S. N. Tikar

Resistance Status of the Malaria Vector Mosquitoes, Anopheles stephensi and Anopheles subpictus Towards Adulticides and Larvicides in Arid and Semi-Arid Areas of India

Abstract Susceptibility studies of malaria vectors Anopheles stephensi Liston (Diptera: Culicidae) and An. subpictus Grassi collected during 2004–2007 from various locations of Arid and Semi-Arid Zone of India were conducted by adulticide bioassay of DDT, malathion, deltamethrin and larvicide bioassay of fenthion, temephos, chlorpyriphos and malathion using diagnostic doses. Both species from all locations exhibited variable resistance to DDT and malathion from majority of location. Adults of both the species were susceptible to Deltamethrin. Larvae of both the Anopheline species showed some evidence of resistance to chlorpyriphos followed by fenthion whereas susceptible to temephos and malathion.

Susceptibility of immature stages of Aedes (Stegomyia) aegypti; vector of dengue and chikungunya to insecticides from India

Susceptibility of Aedes aegypti to some insecticides in different geographic areas was conducted during dengue and chikungunya outbreak. At present, the only method of preventing dengue and chikungunya is to control the vector, which is the weakest link in vector-borne diseases. In our study, the susceptibility of A. aegypti collected from urban areas of Delhi, Mumbai, Jodhpur, Chennai and Coimbatore was evaluated against temephos, fenthion, malathion and DDT. The A. aegypti from different locations exhibited 0.33–7.11, 0.36–3.00, 0.65–2.84 and 2.16–20.8 fold more lethal concentration value of 50% (LC50) to temephos, fenthion, malathion and DDT, respectively, compared to susceptible reference strain. The result reveals that A. aegypti from various locations studied are still susceptible to temephos, fenthion and malathion, whereas low level of DDT resistance was noticed in field-collected A. aegypti. Amongst the insecticides tested, temephos was found to be relatively more effective in controlling A. aegypti, followed by fenthion, malathion and DDT.

Midgut Microbial Community of Culex quinquefasciatus Mosquito Populations from India

The mosquito Culex quinquefasciatus is a ubiquitous species that serves as a major vector for west nile virus and lymphatic filariasis. Ingestion of bloodmeal by females triggers a series of physiological processes in the midgut and also exposes them to infection by these pathogens. The bacteria normally harbored in the midgut are known to influence physiology and can also alter the response to various pathogens. The midgut bacteria in female Cx. quinquefasciatus mosquitoes collected over a large geographical area from India was studied. Examination of 16S ribosomal DNA amplicons from culturable microflora revealed the presence of 83 bacterial species belonging to 31 bacterial genera. All of these species belong to three phyla i.e. Proteobacteria, Firmicutes and Actinobacteria. Phylum Proteobacteria was the most dominant phylum (37 species), followed by Firmicutes (33 species) and Actinobacteria (13 species). Phylum Proteobacteria, was dominated by members of γ-proteobacteria class. The genus Staphylococcus was the largest genus represented by 11 species whereas Enterobacter was the most prevalent genus and recovered from all the field stations except Leh. Highest bacterial prevalence was observed from Bhuj (22 species) followed by Nagrota (18 species), Masimpur (18 species) and Hathigarh (16 species). Whereas, least species were observed from Leh (8 species). It has been observed that individual mosquito harbor extremely diverse gut bacteria and have very small overlap bacterial taxa in their gut. This variation in midgut microbiota may be one of the factors responsible for variation in disease transmission rates or vector competence within mosquito population. The present data strongly encourage further investigations to verify the potential role of the detected bacteria in mosquito for the transmission of lymphatic filariasis and west nile virus. To the best of our knowledge this is the first study on midgut microbiota of wild Cx. quinquefasciatus from over a large geographical area.

Genetic variability in geographical populations of Culex quinquefasciatus Say (Diptera: Culicidae) from India based on random amplified polymorphic DNA analysis.

Genetic variability and environmental factors may influence the refractiveness, propagation of pathogen and transmission of disease. Random amplified polymorphic DNA (RAPD) is one of the widely used molecular markers for population genetic diversity studies. In present study, RAPD is used to ascertain the genetic variability in Culex quinquefasciatus populations collected from various Indian geographical locations. Out of 50 RAPD primers screened, 14 primers exhibited clear, concrete and distinct banding pattern showing up to 100% polymorphism. Primer OPBD3 was tested with DNA of 14 geographical populations from India (including one laboratory population) showed 21 loci representing 14 populations with 100% polymorphism. The genetic diversity among the populations indicated the Shannon index (I) and gene diversity index (H(ST)), 0.48 and 0.31, respectively among the population, displaying rich genetic variation among the Cx. quinquefasciatus populations. Consensus tree showed two clusters indicating the genetic variation among the various geographical populations. The findings of this study may be useful to understand the population variation under different ecological conditions and development of effective vector management strategies.

Variations in life tables of geographically isolated strains of the mosquito Culex quinquefasciatus

Variations in the life tables and other biological attributes of four strains of Culex quinquefasciatus Say (Diptera: Culicidae) from geographically isolated regions of India that had been reared to the fifth generation in the laboratory were assessed under a standardized rearing regime under constant laboratory conditions. Two strains from arid habitats [Jodhpur (JD) and Bikaner (BKN)], one from a semi‐arid inland habitat [Bathinda (BTH)], one from a semi‐arid coastal habitat [Jamnagar (JMN)] and a standard laboratory strain (LAB) were compared. Horizontal life‐table parameters were measured for each strain. Egg mortality ranged from 4.4% (JD and BTH) to 19.5% (BKN). The lowest rate of adult emergence and highest female : male ratio were found in BKN, and the highest rate of adult emergence and lowest female : male ratio were recorded in BTH. The egg‐hatching period was longest in BTH and shortest in LAB. The duration from oviposition to adult emergence was longest in JD and shortest in LAB. Females lived longer than males in all strains. The net reproductive rates (R0) of all field‐derived strains (122.9–162.2) differed significantly between strains and were significantly greater than that of LAB (107.6). Similarly, both the intrinsic rate of increase (rm) and finite rate of increase (λ) were found to be lower in LAB than in the field strains, but the mean generation time (T) and doubling time (DT) were longest in LAB. For several life‐table attributes, JD and BTH clustered together and were more similar to JMN than to BKN and LAB. The results indicate that BTH, BKN and JD can be characterized as r‐strategists, more so than JMN. Overall fecundity increased with age. Differences in annual temperature ranges and mean annual rainfall between locations were positively correlated (r = 0.46–0.97) with egg production, female life expectancy, R0, rm, λ and T. The results suggest that strains of Cx. quinquefasciatus from different geographical areas with contrasting habitats vary in their survival and reproductive strategies accordingly.

Molecular phylogenetic study of Culex quinquefasciatus mosquito from different geographical regions of India using 16S rRNA gene sequences.

Culex quinquefasciatus is a major vector of filariasis and various encephalitis in India and worldwide. Vector control remains the most successful strategy for the suppression of mosquito borne diseases. The genetic structure of vector populations in terms of insecticide resistance and susceptibility or refractoriness to infection may possibly vary. To exploit the genetic variability in vector population could pave the path for the alternative strategies in vector management. The sequences of ribosomal RNA molecules have been widely used for such studies. Here, we examined the molecular phylogenetic relationship among the Cx. quinquefasciatus collected from different geographical regions of India, using 16S ribosomal RNA (16S rRNA) gene nucleotide sequences. The distances among the species were measured using Pearson correlation; the Neighbor-Joining (NJ) method was used for the clustering with appropriate bootstrap values using Data Analysis in Molecular Biology and Evolution (DAMBE) software. The results revealed that the populations are genetically diverse. Based on the distance values and the tree topology on the basis of 16S rRNA sequences reflected the clear biogeographical and geoclimatic pattern among the different geographical populations from India.

Synthesis of some novel phosphorylated and thiophosphorylated benzimidazoles and benzothiazoles and their evaluation for larvicidal potential to Aedes albopictus and Culex quinquefasciatus.

Series of benzimidazole and benzothiazole linked phosphoramidates and phosphoramidothioates (5a-j) and benzimidazole linked phenylphosphoramidates and phenylphosphoramidothioates (10a-e) were synthesized. The title compounds were preliminary screened for mosquito larvicidal properties against Aedes albopictus and Culex quinquefasciatus at different concentration from 40 to 5 mg/L. Among the screened compounds three compounds revealed potential larvicidal effects with 100% mortality in the order of 10e>5j>5e. Compound 10e was found to be the most toxic compound to Ae. albopictus and Cx. quinquefasciatus. The LC50 of 10e against Ae. albopictus was found to be 6.42 and 5.25 mg/L at 24 and 48 h, respectively, whereas it was 7.01 and 3.88 mg/L, respectively in Cx. quinquefasciatus. Temephos was used as positive control.

Molecular Characterization of Migratory Locust, Locusta Migratoria Linn. (Orthoptera: Acrididae: Oedipodinae) From Ladakh Region, India

Outbreak of Locusta migratoria occurred in Ladakh during 2006 which was mainly responsible for devastation of large pasture land and agriculture, which seriously affected phasmina wool industry. Molecular characterization of specimens of Locusta migratoria collected from the Loma area of Ladakh (J &K) revealed that they belong to the subspecies Locusta migratoria migratoria . Mitochondrial 16S r RNA gene sequencing showed 99 % similarity with the subspecies migratoria and 98% similarity with subspecies manilensis .

Fly ash-based Bacillus thuringiensis israelensis formulation: An ecofriendly approach

Vectors play an important role in disease transmission, globally. Despite various advancements in vector management, mosquitoes are still prime vectors of dreadful diseases those influence human health and economy as well. Insecticides have been the most preferred and commonly used tool in the vector management because of their rapid action and visible effects. Although several insecticides in different formulations are in existence, their usage over the years has arisen several problems such as reduced response by vectors in the form of resistance phenomenon and their negative impact on the environment.

The effect of aryl hydrazono ester containing dipeptides (AHEDs) on mosquito egg-laying behaviour

A series of novel aryl hydrazono ester containing dipeptides (AHEDs) were synthesized by using polystyrene-supported 2-isobutoxy-1-isobutoxycarbonyl-1,2-dihydro-quinoline (PS-IIDQ) to study the oviposition responses in Aedes albopictus mosquitoes at 1 ppm and 10 ppm concentrations. Two different synthetic routes have been optimized successfully for the synthesis of target compounds. The pheromone and semiochemical mediated oviposition activity of mosquitoes is a well-known aspect in mosquito behavioral ecology. Structural elucidation of synthesized AHED was achieved by spectral analysis. In a dual choice experiment, the oviposition responses of gravid A. albopictus were evaluated against AHED-1 to AHED-15 at two different concentrations. Among all the compounds, AHED-6 showed the maximum oviposition attractant activity with an oviposition activity index (OAI) of +0.538 at 10 ppm. In contrast to this, AHED-13 exhibited the highest oviposition deterrent activity with an OAI of −0.774 at 1 ppm.