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PubMed1998

[The effect of insecticide resistance on the demographic parameters of 3 strains of Culex quinquefasciatus (Diptera: Culicidae) under laboratory conditions].

The life tables of 3 strains of Culex quinquefasciatus were studied under laboratory conditions: Slab, susceptible to reference; Old Havana, treated with cypermethrin until its fourth generation; and Cotorro, from the field. It was found that the different levels of resistance to organophosphate insecticides and pyrethroids present in the Cotorro and Old Havana strains did not influence either on the duration of the period of development of the immature stages or in the sexual proportion of the emerged adults, but they had a favorable and directly proportional effect on the survival and longevity of the adults. However, they exerted a negative and inversely proportional influence on the reproduction and population growth of these strains. Useful data for the use and management of insecticides within the strategies of control of Culex quinquefasciatus, an important vector of lymphatic filariasis, are provided.

Animals↗
PubMed1998

[Resistance in a strain of Culex quinquefasciatus coming from Medellín, Colombia].

The levels of susceptibility and/or resistance to 5 organophosphate insecticides (malathion, methyl-pyrimifos, clorpirifos, temephos and fenthion), 4 pyrethroids (cypermethrin, deltamethrin, permethrin and lambda-cyhalothrin), and a carbamate (propoxur) were determined in order to know the state of resistance in a strain of Culex quinquefasciatus from a locality of the city of Medellín, Colombia. Resistance to all organophosphate insecticides, though with relatively lower values for methyloirimifos and fenthion, was observed. No resistance to lambda-cyhalothrin and cypermethrin or to propoxur was found. These insecticides may be useful for the control of mosquitoes in Colombia. It was demonstrated by using the piperonil butoxide synergist that the oxidases of multiple function played an important role in the resistance to organophosphate insecticides and pyrethroids. The utilization of S.S.S. tributyl phosphotritiate revealed that the superproduction of unspecific esterases was a mechanism of resistance to organophosphate insecticides, except methyl-pirimifos and for perythroids, except lambda-cyhalothrin. This result should be taken into consideration for the strategies to be used to control Culex quinquefasciatus in Colombia. These two mechanism of resistance are not responsible for the resistance to propoxur. The electrophoretic analysis showed the presence of esterases B1, A6 and B6, which seem to have an important function in resistance.

Animals↗
PubMed1999

Culex (Micraedes) biscaynensis n. sp. from Florida (Diptera: Culicidae).

The female, male, male genitalia, pupa, and larva of Culex biscaynensis, a new species in the Bisulcatus Group of subgenus Micraedes, are described and illustrated. The species, which is presently known only from south Florida, United States, is most similar to Culex (Micraedes) antillummagnorum Dyar.

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PubMed2000

Quantitative analysis of gene amplification in insecticide-resistant Culex mosquitoes.

The amplification of carboxylesterase structural genes followed by their overexpression is the most common mechanism of resistance to organophosphorus insecticides in Culex mosquitoes. Most resistant Culex quinquefasciatus mosquitoes have co-amplified estalpha2(1) and estbeta2(1) genes. Recently, Southern, DNA dot-blot analysis and phosphorimaging technology were used to quantify the est gene copy number in aphids and mosquitoes. Although more accurate than autoradiography, this method relies on probe hybridization, which can be variable. We have directly measured gene and mRNA copy number by using real-time quantitative PCRs in mosquitoes. The acquisition of fluorescence from incorporation of the double-strand-specific dye SYBR GreenI into a PCR product once per cycle is used to provide an absolute quantification of the initial template copy number. Thus it has been possible to show that estalpha2(1) and estbeta2(1) are co-amplified approx. 80-fold in the genome of the resistant PelRR strain of C. quinquefasciatus. The two genes, although co-amplified in a 1:1 ratio, are differentially transcribed: the estbeta2(1) gene from this amplicon has greater transcription than estalpha2(1) in all individual mosquito larvae tested, with an average ratio of 10:1. Purified esterases from mosquito homogenates were found in a ratio of 3:1, which, combined with the quantitative mRNA data, suggests the operation of both transcriptional and translational control mechanisms to regulate the expression of the amplified genes in C. quinquefasciatus insecticide-resistant mosquitoes.

Animals↗
PubMed1998

Rate of resistance development in wild Culex quinquefasciatus (Say) selected by malathion and permethrin.

Wild caught female Culex quinquefasciatus (Say) from Kuala Lumpur were blood fed and reared in the insectarium. The late third stage of the F1 larvae which survived the high selection pressure of malathion and permethrin were reared and colonies were established from adults that emerged. Larvae from these colonies were then subjected in the subsequent 9 generations to higher selection pressure. The rate of resistance development were measured by LC50 value of larval bioassay, LT50 value of adult bioassay and the frequency of the elevated esterase levels. In another set of experiments using the same batch of Culex mosquitos, the larvae were not exposed to any insecticides and the decrease in resistance rate was monitored in each subsequent 9 generations by using similar methods. The heterozygous standard laboratory strain was selected for susceptibility using the single raft sib-selection method. The result showed that the field collected F1 generation was 96.0 and 6.3 fold more resistant to malathion and permethrin, respectively. After selection for about 9 generations the resistance ratio to malathion and permethrin was 6.2 and 767.3 fold more compared to the LC50 values of F1 generations, respectively. Esterase in F1 larvae was 6.0 fold more than the standard laboratory strain.

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PubMed2000

Extended effect of Bacillus thuringiensis H-14 on Culex pipiens adults surviving larval treatment.

Three Bacillus thuringiensis H-14 preparations (a laboratory prepared and two commercial formulations namely, Tecknar and Vectobac) were assayed against third instar Culex pipiens larvae in order to trace their toxic activity on larval treatment. The LC50 values were 0.002, 0.02 and 0.04 ppm. respectively. The laboratory strain was tested on the development of Culex pipiens. Larval mortality, pupation, adult emergence and sex ratio showed significant differences as compared to the non-treated group. Toxic action on the treated larvae with laboratory strain of B. thuringiensis H-14 revealed drastic effect on larval mid-gut epithelium and resulted in extended pathological activity in adults, which survived larval treatments. Nervous and reproductive systems were found to be the most damaged systems in female adults.

Animals↗
PubMed2001

Host preference of Culex quinquefasciatus in Raipur city of Chattisgarh state.

Indoor resting freshly engorged Culex quinquefasciatus collected from three different habitats viz., human, cattle and mixed dwellings of six localities of Raipur city, were analyzed for the source of blood meal by precipitin test. Of the 60 specimens from human dwellings 52 were positive for human blood with an anthropophilic index of 90%. Of the 25 specimens from cattlesheds 15 were positive for human blood with an index of 60%. Of the 20 specimens from mixed dwellings 12 showed human blood with an anthropophilic index of 63.15%. Thus, the Culex quinquefasciatus at Raipur city in Madhya Pradesh state is predominantly anthropophilic in nature irrespective of the nature of habitat of the mosquito vector.

Animals↗
PubMed1999

Pathological alterations in the ovaries of Culex pipiens induced by fixed oil extracts from Thevetia peruvine, Datura stramonium and Acacia sp.

The fixed oil extracts from Thevetia peruvine, Datura stramonium and Acacia sp. were tested on Culex pipiens larvae. The estimated sublethal concentrations (LC50) were used in the present studies. The reproductive potential of females and the histochemistry of their ovaries were determined. The results indicated that oil treatments of larvae caused drastic changes in reproduction potential of female mosquitoes including the ovarian development in the first gonotrophic cycle, fecundity and fertility of treated females. Histological and histochemical studies revealed clear changes in the oocytes of females derived from treated larvae. Treatment with the oils reduced the vitellogenesis, synthesis of proteins, carbohydrates, lipid contents and DNA and RNA materials. The reproduction was always significant and may reflect the shortage in reproductive potential, the state of being disturbed. Generally, these fixed oils merit further investigations as a potential suppressant of Culex pipiens because their abilities to kill the early stages, inhibit growth and development of ovaries and reduce the reproductive potential of adult females. The three oils have variable activities but they are similar in their mode and site of actions.

Acacia↗
PubMed2000

[Effects of Lagenidium giganteum on the activities of three enzymes of Culex quinquefasciatus larvae].

OBJECTIVE: To investigate the possible mechanism underlying the killing of Culex quinquefasciatus larvae by Lagenidium giganteum from the biochemical point of view. METHODS: The activities of alkaline phosphatase(AKP), acid phosphatase(ACP) and esterase(EST) were observed by using calcium-cobalt method, lead nitrate method and naphthol method. Results were photomicrographed and analysed quantitatively by image analysis using computer. RESULTS: The activities of AKP and ACP were decreased while the activities of EST were increased among the infected groups with different infection intensities. CONCLUSIONS: The changes of these enzyme activities might be one of the important mechanisms of action of Lagenidium giganteum against Culex quinquefasciafus larvae.

Acid Phosphatase↗
PubMed2002

[Changes of elements in Culex quinque fasciatus larvae after infected by Lagenidium giganteum (Oomycetes: Lagenidiales)].

OBJECTIVE: To analyze the quantitative change of 18 elements in Culex quinque fasciatus Larvae infected by Lagenidium giganteum (Oomycetes: lagenidiales), and to explore possible mechanism of mosquito-killing by the fungus. METHODS: Elements in the mosquito larvae at different developmental stages from infected and non-infected (control) groups were detected with automatic bioassay machine. RESULTS: At the early stage of infection, content of Ca and Cu in the infected group was markedly lower while the content of Co and Cd were higher than the control. In 24 hrs after infection, the content of Ca, Mg, Na, P, Fe, Zn, Cu, Mn and Cr was significantly lower while that of K, Mo, Co, Ni, Al, Cd and Pb were higher than those in non-infected larvae. No marked difference was found for the content of Sr and B between the two groups. In 48 hrs after infection, considerable difference was found in 17 elements between infected and noninfected larvae, with only one exception of Sr. CONCLUSION: Many elements which play an important role in maintaining the vitality of the mosquito larvae decreased and some of the heavy metal elements accumulated after the infection of Lagenidium giganteum. This might be a part of the killing mechanism to Culex quinque fasciatus larvae.

Animals↗
PubMed2001

[Cloning and identification of deltamethrin-resistance or susceptibility associated genes of Culex pipiens pallens].

OBJECTIVE: To obtain deltamethrin-resistance or susceptibility associated genes of Culex pipiens pallens. METHODS: The differentially expressed genes were obtained by suppression subtractive hybridization (SSH), and identified by cDNA microarray and reverse Northern blotting. RESULTS: 523 and 286 clones were selected respectively in the two directional SSH. 155 and 42 genes were respectively expressed 2-3 and > 3 times higher in the insecticide-resistant strain than in the susceptible strain; 15 and 9 genes were respectively expressed 2-3 and > 3 times higher in the susceptible strain than in the resistant strain. There were 2 genes only expressed in the insecticide-resistant strain. 51 three times differentially expressed clones and 2 specially expressed clones were sequenced. 44 sequences were obtained which belong to 13 new genes. There were 8 over-expressed genes in resistant strain, 7 of which were similar respectively to mitochondrion rRNA gene, 60S ribosomal protein gene, 40S ribosomal protein S4 gene, trypsin gene, chymotrypsin A gene, ospin gene, and 16S ribosomal RNA gene. There were 5 over-expressed genes in susceptible strain, 2 of them being similar with 40S ribosomal protein S29 gene and myosin regulatory light chain 2 gene. In addition, 2 genes specially expressed in resistant strain were similar respectively to glycogen branching enzyme gene and ribosomal protein 46 gene. CONCLUSION: The differentially expressed genes may be associated with deltamethrin-resistance or susceptibility of Culex pipiens pallens.

Animals↗
PubMed2001

[Observation on hemocytes of Culex pipiens quinquefasciatus larvae infected by Lagenidium giganteum].

OBJECTIVE: To explore the possible defensive immunity of Culex pipiens quinquefasciatus larvae after being infected by Lagenidium giganteum. METHODS: To count and analyze morphologically hemocytes of the mosquito larvae with Giemsa's stain and by both phase contrast microscope and ordinary microscope. RESULTS: 1. Following the prolonged duration of infection, the number of hemocytes featured as increase, intense increase and gradual decrease. 2. 48 and 72 h after infection the proportion of plasmatocytes and granulocytes increased significantly, but that of prohemocytes showed a relatively slow increase, while 96 and 120 h after infection the proportion of spherulocytes and oenocytoids increased gradually and that of plasmatocyte and granulocytes showed a slow decrease. 3. After L. giganteum infection, vacuolation and morpholysis were found in plasmatocytes. CONCLUSION: The changes of hemocytes in amount, classification and morphology after infection revealed that Lagenidium giganteum can induce some defensive immune reactions in the larvae of Culex pipiens quinquefasciatus possibly due to a release of antigens or toxic substances by the fungus.

Animals↗
PubMed2003

Emergence of resistance and resistance management in field populations of tropical Culex quinquefasciatus to the microbial control agent Bacillus sphaericus.

In recent years, highly potent mosquitocidal strains of the microbial agent Bacillus sphaericus (Bsph) have been isolated and developed for the control of mosquito larvae around the world. Laboratory selection experiments with the most active strains and their use in large-scale operational mosquito control programs resulted in the emergence of resistance in larvae of the Culex pipiens complex. This generated great concern among vector control agencies around the world, who feared reduced efficacy of this highly active larvicidal agent. To address this issue, the current studies were started to find practical strategies for controlling resistant mosquitoes and more importantly to develop resistance management strategies that would prevent or delay development of resistance. We initiated field studies in 3 low-income communities in Nonthaburi Province, Thailand. In 1 of the communities, larvae of Culex quinquefasciatus that were highly resistant (>125,000-fold) to Bsph strain 2362 were successfully controlled with applications of Bacillus thuringiensis var. israelensis (Bti) alone or in combination with Bsph. To prevent or delay resistance to Bsph, 2 other sites were selected, 1 treated with Bsph 2362 alone and the other treated with a mixture of Bsph 2362 and Bti. Mosquitoes treated with Bsph 2362 alone showed some resistance by the 9th treatment and almost complete failure of control occurred by the 17th treatment. After 9 treatments with the mixture over a 9-month period at another site, no noticeable change in susceptibility to Bsph was detected. During this period, the site treated with Bsph alone required 19 treatments, whereas the site treated with mixtures took only 9 treatments because of slower resurgence of larvae at the site treated with the mixture than at the site treated with Bsph alone. This is the 1st field evidence for delay or prevention of resistance to microbial agents in larval Cx. quinquefasciatus by using mixtures of Bti and Bsph. Further studies on the use of mixtures for the management of field resistance are warranted.

Animals↗
PubMed2003

[Resistance of Culex quinquefasciatus (Say, 1823) to deltamethrin and the use of impregnated mosquito nets in an urban area of Bouaké, Côte d'Ivoire].

The efficacy of pieces of nets treated with two formulations of deltamethrin (concentrated suspension at 1% and tablets at 25%) against two strains of Culex quinquefasciatus ("S-Lab", sensitive strain and "Bouaké", local strain) has been evaluated at the laboratory by experimental tunnels tests. The observed mortality of the sensitive strain has been 2-3 time more important than that of local strain. This observation seems to be linked to Culex quinquefasciatus of Bouaké pyrethrinoids-resistance. The excito-repellency effect of the two formulations has been lower for the local strain than for the sensitive strain. It has also been more important with the tablet at 25% than with concentrated suspension at 1%. The blood feeding rate has been more important for the local strain than for sensitive strain and it has been lower with the tablet at 25% than with the concentrated suspension at 1%.

Animals↗
PubMed1992

Evaluation of methoprene (Altosid XR) sustained-release briquets for control of culex mosquitoes in urban catch basins.

A sustained-release, briquet formulation of methoprene (Altosid XR), applied at a rate of one briquet per catch basin in Saginaw, Michigan, provided ca. 70% reduction in emergence of Culex pipiens and Cx. restuans adults, compared with nontreated catch basins, during a period of 15 wk in the summer of 1990. In a parallel study using one briquet per 10.5 liter bucket, there was 99% reduction in adult emergence of these species for a period of 12 weeks. The difference between catch basins and buckets may be attributable to water movement through the catch basins with each rainfall, causing a dilution of methoprene through time. However, both studies indicated that the briquets released methoprene for 12-15 wk, suggesting that this formulation may offer season-long control of Culex mosquitoes from urban catch basins in Michigan, with a single treatment of insecticide.

Animals↗
PubMed2003

Laboratory and field evaluations of novaluron, a new insect growth regulator (IGR), against Culex mosquitoes.

Limited laboratory and field studies have indicated that the insect growth regulator (IGR) novaluron exhibits good activity against larvae of pest species in the orders Coleoptera, Hemiptera (suborder Heteroptera), and Lepidoptera by both ingestion and contact. We completed laboratory and field studies to evaluate activity and efficacy of novaluron against Culex mosquitoes. In laboratory studies, novaluron was highly active against Cx. quinquefasciatus, as indicated by low levels of inhibition of emergency (IE), at the 50% level, IE50 (0.159 ppb for 2nd-stage larvae and 0.118 ppb for 4th-stage larvae) and IE90, at the 90% level, (0.604 ppb for 2nd-stage larvae and 0.595 ppb for 4th-stage larvae). In outdoor microcosm and mesocosm studies against natural populations, novaluron yielded excellent control of immature Culex mosquitoes for up to 14 days at 1.25, 2.5, and 5 ppb in microcosms, and for up to 7 days at the dosages of 1, 5, and 10 mg/m2 in mesocosms. Based on qualitative observations, novaluron seemed to have a favorable margin of safety for nontarget aquatic invertebrates cohabiting with mosquito larvae. Further large-scale field studies are warranted to evaluate initial efficacy and longevity of novaluron against various mosquito species, as well as its safety for nontarget biota.

Animals↗
PubMed2003

Larval behavior of four Culex (Diptera: Culicidae) associated with treatment wetlands in the southwestern United States.

The diving behavior, aggregation, horizontal distribution under two food regimes, and response to change in ambient light level were studied for fourth instars of four Culex species in the laboratory. Under low food conditions, Cx. erythrothorax larvae dived less frequently, exhibited greater aggregation, and had stronger preferences for the corners of the observation chamber than did larvae of three congeners (Cx. tarsalis, Cx. quinquefasciatus, and Cx. stigmatosoma). Under high food conditions, larvae of all species were more sedentary than under low food conditions; however, the behavior of Cx. erythrothorax larvae changed comparatively little with changes in food abundance. Culex erythrothorax was the most responsive to disturbance (an 11% change in ambient light level), whereas Cx. tarsalis larvae did not respond to small changes in ambient light level. The behavior of Cx. erythrothorax larvae differed significantly from the three congeners studied. Species-specific behavioral differences of larvae may have contributed to the discrepancies of species relative abundance in larval surveys versus emerging adult mosquito collections at constructed wetlands noted in previous studies.

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PubMedDate not supplied

Evaluation of pirimiphos-methyl (50% EC) against the immatures of Anopheles stephensi/An. culicifacies (malaria vectors) and Culex quinquefasciatus (vector of bancroftian filariasis).

BACKGROUND & OBJECTIVES: In India, temephos and fenthion are used as larvicides in fresh and polluted waters. Since use of same insecticide may precipitate resistant, as an alternative bioefficacy of pirimiphos-methyl--an organophosphorus insecticide was evaluated against immatures of Anopheles and Culex species in different breeding habitats in District Ghaziabad (U.P.) and Goa. METHODS: Laboratory bioassays were carried out using standard WHO procedure. LC50 and LC90 were calculated using Probit analysis. Abbott's formula was used to calculate per cent corrected mortality in laboratory exposures while, Mulla's formula was applied for calculating per cent reduction in mosquito immatures under field conditions. RESULTS: Pirimiphos-methyl was found to be most effective against larvae of An. stephensi followed by An. culicifacies and Cx. quinquefasciatus. The LC50 and LC90 values against three species were 0.023, 0.032 and 0.04 ppm; and 0.045, 0.057 and 0.114 ppm respectively. In field, pirimiphos-methyl @ 200 g a.i./ha against Anopheles species and @ 300 g a.i./ha against Culex species can produce > 80% reduction in density of immatures up to one week in different habitats. Pirimiphos-methyl < 0.25 ppm is not toxic to fish. INTERPRETATION & CONCLUSION: Pirimiphos-methyl is more effective against anophelines in clean water than culicines in polluted water. This larvicide should not be used at a concentration above 0.25 ppm in habitats harbouring the larvivorous fish.

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