Invasion potential of the aquarium pet snail Planorbella trivolvis in India: impact of certain abiotic and biotic factors.

Planorbella trivolvis (ramshorn snail) is one of India's most extensively sold exotic aquarium pet snails. The unintentional or deliberate release of P. trivolvis may result in the colonisation and establishment as an invasive snail in freshwater ecosystems. However, the successful invasion of P. trivolvis will depend on several abiotic and biotic factors of the concerned freshwater ecosystem. We have assessed the possibility of overcoming the opposing factors in P. trivolvis invasion through laboratory-based experiments and examined the effects of household-derived pollutants on egg hatchability, adult survivability and fecundity, and temperature (15 to 35 °C) on growth, sexual maturity, and reproduction. Additionally, we have evaluated the potential of native predators as biotic resistance to invasion by prey-choice experiment. The results indicated that egg hatchability, adult survivability, and fecundity were reduced with increasing pollutant concentration. However, the same traits did not differ from a native freshwater snail, Indoplanorbis exustus. The fecundity of P. trivolvis increased with increasing body size, but no considerable differences at different temperature levels suggest a wide range of adaptation to temperature. Faster growth and the requirement of comparatively few days to attain sexual maturity were observed in the higher temperatures. The native predators, Glossiphonia weberi and Diplonychus rusticus, avoided P. trivolvis as prey over the alternative prey snails in most instances, suggesting the masking of biotic resistance against the colonisation. Our observations indicate that the chance dispersal of P. trivolvis from household or commercial aquaria may lead to a possible invasion of freshwater ecosystems under suitable conditions.

Phosphate ion removal from aqueous solution using snail shell dust: biosorption potential of waste shells of edible snails.

The freshwater snails, Filopaludina bengalensis and Pila globosa are widely used for human consumption and as a feed in aquaculture in India and Bangladesh. The generation of shells as a waste product following meat extraction from the live snails incites their utilisation as a potential biomaterial. Shell dust was prepared from the dried shells of F. bengalensis (FSD) and P. globosa (PSD) and employed for phosphate adsorption from aqueous solutions. Batch adsorption experiments were performed to examine the effects of various experimental conditions, such as biosorbent dose, agitation speed, temperature, contact time, pH, initial concentration of phosphate ions, and presence of co-existing ions. SEM, EDS, ICP-OES, FTIR, and XRD results indicated that phosphate ions were adsorbed onto the surface of shell dust particles. The experimental data fitted with the Langmuir isotherm with a maximum adsorption capacity of 62.50 and 66.66 mg g-1 for FSD and PSD. The pseudo-second order kinetic model was well fitted, indicating the chemical adsorption process, and the thermodynamic parameters indicated that the adsorption mechanism of phosphate was spontaneous, feasible, and endothermic. Therefore, the results have established the potentiality of the waste shells of edible snails to be used as an eco-friendly and low-cost biosorbent for phosphate removal from wastewater.

Biodegradation of Paper Wastes by Freshwater Snails: Implications for Management.

The different types of paper wastes constitute a major portion of municipal solid waste. The present study was aimed to justify the use of freshwater snails for the biological degradation of the paper waste and subsequent availability of cellulose from fecal matter. Three aquatic snails Racesina luteola, Indoplanorbis exustus, and Physella acuta were used to degrade newsprint, cardboard, and common writing paper as paper waste. The consumption of papers by the snail species was subjected to statistical analysis, and the results of Kruskal-Wallis test indicated a significant variation in the paper-specific consumption pattern (K = 181.762, df = 2, p <0.0001) and no variation in the species-specific pattern. Among the three types of paper used for the study, cardboard was consumed at the highest rate (4.655 ± 0.401 mg per day), and the per capita consumption remained highest for the snail I. exustus (2.253 ± 0.273 mg per day). The microscopic images and SEM micrographs of the consumed paper revealed prominent grazing and scraping marks by the snails. The disintegration and relaxation of the papers after consumption indicated that they were on the pathway to degradation. The traditional way of degrading paper waste includes physical, chemical, or microbial treatment of paper pulp. This study represents a novel approach considering the freshwater snails as model organisms for the biodegradation process. Considerable amount of cellulose was present in the fecal samples, which can be extracted and purified for utilization as potent raw material.

Temperature dependent variations of life history traits of the land snail Allopeas gracile (Hutton, 1834) (Gastropoda: Subulinidae).

The ambient temperature of the environment influences the life history features of the land snails, thereby affecting the life history strategies. With the temperature being a reliable indicator of the seasonal changes, an attempt to explore the variations in the life history strategies of the pest snail Allopeas gracile (Hutton, 1834) (Gastropoda: Subulinidae) was carried out under four constant temperature grades - 15°C, 20°C, 30°C and 35°C (±1°C) temperatures throughout with laboratory temperature as controlled environment. The snail A. gracile was unable to complete their life cycle at 15°C and 20°C, without reaching reproductive maturity. In contrast, A. gracile maintained at laboratory temperatures (range 25-29 °C) exhibited long life span, longer reproductive period and longer generation time. However, the reproductive rate was highest at temperature 30°C. Perhaps, the warmer environment facilitated rapid growth, fast onset of reproduction with larger body size at early age. At a constant higher temperature of 35°C a state of inactivation was imposed when growth and reproduction became static. Apparently, the expression of the life history traits of A. gracile was supportive of an invasive nature, at a temperature ranging between 25°C and 35°C.

Macroinvertebrates as engineers for bioturbation in freshwater ecosystem.

Bioturbation is recognized as a deterministic process that sustains the physicochemical properties of the freshwater ecosystem. Irrigation, ventilation, and particle reworking activities made by biotic components on sediment beds influence the flow of nutrients and transport of particles in the sediment-water interface. Thus, the biogenic disturbances in sediment are acknowledged as pivotal mechanism nutrient cycling in the aquatic system. The macroinvertebrates of diverse taxonomic identity qualify as potent bioturbators due to their abundance and activities in the freshwater. Of particular relevance are the bioturbation activities by the sediment-dwelling biota, which introduce changes in both sediment and water profile. Multiple outcomes of the macroinvertebrate-mediated bioturbation are recognized in the form of modified sediment architecture, changed redox potential in the sediment-water interface, and elicited nutrient fluxes. The physical movement and physiological activities of benthic macroinvertebrates influence organic deposition in sediment and remobilize sediment-bound pollutants and heavy metals, as well as community composition of microbes. As ecosystem engineers, the benthic macroinvertebrates execute multiple functional roles through bioturbation that facilitate maintaining the freshwater as self-sustaining and self-stabilizing system. The likely consequences of bioturbation on the freshwater ecosystems facilitated by various macroinvertebrates - the ecosystem engineers. Among the macroinvertebrates, varied species of molluscs, insects, and annelids are the key facilitators for the movement of the nutrients and shaping of the sediment of the freshwater ecosystem.

Influence of habitat complexity on the prey mortality in IGP system involving insect predators (Heteroptera) and prey (Diptera): Implications in biological control.

Intraguild predation (IGP) is common in the freshwater insect communities, involving a top predator, intraguild prey (IG prey) and a shared prey. Influence of the habitat complexity on the prey-predator interactions is well established through several studies. In the present instance, the IGP involving the heteropteran predators and the dipteran prey were assessed in the background of the habitat complexity. The three predators Diplonychus rusticus, Ranatra filiformis, and Laccotrephes griseus, one intraguild prey Anisops bouvieri and two dipteran prey Culex quinquefasciatus and Chironomus sp. were used in different relative density against the complex habitat conditions to deduce the impact on the mortality on the prey. In comparison to the open conditions, the presence of the macrophytes and pebbles reduced the mortality of the shared prey under intraguild system as well as single predator system. The mortality of the shared prey was however dependent on the density of the predator and prey. Considering the shared prey mortality, predation on mosquito larvae was always higher in single predator system than chironomid larvae irrespective of identity and density of predators. However, for both the shared prey, complexity of habitat reduced the prey vulnerability in comparison to the simple habitat condition. Higher observed prey consumption depicts the higher risk to predation of shared prey, though the values varied with habitat conditions. Mortality of IG prey (A. bouvieri) in IGP system followed the opposite trend of the shared prey. The lower mortality in simple habitat and higher mortality in complex habitat conditions was observed for the IG prey, irrespective of shared prey and predator density. In IGP system, the shared prey mortality was influenced by the habitat conditions, with more complex habitat reducing the vulnerability of the shared prey and increased mortality of the IG prey. This implies that the regulation of the mosquitoes, in the IGP system will be impeded by the habitat conditions, with the heteropteran predators as the top predator.

Microstructure Analysis and Chemical and Mechanical Characterization of the Shells of Three Freshwater Snails.

The shells of freshwater snails are discarded as waste, which qualify as biological materials with prospective multiple uses. To substantiate this proposition, an attempt was made to elucidate the physical and chemical properties of the shells of three freshwater snails, namely, Bellamya bengalensis, Pila globosa, and Brotia costula. The shells were prepared for electron microscopy and assessment of the calcium carbonate content, apart from the Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and nanoindentation studies. The results indicated that the calcium carbonate content (y) of the shells ranged between 87 and 96% of the total weight (x) and complied with a power regression equation: y = 0.801x 1.016; R 2 = 0.994; r = +0.998; P < 0.001. Observations through SEM depicted different snail species-specific arrangement patterns of calcium carbonate crystals in the diverse layers of shells. The XRD, FTIR, and EDS observations revealed the dominance of the aragonite form of the calcium carbonate crystal in the microstructures of each snail shell with the occurrence of different shell surface functional groups. The Brunauer-Emmett-Teller analysis elucidated the surface textures of shell dust taken from each snail species; in addition, the nanohardness properties indicate the shells as a tough biocomposite exoskeleton. Species-specific variations in the shell morphology, microstructure, and calcium carbonate content were prominent for the three freshwater snails considered for the study. Nonetheless, the physical and chemical properties substantiate that the shells of B. bengalensis, P. globosa, and B. costula qualify as biological materials for sustainable use in various fields including bioremediation, biocatalyst, biomedical applications, and a source of lime. Since the shells of the freshwater snails are discarded as aquaculture waste, subsequent use as a biological material will support the "waste made useful" paradigm in sustainability, both from ecological and economic perspectives.

An insight into the structure, composition and hardness of a biological material: the shell of freshwater mussels.

The shell of the freshwater mussel (Mollusca: Bivalvia) is a composite biological material linked with multifunctional roles in sustaining ecosystem services. Apart from providing mechanical strength and support, the shell is an important site for adherence and growth of multiple types of algae and periphyton. Variations in the shell architecture are observed in the mussels both within a species and among different species. Considering the prospective utility of the shell of the freshwater mussels as a biological material, an assessment of the shell characteristics was accomplished using Corbicula bensoni and Lamellidens marginalis as model species. The calcium carbonate (CaCO3) content of the shells, physical features and mechanical strength were assessed along with the morphometric analysis. The CaCO3 content of the shell (upto 95% to 96% of the shell weight) of both the mussels was positively correlated with the shell length, suggesting increased deposition of CaCO3 in shells with the growth of the species. The cross sectioned views of FE-SEM images of the shells exhibited distinct layered structure with external periostracum and inner nacreous layer varying distinctly. In the growing region, the growth line was prominent in the mussel shells revealed through the FESEM images. In addition XRD, FTIR and EDS studies on the mussel shells confirmed the existence of both aragonite and calcite forms of the calcium carbonate crystals with the incidence of various functional groups. The mechanical strength of the mussel shells was explored through nanoindentation experiments, revealed significant strength at the nanoparticle level of the shells. It was apparent from the results that the shell of the freshwater mussel L. marginalis and C. bensoni qualify as a biological material with prospective multiple applications for human well-being and sustaining environmental quality.

Household Wastes as Larval Habitats of Dengue Vectors: Comparison between Urban and Rural Areas of Kolkata, India.

Porcelain and plastic materials constitute bulk of household wastes. Owing to resistibility and slow degradability that accounts for higher residence time, these materials qualify as potential hazardous wastes. Retention of water permits these wastes to form a congenial biotope for the breeding of different vector mosquitoes. Thus porcelain and plastic wastes pose a risk from public health viewpoint. This proposition was validated through the study on the porcelain and plastic household wastes as larval habitats of Dengue vectors (Aedes spp.) in rural and urban areas around Kolkata, India. The wastes were characterized in terms of larval productivity, seasonal variation and a comparison between urban and rural areas was made using data of two subsequent years. The number of wastes positive as larval habitats and their productivity of Aedes spp. varied among the types of household wastes with reference to months and location. Multivariate analysis revealed significant differences in the larval productivity of the household wastes based on the materials, season, and urban-rural context. Results of Discriminant Analysis indicated differences in abundance of Ae. aegypti and Ae. albopictus for the urban and rural areas. The porcelain and plastic wastes were more productive in urban areas compared to the rural areas, indicating a possible difference in the household waste generation. A link between household wastes with Aedes productivity is expected to increase the risk of dengue epidemics if waste generation is continued without appropriate measures to limit addition to the environment. Perhaps, alternative strategies and replacement of materials with low persistence time can reduce this problem of waste and mosquito production.

Pupal productivity & nutrient reserves of Aedes mosquitoes breeding in sewage drains & other habitats of Kolkata, India: Implications for habitat expansion & vector management.

BACKGROUND & OBJECTIVES: The quality of breeding sites is reflected through the pupal productivity and the life history traits of Aedes mosquitoes. Using nutrient reserves and pupal productivity of Aedes as indicators, the larval habitats including sewage drains were characterized to highlight the habitat expansion and vector management. METHODS: The pupae and adults collected from the containers and sewage drains were characterized in terms of biomass and nutrient reserves and the data were subjected to three way factorial ANOVA. Discriminant function analyses were performed to highlight the differences among the habitats for sustenance of Aedes mosquitoes. RESULTS: Survey of larval habitats from the study area revealed significant differences (P<0.05) in the pupal productivity of Aedes among the habitats and months. Despite sewage drains being comparatively less utilized for breeding, the pupae were of higher biomass with corresponding adults having longer wings in contrast to other habitats. The nutrient reserve of the adults emerging from pupae of sewage drains was significantly higher (P<0.05), compared to other habitats, as reflected through the discriminant function analysis. INTERPRETATION & CONCLUSIONS: The present results showed that for both Ae. aegypti and Ae. albopictus, sewage drains were equally congenial habitat as were plastic, porcelain and earthen habitats. Availability of Aedes immature in sewage drains poses increased risk of dengue, and thus vector control programme should consider inclusion of sewage drains as breeding habitat of dengue vector mosquitoes.

Chironomid midges as allergens: evidence from two species from West Bengal, Kolkata, India.

BACKGROUND & OBJECTIVES: Arthropods of different taxonomic identity including chironomid midges are known to induce allergic response in humans. The present study was done to access two common chironomid species Chironomus circumdatus and Polypedilum nubifer for their sensitizing potential as an allergen in atopic patients and controls. METHODS: Following preparation of allergenic extracts of the two chironomid species separately, 198 atopic patients attending an allergy clinic and 50 age matched controls were tested along with a routine panel of allergens to assess sensitization. RESULTS: The skin prick test (SPT) results revealed that 189 of the 198 patients (95.4%) demonstrated sensitization to both the chironomid species. Higher levels of total IgE was observed in atopic subjects than in the control group. INTERPRETATION & CONCLUSIONS: The results suggest that the chironomid midges Chironomus circumdatus and Polypedilum nubifer can elicit sensitization in humans. A potential risk for allergic reactions by susceptible individuals exists due to these chironomid species, owing to their abundance and chances of contact with human beings. Further studies may be initiated to characterize the nature of the allergens and to assess their clinical relevance.

Consequences of physical disturbance by tadpoles and snails on chironomid larvae.

Indirect interactions among community members impact on organisms. The effects of two snails, banded pond snail, Bellamya bengalensis (Lamarck), and Red-rimmed melania, Melanoides tuberculata (Müller), and tadpoles of Asian common toad, Duttaphrynus melanostictus (Schneider), on nonbiting midge larvae, Chironomus striatipennis Kieffer, were observed in experimental microcosm. Decrease in tube number and tube length of midge larvae was observed compared to control condition due to introduction of selected above mentioned organisms. The direct effects of non-predator organisms on the midge larvae are due to physical disturbance that destroys their tubes. This may result in vulnerability of midge larvae to predators in the wild. So the community structure may be altered by indirect effects, where one or more species, through their direct disturbance, indirectly change the abundance of other species.

ASSESSMENT OF PUPAL PRODUCTIVITY OF AEDES AND CO-OCCURRING MOSQUITOES IN KOLKATA, INDIA.

Monitoring of dengue vectors provide baseline information about the abundance and subsequent management strategy. An appraisal of mosquito abundance using dengue vectors as focal species was made in respect to Kolkata, India as geographical area. The data on immature abundance in the container larval habitats viz, earthen, porcelain and plastic materials were subjected to three-way factorial ANOVA, using months, habitats and species as variables. Similar tests were done on pupal weight and wing length. It was observed that Anopheles subpictus, Culex quinquefasciatus coexist with Ae. aegypti and Ae. albopictus in different container habitats, that varied with months and habitats. Ae. aegypti and Ae. albopictus were found in higher proportions in porcelain and plastic containers. In earthen containers a stable ratio of three mosquitoes was observed. Sex specific variations in pupal weight and wing length were noted in both species of Ae. aegypti and Ae. albopictus. The wing length of adult Aedes mosquitoes showed correspondence with pupal weight suggesting the use of pupal weight can be used as indicator of prospective adult body size. Although less known as container breeding, presence of An. subpictus and Cx. quinquefascistus along with Aedes indicates that availability of waste containers in environment increases risks of dengue and other mosquito borne diseases. The present habitat-based study calls for a strict vector management strategy to reduce the sources of ovipostion in various container habitats to minimize the mosquito vectors and thus potential risk of dengue and other mosquito borne diseases.

Pupal productivity of dengue vectors in Kolkata, India: implications for vector management.

BACKGROUND & OBJECTIVES: Entomological surveillance of the dengue vectors using pupal productivity as indicators can be helpful in effective management. On this basis, an assessment was made on the relative importance of the larval habitats of Aedes mosquitoes in Kolkata, an endemic zone for dengue in West Bengal, India. METHODS: Monthly collection of larvae and pupae of Aedes from larval habitats categorized as earthen, plastic and porcelain containers and tyres, was carried out from selected sites. Pupal weight was recorded and degree of sexual dimorphism was calculated. The data on pupal weight, sexual dimorphism and immature density were used for regression analysis. RESULTS: The number of positive sites for each type of larval habitats varied with months and mosquito species. Based on mean density per month, the plastic containers were the most productive habitats and the tyres were least productive for both Aedes species. The pupal weight of both Ae. aegypti and Ae. albopictus varied with the relative density and type of larval habitats. Significant differences in pupal productivity, positive sites and the proportion of pupae were observed in the habitats. Species-specific differences in the degree of dimorphism were noted with the females being larger in size than males, irrespective of the habitats. INTERPRETATION & CONCLUSIONS: Pupal productivity of Aedes mosquitoes in Kolkata differed in terms of the type of the larval habitats with the immature density affecting the body size of the adults. This habitat-based study is a pioneer effort considering Kolkata and calls for a management plan for source reduction of these habitats to minimize Aedes mosquitoes and thus potential risk of dengue.

Correlation between body size and fecundity in fish louse Argulus bengalensis Ramakrishna, 1951 (Crustacea: Branchiura).

The life history traits like fecundity and body size are useful predictors of life history strategies of organisms. The information on these aspects provided necessary input for control measures for ectoparasites. In view of this, the variations in the life history traits of the fish louse Argulus bengalensis Ramakrishna (1951) were assessed using age as an explanatory factor. The analyses revealed that the body weight (BW) is related to age in males as: y (BW) = 0.03 × (Age)-2.58: and in females as: y (BW) = 0.89 + 0.13x (Age). The body length and age relationship in males is observed as: y (BL) = 2.94 + 0.01x (Age) and in females as: y (BL) = 2.89 + 0.06x (Age). The degree of sexual dimorphism (DD) for BL is positively correlated (r = -0.358; df = 43; P < 0.001) with age while DD for BW is negatively correlated (r = -0.525; df = 43; P < 0.001) with age. The eggs/clutch remained between 02 and 43 for the 21st and 38th day old females. The fecundity as a function of age could be represented as: y (Eggs) = 1.62x (Age)-27.92. The increase in BW with age in female A. bengalensis favoured greater resource allocation for egg production, while in males it likely favours dispersal ability. Since body size and fecundity varied with age, the relative abundance and extent of infestation in fish host would vary with age composition of the population and recruitment of juveniles. The impacts of host specific variations on these features need to be tested further.

Household disposables as breeding habitats of dengue vectors: linking wastes and public health.

An assessment of the household wastes as larval habitats of the dengue vectors was made considering Kolkata, India, as geographical area. Wastes of four major categories, namely, earthen, porcelain, plastic and coconut shells were monitored for positive with immature of either Aedes aegypti or Aedes albopictus. Twenty six types of wastes with varying size and shape, resembling containers, were identified that hosted mosquito immature. The number of waste containers positive for Aedes immature varied significantly (P<0.05) with respect to location, type and month. The relative density of Aedes immature in the waste containers varied significantly (P<0.05) with the types and months. The significant interaction between the month, waste container types and density of Aedes immature suggest that the household wastes are important contributors to the maintenance of the population of Aedes mosquito in the city. Based on the relative density of mosquito immature in the wastes, cluster analysis allowed segregation and classification of the wastes and their importance as mosquito larval habitats. Apparently, the containers that are most frequently disposed off contributed largely to the sustenance of Aedes mosquito population in the city. This calls for a strict legislation towards disposal as well as enhanced management of the household wastes. A link between the wastes disposed and subsequent conversion to the mosquito larval habitats cautions for continuance of Aedes population and possibility of dengue epidemics if the existing management practices are not improved.

Efficacy of indigenous larvivorous fishes against Culex quinquefasciatus in the presence of alternative prey: implications for biological control.

BACKGROUND & OBJECTIVES: Indigenous larvivorous fishes bear potential for regulating vector mosquitoes through trophic interactions. The mosquito prey preference of five indigenous larvivorous fishes in the presence of alternative food items was assessed to highlight their use in mosquito vector management. METHODS: Laboratory experiments were carried out using the larvivorous fishes Ambassis (=Chanda) nama, Parambassis (=Chanda) ranga, Colisa fasciatus, Esomus danricus and Aplocheilus panchax, as predators and IV instar Culex quinquefasciatus larvae as target prey. Mosquito prey preference of these fishes in the presence of chironomid larvae, tubificid worms and artificial fish foods, in varied proportions, were assessed using preference index. RESULTS: The fishes consumed considerable amount of mosquito larvae both in absence and presence of alternative food items. However, the positive selectivity for mosquito larvae at all densities were significantly (p <0.05) affected by the alternative foods. The chironomid larvae and tubificid worms were consumed proportionately higher than expected (p <0.05), while the artificial fish food was consumed at lower than expected proportions (p <0.05). The niche overlap was significantly similar among the fish species suggesting likeliness in predation pattern and prey preference. INTERPRETATION & CONCLUSION: The results reflect that the alternative food items influence the mosquito prey selectivity and thus the efficacy of indigenous larvivorous fishes. While use of these fishes in the wetlands and allied mosquito larval habitats in different parts of the country is suggested, impact of the alternative prey may affect the successful regulation of mosquitoes. Assessment of appropriate predator-prey ratio under natural habitat conditions is recommended to enhance successful mosquito control by these fishes.

Habitat heterogeneity and prey selection of Aplocheilus panchax: an indigenous larvivorous fish.

OBJECTIVE: The ability of the native larvivorous fish Aplocheilus panchax (Hamilton, 1822) (Cyprinodontiformes: Aplocheilidae) as predator of mosquito larvae was assessed under laboratory conditions using multiple prey and habitat conditions. METHODS: The consumption of larvae of the mosquito Culex quinquefasciatus Say 1823 (Diptera: Culicidae) by A. panchax was evaluated in the presence of tubificid worms and chironomid larvae under complex and simple habitat conditions. The number of mosquito larvae consumed in comparison to other prey types was noted and an index of prey selectivity was used to evaluate the preference for mosquito larvae. RESULTS: Aphlocheilus panchax consumed 53 to 65 mosquito larvae in a three hour feeding bout contrast to 29- 38 tubificid worms and 43-62 chironomid larvae depending on the habitat conditions. The prey consumption differed significantly between the habitats and the prey type. The index of prey selectivity was positive for Cx. quinquefasciatus larvae over other alternative prey in all the habitat conditions. CONCLUSION: It is apparent from the study that the larvivorous fish A. panchax can be employed for biological regulation of mosquitoes in rice -fields and similar wetlands where the multiple prey choices are available under complex habitat conditions. However, field studies including other prey species will be required to substantiate this finding.

An assessment of macroinvertebrate assemblages in mosquito larval habitats--space and diversity relationship.

The aquatic bodies designated as mosquito larval habitats are diverse in size and species composition. The macroinvertebrate predators in these habitats are elements that influence the abundance of mosquito species, providing a basis for biological control. Assessment of species assemblage in these habitats will indicate the possible variations in the resource exploitation and trophic interactions and, therefore, can help to frame biological control strategies more appropriately. In the present study, the species composition is being investigated in five different mosquito larval habitats at a spatial scale. A random sample of 80 each of the habitats, grouped as either small or large, was analyzed in respect to the macroinvertebrate species assemblage. The species composition in the habitats was noted to be an increasing function of habitat size (species number = 1.653 + 0.819 habitat size) and, thus, the diversity. The relative abundance of the mosquito immatures varied with the habitat, and the number of useful predator taxa was higher in the larger habitats. In the smaller habitats-plastic and earthen structures and sewage drains, the relative and absolute number of mosquito immatures per sampling unit were significantly higher than the pond and rice field habitats. This was evident in the cluster analysis where the smaller habitats were more related than the larger habitats. The principal component analysis on the species diversity yielded four and six components, respectively, for the smaller and larger habitats for explaining the observed variance of species abundance. The species composition in the habitats was consistent with the earlier findings and support that the abundance of coexisting macroinvertebrate species regulates the relative load of mosquito immatures in the habitats. The findings of this study may be further tested to deduce the relative importance of the habitats in terms of the productivity of mosquito immatures at a temporal scale.