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 = 0.801 x 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.

The life table characteristics of the invasive snail Physa acuta were assessed in the laboratory using the individuals occurring in a newly colonised area in Burdwan, West Bengal, India. Using the changes in the shell length and the body weight of the snails as surrogate, the population growth of the snails was estimated along with longevity and the fecundity schedule. The cohort of P. acuta lived for a maximum of 22 weeks with a life expectancy (ex) of 7.27 weeks and the age-specific survivorship being 0.825. Increment of the shell length of the snails complied with the von Bertalanffy growth equation, lt = 11.75(1 − exp−0.17(t−0.06)), and the observed and the expected data of the length at time t (lt) did not vary significantly (z score = 0.230; P = 0.818; n=20 pairs). Following attainment of sexual maturity between 28 and 42 days, oviposition continued till 20 weeks time, with 0.1-10 eggs laid by each individual. The eggs present per capsule remained between 01 and 11, whilst the net reproductive rate (R0), intrinsic rate of increase (rm) and the finite rate of increase (λ) were 116.07, 0.1 and 1.11, respectively. The observations are similar to those made earlier on the same species but from African and South American continents. The results of the present observation are pioneer in providing the initial studies about the life history of the invasive snail P. acuta in Indian context. Using the present information as a basis, further studies including long-term population monitoring should be initiated to understand the effects of the invasive snail P. acuta in the freshwater ecosystem of West Bengal, India.

Consequences of larval competition at the population level provide explanation for the differences in relative abundance of <em>Aedes aegypti</em> and <em>Aedes</em> <em>albopictus</em> in different geographical regions. The outcome of competition is assessed through the estimates of the life history traits as a response to varying density and resource available for larval development. In the present study, variations in the life history traits due to density-dependent intra- and inter- specific competition involving <em>A. aegypti</em> and <em>A. albopictus</em> were assessed following the minimalist model. The instar-I larvae (0-day old F2 generation) of both <em>Aedes</em> species were reared to the adult stages using the initial rearing density of 1, 2, 4 and 6 (individuals/10ml) in multiple replicates. The age at pupation, pupal weight, adult weight and adult wing length of the individuals were considered as the response variables and surrogates of estimating the competitive interactions. Density dependent variations in the competitive interactions were evident for both the mosquitoes with reference to the selected life history traits. In <em>A. aegypti,</em> the life history traits varied with the levels of competition, which was not observed for <em>A. albopictus</em>. Although the density levels considered in the present instance were lower than in earlier studies, the observations were similar, with <em>A. albopictus</em> being competitively superior. It appears that irrespective of the density levels, interspecific competition affects <em>A. aegypti</em> and thus may bear population level consequences and overall abundance in the areas where both species are present.

ABSTRACT. Competitive interactions between coexistingAedes aegypti and Ae. albopictus have been implied as a crucial factor shaping life history traits and population characteristics. The overlap in resource requirements and similarities in the life history strategies of the two Aedes mosquitoes form a basis for competitive interactions. In the present study, the role of the food quality of the larval habitats in influencing the outcome of competition between Ae. aegypti and Ae. albopictus is evaluated to highlight food quality as a basis for asymmetric competitive outcomes. Instar I larvae of the two mosquitoes were reared using conspecifics or heterospecifics of constant size and equal ratio with four different food types: boiled rice, boiled pulses, a mixture of boiled rice and pulses, and fish food. Competitive interactions were evaluated using age at pupation (AP), pupal weight (PW), dry adult weight (AW) and wing length (WL) with respect to intra-and interspecific competition for the two sexes of each mosquito species. The results show that Ae. albopictus developed faster but achieved a smaller size compared to Ae. aegypti under interspecific competition conditions, the extent of the difference varying significantly with the food type. Given the variety of food resources available in the small container larval habitats, the results of the study imply that food quality may act differentially with respect to larval development and adult body size, depending on the conspecifics or heterospecifics and on the sex of the species concerned. The dominance of one species over the other may also be a consequence of the resource utilization pattern that varies in the larval habitats.

The predatory snail Huttonella bicolor (Hutton 1834) (Gastropda: Streptaxidae) was encountered along with Allopeas gracile (Hutton 1834) (Gastropoda: Subulinidae) during a survey of small land snail species from several terrestrial habitats in Kolkata, India. An evaluation of the predation of H. bicolor as a function of prey size and predator density was carried out using A. gracile as a model prey snail. The predatory interactions were noted with an increasing ratio of 1, 2 and 4 H. bicolor against 10 A. gracile of varied size classes in a defined terrarium. At the end of a 48 h period of exposure, H. bicolor was observed to consume on an average 5.32 ± 0.50 snails depending on the size class and the predator density. The predation pattern varied significantly with the prey size class, as revealed through the logistic equation, y (prey-consumed) = 1 / (1 + exp (-(0.97–0.71*size class-prey))). In a separate experiment, it was observed that the presence of H. bicolor induced a reduction in the fecundity in A. gracile, as revealed through the logistic regression, y (egg laid) = 1 / (1 + exp(-(3.45–0.67*predator-density))). The direct effect of predation and indirect effect of oviposition reduction reflect the efficacy of H. bicolor on population regulation of A. gracile. In view of conservation biological control, the use of the snail H. bicolor as a biocontrol agent may prove beneficial in situations where A. gracile is a pest.