Encephalitis Vector Research Articles

Nanoformulation of poly(ethylene glycol) polymerized organic insect repellent by PIT emulsification method and its application for Japanese encephalitis vector control

The utilization of increased dosage of insect repellents to overcome mosquito resistance has raised environmental concerns globally. In accord to this, we have formulated an efficacious, water-dispersive, nanometric formulation of a poor water-soluble insect repellent, diethylphenylacetamide (DEPA) by poly(ethylene glycol) (PEG) polymerization followed by PIT emulsification method. The critical micelle concentration of PEG in the spontaneously emulsified conventional DEPA droplets was determined, based on the droplets physical stability. Subjecting them to PIT emulsification yielded monodispersed polymeric nanomicelles of DEPA (Nano DEPA) with hydrodynamic mean diameter of 153.74nm. The high-resolution scanning and transmission electron microscopic studies revealed the characteristic core–shell structure of micelle. The comparative efficacy of Bulk DEPA and Nano DEPA was evaluated by larvicidal and WHO cone bioassay against the Japanese encephalitis vector Culex tritaeniorhynchus. The median lethal concentrations (48h) for 3rd instars C. tritaeniorhynchus larvae were found to be 0.416mg/L for Bulk DEPA and 0.052mg/L for Nano DEPA, respectively. The median knockdown concentrations (60min) for the two to three-day-old, sucrose-fed, female adult mosquitoes were 5.372% (v/v) and 3.471% (v/v) for Bulk and Nano DEPA, respectively. Further investigation by histopathological and biochemical studies propound that Nano DEPA exerted better bioefficacy as comparative to its bulk form even at minimal exposure concentrations. Hence, Nano DEPA will serve as an effective alternate in controlling the vector expansion with reduced dosage.

Study of mosquito fauna in rice ecosystems around Hanoi, Northern Vietnam

Species of the Culex vishnui subgroup, Cx. fuscocephala and Cx. gelidus, which are known Japanese encephalitis (JE) vectors, are distributed in rice agroecosystems in Asian countries. Hence, although ecological studies of rice agroecosystems in northern Vietnam are necessary, very few integrated studies of breeding habitats of mosquitoes, including JE vectors, have been conducted. We carried out a field study and investigated the mosquito fauna in six rice production areas in northern Vietnam during the rainy and dry seasons of 2009. Mosquitoes and potential mosquito predators were collected from aquatic habitats by using larval dippers. We collected 1780 Culex individuals (including 254 Cx. tritaeniorhynchus; 113 Cx. vishnui, 58 Cx. vishnui complex, consisting of Cx. vishnui and Cx. pseudovishnui; 12 Cx. gelidus; 1 Cx. bitaeniorhynchus; and 1 Cx. fuscocephala), 148 Anopheles individuals (including 5 An. vagus), 1 Mansonia annulifera, and 1 Mimomyia chamberlaini during the rainy season. During the dry season, we collected 176 Culex individuals (including 33 Cx. vishnui, 24 Cx. tritaeniorhynchus, 8 Cx. vishnui complex, and 1 Cx. gelidus) and 186 Anopheles individuals (including 9 An. tessellatus, 2 An. kochi, and 2 An. barbumbrosus). We found mosquitoes in all aquatic habitats, namely, rice fields, ditches, ponds, wetlands, irrigation canals, and rice nurseries, and Cx. tritaeniorhynchus and Cx. vishnui complex were found in all the above six areas. Heteroptera such as Micronecta, Veliidae, and Pleidae were abundant and widely distributed in both the seasons. The abundance of mosquito larvae was higher in the rice fields, ditches, and ponds during the rainy season than during the dry season. Cx. tritaeniorhynchus, Cx. vishnui complex, Cx. fuscocephala, and Cx. gelidus were abundant in rice agroecosystems (rice fields, ditches, ponds, and wetlands) in northern Vietnam, and their abundance was high during the rainy season. These findings deepen our understanding of mosquito ecology and strengthen mosquito control strategies to be applied in rice ecosystems Vietnam in the future.

Larval control of <i>Culex vishnui</i> group through bio-active fraction of traveller's tree, <i>Ravenala madagascariensis Sonn</i>. (Strelitziaceae)

Background and objectives: Due to ever increasing resistance against synthetic insecticides, mosquito control is fetching a serious problem all over the world. It is imperative to manage the vector population to conquer the mosquito born diseases. The present study was carried out to assess the target specific larvicidal activity of Ravenala madagascariensis against Culex vishnui group, the vector of Japanese Encephalitis. Methods: Crude extracts of R. madagascariensis matureleaves (foliages) ranging from 0.1% to 1.0% concentrations were tested against all the larval instars of Cx. vishnui group. Solvent extractions of matureleaves were carried out through three different solvents viz. petroleum ether, ethyl acetate and acetone from non-polar to polar trend. Larvicidal activities of the active fractions were examined against all the larval instars with graded concentrations ranging from 50 ppm to 250 ppm. LC 50 and LC 90 values were determined by log-probit analyses. Further statistical justifications were done through ANOVA analyses. Effectiveness of the bioactive fractions against non-target populations was executed in laboratory conditions. Phytochemical screening of leaf extract was also carried out. Result and Discussion: At 72 hours post-exposure, highest mortality (100%) with crude extract was found at 0.5% concentrations against all the instars. Amongst the three bioactive fractions, ethyl acetate extractives showed the highest larval mortality. After 72 hours of exposure, 200 ppm and 250 ppm concentration showed 100% mortality against 1 st and 2 nd instars larvae respectively. A 96.00% reduction in 3 rd instars mosquito population was recorded after 72 hours at 250 ppm concentration. However, 4 th instars larvae were subjected to only 84.00% reduction with these experimental set up and at 250 ppm concentration. The results of log probit analyses (95% confidence level) showed that LC 50 and LC 90 values were gradually decreased with the exposure periods having the lowest value at 72 h of exposure to 1 st instars larvae followed by 2 nd , 3 rd and 4 th instars larvae. Mortality rate (Y) was found to be positively correlated with the concentration (X) having a regression coefficient (R 2 ) close to 1 in each case. Phytochemical analyses revealed the qualitative presence of tannin, steroid and alkaloid free glycoside bound anthraquinones. Non target organisms were non-responsive to the bioactive fractions obtained from the plant throughout the experiment. Conclusion: From the above experiment it can be concluded that the mature leaves (foliages) of R. madagascariensis may be a superior larvicide alternative to the synthetic one.

Field evaluation of four widely used mosquito traps in Central Europe.

BackgroundTo monitor adult mosquitoes several trapping devices are available. These are differently constructed and use various mechanisms for mosquito attraction, thus resulting in different trapping sensitivities and efficacies for the various species. Mosquito monitoring and surveillance programs in Europe use various types of mosquito traps, but only a few comparisons have been conducted so far. This study compared the performance of four commercial trapping devices, which are commonly used in Europe.MethodsFour different traps, Biogents Sentinel trap (BG trap), Heavy Duty Encephalitis Vector Survey trap (EVS trap), Centres for Disease Control miniature light trap (CDC trap) and Mosquito Magnet Patriot Mosquito trap (MM trap) were compared in a 4 × 4 latin square study. In the years 2012 and 2013, more than seventy 24-hour trap comparisons were conducted at ten different locations in northern and southern Germany, representing urban, forest and floodplain biotopes.ResultsPer 24-hour trapping period, the BG trap caught the widest range of mosquito species, the highest number of individuals of the genus Culex as well as the highest number of individuals of the species Ochlerotatus cantans, Aedes cinereus/geminus, Oc. communis and Culex pipiens/torrentium. The CDC trap revealed best performance for Aedes vexans, whereas the MM trap was most efficient for mosquitoes of the genus Anopheles and the species Oc. geniculatus. The EVS trap did not catch more individuals of any genus or species compared to the other three trapping devices. The BG trap caught the highest number of individuals per trapping period in urban environments as well as in wet forest, while the CDC trap caught the highest number of individuals in the floodplain biotopes. Additionally, the BG trap was most efficient for the number of mosquito species in urban locations.ConclusionThe BG trap showed a significantly better or similar performance compared to the CDC, EVS or MM trap with regard to trapping efficacy for most common mosquito species in Germany, including diversity of mosquito species and number of mosquitoes per trapping period. Thus, the BG trap is probably the best solution for general monitoring or surveillance programs of adult mosquitoes in Central Europe.

Monitoring of malaria, Japanese encephalitis and filariasis vectors

BackgroundVector monitoring in military stations would help in protecting the armed forces from vector borne diseases such as malaria, Japanese encephalitis and filariasis. MethodsAdult mosquitoes were collected from four villages around a military station in India using light traps and the species composition was estimated. Insecticide susceptibility of disease vectors against DDT, deltamethrin and permethrin was established using WHO kits. ResultsThe known malaria vectors constituted 4.9% of the total mosquito collections and Anopheles philippinensis/nivipes (2.05%) was the most abundant. Japanese encephalitis and dengue vectors constituted 25.3 and 0.05% whereas the known vectors of both Japanese encephalitis and filariasis formed 50.9%. The mean (±SEmean) of annual parasitic index, slide positivity and Plasmodium falciparum percentage among the civilian population during the study period were 1.46 ± 0.37, 1.65 ± 0.77 and 50.2 ± 10.7. The filariasis vector Culex quinquefasciatus was resistant to DDT with 65.4% mortality whereas the DDT resistance in the Japanese encephalitis vector Culex vishnui gr. with 91.9% mortality needs to be confirmed. All other species tested were susceptible to DDT, deltamethrin and permethrin. ConclusionTargeted interventions are needed to reduce the disease burden and vector activity in the villages adjoining the military station. The use of insect repellents, bed nets and repellent impregnated uniforms by the troops should be ensured for protection from vector borne diseases.

Flight Capacity of Adult <I>Culex pipiens pallens</I> (Diptera: Culicidae) in Relation to Gender and Day-Age

Culex pipiens pallens (L.) is the most common mosquito in houses of central and northern China. It is the primary vector of lymphatic filariasis and Japanese encephalitis. The flight range of mosquitoes is an important factor predicting the risk area of transmission of mosquito-borne pathogens to vertebrate hosts. The flight performance of Cx. pipiens pallens was measured with a 26-channel computer-monitored flight-mill system. We found that females had longer flight capability than males for total flight distance (TFD) and total flight duration (TFDr), and females flew faster than males based on mean flight velocity. No significant difference in flight capability was found between different age-groups in males. However, certain age-groups of females showed significant differences in TFDr and TFD. Specifically, TFD and TFDr tended to be shortest for 5- and 6-d-old females. These significant differences in flight capability between ages and genders provide insights to determine the size of operational area to achieve effective control of Cx. pipiens pallens and minimize the risk of the related mosquito-borne epidemic diseases of lymphatic filariasis and Japanese encephalitis.

Mosquitoes established in Lhasa city, Tibet, China

BackgroundIn 2009, residents of Lhasa city, Tibet Autonomous Region (TAR), China reported large numbers of mosquitoes and bites from these insects. It is unclear whether this was a new phenomenon, which species were involved, and whether these mosquitoes had established themselves in the local circumstances.MethodsThe present study was undertaken in six urban sites of Chengguan district Lhasa city, Tibet. Adult mosquitoes were collected by bed net trap, labor hour method and light trap in August 2009 and August 2012. The trapped adult mosquitoes were initially counted and identified according to morphological criteria, and a proportion of mosquitoes were examined more closely using a multiplex PCR assay.Results907 mosquitoes of the Culex pipiens complex were collected in this study. Among them, 595 were females and 312 were males. There was no significant difference in mosquito density monitored by bed net trap and labor hour method in 2009 and 2012. Of 105 mosquitoes identified by multiplex PCR, 36 were pure mosquitoes (34.29%) while 69 were hybrids (65.71%). The same subspecies of Culex pipiens complex were observed by bed net trap, labor hour method and light trap in 2009 and 2012.ConclusionThe local Culex pipiens complex comprises the subspecies Cx. pipiens pipiens, Cx. pipiens pallens, Cx. pipiens quinquefasciatus and its hybrids. Mosquitoes in the Cx. pipiens complex, known to be, potentially, vectors of periodic filariasis and encephalitis, are now present from one season to the next, and appear to be established in Lhasa City, TAR.

Risk Factors for Mosquito House Entry in the Lao PDR

BackgroundConstruction of the Nam Theun 2 hydroelectric project and flooding of a 450 km2 area of mountain plateau in south-central Lao PDR resulted in the resettlement of 6,300 people to newly built homes. We examined whether new houses would have altered risk of house entry by mosquitoes compared with traditional homes built from poorer construction materials.Methodology/Principal FindingsSurveys were carried out in the Nam Theun 2 resettlement area and a nearby traditional rice farming area in 2010. Mosquitoes were sampled in bedrooms using CDC light traps in 96 resettlement houses and 96 traditional houses and potential risk factors for mosquito house entry were recorded. Risk of mosquito house entry was more than twice as high in traditional bamboo houses compared with those newly constructed from wood (Putative Japanese Encephalitis (JE) vector incidence rate ratio (IRR) = 2.26, 95% CI 1.38–3.70, P = 0.001; Anopheline IRR = 2.35, 95% CI: 1.30–4.23, P = 0.005). Anophelines were more common in homes with cattle compared against those without (IRR = 2.32, 95% CI: 1.29–4.17, P = 0.005).Wood smoke from cooking fires located under the house or indoors was found to be protective against house entry by both groups of mosquito, compared with cooking in a separate room beside the house (Putative JE vector IRR = 0.43, 95% CI: 0.26–0.73, P = 0.002; Anopheline IRR = 0.22, 95% CI: 0.10–0.51, P<0.001).Conclusions/SignificanceConstruction of modern wooden homes should help reduce human-mosquito contact in the Lao PDR. Reduced mosquito contact rates could lead to reduced transmission of diseases such as JE and malaria. Cattle ownership was associated with increased anopheline house entry, so zooprophylaxis for malaria control is not recommended in this area. Whilst wood smoke was protective against putative JE vector and anopheline house entry we do not recommend indoor cooking since smoke inhalation can enhance respiratory disease.

Larvicidal activity of green synthesized silver nanoparticles using bark aqueous extract of Ficus racemosa against Culex quinquefasciatus and Culex gelidus

ObjectiveTo investigate the larvicidal activity of synthesized silver nanoparticles (Ag NPs) utilizing aqueous bark extract of Ficus racemosa (F. racemosa) was tested against fourth instar larvae of filariasis vector, Culex quinquefasciatus (Cx. quinquefasciatus) and japanese encephalitis vectors, Culex gelidus (Cx. gelidus). MethodsThe synthesized Ag NPs was characterized by UV-vis spectrum, X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR). The larvicidal activities were assessed for 24 h against the larvae of Cx. quinquefasciatus and Cx. gelidus with varying concentrations of aqueous bark extract of F. racemosa and synthesized Ag NPs. LC50 and r2 values were calculated. ResultsThe maximum efficacy was observed in crude aqueous extract of F. racemosa against the larvae of Cx. quinquefasciatus and Cx. gelidus (LC50=67.72 and 63.70 mg/L; r2=0.995 and 0.985) and the synthesized Ag NPs (LC50=12.00 and 11.21 mg/L; r2=0.997 and 0.990), respectively. Synthesized Ag NPs showed the XRD peaks at 2 θ values of 27.61, 29.60, 35.48, 43.48 and 79.68 were identified as (210), (121), (220), (200) and (311) reflections, respectively. The FTIR spectra of Ag NPs exhibited prominent peaks at 3 425, 2 878, 1 627 and 1 382 in the region 500-3 000 cm−1. The peaks correspond to the presence of a stretching vibration of (NH) C=O group. SEM analysis showed shape in cylindrical, uniform and rod with the average size of 250.60 nm. ConclusionsThe biosynthesis of silver nanoparticles using bark aqueous extract of F. racemosa and its larvicidal activity against the larvae of disease spreading vectors. The maximum larvicidal efficacy was observed in the synthesized Ag NPs.

Bioactivity of &lt;i&gt;Acyranthes aspera&lt;/i&gt; (Amaranthaceae) Foliage against the Japanese Encephalitis Vector &lt;i&gt;Culex vishnui&lt;/i&gt; Group

Background and objective : Failure to develop proper vaccines against mosquito borne diseases, a global health problem, imposes sole reliance on the vector managerial steps for reducing the disease incidences. Easy abundance, cost effectiveness, target specificity as well as bio-degradability of botanicals draw the most attention as vector control agents than their synthetic counterparts which facilitate vector resistance and intoxicate natural resources. The present study estimated larvicidal activities of the crude and solvent extracts of Acyranthes aspera against the vector of Japanese encephalitis Culex vishnui group under laboratory conditions. Methods: Crude extracts of A. aspera foliage ranging from 0.1% to 0.5% concentrations were examined for larvicidal activity against 1 st to 4 th instars larvae of Cx. vishnui group. Extractions of the active fractions were carried out by means of six different solvents in a non-polar to polar approach viz. petroleum ether, n-hexane, ethyl acetate, chloroform: methanol (1:1 v/v), acetone, and absolute alcohol. Dose dependent mortality was established through graded concentrations ranging from 20 ppm to 100 ppm using the bioactive fractions. Further, determinations of LC 50 and LC 90 values of crude and bioactive fractions were accomplished through log-probit analyses. Statistical justifications of the larvicidal property were established through ANOVA analyses regarding instars, time and concentrations as three completely randomized independent variables. Costing impacts on the non-target water fauna of the bio-active portion were assessed under laboratory conditions. Result : In a 72 hour bioassay experiment with crude extract, the highest mortality was recorded in 0.5% concentration. Acetone extractive was found to exert efficient larvicidal activity amongst all the solvent extractives. Cent per cent mortalities were exhibited by 1 st and 2 nd instars larvae at 48 hours of exposure while 3 rd instars larvae showed 97.32% mortality at 72 hours of exposure with LC 50 value of 32.15 ppm. An obvious dose-dependent mortality was established through regression analyses, as the rate of mortality (Y) was positively correlated with the concentration (X). The non-target populations were primarily non-responsive to plant extracts under study. Conclusion : Extract of A. aspera foliage is of great consequence having appreciable larvicidal activity against Cx. vishnui group . The compound is environment friendly and largely non-toxic to non-target organisms.

Insecticide Susceptibility of Field-Collected Populations ofCulex tritaeniorhynchusin the Republic of Korea

The toxicities of 10 insecticides were examined against late third instar Culex tritaeniorhynchus Giles (Diptera: Culicidae) using the direct-contact mortality bioassay. Six geospatially-distant field mosquitoes were collected from Chuncheon-si, Hwaseong, Seosan. Jeonju, Daegu, and Busan in the Republic of Korea. Marked regional variations of insecticide susceptibility were observed. Field populations of Seosan, Jeonju, and Daegu from agricultural areas showed higher to extremely higher insecticide susceptibility to pyrethroids than those of Chuncheon-si, Hwaseong, and Busan strains from non-agricultural areas. Extremely high to low levels of susceptibility were measured: bifenthrin, susceptible ratio (SR) = 2.7–896.3; β-cyfluthrin, SR = 1.8–633.3; α-cypermethrin, SR = 1.2–1,051.9; deltamethrin, SR = 1.3–711.1; permethrin, SR = 1.5–1,053.4; etofenprox, SR = 2.2–29.3; chlorfenapyr, SR = 5.1–103.6; chlorpyrifos, SR = 2.3– 337.0; fenitrothion, SR = 2.0–142.3; and fenthion, SR = 1.4–186.2. Cx. tritaeniorhynchus populations from rice paddies had been under heavy selection pressure due to the agricultural insecticides, and that's why the mosquito species demonstrated high resistance to pyrethroids, which were used for a long time to control agricultural pests in the localities. These results indicate that careful selection and rotational use of these insecticides may result in continued satisfactory control against field populations of Japanese encephalitis vector mosquitoes.

Toxicity of saponin isolated from Gymnema sylvestre R. Br. (Asclepiadaceae) against Culex tritaeniorhynchus Giles (Diptera: Culicidae) Japanese encephalitis vector mosquito in India

To determine the larvicidal activity of various extracts of Gymnema sylvestre against the Japanese Encephalitis vector, Culex tritaeniorynchus in Tamilnadu, India. To identify the active principle present in the promising fraction obtained in Chlorofom:Methanol extract of Fraction 2. The G. sylvestre leaf extracts were tested, employing WHO procedure against fourth instar larvae of C. tritaeniorhynchus and the larval mortalities were recorded at various concentrations (6.25, 12.5, 25.0, 50 and 100 µg/mL); the 24h LC50 values of the G. Sylvestre leaf extracts were determined following Probit analysis. It was noteworthy that treatment level 100 µg/mL exhibited highest mortality rates for the three different crude extracts and was significantly different from the mean mortalities recorded for the other concentrations. The LC50 values of 34.756 µg/mL (24.475-51.41), 31.351 µg/mL (20.634-47.043) and 28.577 µg/mL (25.159-32.308) were calculated for acetone, chloroform and methanol extract with the chi-square values of 10.301, 31.351 and 4.093 respectively. The present investigation proved that G. Sylvestre could be possibly utilized as an important component in the Vector Control Program.

Laboratory evaluation of ethyl acetate and chloroform: methanol (1:1 v/v) extract of Swietenia mahagoni leaf against Japanese Encephalitis vector Culex vishuni group

ObjectiveTo study the larvicidal activity of a furniture tree Swietenia mahagoni L. (S. mahagoni) against mosquito Culex Vishnui group. MethodsDifferent concentrations of crude, chloroform: methanol (1:1 v/v) and ethyl acetate solvent extracts of S. mahagoni mature leaves were treated against Cx. vishnui group larvae. ResultsFive graded concentrations (0.05%, 0.10%, 0.20%, 0.30% and 0.40%) of crude extract of mature leaves and five graded concentrations (10 ppm, 20 ppm, 30 ppm, 40 ppm and 50 ppm) of chloroform: methanol (1:1 v/v) and ethyl acetate solvent extracts showed significant (P<0.05) larval mortalities. LC50, LC90 values were calculated at 24 h, 48 h and 72 h of exposures. Adult Cx. vishnui group mosquitoes exposed to burning coils prepared from S. mahagoni mature leaves showed smoke repellency and toxicity up to 4 h. ConclusionsThis study was a pioneer attempt to establish S. mahagoni as an effective mosquito larvicide.

RAPD-PCR characterization of Bacillus thuringiensis soil isolates from Mizoram with insecticidal activity against Culex tritaeniorhynchus

Background &amp; Aim: Vector-borne diseases are one of the major public health problems in developing countries. Culextritaeniorhynchus (Diptera: Culicidae) could be a vector of filariasis and West Nile encephalitis. The use ofentomopathogenic bacteria like Bacillus thuringiensis (Bt) as larvicides is a viable alternative for the biological controlmosquitoes with a low environmental impact. Hence, an attempt was made to explore the abundance of Bt in Mizoramsoils from different habitats, testing their toxicity against C. tritaeniorhynchus and characterization by following acetateselection, mortality, dissimilarity analysis and RAPD-PCR assay methods. Method: In this present study, nine soilisolates (Mzubt 2,4,5,6,11,23,25,26 and 29) were identified, characterized and evaluated against C. tritaeniorhynchus.The new isolates were compared with two reference strains - Bt israelensis 4Q1 and Bt aizawai 4J3 obtained fromBacillus Genetic Stock Center, USA. Results: The mzubt 2 and mzubt 6 isolates showed higher larvicidal activity thanother isolates, against C. tritaeniorhynchus. RAPD-PCR assay has been optimized that discriminate Bacillusthuringiensis (Bt) isolates from nine different habitats soil covering five districts of Mizoram. All the studied isolatesshowed a diverse RAPD patterns and were different from each other in relation to habitats, toxicity and type of cry genepresent. High polymorphism was observed between Bt isolates which was authenticated through high PIC, RP, EMR andMI values. Further, three major clusters were identified through dissimilarity analysis. Conclusion: No relationshipfound between the type of cry gene in Bt and their toxicity against mosquitoes. The importance of the isolation of nativestrains of Bt in the mosquito management program in Mizoram is highlighted based on the findings.

Synthesis, spectral characterization and larvicidal activity of acridin-1(2H)-one analogues

Acridin-1(2H)-one analogue of 7-chloro-3,4-dihydro-9-phenyl-2-[(pyridine-2yl) methylene] acridin-1(2H)-one, 5 was prepared by using 7-chloro-3,4-dihydro-9-phenylacridin-1(2H)-one, 3 and picolinaldehyde, 4 in the presence of KOH at room temperature. These compounds were characterized by analytical and spectral analyses. The purpose of the present study was to assess the efficacy of larvicidal and repellent activity of synthesized 7-chloro-3,4-dihydro-9-phenyl-acridin-1(2H)-one analogues such as compounds 3 and 5 against the early fourth instar larvae of filariasis vector, Culex quinquefasciatus and Japanese encephalitis vector, Culex gelidus (Diptera: Culicidae). The compound exhibited high larvicidal effects at 50mg/L against both the mosquitoes with LC50 values of 25.02mg/L (r2=0.998) and 26.40mg/L (r2=0.988) against C. quinquefasciatus and C. gelidus, respectively. The 7-chloro-3,4-dihydro-9-phenyl-acridin-1(2H)-one analogues that are reported for the first time to our best of knowledge can be better explored for the control of mosquito population. This is an ideal ecofriendly approach for the control of Japanese encephalitis vectors, C. quinquefasciatus and C. gelidus.

Insecticide Toxicity and Characterization of Cytochrome P450 CYP6BB1 and CYP6P10 in Aedes sollicitans Larvae

Cytochrome P450 monooxygenases (P450s) are involved in biotransformation of endogenous and exogenous compounds, including insecticides, which often result in insecticide resistance in insects. Two P450‐encoding genes, CYP6BB1 and CYP6P10, were identified in Aedes sollicitans, an Eastern Equine Encephalitis vector. We examined mosquitoes collected in Atlantic County, New Jersey, where multiple insecticides have been used. We found that pre‐exposure of the mosquito larvae to pentamethylbenzene (PMB) significantly decreased the toxicity of carbaryl, but not that of spinosad. Gene expression of CYP6BB1 was slightly up‐regulated upon induction by PMB, whereas CYP6P10 remained unchanged. We also compared the Atlantic mosquitoes to another population collected from a location on Long Island where insecticides have not been used. We found that the gene expression level of CYP6P10 in the Long Island population was considerably higher than that in the Atlantic population. The gene expression level of CYP6BB1 was also higher in the Long Island mosquitoes. We concluded that PMB induced P450s that detoxified carbaryl. Whether these two genes are involved in the insecticide detoxification in the mosquitoes will require further studies. (Supported by Rutgers Hatch Fund)

Mosquito biting activity on humans &amp; detection of Plasmodium falciparum infection in Anopheles stephensi in Goa, India

Background & objectives:Knowledge of the bionomics of mosquitoes, especially of disease vectors, is essential to plan appropriate vector avoidance and control strategies. Information on biting activity of vectors during the night hours in different seasons is important for choosing personal protection measures. This study was carried out to find out the composition of mosquito fauna biting on humans and seasonal biting trends in Goa, India.Methods:Biting activities of all mosquitoes including vectors were studied from 1800 to 0600 h during 85 nights using human volunteers in 14 different localities of three distinct ecotypes in Goa. Seasonal biting trends of vector species were analysed and compared. Seasonal biting periodicity during different phases of night was also studied using William's mean.Results:A total of 4,191 mosquitoes of five genera and 23 species were collected. Ten species belonged to Anopheles, eight to Culex, three to Aedes and one each to Mansonia and Armigeres. Eleven vector species had human hosts, including malaria vectors Anopheles stephensi (1.3%), An. fluviatilis (1.8%), and An. culicifacies (0.76%); filariasis vectors Culex quinquefasciatus (40.8%) and Mansonia uniformis (1.8%); Japanese encephalitis vectors Cx. tritaeniorhynchus (17.4%), Cx. vishnui (7.7%), Cx. pseudovishnui (0.1%), and Cx. gelidus (2.4%); and dengue and chikungunya vectors Aedes albopictus (0.9%) and Ae. aegypti (0.6%). Two An. stephensi of the total 831 female anophelines, were found positive for P. falciparum sporozoites. The entomological inoculation rate (EIR) of P. falciparum was 18.1 and 2.35 for Panaji city and Goa, respectively.Interpretation & conclusions:Most of the mosquito vector species were collected in all seasons and throughout the scotophase. Biting rates of different vector species differed during different phases of night and seasons. Personal protection methods could be used to stop vector-host contact.

Mosquitoes and Their Potential Predators In Rice Agroecosystems of the Mekong Delta, Southern Vietnam

Culex tritaeniorhynchus, Cx. gelidus, and Cx. quinquefasciatus, known vectors of Japanese encephalitis (JE), are distributed in rice agroecosystems in Asian countries. Very few integrated studies on the breeding habitats of rice-field mosquitoes, including JE vectors, have been conducted in Vietnam. We investigated the mosquito fauna and potential predators in 8 rice growing areas in the Mekong Delta region of southern Vietnam, during the wet and dry seasons of 2009. Mosquitoes and their predators were collected from a variety of aquatic habitats (rice fields, ponds, wetlands, shrimp ponds, ditches, canals, and rivers). We collected 936 Culex spp. (354 Cx. tritaeniorhynchus, 240 Cx. vishnui s.l., 189 Cx. fuscocephala, and 42 Cx. gelidus), 33 Uranotaenia, 25 Anopheles, and 9 Mimomyia (4 Mi. chamberlaini) in the dry season. During the rainy season, we collected 1,232 Culex spp. (132 Cx. vishnui s.l., 66 Cx. tritaeniorhynchus, 9 Cx. gelidus, 4 Cx. fuscocephala, and 2 Cx. bitaeniorhynchus), 236 Anopheles spp. (40 An. vagus and 1 An. sinensis), and 7 Uranotaenia (3 Ur. lateralis). Heteroptera such as Micronecta, Veliidae, and Pleidae were abundant and widely distributed in both seasons. Based on a stepwise generalized linear model, the abundance of mosquitoes and their predators in rice fields was high when the rice plant length was short and water depth was shallow. Therefore, the use of insecticides during the earlier stages of rice growth should be avoided in order to preserve the predator populations.

The abundance and host-seeking behavior of culicine species (Diptera: Culicidae) and Anopheles sinensis in Yongcheng city, people's Republic of China

BackgroundThe knowledge of mosquito species diversity and the level of anthropophily exhibited by each species in a region are of great importance to the integrated vector control. Culicine species are the primary vectors of Japanese encephalitis (JE) virus and filariasis in China. Anopheles sinensis plays a major role in the maintenance of Plasmodium vivax malaria transmission in China. The goal of this study was to compare the abundance and host-seeking behavior of culicine species and An. sinensis in Yongcheng city, a representative region of P. vivax malaria. Specifically, we wished to determine the relative attractiveness of different animal baits versus human bait to culicine species and An. sinensis.ResultsCulex tritaeniorhynchus was the most prevalent mosquito species and An. sinensis was the sole potential vector of P. vivax malaria in Yongcheng city. There were significant differences (P < 0.01) in the abundance of both An. sinensis and Cx. tritaeniorhynchus collected in distinct baited traps. The relative attractiveness of animal versus human bait was similar towards both An. sinensis and Cx. tritaeniorhynchus. The ranking derived from the mean number of mosquitoes per bait indicated that pigs, goats and calves frequently attracted more mosquitoes than the other hosts tested (dogs, humans, and chickens). These trends were similar across all capture nights at three distinct villages. The human blood index (HBI) of female An. sinensis was 2.94% when computed with mixed meals while 3.70% computed with only the single meal. 19:00~21:00 was the primary peak of host-seeking female An. sinensis while 4:00~5:00 was the smaller peak at night. There was significant correlation between the density of female An. sinensis and the average relative humidity (P < 0.05) in Wangshanzhuang village.ConclusionsPigs, goats and calves were more attractive to An. sinensis and Cx. tritaeniorhynchus than dogs, humans, and chickens. Female An. sinensis host-seeking activity mainly occurred from 19:00 to 21:00. Thus, we propose that future vector control against An. sinensis and Cx. tritaeniorhynchus in the areas along the Huang-Huai River of central China should target the interface of human activity with domestic animals and adopt before human hosts go to bed at night.

Mosquito Species (Diptera: Culicidae) Reported from Shandong Province, China

Field surveys were conducted in 2007 - 2009 to determine the diversity of mosquito species occurring in Shandong Province, China. As a result, 31 species of mosquitoes were identified. Culex pipiens pallens Coquillett was the most common species collected. Aedes albopictus Skuse, Anopheles sinensis Wiedemann, and Cx. tritaeniorhynchus Giles also were commonly collected. These 4 species have been documented as the vectors of malaria, dengue, and epidemic encephalitis in China. At least 10 species identified are disease vectors in Shandong Province, and other species could be considered potential vectors of other diseases. Mosquito larvae were routinely collected from natural and artificial structures containing water. The diversity of these water-filled containers might explain the cooccurrence of various culicid species in some localities surveyed. The ecology and breeding behavior of these mosquito species should be further studied to optimize surveillance and management programs and to prevent the emergence of mosquito-transmitted diseases in human and other animal populations in the area.