Mosquitoes exploit almost all types of aquatic habitats for breeding. Prevailing physicochemical parameters in these habitats are important factors for survival and development of mosquito. Here, six water samples from Atlantic Ocean, River, well, distilled (control), rain and borehole water were used to culture Anopheline eggs collected from pure bred of Kisimu species. The development of eggs to 1st, 2nd, 3rd and 4th instars larval, pupal and adult stages were observed from day 1 to 6 using six replicates of each water sample. The number of eggs laid (fecundity) by the emerged adults were estimated using counting microscope. Level of development in emerged adults was determined using the wing size. The analysis of the physicochemical parameters of the water samples was carried out in the Nigerian Institute of Marine and Oceanography. The physicochemical characteristics were compared with the
rates of development and fecundity of the Anopheline species. Statistical analysis using ANOVA indicates no significant difference (P > 0.05) in the hatchability of the eggs. However, the rates of larval development to pupal stage and subsequent adult emergence showed a level of significant difference (P  0.05). This study provides information on mosquito ecology in relation to breeding habitat which may have bearing on vector population and distribution as well as malaria transmission in a particular area

Anyasor, GN

Awolola, TS

Ibidapo, CA

Momoh, OO

Obansa, JB

Oduola, OA

Ogunnowo, AA

Oyewole, IO

English

AJOL - African Journals Online

African Journal of Environmental Science and Technology Vol. 3 (12), pp. 447-452, December, 2009 Available online at http://www.academicjournals.org/AJEST ISSN 1991-637X © 2009 Academic Journals    Full Length Research Paper  Physico-chemical characteristics of Anopheles breeding sites: Impact on fecundity and progeny development  I. O. Oyewole1*, O. O. Momoh1, G. N. Anyasor1, A. A. Ogunnowo1, C. A. Ibidapo2, O. A. Oduola3, J. B. Obansa3 and T. S. Awolola4  1Babcock University Ilisan Remo, Nigeria. 2Lagos State University, Lagos, Nigeria. 3University of Lagos, Nigeria. 4The Nigerian Institute of Medical Research, Yaba, Lagos, Nigeria.  Accepted 23 September, 2009  Mosquitoes exploit almost all types of aquatic habitats for breeding. Prevailing physicochemical parameters in these habitats are important factors for survival and development of mosquito. Here, six water samples from Atlantic Ocean, River, well, distilled (control), rain and borehole water were used to culture Anopheline eggs collected from pure bred of Kisimu species. The development of eggs to 1st, 2nd, 3rd and 4th instars larval, pupal and adult stages were observed from day 1 to 6 using six replicates of each water sample. The number of eggs laid (fecundity) by the emerged adults were estimated using counting microscope. Level of development in emerged adults was determined using the wing size. The analysis of the physicochemical parameters of the water samples was carried out in the Nigerian Institute of Marine and Oceanography. The physicochemical characteristics were compared with the rates of development and fecundity of the Anopheline species. Statistical analysis using ANOVA indicates no significant difference (P > 0.05) in the hatchability of the eggs. However, the rates of larval development to pupal stage and subsequent adult emergence showed a level of significant difference (P < 0.05). Also, wing length for determining adult size showed no significant difference (P > 0.05). This study provides information on mosquito ecology in relation to breeding habitat which may have bearing on vector population and distribution as well as malaria transmission in a particular area.  Key words: Malaria, Anopheles mosquitoes, breeding habitat, physico-chemical properties.   INTRODUCTION  Mosquitoes exploit almost all types of lentic aquatic habitats for breeding. Larvae of Anopheles mosquitoes have been found to thrive in aquatic bodies such as fresh or salt water marshes, mangrove swamps, rice fields, grassy ditches, the edges of streams and rivers and small, temporary rain pools. Many species prefer habitats with vegetation while some breed in open, sunlit pools. A few species breed in tree holes or the leaf axils of some plants (CDC, 2004). Anopheline species are known to be ground pool breeders, although large numbers have been observed in gutters, periodomestic runoff and domestic containers (Mafiana et al., 1998; Aigbodion  and  Odiachi,      *Corresponding author. E-mail: oyewoleio@gmail.com. 2003). Anopheles mosquito has been found to breed in clear water of suitable pH, temperature and nutrient composition (Okorie et al., 1978). However, high water current and flooding have been reported to lead to Anopheles species larval deaths due to reduction in oxygen tension causing physical harm to the larvae (Okogun, 2005). Water of a near neutral pH 6.8 - 7.2 was found most optimal for the weakening of the egg shells for the first instar larvae stage to emerge (Okogun et al., 2003). Various chemical properties of the larval habitat related to vegetation, ranging from pH, optimum tempe-rature, concentration of ammonia, nitrate and sulphate have been found to affect larval development and survival (Mutero et al., 2004). The present study exa-mined under laboratory conditions some of the physico-chemical  parameters  germane  to  the  survival,  growth,  448    Afr. J. Environ. Sci. Technol.    development and fecundity in Anopheles gambiae.   MATERIALS AND METHODS  Water sample collection and analysis  Water samples were collected from the following sites: Majidun river in Majidun, Ikorodu Local Government Area of Lagos State, well located about 3 km from Majidun River, borehole water located in Abule Egba, Agege Local Government Area of Lagos State, Atlantic Ocean at Victoria Island in Lagos, Rain water from Nigerian Institute of Medical Research (NIMR) compound at Yaba, Lagos and distilled water from the insectary unit in NIMR. The water samples were kept in clean, dry 5-litre jerry cans prior use. One litre of each water sample was analyzed for physico-chemical constituents from the Nigerian Institute of Oceanography and Marine Research (NIOMR). Conductivity and salinity were measured using YSI moulting meter, salinometric method for salinity and conductance for conductivity. Nitrate, sulphate, and phosphate were measured using spectrophotometer HACHDR 2000 while iron, silica, copper, zinc, calcium, magnesium, cadmium and lead were measured using Flame Atomic Absorption Spec-trometry (FAAS). Surface water temperature and dissolved oxygen were determined using thermometric method; pH using potentiometric method, turbidity, total dissolved solids, total suspended solids and colour were determined using spectrophoto-metric technique while alkalinity and total hardness were obtained via titration.   Progeny development and fecundity  Water samples of different sources were put into 6 different plastic containers, each representing 6 replicates while distilled water was used as control. One hundred and twenty eggs of pure culture A. gambiae from Kisimu in Kenya were bred in each of the water samples. The mosquitoes were culture from egg to the adult stage. The first instar larvae emerged on day 2 and this was monitored in all the water samples. All the instar larvae were fed with mashed biscuit of low fat (12.30 g) plus yeast capsules (7.59 g). Pupae began to emerge after day 8 followed by adult emergence on day 3 post pupal emergence. The plastic bowls were covered with nets to prevent adults from flying out. Aspirator was used to collect the emerged mosquito from each water sample into rearing cages. These were provided with 10% glucose solution (w/v) in cotton wool placed in plastic tubes while 3 - 4 day old female mosquito was fed with blood meals from the forearm of a human volunteer twice a day to aid egg production. Filter papers sprinkled with distilled water were placed in each cage for egg collection. The experiment was maintained under room temperature. Number of eggs collected was estimated with the aid of counting microscope (stereomicroscope).   Determination of wing length  The wings of 10 mosquitoes from each water sample were removed gently with forceps and mounted on microscope glass slide. Wings were measured using dissecting microscope to the nearest 0.1 mm with an ocular micrometer from the distal end of the alula to tip, excluding the fringe scales.   Statistical analysis  Data collected were analyzed using SPSS software (version 10 for windows, SPSS inc. Chicago, IL) and Analysis of variance (ANOVA) was used as test statistics.     RESULTS  The results of the physicochemical analysis of various water samples showed that rain water constitutes the highest pH while Atlantic Ocean recorded the highest conductivity. Zero salinity was recorded in the borehole, distilled and rain water samples, however, highest levels of salinity and sulphate were recorded in Atlantic Ocean. Turbidity was highest in River but zero turbidity was recorded in distilled and rain water. Copper and zinc were absent in all the water samples (Table 1). The proportion of emerged larvae and pupae from day 1 to 6 and the mean of the six replicates from different water samples are summarized in Tables 2 and 3. The emerged larvae were highest in distilled and river water respectively while borehole and rain water produced the least. However, statistical analysis showed that there was no significant difference (P > 0.05) in larvae emergence from mosquito eggs exposed to all the water samples. On the day 1(F(5,30) = 1.331, P = 0.28), day 2 (F(5,30) = 0.956, P = 0.46), day 3 (F(5,30) = = 0.795, P = 0.56), day 4 (F(5,30) = 54.715, P = 0.23), day 5 (F(5,30) = 24.493, P = 0.13) and  day 6 (F(5,30) = 24.017, P = 0.100). Pupal emergence showed a level of significant difference (P < 0.05) on day 1(F (3,20) = 3.11, P = 0.049) and day 3(F(3,20) = 5.20, P = 0.008) for larvae reared in River water, Atlantic Ocean, distilled and well water samples. However, there was no significant difference on day 2 (F(3,20) = 1.027, P = 0.402) and day 4(F(3,20) = 1.824, P = 0.175) of  pupae emergence in these water samples. Table 4 shows the emergence of adult mosquitoes of which the least was recorded in well water with highest mortality rate. Fecundity rate of the survived mosquitoes from different water samples are shown in Table 5. Table 6 showed the mean length of wings measured from 10 mosquitoes collected from the six water samples. There was no statistical difference (F (3,36) = 0.073, P = 0.974) in the length of wings of the adult mosquito from all the water samples.    DISCUSSION  Knowledge of the local epidemiology and ecology of malaria/vector is germane to control and reduction in malaria transmission. One of the major reasons for the study of mosquito ecology is to glean information on factors that may determine oviposition, survival, the spatial and temporal distribution of this important disease vector. Water is an important component of ecosystem and its quality in the breeding site is an important determinant of whether or not the female mosquitoes will lay their eggs and the resulting immature stages will successfully complete their development to the adult stage (Piyaratne et al., 2005). In the present study, A. gambiae seems to prefer river and ocean as breeding habitat since these water bodies contain physico-chemical properties such as calcium,Oyewole et al.      449    Table 1. Physicochemical parameters in the six water samples.  Physicochemical parameters Well water River water Borehole water Atlantic ocean Distilled water Rain water Temperature(0C) 30.10 30.40 30.50 27.70 29.40 29 Dissolved oxygen (mg/L) 9.77 9.73 9.82 9.94 9.27 9.20 pH 6.15 6.51 4.74 7.11 7.16 7.54 Conductivity (µS/cm) 375 308.20 71 30800 20.30 6 Total Dissolved solids (mg/L) 187.50 154 36 15400 10.15 3 Salinity (%) 0.30 0.10 0 18 0 0 Turbidity (FTU) 10 30 1 15 0 0 Colour (Pt-Co) 43 353 0 37 0 0 Total Suspended Solids (mg/L) 1 12 0 5 0 0 Sulphate (mg/L) 51 0 0 3400 0 0 Nitrate (mg/L) 1.30 2.60 2.20 4.8 1.50 1.80 Iron (mg/L) 0.12 0.11 0.16 0.14 0.12 0.09 Silica (mg/L) 4.10 10.10 4.50 0.40 2.20 1.30 Phosphate (mg/L) 0 0.17 0 0.79 0.25 0 Alkalinity 204 40 20 120 20 4 Total Hardness (mg/L) 230 60 80 9000 120 20 Lead (mg/L) 0 0 0 0.016 0 0 Copper (mg/L) 0 0 0 0 0 0 Zinc (mg/L) 0 0 0 0 0 0 Calcium (mg/L) 140 110 45 5000 15 6 Magnesium (mg/L) 50 40 15 2300 15 2 Cadmium (mg/L) 0 0 0 0.0028 0 0    magnesium sulphate, nitrate, phosphate and dissolved solids in high proportion as nutrient composition. Other factors such as optimum temperature, pH and dissolved oxygen might have provided conducive environment for survival and breeding activity of the Anopheline species. Geller et al. (2000) reported that under laboratory conditions, A. gambiae carries out normal development when pH varies as much as from 4.0 to 7.8 as long as there is sufficient phytoplankton and zooplankton for it to consume. Also cool, still and clear water with suitable pH, temperature and nutrient composition has been found to encourage breeding in Anopheles species (Okorie et al., 1978; Okogun, 2005). However, high water current and flooding are detrimental to Anopheles larval survival due to reduction in oxygen tension and invariably physical harm to the larvae. These attributes may not be uncommon in oceanic water, hence, naturally it is not expected to support growth of the Anopheline mosquito. The growth and survival of Anopheline species in oceanic water as observed in the present study may be attributed to the laboratory conditions under which the experiment was carried out and the presence of other factors brackish water in the coastal areas with low water current, less flooding and as little saline content as 18‰  necessary for growth in the water sample. However, as found in oceanic water in this study could support breeding activity in Anopheline mosquito. Meanwhile, there was no significant difference in hatching of eggs in all the six water samples, but the rate of oviposition was significantly high in well, river, Atlantic Ocean and distilled water respectively, this may indicate that Anopheline mosquito discriminately lays its eggs in preferred water body. However, there was a discriminate growth of both the larvae and pupae in all the water samples while growth was significantly high in specimen cultured in both river and ocean water samples. Various chemical properties of the larval habitat in relation to vegetation, optimum pH and temperature, concentration of ammonia, nitrate and sulphate have been reported to affect larval development and survival (Pal, 1945; Mutero et al., 2004). High mortality rate recorded in the larvae cultured in well water could be due to the high alkaline content of this aquatic habitat. Previous reports have shown that the mosquito larvae can survive well in neutral or slightly alkaline water habitat (MacGregor, 1929; Abdullah and Merden, 1995; Pelizza et al., 2007. However, MacGregor (1929) reported that tree-hole mosquitoes (Finlaya geniculata) bred in water of a pH value of 4.4 developed and survived better than those from the local streams with a pH value of 8.2 - 8.4 which succumbed or remained stunted. Other factors associated with growth and survival of mosquito larvae includes temperature, pH and salinity of the breeding habitat. The present study showed that the growth rate of the emerged adults is independent of the water source as indicated in the sizes of their  wings.  The  implication  of  this  is  that  breeding  450    Afr. J. Environ. Sci. Technol.     Table 2. Larval emergence from the six water samples.  Water Samples Days of Emergence Mean ± S.D River water 1 14.50 ± 2.26  2 16.83 ± 2.23  3 17.17 ± 2.14  4 16.67 ± 2.73  5 16.50 ± 2.51  6 16.67 ± 2.50    Borehole water 1 12.0 ± 1.67  2 15.5 ± 2.95  3 15.67± 2.94  4 1.83 ± 1.72  5 1.00 ± 1.26  6 0.50 ± 0.55    Atlantic ocean 1 13.83 ± 2.23  2 14.67 ± 1.97  3 15.33 ± 1.80  4 14.83 ± 2.14  5 13.83 ± 2.99  6 10.33 ± 4.13    Rain water 1 14.33 ± 3.39  2 15.83 ± 2.56  3 16.33 ± 3.14  4 1.83 ± 2.79  5 1.83 ± 2.99  6 0.00 ± 0.00    Distilled water 1 15.50 ± 1.97  2 17.00 ± 1.55  3 17.5 ± 1.22  4 15.83 ± 2.32  5 10.67 ± 4.50  6 9.50 ± 4.42    Well water 1 14.67 ± 3.08  2 16.50 ± 1.87  3 16.50 ± 1.87  4 14.33 ± 2.16  5 12.33 ± 4.03  6 11.33 ± 4.59  Note: No significant difference recorded. Six replicates were used per day for each water sample    blood meal volume of the adult mosquitoes which are factors of body size (Lyimo et al., 1992). The present study highlights some of the factors resident in different bodies of water and the impact of such  factors  on  survi-   Oyewole et al.      451    Table 3. Pupal emergence from the six water samples.  Water Samples Days of Emergence Mean ± S.D River water 1* 0.83±0.15  2 5.00±3.29  3a 6.67±2.88  4 0.17±0.41    Borehole water 1* NIL  2 NIL  3 a NIL  4 NIL    Atlantic ocean 1* 0.17±0.41  2 2.50±1.87  3 a 1.00±0.63  4 1.50±1.38    Rain water 1* NIL  2 NIL  3 a NIL  4 NIL    Well water 1* 0.33±0.52  2 4.83±2.48  3 a 2.83±4.45  4 0.67±1.21    Distilled water(control) 1* 0.00±0.00  2 4.33±3.20  3 a 1.50±1.38  4 0.5±0.84  *, indicates a significant difference; a, indicates a significant difference. Note: Six replicates were used per day for each water sample.     Table 4. Emergence and Mortality rate of adult mosquitoes.  Water samples Mosquito emergence Number of death Number survived Mortality rate (%) Rain water 34 27 7 79.4 Borehole water 28 23 5 82.1 River water 73 52 21 71.2 Distilled water 42 31 11 73.8 Well water 58 53 5 91.4 Atlantic ocean 29 20 9 69.0    val, growth, development and breeding activity of A. gambiae. Important of this study cannot be overem-phasized in formulating control strategies against this important malaria vector through proper environmental planning and management that will help in reducing breeding habitat. 452    Afr. J. Environ. Sci. Technol.    Table 5. Fecundity rate of the survived mosquitoes from different water samples.  Water sample Number of survived adult mosquitoes Total number of eggs laid Borehole water 15 213 Distilled water 31 367 Atlantic Ocean 21 711 Rain Water 18 174 River water 52 732 Well water 53 1802      Table 6. Mean length of wings of 10 mosquitoes from each water sample.  Water samples Number of mosquitoes Mean length of wings (mm) Standard deviation Distilled water 10 3.00 0. 33 Ocean water 10 3.30 0.36 Well water 10 3.27 0.38 Borehole water 10 3.28 0.41  River   water 10 3.27 0.35 Rain water 10 3.34 0.44    REFERENCES  Aigbodion FI, Odiachi, FC (2003). Breeding sites preferences of Anopheline Mosquitoes in Benin City, Nigeria. Niger. J. Entomol. 20: 1-7. Abdullah MA, Merden AI (1995). Distribution and ecology of the mosquito fauna in Southwestern Saudi Arabia. J. Egypt. Soc. Parasitol., 25(3): 815-837. Centre for Disease Control and Prevention (2004). Life stages of Anopheles mosquitoes. MMWR 52: 989-997. Geller N, Graczyk TK, Patz JA, Vittor AY (2000). Effects of environ-mental changes on emerging parasitic diseases. Int. J. Parasitol. pp.1495-1405. Lyimo EO, Takken W,  Koella, JC (1992). Effect of rearing temperature and larval density on larval survival, age at pupation and adult size of Anopheles gambiae. Entomol. Exp. Appl. 63: 265-271. MacGregor ME (1929). The significant of  pH in the development of mosquito larvae. Parasitology, 21: 132-157.  Mafiana CF, Annaeema LO, Olatunde GO. (1998). Breeding Sites of larval mosquitoes in Abeokuta, Nigeria. Niger. J. Entomol. 15: 136-143. Mutero CM, Nga’ang’a PN, Wekoyela P, Githure J, Konradsen F (2004). Ammonium sulphate fertilizer increases larval populations of Anopheles arabiensis and culicine mosquitoes in rice fields. Acta Trop. 89: 187-192. Okogun GRA (2005). Life table Analysis of Anopheles malaria vectors: generational mortality as tool in mosquito vector abundance and control studies. J. Vector Borne Dis. 42: 45-53.               Okogun GRA, Bethran EB, Anthony N, Okere Jude C,  Anegbe C. (2003). Epidemiological Implications of Preferences of Breeding Sites      of Mosquito species in Midwestern Nigeria. Ann. Agric. Environ. Med. 10: 217-222. Okorie TG (1978). The breeding site preferences of mosquitoes in Ibadan, Nigeria. Niger. J. Entomol. 1: 71-80. Pal R (1945). On the bionomics of Anopheles culicifacies Giles, Pt II: the ecology of the immature stages. J. Malaria Insti. India 6: 53-74. Pelizza SA, Lopez Lastra CC, Becne JJ, Bisara V, Garcia JJ (2007). Effects of temperature, pH and Salinity on the infection of Leptolegnia Capmany Seymour (Peronosporomycetes) in mosquito larvae. J. invertebrate Pathol. 96(2):133-137. Piyaratne MK, Amerasinghea FP, Amerasinghea PH, Konradsen F (2005). Physico-chemical characteristics of Anopheles culicifacies and Anopheles varuna breeding water in a dry zone stream in Sri Lanka. J. Vector Borne Dis. 42: 61–67.                

Physico-chemical characteristics of Anopheles breeding sites: Impact on fecundity and progeny development

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Physico-chemical characteristics of Anopheles breeding sites: Impact on fecundity and progeny development

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