Mosquito Control Strategies Research Articles

Transferrin expression profile during bacteria infection in Aedes aegpyti mosquitoes

Female mosquitoes require a blood meal containing iron for egg production; therefore discovering the role of iron and iron‐related proteins has significance in limiting mosquito reproduction. Transferrins are a family of iron‐binding proteins involved in iron uptake, immunity, cell growth, and blood and hormone responses during oogenesis. In hens, serum transferrin (Tf1) functions in iron transport, while ovotransferrin (Tf2) has an antimicrobial role in egg whites. The expression profile of Tf1 and Tf2 mRNA in the yellow fever mosquito, Aedes aegypti, was investigated at various life stages and during infection using real time RT‐PCR. In A. aegypti larval CCL‐125 cells treated with E. coli/B. subtilis and iron, Tf1 showed a time‐dependent, significant increase, while Tf2 expression decreased with bacteria treatment. Fat body (FB) tissues collected from blood‐fed females post bacteria injection contained more Tf1 and Tf2 transcripts than either midgut (MG) or ovary (OV). Infection caused a significant decrease in Tf1 and Tf2 levels in FB, a decrease in Tf1 and increase in Tf2 in MG, and an increase in Tf1 and decrease in Tf2 in OV at 72 hrs post blood meal. Further studies will measure Tf expression in eggs, larvae, pupae, males and sugar or blood‐fed females to reveal developmental, sex‐specific and reproductive roles. These findings may provide targets for mosquito vector and pathogen control strategies. This work was supported by funds from the National Institutes of Health (GM056812), the Agricultural Experiment Station, the College of Agriculture and Life Sciences and the BIO5 Institute for Collaborative Bioresearch at The University of Arizona.

Characterization of Mosquito Iron Regulatory Protein 1 in Aedes aegypti mosquito

The spread of insect‐transmitted diseases is prevalent due to the female blood‐feeding mosquitos’ ability to carry pathogens. The iron component of the blood meal is critical for mosquito oogenesis, and thus, the manipulation of iron metabolism is a potential option to develop mosquito control strategies and decrease the transmission of these diseases. A major protein in iron metabolism is iron regulatory protein 1 (IRP1). IRP1 controls translation of several proteins involved in iron metabolism. In mammals, phosphorylation occurs at two sites by protein kinase C (PKC) and alters IRP1 interaction with mRNA. Mosquito IRP1 contains one site homologous to the mammalian IRP1 as well as a second unique site. Phosphorylation at the unique site may explain the different behavior of mosquito IRP1. This study attempts to determine if mosquito IRP1 is phosphorylated. Aedes aegypti (yellow fever mosquito) CCL‐125 cells or Anopheles gambiae 4a3b cells were treated with phorbol‐12‐myristate‐13‐acetate (PMA) to stimulate PKC. We report our efforts to detect IRP1 phosphorylation in these cells using SDS‐PAGE, fluorescent staining and treatment of the cells in the presence of 32P‐orthophosphate followed by immuno‐precipitation. Experiments using mammalian cells served as controls. In the long term, this investigation will contribute to the solution of mosquito population control and reduction of infectious disease.

Urban Wet Environment as Mosquito Habitat in the Upper Midwest

Sampling of Culex larval habitat plays an important role in West Nile virus surveillance and control programs. Although many cities have established mosquito sampling programs and abatement districts, there is relatively little information describing the extent and ecology of urban surface waters and stormwater systems in different geographic areas and how these parameters affect mosquito communities and control strategies. An aerial survey of the city of Madison, Wisconsin revealed 521 above-ground wet sites. These included both constructed stormwater systems (ditches, retention ponds, detention ponds) and natural wetlands (marshes, flood areas, creeks, and rivers). Repeat sampling of 351 of these sites was conducted during 2004 and 2005. The majority of sites, 58% in 2004 and 72% in 2005, yielded no mosquito larvae, suggesting that physical and biological features of these wet sites limit the development of mosquito larvae. For both years, analysis of the positive samples revealed that less than 25% of sites produced Culex spp. while a small number of ditches and detention ponds were consistent "superproducers" of Culex larvae from year to year. This information will facilitate comparisons across geographical areas and provides insight into local variation in the public health risk due to mosquito transmission of human disease agents.

Cross-induction of detoxification genes by environmental xenobiotics and insecticides in the mosquito Aedes aegypti: Impact on larval tolerance to chemical insecticides

The effect of exposure of Aedes aegypti larvae to sub-lethal doses of the pyrethroid insecticide permethrin, the organophosphate temephos, the herbicide atrazine, the polycyclic aromatic hydrocarbon fluoranthene and the heavy metal copper on their subsequent tolerance to insecticides, detoxification enzyme activities and expression of detoxification genes was investigated. Bioassays revealed a moderate increase in larval tolerance to permethrin following exposure to fluoranthene and copper while larval tolerance to temephos increased moderately after exposure to atrazine, copper and permethrin. Cytochrome P450 monooxygenases activities were induced in larvae exposed to permethrin, fluoranthene and copper while glutathione S-transferase activities were induced after exposure to fluoranthene and repressed after exposure to copper. Microarray screening of the expression patterns of all detoxification genes following exposure to each xenobiotic with the Aedes Detox Chip identified multiple genes induced by xenobiotics and insecticides. Further expression studies using real-time quantitative PCR confirmed the induction of multiple CYP genes and one carboxylesterase gene by insecticides and xenobiotics. Overall, this study reveals the potential of xenobiotics found in polluted mosquito breeding sites to affect their tolerance to insecticides, possibly through the cross-induction of particular detoxification genes. Molecular mechanisms involved and impact on mosquito control strategies are discussed.

Discovery of an alternate metabolic pathway for urea synthesis in adult Aedes aegypti mosquitoes.

We demonstrate the presence of an alternate metabolic pathway for urea synthesis in Aedes aegypti mosquitoes that converts uric acid to urea via an amphibian-like uricolytic pathway. For these studies, female mosquitoes were fed a sucrose solution containing (15)NH4Cl, [5-(15)N]-glutamine, [(15)N]-proline, allantoin, or allantoic acid. At 24 h after feeding, the feces were collected and analyzed in a mass spectrometer. Specific enzyme inhibitors confirmed that mosquitoes incorporate (15)N from (15)NH4Cl into [5-(15)N]-glutamine and use the (15)N of the amide group of glutamine to produce labeled uric acid. More importantly, we found that [(15)N2]-uric acid can be metabolized to [(15)N]-urea and be excreted as nitrogenous waste through an uricolytic pathway. Ae. aegypti express all three genes in this pathway, namely, urate oxidase, allantoinase, and allantoicase. The functional relevance of these genes in mosquitoes was shown by feeding allantoin or allantoic acid, which significantly increased unlabeled urea levels in the feces. Moreover, knockdown of urate oxidase expression by RNA interference demonstrated that this pathway is active in females fed blood or (15)NH4Cl based on a significant increase in uric acid levels in whole-body extracts and a reduction in [(15)N]-urea excretion, respectively. These unexpected findings could lead to the development of metabolism-based strategies for mosquito control.

Evaluation of Bednets After 38 Months of Household Use in Northwest Ghana

A total of 255 bednets were collected 38 months after distribution in Lawra District of northwest Ghana to examine their physical condition and residual insecticide levels. Physical condition varied from nearly pristine to highly damaged. In 50 selected nets, 2023 holes > or = 0.5 cm and 31 holes > or = 10 cm were counted. The incidence of holes increases toward the bottom edge of the net. Seam failures were found in 50% of the nets. Repairs, mostly sewn, were evident in 64% of the nets. Using a combination of bromine x-ray fluorescence (XRF) spectrometry, high-pressure liquid chromatography, and cone bioassays, it was determined that 14.9% of the nets had retained full insecticidal strength. These results highlight the value of real-world data on bednet longevity to guide decisions regarding mosquito control strategies, bednet purchasing, frequency of bednet replacement, and product development.

西宮市における蚊幼虫の発生状況調査（3）：GISによる幼虫発生状況の解析と防除対策立案にむけて

西宮市における蚊幼虫の発生状況調査（3）：GISによる幼虫発生状況の解析と防除対策立案にむけて

Insecticide Resistance in Potential Vector Mosquitoes for West Nile Virus in Japan

Culex pipiens complex is the significant vector mosquito of West Nile virus. To take stock of the current situation of insecticide susceptibilities and design an ideal mosquito control strategy, we collected Culex pipiens pallens Coquillet, Culex pipiens form molestus Forskal, and Culex quinquefasciatus Say from fields in Japan and conducted bioassays for five larvicides (fenitrothion, temephos, etofenprox, diflubenzuron, and pyriproxyfen) by using a larval dipping method. Among five insecticides tested, obvious reduced susceptibilities were observed for etofenprox, which is the only pyrethroid compound registered as a larvicide in Japan. Twenty-two of 56 colonies exhibited a >10% survival rate at the etofenprox concentration of 5.7 microg/ml, which is a 10 times higher concentration of the working solution. The LC50 of a colony collected from Fukuoka prefecture for etofenprox exceeded 60 microg/ml (resistance ratio >2,307), and this colony also exhibited cross-resistance to other pyrethroids, permethrin (299-fold) and phenothrin (1,200-fold). The insect growth regulators diflubenzuron and pyriproxyfen were found to be sufficiently effective enough to control Culex larvae present, but decreased sensitivities to these insecticides were slightly detected in some colonies of Cx. p. form molestus collected from urban areas. Several etofenprox-resistant colonies of Cx. p. form molestus exhibited simultaneously decreased susceptibilities to other insecticides, including temephos, diflubenzuron, and pyriproxyfen.

A24 西宮市における蚊幼虫の発生状況調査 (3) : GISによる幼虫発生状況の解析と防除対策立案にむけて(第59回日本衛生動物学会大会特集)

A24 西宮市における蚊幼虫の発生状況調査 (3) : GISによる幼虫発生状況の解析と防除対策立案にむけて(第59回日本衛生動物学会大会特集)

Two chemosensory receptors together mediate carbon dioxide detection in Drosophila

Blood-feeding insects, including the malaria mosquito Anopheles gambiae, use highly specialized and sensitive olfactory systems to locate their hosts. This is accomplished by detecting and following plumes of volatile host emissions, which include carbon dioxide (CO2). CO2 is sensed by a population of olfactory sensory neurons in the maxillary palps of mosquitoes and in the antennae of the more genetically tractable fruitfly, Drosophila melanogaster. The molecular identity of the chemosensory CO2 receptor, however, remains unknown. Here we report that CO2-responsive neurons in Drosophila co-express a pair of chemosensory receptors, Gr21a and Gr63a, at both larval and adult life stages. We identify mosquito homologues of Gr21a and Gr63a, GPRGR22 and GPRGR24, and show that these are co-expressed in A. gambiae maxillary palps. We show that Gr21a and Gr63a together are sufficient for olfactory CO2-chemosensation in Drosophila. Ectopic expression of Gr21a and Gr63a together confers CO2 sensitivity on CO2-insensitive olfactory neurons, but neither gustatory receptor alone has this function. Mutant flies lacking Gr63a lose both electrophysiological and behavioural responses to CO2. Knowledge of the molecular identity of the insect olfactory CO2 receptors may spur the development of novel mosquito control strategies designed to take advantage of this unique and critical olfactory pathway. This in turn could bolster the worldwide fight against malaria and other insect-borne diseases.

Prospects for the Mosquito Baculovirus Cuninpv as a Tool for Mosquito Control

CuniNPV is a pathogen of Culex mosquitoes, vectors of West Nile virus and other forms of encephalitis. Successful development of CuniNPV requires an efficient production system and formulated product that incorporates magnesium, an essential component for transmission. It may be possible to develop mosquito baculoviruses as a new type of biopesticide by microencapsulating the virus and magnesium into formulations that would be effective regardless of the water quality. In addition, this new insight on transmission may facilitate the discovery and development of additional baculoviruses for the control of other important mosquito vectors. Biological mining of the CuniNPV genome and investigations to understand virus-mosquito interactions at the molecular level offer exciting possibilities for the development of novel mosquito control strategies and tools. Understanding the molecular mechanisms of infection will provide the opportunity to devise new control strategies, for example, compromising the defensive systems of the mosquito (proteases for the peritrophic matrix) or exploiting receptors used by the virus to specifically deliver toxins to mosquito larvae via the midgut. As additional baculovirus genomes become available, comparative genomics could lead to a more informed understanding of how the virus exploits its host as well as the factors responsible for the genus-specific host range of most known mosquito baculoviruses.

Generation of a novel Wolbachia infection in Aedes albopictus (Asian tiger mosquito) via embryonic microinjection

Genetic strategies that reduce or block pathogen transmission by mosquitoes are being investigated as a means to augment current control measures. Strategies of vector suppression and replacement are based upon intracellular Wolbachia bacteria, which occur naturally in many insect populations. Maternally inherited Wolbachia have evolved diverse mechanisms to manipulate host insect reproduction and promote infection invasion. One mechanism is cytoplasmic incompatibility (CI) through which Wolbachia promotes infection spread by effectively sterilizing uninfected females. In a prior field test, releases of Wolbachia-infected males were used to suppress a field population of Culex pipiens. An additional strategy would employ Wolbachia as a vehicle to drive desired transgenes into vector populations (population replacement). Wolbachia-based population suppression and population replacement strategies require an ability to generate artificial Wolbachia associations in mosquitoes. Here, we demonstrate a technique for transferring Wolbachia (transfection) in a medically important mosquito species: Aedes albopictus (Asian tiger mosquito). Microinjection was used to transfer embryo cytoplasm from a double-infected Ae. albopictus line into an aposymbiotic line. The resulting mosquito line is single-infected with the wAlbB Wolbachia type. The artificially generated infection type is not known to occur naturally and displays a new CI crossing type and the first known example of bidirectional CI in Aedes mosquitoes. We discuss the results in relation to applied mosquito control strategies and the evolution of Wolbachia infections in Ae. albopictus.

New strategy against Aedes aegypti in Vietnam

The container-breeding mosquito, Aedes aegypti, is the major global vector of dengue viruses, causing around 50 million infections annually. We have developed a mosquito control strategy, incorporating four elements: (1) a combined vertical and horizontal approach that depends on community understanding; (2) prioritised control according to the larval productivity of major habitat types; (3) use of predacious copepods of the genus Mesocyclops as a biological control agent; delivered by (4) community activities of health volunteers, schools, and the public. We have previously reported that, from 1998 to 2003, community-based vector control had resulted in A aegypti elimination in six of nine communes, with only small numbers of larvae detected in the others. Here, we report eradication in two further communes and, as a result of local expansion after the project in three northern provinces, elimination from 32 of 37 communes (309730 people). As a result, no dengue cases have been detected in any commune since 2002. These findings suggest that this strategy is sustainable in Vietnam and applicable where the major sources of A aegypti are large water storage containers.

Pesticides and public health: integrated methods of mosquito management.

Pesticides have a role in public health as part of sustainable integrated mosquito management. Other components of such management include surveillance, source reduction or prevention, biological control, repellents, traps, and pesticide-resistance management. We assess the future use of mosquito control pesticides in view of niche markets, incentives for new product development, Environmental Protection Agency registration, the Food Quality Protection Act, and improved pest management strategies for mosquito control.

ESTERASE PHENOTYPES IN NATURAL POPULATIONS OF CULEX PIPIENS PALLENS (DIPTERA: CULICIDAE) AND THEIR VARIATIONS UNDER INSECTICIDE SELECTION

Abstract Three populations of Culex pipiens pallens Coquillett, from Hangzhou, Linhai and Jinhua, were determined for their probability of resistant esterase phenotypes. Further, each population was selected with dipterex, chlorpyrifos, temephos and malathion at a given dose of 60%-70% mortality and was determined for the variation of resistant esterase phenotypes in its offspring. The results indicated that esterase B1 phenotype was dominant in three populations although different natural populations have a different probability distribution of esterase B phenotypes. Insecticide selection showed that various esterase loci seemed to have different selective advantages under different insecticide pressures. The esterase B1 phenotype was selected under temephos, and the esterase B2 phenotype was selected under dipterex and chlorpyrifos. Except for the esterase B1 phenotype, the heterozygote of B1/B2 phenotypes was detected under malathion pressure. These results are discussed in relation to the selective advantages of esterase genes to OP pressure and mosquito control strategies.

Distribution of organophosphate and carbamate resistance in Culex pipiens quinquefasciatus (Diptera: Culicidae) in West Africa.

The distribution of organophosphate and carbamate resistance was investigated in 33 samples of Culex pipiens quinquefasciatus Say from 25 cities in Côte d'Ivoire and Burkina Faso. Organophosphate resistance levels were higher in Côte d'Ivoire than in Burkina Faso. Chlorpyrifos resistance ratios at LC95 ranged from 4 to 30 times in Côte d'Ivoire and from 3 to 6 times in Burkina Faso. For temephos, ratios ranged from 3 to 18 and from 1 to 2, respectively. Of 27 samples from Côte d'Ivoire, 25 also displayed cross resistance to carbamates as shown by a mortality plateau in bioassays with propoxur and carbosulfan (similar to chlorpyrifos). Cross resistance to organophosphates and carbamates was caused by an insensitive acetylcholinesterase allele (AceR). This gene was absent from Burkina Faso, except in Niangoloko near the Côte d'Ivoire border. Organophosphate resistance also was associated with the presence of A2-B2 overproduced esterases which had higher frequencies in Côte d'Ivoire (75-100%) than in Burkina Faso (40-50%). Two other esterases with the same electrophoretic mobility as C2 from Puerto Rico and B1 from California were identified for the 1st time in West Africa. "C2" was widespread, whereas "B1" was present in only a few mosquitoes from Côte d'Ivoire. These differences in resistance patterns should be taken into consideration in planning urban mosquito control strategies within 2 countries.

Resistance to Bacillus sphaericus involves different mechanisms in Culex pipiens (Diptera:Culicidae) larvae.

Field Culex pipiens pipiens (L.) mosquitoes that were collected after a control failure with Spherimos in southern France developed high resistance (> 10,000-fold) to Bacillus sphaericus crystal toxin after < 8 generations of laboratory selection. We show that this resistance is encoded by a single major recessive gene on linkage group I at 22.1 recombination units from the sex locus, and that it is not associated with any loss of binding affinity between brush border membrane fractions and the B. sphaericus radiolabeled toxin. Thus, in Southern France, resistance differs from the high B. sphaericus resistance developed after laboratory selection of Californian C. p. quinquefasciatus. This demonstrates that at least 2 different mechanisms may confer high levels of resistance to B. sphaericus crystal toxin in mosquitoes of the C. pipiens complex. These results have important implications for mosquito control strategies.

Resistance monitoring in Culex pipiens (Diptera: Culicidae) from central-eastern France.

Insensitive acetylcholinesterase (AceR) and five over-produced esterases (A1, A2 and B2, and A4 and B4) involved in detoxification are responsible for resistance to organophosphorous insecticides (OPs) in Culex pipiens L. from the Rhône-Alpes region, where C. pipiens control is mainly accomplished with the OPs temephos and chlorpyrifos using 0.15 mg/liter doses. The strong linkage disequilibria observed between esterases A1 and Est-20(0.64), esterases A4 and B4, and esterases A2 and B2 indicate that these genes were introduced in the Rhône-Alpes region. AceR and esterase A1, which appeared in the south of France 3 yr before the start of mosquito control in Rhône-Alpes, had the highest frequencies. All resistant genotypes were shown to be killed by 0.15 mg/liter temephos in natural breeding sites, but not by 0.15 mg/liter chlorpyrifos. These results are discussed in relation with mosquito control strategies.

SEASONAL ABUNDANCE OF POTENTIAL MALARIA VECTORS IN THE TORRES STRAIT, 1985–861

AbstractTo determine the potential malaria vectors and their seasonal abundance in the Torres Strait, EVS carbon dioxide baited light traps were placed on the major populated islands and operated weekly. Anopheles farauti Laveran s.l. was abundant on Boigu Island from April to late June and on Saibai Island from January to August. An hilli Woodhill and Lee was abundant on Boigu and Horn Islands from April to late June. An. farauti s.l. was also trapped on Horn, Yam and Yorke Islands, and An hilli on Saibai, Thursday and Yam Islands. An. amictus Edwards, An annulipes Walker s.l., An bancroftii Giles, An meraukensis Venhuis and An novaguinensis Venhuis were also recorded on various islands. The contrasting ecological characteristics of the islands were reflected in collections and it is suggested mosquito control strategies be tailored accordingly.

Bacillus sphaericus for the control of mosquitoes

AbstractFrom 1972 to 1977 a large laboratory effort was devoted to determining data on efficacy, safety, environmental impact (on nontarget organisms), and some preliminary field work using several isolates of Bacillus sphaericus. The B. sphaericus strains were found to be specific in their mosquito larvicidal activity, not causing mammalian toxicity nor apparent perturbation of the environment. During this period several fermentation and industrialization problems were investigated so that by 1978, using new strains and cultures, it was possible to have prepared kilogram amounts of an active dry stable powder, of strain 1593, for field evaluation. These field evolution. These field evaluations are presently still in progress. Control has been seen particularly against Culex, Anopheles, and Psorophora species, with some what less control aganst Aedes species. Unlike the agriculturally oriented Bacillus thuringiensis candidates, B. sphaericus bacterial cell, which is digested in the larval midgut (within a peritrophic membrane), releasing a toxin as early as 15 min after ingestion. Subsequent death of the larva ensues. Recent evidence suggests that applied B. sphaericus powder will survive in aquatic situations (ditches, ponds, and tree holes) for at least nine month. Comparisons of the B. sphaeicus strains with recently isolated strains of B. thuringiensis (var. israelensis), the latter being particularly active against Aedes species, indicates that they may be useful complements of each other in overall mosquito control strategies. The recent isolation of several new strains of B. thuringiensis, from WHO‐CCBC accessions from Roumania, indicate that although the B. thuringiensis isolate is a rare event when compared to the occurrence of B. sphaericus isolates (they usually occur together in accessions from which B. thuringiensis is isolated), several new useful strains of B. thuringiensis should be anticipated. The longevity of the B. thuringiensis strains in the wild has not yet been investigated.