Parasitology and  Microbiology Research Laboratory, Department of Zoology, The University of Burdwan. Golapbag Burdwan, Pin: 713104 India

Corresponding author email: soumen.microbiology@gmail.com

Article Publishing History

INTRODUCTION

Mosquitoes belonging to several genera mainly Anopheles, Culex and Aedes serves as nuisance vectors of numerous deadly diseases like malaria, filaria, dengue etc. occurring throughout the world (Mondal et al, 2015). Several species of Anopheles mosquitoes severs as a vector of different types of malaria in tropical and subtropical countries . Anopheles gambiae and Anopheles funestus serves as the main malarial vector in African countries (Lindh et al, 2005).Whereas Anopheles culicifacies serves as the main malarial vector in Asian countries (Chatterjee and Chandra, 2000;Chavshin et al, 2014 Lindh et al, 2015 Seal et al 2018).

It was reported that in some rural areas of Hooghly district, West Bengal Anopheles subpictus Grassi serves as the main malarial vector (Chatterjee and Chandra, 2000). Some Culex species mostly Culex vishnui group and Culex quinquifasciatus serves as a vector of Japanese encephalitis, lymphatic filariasis in many regions of India (Kanojia et al 2003) and West Bengal also (Chandra et al, 2007; Azmi et al, 2015), whereas some species of Aedes mosquitoes like Aedes aegypti and Aedes albopictus globally transmits dengue fever (Gubler  2002). In all the cases adult female mosquitoes are responsible for the transmission of disease causing pathogens. So, the prevalence of these diseases is strongly coincides with the prevalence of two factors: one is the abundance of the respective vectors and second one is the introduction of the disease causing pathogens in the suitable host, which are mostly dependent on environmental conditions like temperature, humidity, rainfall, availability of suitable breeding grounds, (Khan et al, 2017).

For the purpose of management of diseases, adult control strategies are mostly used today, which uses several insecticides like DDT, malathion, pyrethroid to control the adult mosquitoes. In this regard it is very important to have a better knowledge about the ecology of mosquitoes especially their resting site preference and biting behavior throughout the different times of a year (Alten et al, 2000). Reports on prevalence of different mosquitoes in rural and urban areas of Hooghly district, West Bengal are very scanty. So, the present study has been aimed to determine the month wise prevalence of three genera of adult mosquito vectors like Anopheles, Culex and Aedes in some rural and urban areas of Hooghly district, West Bengal, India along with the species composition of anopheline mosquitoes and to find out their correlations with some environmental factors like temperature and humidity throughout the year. This study would have a great impact on better understanding of mosquito ecology and their proper management strategies in the study areas.

MATERIALS AND METHODS:

The entire study was performed monthly for one year starting from January’2018 to December’2018.The entire study was carried out in some rural and urban areas of Hooghly district, West Bengal, India. For the collection of adult mosquitoes four human habitations and four cattle sheds were fixed in both rural and urban areas. The location of the study areas were recorded with a hand held GPS (Germin Etrex201 model) and thereafter these way points were superimposed on study area map and satellite image (Fig.1).

The adult mosquitoes were collected by hand collection method from four fixed human habitations and four cattle sheds in each of rural and urban areas of Hooghly. Four man hours (two for human habitations and two for cattle sheds) were employed for the collection of the adult mosquitoes and the collection was done in three different time periods (morning: 6 am – 8 am; afternoon: 4 pm – 6 pm and  night: 10 pm-12 am) of the same day in the first week of every month. The duration of collection time was fifteen minutes in each place. Both the indoor biting and resting mosquitoes were collected in test tubes with a small piece of net plugged at mouth of the tubes and on the next day they were brought to the Parasitology and Microbiology Research Laboratory for their identification. The environmental temperature and humidity of the collection points were recorded by Fischer Scientific machine.

In laboratory the mosquitoes were anesthetized by applying chloroform to cotton and plugging on the opening of the tubes containing adult mosquitoes. Then the mosquitoes were shorted morphologically according to the genus under a dissecting binocular. The total number of Anopheles, Culex and Aedes mosquitoes were noted down. Then the collected Anopheles mosquitoes were sorted out according to the species following Nagpal and Sharma (1995) and their numbers were noted down. Statistical analysis was performed following Zar, (1999) using SPSS software version 16.0.

RESULTS AND DISCUSSION

The locations of cattle sheds and human habitations in rural and urban study areas are given in Figure 1. The distance between rural and urban areas was 37.72km (Figure 2). Total 4754 Anopheles (56.36%), 3312 Culex (39.26%) and 369 Aedes (4.37%) mosquitoes were collected from rural areas and 3766 Anopheles (50.16%), 3302 Culex (44.38%) and 372 Aedes (5%) mosquitoes were collected from urban areas throughout the year. Month wise prevalence of three genera of adult mosquitoes (Anopheles, Culex and Aedes) in human habitations and cattle sheds in rural areas and urban areas are given in Table 1-3 and in Table 4-6 respectively. During the whole study period Anopheles and Culex mosquitoes showed higher prevalence in cattle sheds (81.42±7.14 and 77.67±7.02 respectively) than human habitations (50.64±4.58 and 50.92±4.2 respectively) in rural areas which was statistically significant (p<0.01).

Table 1. Month wise prevalence of three genus of mosquitoes (Anopheles, Culex and Aedes) in human habitations and cattle sheds in rural areas of Hooghly District (Day time: 6a.m-8a.m from Jan’2018-Dec’2018)

Month	Temperature (0C)	Humidity (%)	Number of collected Mosquitoes
			Anopheles		Culex		Aedes
			H.H	C.S	H.H	C.S	H.H	C.S
January	14.00C	58.1%	12	27	10	15	0	0
February	18.10C	51.5%	36	88	20	28	08	04
March	27.40C	62.1%	42	86	32	52	10	02
April	28.20C	63.2%	48	64	62	94	05	08
May	29.40C	67.7%	28	52	36	68	09	03
June	30.00C	76.2%	36	64	48	74	18	02
July	29.20C	79.7%	68	112	76	132	13	04
August	28.20C	81.8%	82	146	92	156	18	03
September	28.70C	77.0%	84	124	68	96	20	06
October	23.40C	70.3%	40	56	36	48	28	15
November	22.60C	66.7%	22	32	30	44	11	05
December	15.20C	61.2%	15	18	37	42	0	0

^*H.H- Human Habitation, C.S- Cattle Shed

Table 2. Month wise prevalence of three genus of mosquitoes ( Anopheles, Culex and Aedes) in human habitations and cattle sheds in rural areas of Hooghly District (Dusk time: 4p.m-6p.m from Jan’2018-Dec’2018)

Month	Temperature (0C)	Humidity (%)	Number of collected Mosquitoes
			Anopheles		Culex		Aedes
			H.H	C.S	H.H	C.S	H.H	C.S
January	18.00C	59.3%	19	32	15	21	0	0
February	21.40C	56.6%	56	96	28	44	05	0
March	28.70C	60.4%	68	124	38	56	09	0
April	29.80C	68.7%	68	82	82	120	05	07
May	30.70C	62.5%	34	58	44	72	10	05
June	32.10C	71.4%	44	76	56	80	16	03
July	30.80C	73.5%	72	122	82	144	10	18
August	28.70C	78.2%	84	136	86	132	0	0
September	29.80C	75.0%	96	132	72	98	17	09
October	24.00C	66.4%	48	64	56	64	21	04
November	23.20C	66.6%	24	38	36	56	08	07
December	21.60C	62.7%	14	22	40	46	0	0

^*H.H- Human Habitation, C.S- Cattle Shed

Table 3. Month wise prevalence of three genus of mosquitoes ( Anopheles, Culex and Aedes) in human habitations and cattle sheds in rural areas of Hooghly District (Night time: 10p.m-12a.m from Jan’2018-Dec’2018)

Month	Temperature (0C)	Humidity (%)	Number of collected Mosquitoes
			Anopheles		Culex		Aedes
			H.H	C.S	H.H	C.S	H.H	C.S
January	12.50C	57.2%	16	21	15	18	0	0
February	20.10C	58.7%	40	108	24	40	0	0
March	29.00C	63.6%	86	146	36	112	03	0
April	30.10C	65.4%	56	76	70	102	02	0
May	30.50C	69.2%	48	72	56	80	0	0
June	32.20C	78.7%	54	84	56	88	02	01
July	30.40C	73.8%	84	146	96	172	04	02
August	28.90C	76.5%	94	152	100	156	0	0
September	28.30C	72.0%	112	146	88	108	04	0
October	23.20C	60.6%	56	68	48	56	05	0
November	23.70C	62.2%	28	46	32	44	0	0
December	19.80C	56.9%	09	15	30	38	0	0

^*H.H- Human Habitation, C.S- Cattle Shed

Table 4. Month wise prevalence of three genus of mosquitoes (Anopheles, Culex and Aedes) in human habitations and cattle sheds in urban areas of Hooghly District (Day time: 6a.m-8a.m from Jan’2018-Dec’2018)

Month	Temperature (0C)	Humidity (%)	Number of collected Mosquitoes
			Anopheles		Culex		Aedes
			H.H	C.S	H.H	C.S	H.H	C.S
January	13.80C	55.9%	14	27	19	29	0	0
February	19.80C	57.6%	28	40	16	36	0	0
March	28.40C	60.1%	38	56	48	42	10	0
April	31.40C	66.5%	32	56	40	68	8	0
May	29.60C	66.2%	22	36	28	56	11	04
June	30.20C	68.7%	24	46	42	56	12	03
July	29.50C	75.2%	48	88	56	96	12	02
August	29.10C	74.2%	66	112	82	106	12	06
September	26.70C	75.2%	72	96	56	68	09	0
October	26.60C	66.2%	36	48	28	36	16	08
November	24.70C	62.4%	20	28	26	34	21	12
December	20.30C	58.5%	08	16	25	38	0	0

^*H.H- Human Habitation, C.S- Cattle Shed

Table 5. Month wise prevalence of three genus of mosquitoes (Anopheles, Culex and Aedes) in human habitations and cattle sheds in urban areas of Hooghly District (Dusk time: 4p.m-6p.m, Jan’2018-Dec’208)

Month	Temperature (0C)	Humidity (%)	Number of collected Mosquitoes
			Anopheles		Culex		Aedes
			H.H	C.S	H.H	C.S	H.H	C.S
January	15.90C	59.2%	18	29	16	36	0	0
February	23.30C	57.8%	44	72	24	44	0	0
March	32.30C	62.2%	58	96	28	46	0	0
April	30.50C	62.7%	58	68	52	66	12	6
May	31.70C	63.4%	28	48	38	62	12	8
June	33.70C	72.3%	36	68	42	64	14	10
July	32.10C	77.3%	64	96	72	104	8	16
August	29.60C	76.8%	76	114	88	112	16	18
September	28.00C	78.7%	64	84	58	88	16	09
October	27.70C	64.6%	44	56	40	56	20	10
November	25.90C	58.2%	24	36	32	46	04	0
December	20.70C	55.9%	16	30	30	51	0	0

^*H.H- Human Habitation, C.S- Cattle Shed

Table 6. Month wise prevalence of three genus of mosquitoes (Anopheles, Culex and Aedes) in human habitations and cattle sheds in urban areas of Hooghly District (Night time: 10p.m-12a.m, Jan’2018-Dec’2018)

Month	Temperature (0C)	Humidity (%)	Number of collected Mosquitoes
			Anopheles		Culex		Aedes
			H.H	C.S	H.H	C.S	H.H	C.S
January	11.60C	58.9%	11	17	19	18	0	0
February	21.20C	59.4%	24	36	16	28	0	0
March	30.00C	63.5%	64	106	42	82	03	0
April	29.80C	66.5%	52	74	62	92	09	0
May	31.90C	66.6%	42	66	48	72	06	03
June	30.30C	68.7%	46	66	38	72	0	0
July	28.60C	76.2%	72	92	66	112	0	0
August	29.70C	72.6%	84	122	92	128	08	0
September	27.80C	75.6%	104	116	72	88	0	0
October	24.20C	68.4%	44	64	36	48	04	05
November	23.50C	62.5%	24	28	34	48	09	0
December	19.90C	60.5%	10	18	42	49	0	0

^*H.H- Human Habitation, C.S- Cattle Shed

In case of urban areas the mean density of Anopheles and Culex mosquitoes were also significantly higher (p<0.01) in cattle sheds (62.53±5.23 and 63.25±4.6 respectively) than human habitations (42.08±3.90 and 43.14±3.41 respectively). Whereas in both rural and urban areas Aedes mosquitoes showed more prevalence (p<0.01) in human habitations (7.25±1.24 and 7.0±1.08 respectively) than cattle sheds (3.0±0.72 and 3.33±0.83 respectively) in the study areas. There is no significant difference in the prevalence of total number Anopheles (p=0.289), Culex (p=0.058) and Aedes (p=0.949) mosquitoes between rural and urban areas. Prevalence of these three genus of mosquitoes showed positive correlation with environmental temperature and humidity. On the other hand Anopheles and Culex mosquitoes showed higher prevalence during night time in human habitations and cattle sheds in both rural and urban areas (Figure 3 & Figure 4) whereas prevalence of Aedes mosquitoes in night time is significantly lower than the day time in the study areas (Figure 5).

Figure 1: Location map of the study areas

Figure 2: Distance between rural and urban sample sites

Figure 3: Percentage of Anopheles mosquitoes collected in three different times from Human habitations and Cattle sheds of Rural & Urban areas of Hooghly District (Jan’2018-Dec’2018).

Figure 4: Percentage of Culex mosquitoes collected in three different times from Human habitations and Cattle sheds of Rural & Urban areas of Hooghly District (Jan’2018-Dec’2018).

Figure 5: Percentage of Aedes mosquitoes collected in three different times from Human habitations and Cattle sheds of Rural & Urban areas of Hooghly District (Jan’2018-Dec’2018).

Species composition of Anopheles mosquitoes showed a significant difference (p<0.01) in different months of the year, which also differ among rural and urban regions of the study area (Figure 6 & Figure 7). Four species of Anopheles mosquitoes were recorded in both rural and urban areas: An. barbirostris, An. subpictus, An. annularis and An. vagus. Monthly prevalence of different species of Anopheles also showed a significant difference between rural and urban areas (p < 0.01). In case of rural areas the peak month of prevalence of An. barbirostris was recorded during the month of January whereas in case of urban areas the prevalence of this species was found to be very low throughout the year. An. subpictus was more prevalent in rural areas than urban sites. This mosquito species showed two peaks, one during june-july and another during September-October in rural areas. Prevalence of An. annularis and  An. vagus found to be  high in urban areas in comparison with rural areas.

Figure 6: Month wise species composition of Anopheles mosquitoes in rural areas of Hooghly district (Jan’2018-Dec’2018).

Figure 7: Month wise species composition of Anopheles mosquitoes in urban areas of Hooghly district (Jan’2018-Dec’2018)

During the winter season starting from November to January there is a sharp decline in the prevalence of all of the three genera of mosquitoes which reflects to the fact that there are some strong correlation between the mosquito oviposition to egg hatching with the environmental temperature. In a field study at Gorakhpur district of Uttar Pradesh, Kanojia et al (2003) observed that there was a short peak of Culex quinquifasciatus in the month of March and a long peak of Culex tritaeniorhynchus in the month of September. They concluded that abundance of this species was related with rice cultivation as because they are mainly paddy field breeders. The present study also recorded higher abundance of Culex and Anopheles mosquitoes in the month of August, which may be due to the much availability of breeding sites during this time. Reports of several studies indicated that Culex quinquifasciatus as the most house frequenting mosquitoes, their prevalence in human habitations is higher than the cattle sheds (Chandra et al, 2013; Azmi et al, 2015).

The present study recorded higher prevalence of Culex and Anopheles mosquitoes in cattle sheds than human habitations in both rural and urban areas of Hooghly, West Bengal. It may be due to their resting habitat preferences in cattle sheds or zoophilic nature. As in many areas mosquito control strategy involves the control of adult mosquitoes by spraying insecticides, so it is very much necessary to have a better knowledge about the mosquito ecology, their biting behavior and resting habitat preferences. The present study found that in the rural and urban areas of Hooghly district, West Bengal, among three mosquito genera, the abundance of Anopheles and Culex is more than the Aedes throughout the year. Besides this although the prevalence of Aedes mosquitoes was less but they prefer to rest in human habitations than cattle sheds which throw a light on their anthropophilic behavior. On the other hand Culex and Anopheles mosquitoes prefer to rest more in cattle sheds than human habitations in both rural and urban areas which indicated that they also prefer to feed cattle blood besides human blood.

Species composition of Anopheles mosquitoes were different in case of rural and urban areas of Hooghly. An. subpictus is more dominant species in the rural areas where as An. vagus found to be more prevalent in urban regions of Hooghly. Anopheles subpictus Grassi has been incriminated as a primary vector of malaria in rural areas of Hooghly, West Bengal (Chatterjee et al, 2000). The present study recorded two peak months of prevalence of this vector, one during June-July and another during September-October, which strongly coincides with the emergence of malaria in the study areas.

CONCLUSION

Present findings are highly significant in understanding the mosquito ecology in the study areas and to have a better knowledge on their resting habitat preferences. This study  has indicated that Anopheles and Culex mosquitoes are more prevalent in cattle sheds besides human habitations. So, much care must be taken in the cattle sheds also during the application of insecticides to control the adult mosquitoes. Present study will illuminate about the resting-habitats of three genera of mosquitoes in relation to mosquito ecology so that proper management strategies may be taken with a view to prevent the mosquito borne diseases in the endemic areas of Hooghly District.

ACKNOWLEDGEMENTS

The authors are thankful to University Grants Commission (UGC) for providing financial support and to The University of Burdwan for providing proper infrastructure to carry out this work.

Conflict of interest: The authors declare that they have no conflict of interest.

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