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PubMed1992

Evaluation of neem, Azadirachta indica, with and without water management, for the control of culicine mosquito larvae in rice-fields.

Applications of neem, Azadirachta indica (Meliaceae), to rice-fields were evaluated with the dual objective of controlling the culicine mosquito vectors of Japanese encephalitis virus (JEV) and enhancing the grain yield. Since crude neem products deteriorate under improper storage conditions, a laboratory bioassay was developed to screen neem cake powder against mosquito larvae, Culex quinquefasciatus. Only samples of neem giving over 90% bioassay mortality were used in field trials. When good quality neem cake powder was applied at the dose of 500 kg/ha, either alone or coated over urea, there was a striking reduction in the abundance of late instar culicine larvae and pupae. Only fourteen pupae were obtained over a period of 13 weeks in neem cake powder treated plots, and four in those treated with neem coated urea, compared with 101 in control plots. Both treatments were significantly less than the control, but on par with one another. In another field trial, neem cake coated urea was tested at 500 and 250 kg neem/ha in combination with water management practices. No reduction in efficacy was noted at the lower dose. Larval abundance in plots under water management alone did not differ significantly from the controls, but was significantly reduced when water management was combined with neem products. Two stable formulations, 'Neemrich-I' (lipid rich) and 'Neemrich-II' (azadirachtin rich), also gave good suppression of immature culicines. All the treatments with neem also gave higher grain yield than the control.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Evaluation of methoprene effect on Aedes aegypti (Diptera: Culicidae) development in laboratory conditions.

Several Brazilian Aedes aegypti populations are resistant to the larvicidae temephos. Methoprene, that inhibits adult emergence, is one of the alternatives envisaged by the Brazilian Dengue Control Program (PNCD). However, at Brazil vector infestation rates are measured through larvae indexes and it has been claimed that methoprene use in the field could face operational problems. In order to define a standardized protocol, methoprene effect was evaluated in laboratory conditions after continuous exposure of larvae (Rockefeller strain) to a methoprene formulation available to the PNCD. Methoprene-derived mortality occurs mainly at the pupa stage and pupa development is inversely proportional to methoprene concentration. Number and viability of eggs laid by treated and control females are equivalent. A methoprene dose-dependent delay in the development was noted; however, strong correlations were found for total mortality or adult emergence inhibition if data obtained when all control mosquitoes have emerged are compared to data obtained when methoprene-treated groups finish development. The cumulative record of total methoprene-induced mortality at the time control adults emerge is proposed for routine evaluation of field populations. Mortality of all specimens, but not of larva, could account for adult emergence inhibition, confirming the inadequacy of larvae indexes to evaluate methoprene effect.

Aedes↗
PubMed1989

[Studies on the surveillance and purifying measures for filariasis in controlled areas].

This paper reports the results of longitudinal surveillance of filariasis for 4 years in Jining City, Shandong, where the disease has been controlled. It showed that the microfilaremia rate dropped from 0.48% to 0.03% and no new case was found and the natural infective rate of the main vector mosquito Culex pipiens fell from 0.45% to 0.03% and no larva III was detected. The purifying measures should put emphasis on the management of migrating persons repeatedly examining and treating old microfilaremia cases, the border areas with high microfilaremia rate, as well as working out a plan to cure the advanced patients and mosquito control measures with special reference to construction of new village settlements.

Adult↗
PubMed1975

Infection of the mosquito Aedes aegypti with infectious West Nile virus-antibody complexes.

Aedes aegypti fed through chick skin membranes on West Nile virus-homologous antiserum mixtures shown by an anti-globulin neutralization test to be highly infectious complexes (in terms of plaque formation in tissue culture) failed to become infected. Control mosquitoes fed on West Nile virus--normal rabbit serum mixtures containing similar or smaller amounts of infectious virus were shown to become infected. Mosquitoes ingesting suspensions of West Nile virus previously incubated with Murray Valley encephalitis or Ntaya antiserum became infected at significantly lower rates (P = less than 0-05) than controls ingesting West Nile virus-normal rabbit serum mixtures. West Nile virus--17D yellow fever or dengue--2 antiserum mixtures did not produce significantly reduced infection rates in Ae. aegypti when compared to controls.

Aedes↗
PubMed1993

Transovarial transmission of chikungunya virus by Aedes albopictus mosquitoes ingesting microfilariae of Dirofilaria immitis under laboratory conditions.

Female Aedes albopictus mosquitoes of the Miki strain were experimentally fed on defibrinated sheep blood containing 5 x 10(7) PFU of chikungunya virus and 20,000 microfilariae of Dirofilaria immitis per milliliter. Fully engorged mosquitoes transmitted the virus to a small percentage of the F1 progeny, but females of the F1 generation did not transmit the virus to the F2 progeny. The control mosquitoes that ingested the virus without microfilariae did not transmit the virus to their eggs, larvae, or pupae in the F1 or F2 generations. These results showed that A. albopictus of this strain that concurrently ingested the virus and microfilariae transmitted the virus by the transovarial route under experimental conditions.

Aedes↗
PubMed1995

Mosquito sensitivity to a scorpion neurotoxin expressed using an infectious Sindbis virus vector.

The scorpion, Androctonus australis Hector, produces an insect-specific toxin (AaHIT) encoded by the Scotox gene. To assess the toxicity of AaHIT for mosquitoes, we have taken a novel approach to express the Scotox gene in vivo. We have engineered a double subgenomic Sindbis (dsSIN) virus that contains the Scotox gene in the viral genome and intrathoracically inoculated the virus (TE/3'2J/Scotox) into mosquitoes (Aedes aegypti, Ae. triseriatus and Culex pipiens), houseflies (Musca domestica) and ticks (Dermacentor andersoni). Mosquitoes, which normally show no pathologic effects from Sindbis (SIN) virus infections, died 1-5 days after infection with TE/3'2J/Scotox virus. Neither flies nor ticks were killed. The mosquitocidal action of AaHIT in mosquitoes makes AaHIT a potential candidate for inclusion in molecular-based methods of mosquito control. The expression of an arthropod gene in vivo demonstrates the utility of dsSIN expression vectors for future use to examine and potentially disrupt endogenous gene functions in mosquitoes.

Aedes↗
PubMed2006

Predicting outbreaks: a spatial risk assessment of West Nile virus in British Columbia.

BACKGROUND: West Nile virus (WNv) has recently emerged as a health threat to the North American population. After the initial disease outbreak in New York City in 1999, WNv has spread widely and quickly across North America to every contiguous American state and Canadian province, with the exceptions of British Columbia (BC), Prince Edward Island and Newfoundland. In this study we develop models of mosquito population dynamics for Culex tarsalis and C. pipiens, and create a spatial risk assessment of WNv prior to its arrival in BC by creating a raster-based mosquito abundance model using basic geographic and temperature data. Among the parameters included in the model are spatial factors determined from the locations of BC Centre for Disease Control mosquito traps (e.g., distance of the trap from the closest wetland or lake), while other parameters were obtained from the literature. Factors not considered in the current assessment but which could influence the results are also discussed. RESULTS: Since the model performs much better for C. tarsalis than for C. pipiens, the risk assessment is carried out using the output of C. tarsalis model. The result of the spatially-explicit mosquito abundance model indicates that the Okanagan Valley, the Thompson Region, Greater Vancouver, the Fraser Valley and southeastern Vancouver Island have the highest potential abundance of the mosquitoes. After including human population data, Greater Vancouver, due to its high population density, increases in significance relative to the other areas. CONCLUSION: Creating a raster-based mosquito abundance map enabled us to quantitatively evaluate WNv risk throughout BC and to identify the areas of greatest potential risk, prior to WNv introduction. In producing the map important gaps in our knowledge related to mosquito ecology in BC were identified, as well, it became evident that increased efforts in bird and mosquito surveillance are required if more accurate models and maps are to be produced. Access to real time climatic data is the key for developing a real time early warning system for forecasting vector borne disease outbreaks, while including social factors is important when producing a detailed assessment in urban areas.

Animals↗
PubMed2005

Evaluation of various control agents against mosquito larvae in rice paddies in Taiwan.

A field test was conducted in rice paddies adjacent to Wufeng, Taichung County in Central Taiwan to evaluate the efficacy of control agents against mosquito larvae. The agents included Bacillus thuringienesis israelensis (Bti), two Lagenidium giganteum products (Lg product A and T), and temephos. The major mosquito species found in the rice paddies were Culex tritaeniorhynchus/vishnui and Anopheles sinensis. Compared to controls, a 7-day treatment with Bti or Lg products A and T caused overall reductions in the number of immatures (larvae and pupae) of Cx. tritaeniorhynchus/vishnui of 77.5%, 49.7%, and 21.9%, respectively, whereas temephos caused an increase of 66.9%. The overall reductions in An. sinensis were 85.4%, 8.6%, 44.6%, and 92.1%, respectively. There was no significant reduction in the number of mosquito larvae following 42 days of treatment with these agents. In summary, 1-week treatments with both biological control agents produced moderate overall reductions in mosquito larvae in rice paddies. The insecticide temephos, on the other hand, was very effective at suppressing the larvae of An. sinensis but significantly increased the number of Cx. tritaeniorhynchus/vishnui larvae in temephos-treated plots.

Animals↗
PubMed2005

The ferritin light-chain homologue promoter in Aedes aegypti.

Promoters that direct the expression of antipathogenic molecules to primary sites of pathogenic invasions provide a means to interfere with these invasions. Thus, they have the potential to be used in mosquito control. However, exogenous elements are known to lower the fitness of most insects, and given the ability of insects to evolve rapidly, all currently known promoters could be rendered useless. As transgenic mosquitoes may be a major component in the fight against mosquito-borne diseases, the identification of new mosquito promoters is needed. The promoter of the Aedes aegypti ferritin light-chain homologue (LCH) gene, a gene whose expression is induced in gut tissues during blood feeding has been identified and mapped. Transfection data indicate that the ferritin LCH promoter is a strong promoter. DNase I footprinting data and Transfac analyses suggest that the ferritin LCH promoter contains putative GATA, E2F, NIT2, TATA and DPE sites. These data together provide the first detailed map of a known ferritin LCH gene.

Aedes↗
PubMed2005

Evaluation of upstream point treatment in flowing water ditches by Aquabac (Bacillus thuringiensis var. israelensis) against Culex quinquefasciatus.

The effectiveness of the upstream point treatment by AQUABAC Biolarvicide (Bacillus thuringiensis var. israelensis, Biological Larvicide Aqueous Suspension) against Culex quinquefasciatus Say in slow-flowing water ditches has been evaluated in St. Augustine Beach, St. Johns County, FL. The upstream point treatment by AQUABAC (liquid) at 0.5 liter/acre provided significant levels of larval control of Cx. quinquefasciatus for all sections of the downstream for 9 days. The upstream point treatment method by larvicides may have potential for use, minimize environmental impacts, and reduce cost and labor in mosquito-control operation for slow-flowing water ditches.

Animals↗
PubMed2005

Efficacy of a Bacillus thuringiensis israelensis tablet formulation, vectobac DT, for control of dengue mosquito vectors in potable water containers.

VectoBac DT, a tablet formulation of Bacillus thuringiensis israelensis (Bti) was evaluated for the potential control of dengue vectors in various types of potable water containers. On introduction to containers, the tablet sinks to the bottom and the Bti toxins are found concentrated at the sides and the base, while the treated water column is free of Bti toxins within 24 hours after tablet introduction. In a simulated study, earthen, HDPE and plastic containers were kept covered and laboratory-bred larvae were introduced to determine the control by the tablet. The efficacy and persistence of the tablet, with a control of > 90%, was significantly longer in earthen containers in comparison to the HDPE and plastic containers. Efficacy and persistence were observed in earthen containers for a minimum period of 5.5 months (166 days) both without water replenishment and with weekly, 50% water volume, replenishment, and for a maximum period of 2.2 months (66 days) with daily, 50% water volume, replenishment. In plastic and HDPE containers, the tablet activity had a persistence of 2.1 months (63 days) without water replenishment and 1.8 months (54 days) with weekly water replenishment. The efficacy and persistence of the VectoBac DT was significantly longer in the earthen containers, with or without regularly treated water exchange, due to the Bti toxins being embedded in the porous earthen container surfaces, which protects them from rapid degradation. Lesser toxin amounts are removed from the water column during water exchange. The efficacy of VectoBac DT was also evaluated for the control of natural infestation of Aedes larvae which were resistant to temephos at the WHO diagnostic dosage of 0.012 mg/l. The tablet significantly reduced the pupal density by 8 fold in earthen containers for 67 days and 5 fold in HDPE containers for 55 days in comparison to untreated containers (p < 0.05). However, the tablet was effective for a shorter period of 25 days post-tablet-introduction due to fungal infestation in the treated plastic containers. There is a need to determine the capacity of the VectoBac DT to reduce the dengue vector population to a threshold which will prevent dengue outbreaks in dengue endemic areas.

Aedes↗
PubMed1990

[Recent achievements and perspectives in medical entomology and vector control].

High technologies of molecular biology and genetics, supported by computer use brought considerable advances in taxonomy, physiology, host/parasite relationships, ecology and epidemiology. New insecticides, IGR and bacteria are now available. Both simple methods (e.g. tsetse trapping, impregnated bednets) and large programs using heavy material (e.g. O. C. P. in West Africa, mosquito control in Northern hemisphere) have been successful. Guineaworm control lies in an intermediate position. Malaria control has difficulties and needs new tools and a better use of those already existing. A few progresses are noticed in biological and genetical control. Appropriate structures, well trained and motivated personnel, adequate funding and political willingness are the keys for the implementation of any control programme.

Animals↗
PubMedDate not supplied

[South-East Asian arboviruses (author's transl)].

The South-East Asian arbovirological pathology is dominated by dengue fever, of which haemorrhagic forms constitute an important public health problem. The incidence of the disease is increasing from year to year, especially in large urban areas of this region and it is expected that the development of a vaccine in the near future will make it possible to improve the actual prevention only based on mosquito control, directed against domestic and peridomestic Aedes. Almost equally worrying is the epidemiological situation of Japanese encephalitis, which recently gave rise to important outbreaks in the Indian sub-continent, the transmission of which is ensured by rural mosquitoes and is very difficult to interrupt. Other arbovirus diseases are of secondary importance; they can involve dengue-like syndromes, meningo-encephalitic syndromes or haemorrhagic syndromes, and constitute public health problems only sporadically.

Adolescent↗
PubMed1994

[Importance and role of spreading larvicides on the soil in river beds for the control program against onchocerciasis in west Africa].

The control of blackfly is based on larvicide spraying in rivers where the insects breed and their larval stages are vulnerable. The first technique for large-scale operations, consists of using aircraft in the same way as for mosquito control and crop protection operations. The second technique, which will be discussed in this paper, consists of ground treatment of rivers, either directly with a container or with a spraying pump or by boat spraying insecticide in cross strip. In areas of West Africa where onchocerciasis is still prevalent, ground treatment is done to support aerial operations and to a lesser extent to control nuisance in areas where the endemicity of the disease is low. In onchocerciasis-freed zones, control of blackfly aims only at suppressing the nuisance in order to enhance the socio-economic development in areas at unfair disadvantage. This distinction is important for determining the responsibilities of various groups. Vector control to interrupt the transmission of onchocerciasis is the mandate of OCP while the control of nuisance is the responsibility, depending on the circumstances, of the private sector, the government and/or village communities. In this paper, we have attempted to highlight the objectives of such treatments, the responsibilities of various groups and the prospects in West African countries located in the Onchocerciasis Control Programme area. We also present the situation of ground larviciding in countries outside the Programme, in temperate as well as tropical conditions, in order to provide some basis for the development of ground treatment strategies in the OCP area.

Africa, Western↗
PubMed1992

Defined medium supporting development of cleansed Plasmodium berghei ookinetes in Anopheles stephensi.

Hamsters blood infected with Plasmodium berghei was cultured in vitro for the development of ookinetes. The ookinetes were separated from blood components, suspended in various defined media and fed to Anopheles stephensi through a membrane. The development of the oocysts and infective sporozoites was recorded. Mosquitoes infected with ookinetes suspended in L15 formulated into L15-B, L15-D (a medium specially modified for this purpose), IPL-41 or 199 media with no proteins added, developed at least as many oocysts as the control mosquitoes fed ookinetes suspended in blood. Ookinetes suspended in the L15-B medium yielded more oocysts than after feeding ookinetes suspended in L15-B with 5% casein. Sporozoites from mosquitoes maintained on blood, L15-B, L15-D, or L15-B with 5% casein were shown to be infective to hamsters. Mosquitoes fed ookinetes suspended in sucrose solutions showed very few oocysts, but the yield was increased when a blood meal was given 2-4 days after the infective meal. Some of the oocysts which had developed from the ookinetes suspended in artificial media were found to have degenerated. The described system could be potentially useful for a study of the interaction between the vector physiology and the parasite. The possible use of the system to learn which media should be developed in the future for in vitro cultivation of oocysts is discussed.

Animals↗
PubMed2003

Efficacy of two organophosphorus insecticides, Reldan & Dursban against the larvae of Culex quinquefasciatus.

BACKGROUND & OBJECTIVES: The resistance in vectors to conventional insecticides warrants development of newer insecticides for mosquito control besides use of other counter-measures. The present study was undertaken to test the efficacy of a new and toxicologically safe organophosphorus compound, Reldan (chlorpyrifos-methyl) and compare its efficacy with Dursban (chlorphyrifos-ethyl) against larvae of different mosquito vectors under laboratory conditions and against Culex quinquefasciatus in three larval habitats. METHODS: The susceptibility of larvae of mosquito vector species to Reldan and Dursban was determined by following the standard procedure and the LC50 in mg/l values were calculated by probit analysis. The insecticides were evaluated in the larval habitats of C. quinquefasciatus in and around Pondicherry. The percentage reduction in larval density was calculated using Mulla's formula and duration showing more than 80 per cent reduction was calculated by annotating the graph obtained by plotting percentage reduction in larval density against days of post-treatment. RESULTS: Dursban and Reldan were effective against Anopheles fluviatilis larvae at lower LC50 of 5.90 x 10(-7) and 1.07 x 10(-9) mg/l respectively compared to other species of mosquitoes. Dursban and Reldan were equally effective against Aedes aegypti, An. stephensi and An. culicifacies. Reldan was about nine times more effective than Dursban against C. quinquefasciatus with respective LC50 of 1.17 x 10(-4) and 1.34 x 10(-3) mg/l. Field evaluation of these insecticides against C. quinquefasciatus showed that Reldan and Dursban at the application rate of 500 g (ai)/ha reduced immature density by more than 80 per cent for a mean duration of 4.0 and 4.5 days and 4.6 and 3.7 days in cesspits and cement tanks respectively. In U-drains, at 500 g (ai)/ha, Reldan was effective for a period of 3.6 days whereas, Dursban was not effective. It was effective for 4.0 days only at 1000 g(ai)/ha. There was no significant increase in the residual activity of both Dursban and Reldan with increase in application rates. INTERPRETATION & CONCLUSION: In view of the lack of sustained control with the applications, it is inferred that these insecticides will be of limited use as larvicides against C. quinquefasciatus breeding in polluted habitats.

Animals↗
PubMed1997

Mixed-genotype infections of the rodent malaria Plasmodium chabaudi are more infectious to mosquitoes than single-genotype infections.

Interactions between parasite genotypes sharing a host are poorly understood, but have important consequences for the epidemiology and evolution of the parasite. In mixed-genotype malaria infections, patterns of asexual replication and transmission favoured by natural selection may be different from those in single-genotype infections. The infectivity to mosquitoes of mixed-genotype and single-genotype infections were compared using 2 clones of Plasmodium chabaudi inoculated into mice either together or alone. Mice given mixed-clone infections received the sum of the inocula given to the single-clone controls. Mosquitoes were fed on the mice and the numbers of oocysts which developed were counted to assess transmission intensity. For 3 combinations of starting inocula and feed days, mixed-clone infections produced more oocysts per mosquito than the sum of the 2 single-clone infections. This effect was correlated with an increase in gametocyte density, but was less clearly related to asexual infection parameters. The results show that interactions between clones in mixed-clone infections can profoundly affect transmission.

Animals↗