Abstract. U.D. Manawadu, K.H.M.A. Deepananda and H.C.E. Wegiriya*

Transcription

1 Proceedings of the Third Academic Sessions Comparative study on the diversity and abundance of mosquito fauna in relation to anthropogenic activities and environmental factors in selected sites of Matara area U.D. Manawadu, K.H.M.A. Deepananda and H.C.E. Wegiriya* Department of Zoology, University ofruhuna, Matara. *Correspondence: Abstract Adult anthropophilic mosquito populations were surveyed by trapping fortnightly with mouth aspirator and human bait technique for three months during May to July, 2004, at four sites in urban and rural dwellings and environs of the Matara area, in relation to anthropogenic activities and environmental quality. Seven mosquito species belonging to five genera, i.e., Aedes albopictus, Aedes egypti, Armigerus subalbatus, Culex hutchinsoni, Culex quinquefasciatus, Mansonia uniform is. Mymomia sp., were encountered with diverse. abundances. Mosquito abundances were higher in urban areas and C. quinquefasciatus was the leading indoor resting species in Matara area. Outdoor sampling revealed that A. albopictus, A. subalbatus and C. quinquefasciatus were the predominant anthropophilic mosquitoes showed higher biting rate in Matara area. Multiple regression analysis indicated that mosquitoes prefer low salinity levels in water. A negative association of mosquito abundance with Dissolved Oxygen (DO) and positive association with Biological Oxygen Demand (BOD) indicated that mosquitoes prefer polluted environments. Additionally, higher precipitation was an important factor influencing mosquito abundance. In conclusion, anthropogenic activities play major role in mosquito abundance and urban areas provide preferred breeding sites for anthropophilic mosquitoes. Further studies on mosquito fauna and environmental alterations over the year desire to achieve more significant relationships with mosquito abundance and altered water quality parameters. Introduction Mosquitoes (Diptera: Culicidae) are very common insects that are present throughout the world, except in Antarctica. As a group, mosquitoes have adapted to complete their life cycle in diverse aquatic habitats (Crans, 1999; Mark and Fradin, 1998). Artificial containers such as tires, stock troughs, bottles and cans, provide major sources of breeding habitats for mosquitoes worldwide. The number of mosquitoes that are vectors of human diseases can be proportional to the availability of such artificial larval habitats (Wang et.al., 2000). The female mosquito lays her eggs, up to several hundred at a time, on the surface of water or in an area subjected to flooding. Un-hatched eggs of some species can withstand weeks to months of desiccation, remaining viable until the right environmental conditions for hatching. Male mosquitoes feed primarily on flower nectar and natural other sugary secretions. Though, females may feed on sugary substances to obtain energy for flight and dispersal, they require a blood meal to produce eggs in ovaries (Service, 1986). In a single feeding, a single mosquito typically consumes more than its own weight in blood (Mark and Fradin, 1998). Some mosquito species are zoophilic (preferring to feed on animals) and others are anthropophilic (showing preference for human blood). Members of genera Anophele, Culex and Aedes are most commonly responsible for biting humans (Mark and Fradin, 1998). Certain species of mosquitoes prefer to feed at twilight or night time while others bite mostly during the day. Mosquitoes are vectors of some of the most important diseases such as malaria, filariasis and dengue (Belding, 1942). They are known to be a substantial threat, due both to its cosmopolitan nature and vectorial importance (Simsek, 2003). Sri Lanka has suitable climatic conditions for mosquitoes to breed throughout the year (Manawadu et.al., 2005). Hence, mosquitoes are important insect pests from both a nuisance and a health point-of-view for human and domestic animals in many rural, suburban, and urban areas of Sri Lanka. Human migration, urbanization, development schemes and projects leading to availability of breeding places for mosquitoes tend to enhance the prevalence of mosquitoes and mosquito borne diseases. Despite eradication programs, mosquitoes still constitute a severe nuisance and pose a threat to human health in many urban areas than suburban or rural areas. Matara is situated in an area endemic to several mosquito borne diseases especially for bancroftian filiariasis (Dissanayeka and Jayasekera, 1989; Manawadu et.al., 2005). Effective control of mosquito borne diseases through vector management requires information on distribution and abundance of vectors in the target area. Therefore, the present study was carried out to investigate species diversity and abundance of anthropophilic mosquito fauna in urban and rural sites of Matara area with special reference to anthropogenic activities leading to conventional alterations of the environmental parameters that affect"mosquitoes. 121

2 Proceedings of the Third Academic Sessions Materials and Methods Study sites Matara area was selected as the study area to carry out the present investigation. In order to compare the mosquito abundance in urban and rural areas, four sampling sites were selected, i.e., two sites representing urban areas (Polhena and Hittatiya) and two sites from rural areas (Godagama and Talpawila). Polhena is situated 2 km south-west of the Matara town along the coastal belt. This area comprises of a large number of different types of houses showing different income levels. Coconut husk pits are common in this area especially along the coastal belt. Hittatiya is situated about 2 km countryside from the Matara town. It is rather a highly populated area and drainage water ditches are badly maintained leading to blockage of household effluents. Godagama is a rural village about 6 km northwest to the Matara town. Coconut and vegetable plantations are common in this area. Talpawila is also a rural area situated about 6 km east to the Matara town. Paddy and coconut plantations are common in this area. Sampling Entomological studies were carried out six times at fortnightly from May to July 2004 in each sampling area. Five houses were randomly selected for mosquito sampling from each sampling site. On each occasion, both indoor and out door mosquitoes were sampled during to 18.30h, using a mouth aspirator (Thavara et al., 2001). Briefly, indoor collectors sampled resting mosquitoes from walls and darker areas of rooms, for 20 minutes. The outdoor collectors bared their legs between the knee and the ankle and collected all landing and biting mosquitoes individually in to vials. Mosquito samples were processed and identified up to the species level with the use of keys and with the assistance of the Antifilarial unit, Matara. All biting mosquitoes collected by two volunteers in five houses were pooled and the biting rate was calculated to be the number of bits per man-hour. Resting rate calculated in similar way described previously. Environmental factors Temperature and water quality parameters were assessed in order to relate to the mosquito abundance, i.e., Temperature, ph and electrical conductivity in-situ, were measured using thermometer portable digital ph and Conductivity meter respectively. Dissolved Oxygen (DO), Biological Oxygen Demand (BODs) and Salinity were measured using standard method described elsewhere (Golterman et al., 1978). Environmental parameters were assessed within 25m from the dwellings. To relate the extent of mosquito abundance to rainfall, Rainfall data was obtain from May to July from Matara, Talpawila and Godagama Meteorological stations. Data analysis Multiple regression analysis was used to examine the relationship between environmental factors and mosquito abundance. The independent variables were the environmental factors. The dependant variable was mosquito abundance. Correlation between environmental variables and the mosquito abundance iri each separate sampling site were determined using conventional linear correlation (pearson's coefficient). Results Species diversity and abundance Seven mosquito species belonging to five genera, i.e., Aedes albopictus, Aedes egypti, Armigerus subalbatus, Culex hutchinsoni, Culex quinquefasciatus, Mansonia uniformis, Mymomia sp., were encountered in the four sampling locations at varying percentage abundances. Of them, C. quinquefasciuatus was the species with the highest abundance in indoor collections at all sites except in Godagama. Moreover, C. quinquefasciatus was prominent in indoor collections while A. subalbatus was dominant in outdoor collections. C. hutchinson; showed the lowest abundance in all sampling sites. Mymomia sp. was recorded only in the outdoor collection at Polhena at a very low abundance. Percentage abundance of each species at each sampling site is summarized in table 1. Though, mosquito diversity and abundance at each sampling site varied, there were no significant differences in mosquito abundance between urban and rural areas (p>0.05). 122

3 Table 1: Proceedings of the Third Academic Sessions Percentage abundance of mosquito species at indoor and outdoor collections in each sampling site. Percentage abundance (%) Species Hittatiya Polhena Talpawila Godagama In door Outdoor In door Outdoor Indoor Outdoor Indoor Outdoor C. quinquefasciatus A. subalbatus A. egypti A. a/bopictus C. hutchinsoni NR NR M. uniformis NR \ NR Mymomia sp. NR NR NR 0.88 NR NR NR NR NR - Not recorded Entomological studies 0,. i'.12 0 " to ".! ;; 8." '6 ~!- 4.e "" om DJlural M.os:qqito species Figure 01: Biting rate for mosquito species at urban and rural sites Biting rate: The adult mosquito biting rate calculated species wise for outdoor mosquitoes at each sampling site recorded different values. A. subalbatus showed highest biting rates at both Hittatiya and Talpawila sites, while A. albopictus and M uniformis showed the highest biting rate at Polhena and Godagama respectively. In addition, C. quinquefasciatus showed considerably high biting rates at all sites, especially at Polhena. Figure 1 depicts the calculated biting rate for each species in the four sampling sites. Resting rate: C. quinquefasciatus showed a higher resting rate at Hittatiya, Polhena and Talpawila localities, while M uniformis showed the higher resting rate at Godagama site. Other species were encountered in minor numbers representing lower resting rate at each sampling site. Resting rates for each species encountered in urban and rural sites are depicted in Figure 2. Urban Figure 02: Resting rates for adult mosquito species in urban and rural sites \23

4 Proceedings of the Third Academic Sessions Environmental parameters Rainfall and temperature: There were no significant differences in atmospheric temperature in the four sampling localities during the study period. Atmospheric temperature recorded within two weeks intervals during the three month period at each sampling site is summarized in table 2. Table 02: Atmospheric temperature (0C) at ach sampling site during the study period. d Hittatiya Polhena Talpawila Godagama Samp I mg perro (0C) (0C) (ac) (DC) Early May Late May Early June Late June Early July Late July Though, rainfall data were not significantly different between sampling sites, the rainfall data showed some variation among the sampling sites with rises and falls. Mean precipitation at the urban sites (Hittatiya and Polhena), Talpawila and Godagama are depicted in Figure j,- Urban sites --Talpawla 7 r Ii.,»: is.'''''''''' 14" " "-..., 6 ',., , '~",.., Godagama :L l--- Early May late May.-, i EarlyJune latejune Earlvjulv lalejuiy MoIih Figure 03: Mean precipitation during study period Water quality parameters: Water quality parameters, i.e., DO, BOD, salinity, conductivity and ph, showed variation patterns with rise and falls at the four sampling sites, during the study period. The mean values of each parameter for each sampling locality are summarized in Table 4. The DO and BOD level of the four sites were not significantly different from each other. (p>0.05) However, DO and BOD values were considerably higher in Polhena and Talpawila sites relatively to the other two sites, Hittatiya and Godagama. Higher electrical conductivity was recorded form the Polhena site. But there was no significant variation in salinity among the four sampling sites (p>o.05). However, ph in the four sites varied significantly from each other (p~ 0.05) with the highest ph values observed from the Godagama site. Table 4: Water Quality parameters at each site during the study period (ranges are denoted in parentheses) Sampling site Parameter Hittatiya Polhena Talpawila Godagama DO (mgll) 1.5 (0.1-8) 4.96 ( ) 4.96 ( ) 2.23 ( ) BOD (mgil) 1.07 ( ) 3.8 ( ) 3.96 ( ) 1.82 ( ) ph 3.8 ( ) 5.05 ( ) 4.85 ( ) 7.06 ( ) Salinity (ppt) 0.03 ( ) 0.05 ( ) 0.05 (O.oI - 0.2) 0.09 ( ) Conductivity (us) (1-953) 1520 (1-5680) 108 (1-204) 1001( ) Environmental parameters and mosquito abundance There was a strong positive association between mosquito abundance and DO (r=0.84 I), and 124

5 Proceedings of the Third Academic Sessions BOD (r=0.836) at Hittatiya sampling site where DO and BOD levels were minimum than the other three sites. In contrast, a negative association between mosquito abundance and DO (r=0.556) and BOD (r=-0.509) were observed at Godagania site where DO and BOD values were 2.23 and 1.82 (mgil), respectively. Low salinity levels and mosquito abundance showed significant (p:s0.05) relationship at Hittatiya site. Similarly, higher salinity levels, especially from Polhena to Godagama sites, had strong negative association with mosquito abundance. However, mosquito abundance with conductivity showed the strong negative association at Hittatiya site and positive association at Godagama site. Mosquito abundance and ph showed the negative association at Polhena site. Association derived using Pearson correlation coefficient (r) between mosquito abundance and environmental parameters are summarized in Table 4. Negative effect of salinity on mosquito abundance was prominent in rural areas than in urban areas. In Contrast negative relationship between mosquito abundance and ph was strong at urban sites where ph values were lower than the rural areas. Table 4: Relati onsh'ip b etween mosquito abun dance and envtronmenta parameters Environmental Parameter Mosquito in the study site Polhena Talpawila DO (mgll) BOD (mgll) Salinity (ppt) Conductivity ph (118) Hittatiya abundance Godagama + Significant at Discussion The present investigation showed that seven mosquito species i.e., C. quinquefasciatus, A. subalbatus, A. egypti, A. albopictus, C. hutchinsoni, M uniformis, Mymomia sp., were present in Matara area with a greater abundance. Some mosquito species have adapted to living in various types of habitats but most are specialized only for a few types of habitats (Simsek, 2003). Hence, diversity of mosquito species greatly varied from place to place on availability of suitable habitats. In the present study two different types of habitats were selected in order to compare the mosquito abundance. Of the seven species encountered, C. quinquefasciatus, vector of Wuchereria bancrofli in Sri Lanka, was the most prevalent species in urban sites as well as in a rural study site, Talpawila. Their abundance agreed with previous observations and C. quinquefasciatus was restricted to congested coastal towns along the south-west coastal belt of Sri Lanka (Dissanayeka and Jayasekera, 1989). Also, C. quinquefasciatus prefers to breed in polluted water. This investigation carried out in the evening hours from to 18.30h recorded C. quinquefasciatus as the prominent indoor resting species, as their biting activities mainly take place at night. In contrast, A. subalbatus was the prominent species in outdoor collections. Normally, they rest on vegetation (shrubs and grasses) and biting activities mainly take place during evening hours. When considering the resting rate, C. quinquefasciatus was the most abundant in urban sites especially in Hittatiya and Polhena. The prolific breeding of C. quinquefasciatus was in the coconut husk pits in Matara area (Dissanaike, 1991). Also, females lay their eggs in man made containers, such as cans, water receptacles, bottles, and storage tanks with polluted water that is unsuitable for drinking purposes. Also, this species was associated with urbanization and towns with poor and inadequate drainage and sanitation (Service, 1986). Such habitats are prevalent in Polhena area, thus C. quinquefasciatus thrives in this area. The atmospheric temperature was more or less constant during the study period in the four study sites. The present study was carried out during the south-west monsoon period and the mean rainfall in different study sites did not significantly differ from each other. However, higher mean rainfall was observed in early May and early July at urban sites and Talpawila. Previous studies in similar sites showed that rainfall largely affected the larval mosquito population (Manawadu, et.al., 2005). In addition, human activities always interfered with the water quality of breeding habitats of mosquitoes. Therefore, the abundance of man biting mosquito populations were higher in urban sites than in the suburban or rural sites, wherein human activities in the latter sites were minor leading to lower availability of effective breeding habitats. Water quality parameters were more or less different in urban and rural sites and did not give the valid picture for expected values especially in rural site. Of the rural sites, impact of anthropogenic activities on the environment at Godagama was greater due to recent development projects and 125

6 Proceedings of the Third Academic Sessions Nilwala river project. Likewise, Talpawila is now becoming populated due to human migration but it still remains several rural characteristics. Vegetations were highly abundant in this area and marshy land was found on one side of the village. As Polhena 'area is covered with coconut husk pits, it increased the breeding places for the mosquitoes. Hittatiya was highly populated area with poor drainage of household effluents and water. As a whole, in urban sites, there were much water filled artificial and man made breeding places than rural sites and most of them were polluted due to anthropogenic activities. Abundance and biting rate of mosquito species in urban sites was higher for many mosquito species encountered. Similar results were observed on larval indices, i.e., Breteau index, Container index and House index, in these sampling sites (Manawadu, et.al., 2005). But, due to environmental factors, statistically significant difference of mosquito abundance between urban and rural sites was not found. Mosquito abundance normally increases with high level of BOD. Regression analysis showed some relationship between environmental factors and mosquito abundance. Negative relationship of mosquito abundance with DO and positive relationship with BOD level in Polhena and Hittatiya indicated that mosquitoes preferred polluted environments. In addition, this study revealed a possible relationship between mosquito abundance and salinity level, i.e., higher mosquito abundance found at lower salinity levels. However, these relationships derived from the present investigation do not warrant valid conclusions, as sampling period of three months is not adequate to predict to derive proper conclusions. Rainfall played a major role for increasing the abundance of mosquitoes, especially in urban sites. Therefore, anthropogenic activities in addition to the habitat characteristics may be a major factor affecting the mosquito abundance. A. subalbatus showed higher biting rate at Polhena and Talpawila, where their breeding sites are polluted water filled habitats. The higher abundance of breeding sites has a direct impact on the population abundance. As discussed previously, Godagama showed different patterns from the normal trend, due to its habitat characteristics. Most abundant species in Godagama area was M uniformis (48.93%), vector of rural filariasis. Usually these mosquitoes lay their eggs under surface of aquatic vegetation, such as Pistia stratiotes, Salvinia sp. and Eichomia sp. High abundance of aquatic vegetation may be responsible for the higher abundance of M uniformis in Godagama area. In addition, marshy land beside the village may be a favorable breeding place for M uniform is. In conclusion, addition to the habitat characteristics, anthropogenic activities play a major role in prevalence of mosquito species. Urban areas provide preferred variable types of breeding places for higher occurrence of anthropophilic mosquitoes. Between the two habitat types studied, the most suitable habitat type for mosquitoes is the urban areas with higher abundance of polluted water. Acknowledgement We acknowledge Mr. Giridasa Jayarathne and his staff of the Antifilarial unit, Matara, for their assistance to identify the mosquito species. References Belding, D.1. (1942). Test book of Clinical Parasitology. D. Appleton, New York. 888pp. Crans, W J., (1999). The mosquito habitats of New Jersey. Wing Beats, American Mosquito Control Association. Volume 10, Number 3.. Dissanaike, A.S. (1986). Control of Filariasis in Ceylon. Proceeding of seminar on Filariasis and Immunology of parasitic infections and laboratory meeting Dissanayake, S., Jayasekara, N. (1989). Bancroftian Filariasis in Sri Lanka: an Over view of current knowledge. Journal of National Science council of Sri Lanka, 17(2): Golterrnan H.L., Clymo R.S., Ohnstad M.A.M. (1978). Methods for Physical and Chemical analysis of fresh water. Blackwell Scientific publications, Oxford London. ppl-123 Manawadu, V.D., Deepananda, K.H.MA, Wegiriya, H.C.E. (2005). Diversity and abundance of mosquito larvae in urban and rural sites of Matara area. Proceedings of the third Science Symposium, University of Ruhuna, Sri Lanka 3: Mark, S. and Fradin, M.D. (1998). Mosquitoes and Mosquito Repellents, a Clinical Guide. Annals of Internal Medicine. 128 (11): Service, M.W (1986). Lecture Notes on Medical Entomology, 1: 1-2 and 2: Simsek, F. M. (2003). Seasonal population dynamics and breeding habitat diversity of Culex pipiens Linnaeus, 1758 (Diptera: Culicidae) in Golbasi District, Ankara, Turkey. J. Ent. Res. Soc. 5(1): Thavara, U., Tawatsin, A., Chansang, C., Kong-ngamsuk, W., Paosriwong, S., Boon-Long, J., Rongsriyam, Y., Komalamisra, N. (2001). Laraval occurrence, oviposition behaviour and biting activity of potential mosquito vectors of dengue on Samui Island. Thailand. Journal of Vector Ecology, 26(2): Wang, C.1I., Chang, N.T., Wu, H.lI., Ho, C.M. (2000). Integrated control of the dengue vector Aedes aegypti in LiuChill village, Ping-Tung County, Taiwan. J. Am. Mosq. Contr. Assoc. 16: