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[Reevaluation of the biological control of vector mosquitoes using predatory larvae of Toxorhynchites mosquitoes].

Attempts to control mosquito-borne disease using predatory mosquitoes such as Toxorhynchites larvae have led to indefinite results for many years, mainly because of the lack of adequate species or strains of Toxorhynchites. Recent improvements of natural and artificial matings of adults in the laboratory and of mass breeding of larvae, however, have made it possible to establish laboratory colonies of most Toxorhynchites species whenever and wherever necessary. Effects of biological control by releasing large numbers of Toxorhynchites mosquitoes should be reevaluated from a new concept of comparing the usual chemical insecticides with the living and flying "insecticides" which cause no environmental pollution.

Animals↗

Evaluation of mosquito fish Gambusia affinis in the control of mosquito breeding in rice fields.

The mosquito control potential of Gambusia affinis, a mosquito fish, was evaluated in rice fields in the Shahjahanpur district of Uttar Pradesh. This fish, at a stocking rate of 5 fishes/sq m, significantly reduced the larval and pupal densities in experimental fields as compared to control fields during the entire observation period of 42 days. Control of mosquito breeding in rice fields through this fish seems to be promising.

Animals↗

Field efficacy of mosquito coil formulations containing d-allethrin and d-transallethrin against indoor mosquitos especially Culex quinquefasciatus Say.

Comparative field efficacy studies of four mosquito coil formulations containing active ingredient of d-allethrin (0.19 or 0.28 w/w) and d-transallethrin (0.12 or 0.16% w/w) and blank coils without active ingredient were carried out in living rooms (mean size 54.1 m3) of residential houses in a squatter area in Butterworth, Malaysia. The major indoor biting mosquitos collected in the test site were that of Culex quinquefasciatus Say (84.7%). Mean percentage reduction of blank coils, coils with 0.19 and 0.28% d-allethrin and coils with 0.12 and 0.16% d-transallethrin were 29.0, 71.7, 70.9, 75.0 and 72.6%, respectively. The use of coils as a mean of personal protection against mosquitos is discussed.

Allethrins↗

Modelling prey-predator cycles using hemipteran predators of mosquito larvae for reducing world-wide mosquito-borne disease incidence.

Diplonychus indicus is an aquatic hemipterous bug known to be a voracious predator of dipteran larvae, among others, and to show a selective predation for mosquito larvae when exposed to a mixed prey diet. A datum consisted of the percentage of the fourth instar of (25) culicine mosquitoes killed by the bug. Data around the clock, published earlier (from starved adult males of this bug), reanalyzed by single cosinor, reveal a circasemidian rhythm (p = 0.004). This result prompts the recommendation of studying the time structure of prey-predator cycles further to evaluate the merits or demerits of introducing the bug in the field with the aim of reducing worldwide mosquito-borne disease incidence.

Animals↗

Analysis of the endocytic pathway mediating the infectious entry of mosquito-borne flavivirus West Nile into Aedes albopictus mosquito (C6/36) cells.

The initial interaction between mosquito-borne flavivirus West Nile and mosquito cells is poorly characterized. This study analyzed the endocytic and the associated signaling pathway that mediate the infectious entry of West Nile virus (WNV) into mosquito cell line (C6/36). Pretreatment of C6/36 cells with pharmacological drugs that blocks clathrin-mediated endocytosis significantly inhibited virus entry. Furthermore, the transfection of functional blocking antibody against clathrin molecules and the overexpression of dominant-negative mutants of Eps15 in C6/36 cells caused a marked reduction in WNV internalization. WNV was shown to activate focal adhesion kinase (FAK) to facilitate the endocytosis of virus but not the mitogen-activated protein kinases (ERK1 and ERK2). Subsequent to the internalization of WNV, the virus particles are translocated along the endosomal pathway as revealed by double-immunofluorescence assays with anti-WNV envelope protein and cellular markers for early and late endosomes. Specific inhibitor for protein kinase C (PKC) was shown to be highly effective in blocking WNV entry by inhibiting endosomal sorting event. The disruption of the microtubule network using nocodazole also drastically affects the entry process of WNV but not the disruption of actin filaments by cytochalasin D. Finally, a low-pH-dependent step is required for WNV infection as revealed by the resistance of C6/36 cells to WNV infection in the presence of lysosomotropic agents.

Actin Cytoskeleton↗

Stable integration and expression of mosquito-larvicidal genes from Bacillus thuringiensis subsp. israelensis and Bacillus sphaericus into the chromosome of Enterobacter amnigenus: a potential breakthrough in mosquito biocontrol.

Previously, we have successfully integrated a spectinomycin/streptomycin resistance gene into Enterobacter amnigenus strain An11, a potential host for mosquito control, using in vivo recombination via homologous recombination (An11S4::Omega). We now report the successful transfer of two mosquito-larvicidal genes, cry4B from Bacillus thuringiensis subsp. israelensis and binary toxin genes from Bacillus sphaericus, into the host genome. To facilitate the screening procedure, the E. amnigenus derivative, An11S4::Omega, was used as a host. The integration of both toxin genes by two successive crossover events interrupted the Omega region yielding two integrants designated An11S4::cry4B and An11S4::Omega::bin, respectively. Differences in the integration efficiency of these toxin genes were observed. The presence of both genes in the target sites of the host genome was verified by PCR. Cry4B was expressed weakly from An11S4::cry4B, but no expression of the binary toxin gene could be detected from An11S4::Omega::bin. Nevertheless, these two integrants exhibited mosquito-larvicidal activity against Aedes and Culex, suggesting that both proteins were expressed, but at very low levels.

Animals↗

DEET mosquito repellent sold through social marketing provides personal protection against malaria in an area of all-night mosquito biting and partial coverage of insecticide-treated nets: a case-control study of effectiveness.

DEET (diethyl-3-methylbenzamide), the widely used mosquito repellent, has the potential to prevent malarial infection but hitherto there has been no study demonstrating this possibility during normal everyday use. Mosbar, a repellent soap containing DEET, was promoted through social marketing in villages in eastern Afghanistan. This was followed up with a case-control study of effectiveness against malarial infection conducted through local clinics. Mosbar was purchased by 43% of households. Reported use of insecticide-treated nets (ITNs) was 65% among the control group. There was a strong association between Mosbar use and ITN use, as 81% of Mosbar users also possessed ITN. The use of Mosbar was associated with a 45% reduction in the odds of malaria (95% CI: -11% to 72%, P=0.08) after adjusting for ITN and other unmatched factors. Ownership of ITNs was associated with a 46% reduction in the odds of malaria (95% CI: 12% to 67%, P=0.013) after adjusting for Mosbar and other unmatched factors. The greatest reduction in the odds of malaria was associated with combined use of Mosbar and ITN (69% reduction, 95% CI: 28% to 87%, P=0.007). The association between recalled use of Mosbar 10 days ago (nearer the time of infection) and reduction in malarial infections (adjusted odds ratio 0.08, 95% CI: 0.01-0.61, P=0.001) was significantly stronger than that shown by current use of Mosbar. Most purchasers of Mosbar were satisfied with the product (74%), although a minority said they preferred to use only ITN (8%). The local mosquito vectors, Anopheles stephensi and A. nigerrimus, started biting shortly after dusk and continued biting until early morning. It was shown that Mosbar prevented biting throughout this period. In regions where mosquito vectors bite during evening and night, repellents could have a useful supplementary role to ITN and their use should be more widely encouraged.

Adolescent↗

Seroprevalences of antibodies against thoracic proteins of three species of mosquito, among the residents of an area where filariasis is endemic: relationship with the mosquito densities.

Attempts were made to correlate the numbers of indoor-resting Culex quinquefasciatus, Armigeres theobold and Anopheles vagus in Raipur, Chattisgarh state, India, with the seroprevalences, among the city's microfilaraemic and 'endemic normal' residents, of antibodies reacting with thoracic proteins from the adult females of each of these species. Overall, 6478 female mosquitoes were collected in about 176 man-hours spread over a 12-month period. Antibodies to Cx. quniquefasciatus, the commonest species and the only one to be prevalent in all seasons of the year, were detected in 90% of the microfilaraemic subjects and 27% of the endemic normal. Although Armigeres theobold only constituted 5% of the mosquitoes collected, 96% of the microfilaraemic subjects and 69% of the endemic normal subjects had antibodies against thoracic proteins of this species (almost 50% of all the sera having high titres of such antibodies). Antibodies to An. vagus were detected, although almost always at very low titres, in 84% of the microfilaraemic subjects and 42% of the endemic normal. Thus, the seroprevalence of antibodies to thoracic antigens from a mosquito species bore no relationship with the indoor-resting densities of that species.

Animals↗

Diel changes in adult mosquito microhabitat temperatures and their relationship to the extrinsic incubation of arboviruses in mosquitoes in Kern County, California.

Microhabitat temperatures experienced by nocturnally active Culex tarsalis Coquillett mosquitoes were measured in the southern San Joaquin Valley of California. Temperatures of the diurnal resting shelter and nocturnal activity air space were measured by digital recorder at three Cx. tarsalis habitats in Kern County. Temperatures measured by digital recorders agreed well with temperatures recorded concurrently at nearby California Irrigation Management and Inspection System weather stations. Monthly temperatures among habitats were combined to depict the diel temperature regimen experienced by female Cx. tarsalis as a consequence of daily movement between the diurnal resting shelter and nocturnal air space. Transitions between the two microhabitats corresponded to the times of mosquito ingress and egress (i.e., sunrise and sunset). The composite daily temperature mean ranged from 7.4 degrees C in December to 21.5 degrees C in July, and temperature extremes seldom exceeded a daily maximum of 25.0 degrees C during the summer or dropped below a daily minimum of 5.0 degrees C during the winter. Overall, mosquitoes occupied a composite thermal environment where the extrinsic incubation of an arbovirus would have occurred at ambient temperatures that were cooler than either the diurnal resting shelter or activity air space.

Animals↗

Enhanced T-cell response to mosquito extracts by NK cells in hypersensitivity to mosquito bites associated with EBV infection and NK cell lymphocytosis.

Hypersensitivity to mosquito bites is characterized by severe systemic as well as local symptoms, and associated with chronic active EBV infection and NK cell lymphocytosis. In this HEN disease, we investigated the response of PBMC to MSG extracts. PBMC were taken from three defined cases of HEN disease, three borderline cases, five individuals with simple exaggerated reactions to mosquito bites without systemic symptoms (simple responders), and eight healthy donors. PBMC, or purified CD4+, CD8+ or CD56+ cells, were cultured with MSG extracts prepared from each of five mosquito species to examine their proliferation and cytokine secretion. The patients with HEN disease had high stimulation indices with variations in responses to the extracts from Aedes albopictus, Aedes aegypti, Anopheles sinensis and Culex pipiens pallens. However, a non-Japan-habitant species Anopheles stephensi did not stimulate the patients' PBMC. Some borderline or simple responders showed moderate proliferation, and healthy donors had no reactive PBMC. In HEN disease, both CD56+ NK cells (producing IFN-gamma) and CD4+ Th0 cells (producing IL-4 and IFN-gamma) were increased in the blood. CD4+ cells, but not CD56+ NK cells or CD8+ cells, propagated in response to MSG extracts. However, this response of CD4+ cells and their IL-4 production were strongly enhanced by coexisting CD56+ cells. We suggest that the CD4+ T cell serving as the primary responder to MSG antigen and the NK cell functioning as the enhancer are both pathogenic in the development of HMB.

Animals↗

Host-feeding habits of Culex and other mosquitoes (Diptera: Culicidae) in the Borough of Queens in New York City, with characters and techniques for identification of Culex mosquitoes.

The host-feeding patterns of mosquitoes (n = 247) collected in the Borough of Queens in New York City in July and August 2000 were investigated using an indirect ELISA and a polymerase chain reaction (PCR)-heteroduplex assay. Culex pipiens L. and Cx. restuans Theobald fed primarily on birds, and their feeding habits support their implication as enzootic vectors of West Nile virus. Culex salinarius Coquillett and Coquillettidia perturbans (Walker) fed mainly on mammals, with fewer blood meals taken from birds, and these two species are potential bridge vectors of West Nile virus. Culex mosquitoes took blood meals (n = 54) from 11 different avian species. Only the northern cardinal (Cardinalis cardinalis), American robin (Turdus migratorius), and Brown-headed cow bird (MolIothrus ater) were fed upon by all three Culex species. Multiple blood feedings on avian hosts were detected in Cx. pipiens and Cx. restuans. Species identifications of Culex mosquitoes made using morphological characteristics were confirmed with a PCR assay that employed species-specific primers. All Cx. pipiens (n = 20) and Cx. salinarius (n = 10) specimens were correctly identified, but three (20%) of 15 Cx. restuans were misidentified as Cx. pipiens.

Animals↗

Maxillae and mandibles of male mosquitoes and female autogenous mosquitoes (Diptera: Culicidae).

Maxillae and mandibles of males of 44 species of 12 mosquito genera and females of three autogenous genera and two partially autogenous species were examined under light microscopy and scanning electron microscopy. The maxillae and mandibles of male mosquitoes are delicate, tape-like structures with lengths characterizing genera or higher level classification units. Five patterns are recognized: (A) long maxillae and mandibles with mandibles longer than maxillae in Anopheles; (B) long maxillae and mandibles with maxillae longer than mandibles in Toxorhynchites; (C) short or intermediate lengths of maxillae with short mandibles in Aedes, Armigeres, Culex, Ochlerotatus, Orthopodomyia, and Uranotaenia; (D) short or intermediate length of maxillae with no mandibles in Mimomyia and Tripteroides; and (E) no maxillae and mandibles in Malaya and Topomyia. Maxillary and mandibular lengths of male mosquitoes show a positive correlation. Length of maxillae and mandibles of autogenous females are reduced to the same level as conspecific males. In contrast, females of partially autogenous species have complete maxillae and mandibles as in females of anautogenous species.

Animals↗

A list of the mosquitoes housed in the mosquito museum at the Vector Control Research Centre, Pondicherry, India.

The establishment of a mosquito museum at the Vector Control Research Centre, Pondicherry, India, is reported. The collection at present contains more than 14,800 adult mosquitoes, including 8,426 that are individually pinned. The collection also includes some 1,048 male and female genitalia preparations, and 815 larval and 444 pupal exuviae on microscope slides. Mosquitoes of 19 genera, 37 subgenera, and 181 species are housed in the museum, representing about 50% of the known species from India. A list of the species is provided.

Aedes↗

[A comparative analysis of the potential epidemiological importance of mosquitoes in the genus Anopheles under the anthropogenic landscapes in the Chu Valley, Kyrgyz Republic. III. The age composition of the females in natural populations of the dominant malarial mosquito species].

The age composition of female malaria mosquitoes prevailing under the conditions of the man-made areas of the piedmont zone of the Chu River Valley, Republic of Kirghizia. That of the natural An. claviger and An. messeae populations was examined throughout the period of mosquito activity in the season of 1992. The physiological age of female malaria mosquitoes was determined by the expansion of ovarioles with terminal legs (Polovodova, 1947; Detinova, 1949), the maximum quantities of the expansions being borne in mind (Anufrieva, Artem'ev, 1981). A total of 2,606 females were dissected. In the piedmont zone of the Chu River Valley An. claviger and An. messeae were found to make at least five and six cycles, respectively, which is suggestive of their potential epidemiological significance.

Aging↗

A classification system for mosquito life cycles: life cycle types for mosquitoes of the northeastern United States.

A system for the classification of mosquito life cycle types is presented for mosquito species found in the northeastern United States. Primary subdivisions include Univoltine Aedine, Multivoltine Aedine, Multivoltine Culex/Anopheles, and Unique Life Cycle Types. A montotypic subdivision groups life cycle types restricted to single species. The classification system recognizes 11 shared life cycle types and three that are limited to single species. Criteria for assignments include: 1) where the eggs are laid, 2) typical larval habitat, 3) number of generations per year, and 4) stage of the life cycle that overwinters. The 14 types in the northeast have been named for common model species. A list of species for each life cycle type is provided to serve as a teaching aid for students of mosquito biology.

Animals↗

Studies with equine infectious anemia virus: transmission attempts by mosquitoes and survival of virus on vector mouthparts and hypodermic needles, and in mosquito tissue culture.

Biological and mechanical transmission trials with Psorophora columbiae (Dyar and Knab) and Aedes sollicitans (Walker) and ponies acutely infected with equine infectious anemia virus (EIAV) were negative. The EIAV antigen was detected by radioimmunoassay in Ae sollicitans immediately after the mosquitoes had fed on an acutely ill pony, but not 14 days after feeding. Psorophora columbiae mosquitoes had detectable EIAV antigen as determined by radioimmunoassay 24 hours after they fed on an acutely ill pony; this antigen was not detected again until 6 days after feeding and was still detected 14 days after feeding. The EIAV was detected on hypodermic needles held at 25 C for 96 hours, but was not detected 120 hours after the needles were dipped in solutions of EIAV. The virus was detected on the mouthparts of mosquitoes for 1 hour after they had fed on an EIAV-rich medium, but was not detected 4 hours after feeding. Culex pipiens quinquefasciatus Say ovarian cells maintained the infectivity of EIAV for 10 weekly passages, but no evidence for virus multiplication was obtained.

Aedes↗

Do traditional mosquito repellent plants work as mosquito larvicides?

Plant derived larvicides were evaluated in Kamhororo, an area of Zimbabwe. Twenty five third and fourth instar An. gambiae s.s mosquito larvae were used per test according to the method of WHO. All larvicides were effective against the An. gambiae s.s mosquito larvae and were comparable to studies done in Tanzania using Orange peel extracts. The extracts of the plant Ocimum canum (LC50 = 54, 94 x 10(3) ug/ml) were more effective in killing the larvae than Lippia javanica (LC50 = 125,34mg x 10(3) ug/ml). These concentrations are higher when considering commercial larvicides.

Animals↗

Bioefficacy of mosquito mat, coil and dispenser formulations containing allethrin group of synthetic pyrethroids against mosquito vectors.

The bioefficacy of mats, coils and dispensers containing allethrin group of synthetic pyrethroids was studied against laboratory strains of Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi. Except esbiothrin in the mat formulation which was 100 and 178 times more effective against Cx. quinquefasciatus than against Ae. aegypti and An. stephensi with KT50 of 0.005, 0.5 and 0.89 min. respectively, all the three allethrins in mat or coil formulations were equally effective against the three vector mosquitoes. When compared to mat formulations of d-allethrin and bioallethrin, mat formulation of esbiothrin was 156 and 144 times more effective against Cx. quinquefasciatus. It was 162 times more effective against Cx. quinquefasciatus than in the coil formulation. Dispenser containing d-allethrin was the least effective against Cx. quinquefasciatus (KT50: 2.65 min.) and Ae. aegypti (KT50: 4.68 min.) but as effective as coil against An. stephensi. When mat and dispenser heated or coil burnt continuously for 10 hours the knockdown was consistently above 60% in all the three vector species but mortality was not consistently > 60% in Ae. aegypti. Repellent effect of the formulations ranged from 0.0 to 80.3%, 0 to 57.3% and 59.2 to 78.3% against Cx. quinquefasciatus Ae. aegypti and An. stephensi respectively. Repellency was more against An. stephensi than against the other two species. Mats and coils deterred > 50% of the mosquitoes from feeding on the chicken (range: 50 to 99.52%) but in case of dispenser the effect was only 14.72 to 65.01%. The use of these formulations as a control tools in reducing man-vector contact is discussed.

Allethrins↗