. assamica, O. signifera in the stumps of D. sikkimensis and Oc. japonicus in stumps of B. nutans. It may be due to similar habitat provided by the bamboo stumps. In line with the study of Aditya et al[9], Sunahara and Mogi[22] also observed only three larval species, namely T. bambusa, Ae. albopictus and Ae. japonicus within bamboo stumps in Northern Kyushu, Japan (elevation 300–500 m). The presence of Ae. albopictus (25%) in the bamboo stumps is in line with the present study. Moreover, one of the perceptible finding of the present investigation is the preference of Ae. albopictus for D. hamiltonii and P. assamica which may be due to preference of this species for suburban areas[24] and the presence of bamboo stumps near the human habitation in Sikkim. However, unlike the study of Sunahara and Mogi[22] where Ae. albopictus (25%) was found to be an abundant species, Oc. japonicus were found most abundant (34.25%) in the present study. Moreover, T. Bambusa and Ae. japonicus were not observed in the present study. This may be due to the differences in geographical locations and elevation gradients of the two study sites (elevation 200–8598 vs. 300–500 m). Moreover, a higher number of species was recorded by Sunahara et al[25] in bamboo stumps of Flores, Indonesia reporting 12 species of mosquitoes under 7 genera. The presence of mosquito species, Ae. albopictus, O. signifera, Ar. subalbatus and Tx. splendens in that study is in accordance with the present study. Nevertheless, the study of Sunahara et al[25] is limited by nonconsideration of bamboo species variety to study the distribution of different mosquito species.

The mosquito species similarity test among the four different species of bamboo showed similarity only between D. hamiltonii and P. assamica (0.374); however, the similarity index was not very high. The observed similarity may be due to the similar kind of habitat shared by both the species of bamboo which in turn provides the similar kind of microhabitat and resource availability for the different species of mosquitoes. Among all the study sites, mosquito diversity was highest at Ranipool which may be due to the lower elevation (870 m) and warmer climatic conditions of the region which are conducive for mosquito breeding.

The present study was undertaken only for a very short period, i.e. from July to October 2017. The structural complexity in terms of vegetation, amount of detritus and species composition of other organisms in the bamboo stumps were not studied. Besides, the distribution of mosquito larvae was studied only in a few bamboo stumps of urban areas of Gangtok. Considering these limitations, the present study gives first-hand information on the diversity of mosquito larval species in bamboo stumps of Gangtok.


  Conclusion Top


The study showed the larval mosquito diversity in the bamboo stumps of Gangtok, Sikkim. The presence of Aedes, Ochlerotatus and Armigeres which are the vectors of dengue, West Nile fever, and filariasis, respectively is of serious concern as Gangtok is a tourist place visited by people from all over the world and if pathogens are accidentally introduced in this region, it shall lead to an introduction of diseases which are rare to this region. The present study may help to understand the bioecology of the mosquito larvae in the region to devise suitable mosquito control programmes considering the species diversity and their preferred breeding habitats like bamboo. Future studies including the survey of a large number of bamboo stumps both in urban and rural areas of Sikkim may provide better insight on the mosquito diversity in the bamboo stumps of Sikkim.


  Acknowledgements Top


The authors are grateful for the assistance in species identification provided by Dr Santosh Kumar Rai and Dr Arun Chetteri of Department of Botany, Sikkim University, Sikkim.

Ethical statement: Not applicable.

Conflict of interest: None.

 
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    Tables

  [Table 1], [Table 2], [Table 3]



 

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