Screening of some weeds for larvicidal activity against Aedes albopictus, a vector of dengue and chikungunya.

BACKGROUND & OBJECTIVES: Screening of crude extracts of plants facilitates the establishment of highly effective extract for mosquito control. This practice should be preferred before in depth study of plant extracts rather than spending much efforts and energy in detailed examinations for practically ineffective extracts. In this study, leaf powders of four weed plants were used for the quick screening of effective plant extract as larvicide against III instar larvae of Aedes albopictus Skuse. At the same time, effect of different seasons on the larvicidal efficacy of plants and selection of proper solvents for further investigation were also studied. METHODS: Leaves of Vernonia cinerea, Prosopis juliflora, Hyptis suaveolens and Malvastrum coromandelianum plants were collected in summer, winter and rainy seasons from Madhya Pradesh region (India). To assess the larvicidal efficacy the suspensions of leaf powders in different solvents (isopropanol, methanol, acetone, dimethylsulfoxide and water) were used for larvicidal bioassay. The mortality counts were made after 24 h and the LC50 and LC90 values were calculated. RESULTS: Results showed that leaf powder of V. cinerea in acetone collected during summer showed highest efficacy with LC50 value of 0.22 g/l and LC90 of 0.96 g/l followed by methanolic solution of P. juliflora with LC50 of 0.44 g/l and LC90 value as 1.85 g/l. Amongst all solvents, leaf powder in acetone; while among seasons, summer collected plant materials were found to be more effective larvicides as compared to others. INTERPRETATION & CONCLUSION: Summer and winter collected leaves of V. cinerea and P. juliflora dissolved in the solvents of medium polarity range showed significant larval toxicity and thus suggests a detailed study on these plants as potential larval control agents.

Control of Aedes aegypti and Ae. albopictus, the vectors of dengue and chikungunya, by using pheromone C21 with an insect growth regulator: Results of multicentric trials from 2007-12 in India.

BACKGROUND & OBJECTIVES: Aedes mosquito control has gained much importance nowadays in view of rise in number of reported cases of dengue and chikungunya in India and other countries. In the present study, C21 attracticide (containing a pheromone and an insect growth regulator­IGR, developed by Defence Research and Development Establishment (DRDE), Gwalior, India was tested for its feasibility for surveillance and control of Aedes mosquito in a multicentric mode from October 2007 to June 2012 in urban (Delhi, and Bengaluru district, Karnataka) and suburban (Alappuzha district, Kerala) settings of the country in three phases. METHODS: Across the randomly selected households in each study area, two to four containers treated with attracticide (experimental) and untreated (control) were placed and monitored by trained surveillance workers on weekly/ fortnightly basis for determining the presence of eggs, larvae and pupae. Container positivity, percent larvae, egg and pupae collected were determined during different phases and analyzed statistically using SPSS 18.0. RESULTS: Container positivity was found statistically significant at Bengaluru and Alappuzha, Kerala while in Delhi, it was found non-significant. Eggs collected from experimental containers were significantly higher in comparison to control at all the locations except Delhi. Also larvae collected from control containers were significantly higher at all the locations except Bengaluru. Pupae collected from control containers remained significantly higher at all the locations as no pupal formation was recorded from experimental containers. INTERPRETATION & CONCLUSION: The use of C21 attracticide hampered pupal formation, thus inhibiting adult population in the study areas. The study established that C21 attracticide was efficacious in the field conditions and has potential for use in surveillance and management of dengue and chikungunya mosquitoes.

Oviposition deterrent activity of three mosquito repellents diethyl phenyl acetamide (DEPA), diethyl m toluamide (DEET), and diethyl benzamide (DEB) on Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus.

Oviposition deterrent activity of three mosquito repellents namely diethyl phenyl acetamide (DEPA), diethyl benzamide (DEB) along with diethyl toluamide (DEET) was studied in the laboratory against Aedes aegypti, A. albopictus, and Culex quinquefasciatus mosquitoes. All the repellents evaluated at three log concentrations 0.1, 0.01, and 0.001% in comparison with control by dual choice method. The oviposition response and oviposition activity index (OAI) was estimated by counting number of eggs laid in both the treatment and control. Mean OAI determined for A. aegypti was in the range of -0.23 to +0.22, -0.3 to +0.27, and +0.04 to +0.33 for DEPA, DEET, and DEB, respectively, whereas it was -0.77 to -0.035, -0.92 to +0.001, and -0.77 to -0.07 for A. albopictus and -0.927 to -0.251, -1 to -0.41, and -0.94 to -0.17 for C. quinquefasciatus. The oviposition deterrent activity was observed in the order of DEET > DEPA > DEB. Similarly, the response of species toward the repellents as oviposition deterrent was in the trend of C. quinquefasciatus > A. albopictus > A. aegypti. The finding suggests potential role of mosquito repellents as oviposition deterrent.

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 (R(0) ) 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 (r(m) ) 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, R(0) , r(m) , 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.

Resistance status of the malaria vector mosquitoes, Anopheles stephensi and Anopheles subpictus towards adulticides and larvicides in arid and semi-arid areas of India.

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.

Temephos-induced resistance in Aedes aegypti and its cross-resistance studies to certain insecticides from India.

A temephos-induced resistance in Aedes aegypti that was developed for 24 generations exhibited 20.3-fold resistance as compared to susceptible strain. The diagnostic dose of temephos 0.02 mg/l exhibited gradual decrease in larval mortality with the progression of generations. An operational dose (1 mg/l) exhibited the LT(50) value of 41.42 min in the susceptible population, whereas the value of the resistant population increased to 72.62, 108.86, 122.34, 182.03, 244.82 and 304.86 min in the fourth, eighth, 12th, 16th, 20th and 24th generation, respectively. The study carried out showed 120 min as the cut-off limit for differentiation between susceptible and resistant A. aegypti. Cross-resistance studies showed a varied degree of cross-resistance to fenthion, chlorpyrifos, malathion and DDT, whereas comparatively higher cross-resistance was observed to chlorpyrifos. Study on diagnostic doses of insecticides to A. aegypti females indicated a gradual decrease in adult mortality at every eighth generation as compared to susceptible population when exposed to malathion 0.8%, fenthion 0.25%, DDT 4%, permethrin 0.25% and temephos 6.5%, whereas little or no change in mortality when exposed to lambda-cyhalothrin 0.03% and propoxur 0.1%, was observed. Thus, the expression of larval resistance was observed in adult stages also.

Temperature-dependent variation in toxicity of insecticides against Earias vitella (Lepidoptera: Noctuidae).

The toxicity of synthetic pyrethroids was found to be negatively correlated with temperature, whereas contrasting correlation was observed with the toxicity of organophosphorous compounds chlorpyriphos and quinalphos, which was most toxic at higher temperature. A similar phenomenon was observed in endosulfan at higher temperature and humidity combination. The insecticide molecules indoxacarb and spinosad were effective among the insecticides tested. Indoxacarb was effective at lower temperature, and spinosad was effective at all the temperature and relative humidity combinations with minor difference in LD50 values. During both the years, however, the levels of resistance were higher in second year compared with previous year.

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.

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.

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.