Nabaneeta Saha

Microbial siderophores: a mini review.

Iron is one of the major limiting factors and essential nutrients of microbial life. Since in nature it is not readily available in the preferred form, microorganisms produce small high affinity chelating molecules called siderophores for its acquisition. Microorganisms produce a wide variety of siderophores controlled at the molecular level by different genes to accumulate, mobilize and transport iron for metabolism. Siderophores also play a critical role in the expression of virulence and development of biofilms by different microbes. Apart from maintaining microbial life, siderophores can be harnessed for the sustainability of human, animals and plants. With the advent of modern molecular tools, a major breakthrough is taking place in the understanding of the multifaceted role of siderophores in nature. This mini review is intended to provide a general overview on siderophore along with its role and applications.

A comparative study of predation of three aquatic heteropteran bugs on Culex quinquefasciatus larvae

The aquatic bugs Anisops bouvieri Kirkaldy 1704 (Heteroptera: Notonectidae), Diplonychus (=Sphaerodema) rusticus Fabricius 1781, and Diplonychus annulatus Fabricius 1781 (Heteroptera: Belostomatidae) are common members of the freshwater insect communities of the East Calcutta Wetlands along the eastern fringe of Kolkata, India. These insects are established predators of dipteran larvae and other organisms. A comparative account of their predatory efficiency was made using larvae of Culex quinquefasciatus Say 1823 in the laboratory. It was revealed that a single adult of A. bouvieri could consume 28–34 fourth-instar mosquito larvae per day, D. rusticus 11–87 fourth-instar mosquito larvae per day, and D. annulatus 33–122 fourth-instar mosquito larvae per day, depending upon the prey and predator densities. The mean predation rate of A. bouvieri and D. annulatus remained stable over a 6-day feeding period but varied for D. rusticus. The predatory impact (PI) values were 14.77–17.31, 46.9–55.73, and 61.74–72.72 larvae/day for A. bouvieri, D. rusticus, and D. annulatus, respectively. Compared to these, the clearance rate (CR) value range was 9.06–13.25 for A. bouvieri, 13.64–15.99 for D. rusticus, and 13.50–16.52 larvae l/day/predator for D. annulatus. The values of mutual interference, “m,” remained 0.06–0.78 for A. bouvieri, 0.003–0.25 for D. rusticus, and 0.09–0.27 for D. annulatus, and did not vary between the days. The difference in predatory efficiency, CR, and PI values varied significantly among the three predators, indicating the possible difference in the function as predators occupying the same guild. It can be assumed that these predators play an important role in larval population regulation of mosquitoes and thereby impart an effect on species composition and interactions in the aquatic insect communities of the wetlands and other similar habitats where they occur.

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.

Prey preferences of aquatic insects: potential implications for the regulation of wetland mosquitoes

Wetlands are potential sites for mosquito breeding and are thus important in the context of public health. The use of chemical and microbial controls is constrained in wetlands in view of their potential impact on the diverse biota. Biological control using generalist aquatic insects can be effective, provided a preference for mosquito larvae is exhibited. The mosquito prey preferences of water bugs and larvae of odonate species were evaluated using chironomid larvae, fish fingerlings and tadpoles as alternative prey. Manlys selectivity (αi) values with 95% confidence intervals (CIs) were estimated to judge prey preference patterns. Multivariate analysis of variance (manova) and standardized canonical coefficients were used to test the effects of density on prey selectivity. The αi values indicated a significant preference (P < 0.05) in all of the insect predators tested for mosquito larvae over the alternative prey as a density‐dependent function. On a comparative scale, chironomid larvae had the highest impact as alternative prey. In a multiple‐prey experiment, predators showed a similar pattern of preference for mosquito larvae over alternative prey, reflecting a significant (P < 0.05) niche overlap. The results suggest that, in a laboratory setting, these insect predators can effectively reduce mosquito density in the presence of multiple alternative prey.

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.

Mosquito Prey Vulnerability in Intraguild Predation Between Ranatra filiformis and Anisops bouvieri: Implications in Biological Control

Wetlands are common habitats of a range of predatory water bugs (Heteroptera) constituting a guild that exhibit similar dietary choice including mosquito. Differences in body size and micro habitat preference among the heteropteran guild members provide a fair possibility of intraguild predation that can influence the regulatory effect on the prey species. This proposition was tested under laboratory conditions, using varying density of Ranatra filiformis (IG predator) and Anisops bouvieri (IG prey) as predators against mosquito larvae as shared prey. Compared to single predator system, mosquito larvae were proportionately less vulnerable to predation in intraguild predation (IGP), at low density of shared prey. In IGP system, vulnerability of shared prey increased with increase in density accompanied by a decline in mortality of IG prey. The mean mortality of shared prey and IG prey increased with the density of IG predator. It was apparent that the mosquito prey vulnerability was enhanced with increase in density of mosquito and R. filiformis while reducing the mortality of A. bouvieri partly. The interaction between R. filiformis and A. bouvieri as a part of IGP system indicate about the possible mechanism of coexistence of predators and prey in the wetlands. The density dependent effects on reduction and enhancement of shared prey (mosquito) mortality indicate that appropriate ratio of R. filiformis, A. bouvieri and mosquito larvae will be required to make biological regulation of wetland mosquitoes feasible.

Intraguild Predation in Heteroptera: Effects of Density and Predator Identity on Dipteran Prey

In tropical freshwaters, different species of water bugs (Heteroptera) constitute a guild sharing similar prey resources including chironomid and mosquito larvae. Assuming possibilities of intraguild predation (IGP) among the constituent members, an attempt was made to evaluate the effects of prey and predator density on the mortality of mosquito and chironomid larvae (shared prey), using Laccotrephes griseus Guérin-Méneville (Hemiptera: Nepidae) and Ranatra filiformis Fabricius (Hemiptera: Nepidae) as IG predators and Anisops bouvieri Kirkaldy (Hemiptera: Notonectidae) as IG prey. The predation on mosquito and chironomid larvae varied with the density and combinations of the predators. When present as conspecific IG predators, L. griseus exhibited greater effect on the prey mortality than R. filiformis. The effects on shared prey suggest that the two predators are not substitutable in terms of the effect on the shared prey mortality. The mortality of A. bouvieri (IG prey) at low shared prey density was significantly different (p < 0.05) from high shared prey density. In view of predatory effect of the heteropteran predators on the dipteran larvae, the results suggest possible interference by the presence of A. bouvieri as an intermediate predator. It seems that the presence of heteropteran predators including A. bouvieri as IG prey may benefit the dipteran prey under situations when the density is low in tropical waters. The intensity of the predatory effect may differ based on the species composition at IG predator level. For mosquito biological control, the interactions between the predators may not be substitutable and are independent in their effects.