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.

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.