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PubMed1994

A simple technique for the preparation of polytene chromosomes from Culex quinquefasciatus.

Preparation of polytene chromosomes in Culex species is very difficult and the available techniques are not always reproducible. Presuming these problems might be due to lack of an appropriate technique to deal with these long and fragile chromosomes invested with ectopic pairings and sticky ends, certain promising methods with several modifications have been tried. During the process, recently, a simple and reproducible method was developed for obtaining good polytene chromosomes from Culex quinquefasciatus. The detailed methodology with precautions and its advantages over other reported techniques are described.

Animals↗
PubMed1994

[The effect of Culex family mosquito larva on the sensitivity of Anopheles mosquitos with various karyotypes to the entomopathogenic bacteria Bacillus thuringiensis subsp. Israelensis].

Culex (C. modestus) and Anopheles (A. beklemishevi and A. messeae) larvae mosquito were treated with Bacillus thuringiensis subsp. israelensis (Bti) bacterium together and separately. It was determined that the presence of C. modestus reduced the mortality of Anopheles larvae and altered the results of the selection of genotypes resistant to Bti of the polymorphic species of A. messeae, C. modestus larvae consumed the pathogen more rapidly and protected the sensitive individuals of A. messeae with "northern" chromosomal inversions from destruction. The correlation of the selection of cohabiting Anopheles and Culex mosquitoes as well as the relation between the specific diversity and the stability of communities are discussed.

Animals↗
PubMed1993

Laboratory and field evaluation of Spherix, a formulation of Bacillus sphaericus (B-101), to control breeding of Anopheles stephensi and Culex quinquefasciatus.

Spherix, a powder formulation of Bacillus sphaericus strain B-101, serotype H5a 5b, was evaluated against larvae of Anopheles stephensi and Culex quinquefasciatus in both the laboratory and field. In laboratory tests the formulation @ 0.1 g/sq m produced 100% mortality against larvae of both mosquito species at room temperature (28-32 degrees C). The larvicidal activity of Spherix against An. stephensi @ 0.5 g/sq m persisted for over 12 weeks under laboratory conditions. Field evaluation of Spherix @ 0.25-2.0 g/sq m produced 95-100% reduction in the larval density of both An. stephensi and Culex quinquefasciatus within 48 h in different habitats, and the larvicidal activity persisted for 2-4 weeks in water habitats.

Animals↗
PubMed1993

Effect of the insect growth regulator methoprene on the ovipositional behavior of Aedes aegypti and Culex quinquefasciatus.

Laboratory and field tests were conducted to determine the attractiveness of the insect growth regulator methoprene to ovipositing mosquitoes when presented at concentrations used in mosquito control programs. Laboratory experiments indicated that ovipositing Culex quinquefasciatus and Aedes aegypti were not attracted to methoprene. In field experiments, Culex stigmatosoma and Cx. quinquefasciatus larval dip counts in experimental ponds treated with methoprene briquets were not significantly different from untreated control ponds. Water taken from these methoprene-treated ponds was not attractive when compared with water taken from untreated ponds to ovipositing Cx. quinquefasciatus in laboratory experiments. These studies provide strong evidence that methoprene is not attractive to ovipositing mosquitoes at concentrations within the range of field applications.

Aedes↗
PubMed1996

Coamplification of esterase A and B genes as a single unit in Culex pipiens mosquitoes.

In Culex pipiens mosquitoes, resistance to organophosphorous insecticides often results from increased detoxification by two types of esterases, A and B, which are closely linked. Overproduction of all esterase B so far investigated (B1, B2, B4, B5 and B6) is from gene amplification. An esterase A gene (esterase A2) has recently been cloned from mosquitoes with the overproduced esterases A2 and B2, and amplification of this gene has also been reported. We describe the cDNA sequences of three additional esterase genes from insecticide-resistant strains of Culex pipiens originating from France and California which show at least 93 per cent homology with the esterase A2 gene sequence. Restriction enzyme mapping shows that the esterase A gene lies within 2.2 kb of the esterase B gene. In mosquitoes with overproduced esterases A2 and B2, the amplification level of esterase A is equal to that of esterase B suggesting that the genes are coamplified. Furthermore, we show that in one strain with an overproduced A esterase (A1), gene amplification cannot account for the increased protein level. This indicates that overproduction of esterases A can be achieved through two different mechanisms: gene amplification and a regulatory mechanism--the nature of which remains to be identified.

Animals↗
PubMed1994

Effects of a natural marsh fire on larval populations of Culex Salinarius in east Texas.

A natural marsh fire caused by lightning suppressed Culex salinarius larval populations for 2 months following the fire. Removal of emergent vegetation and higher water temperatures rendered burned-area pools unsuitable either for larval development or deposition of eggs or both. With a drop in seasonal ambient temperature and a regrowth of emergent vegetation, the burned areas returned to being suitable larval development sites for Culex salinarius. no differences in water salinity or pH were observed between burned and unburned locations.

Animals↗
PubMed1997

Response of Culex quinquefasciatus to visual stimuli.

The vision of Culex quinquefasciatus was studied in the laboratory. The attractiveness of colors (black, white, brown, yellow, blue, a skin tone) was evaluated with respect to the collection of Cx. quinquefasciatus in natural light, in the dark, and in ultraviolet light. Culex quinquefasciatus prefers both black and brown in natural light and ultraviolet light, but, as expected, there is no preference in the dark. There were no significant differences among the other 4 colors in natural light and ultraviolet light.

Analysis of Variance↗
PubMed1997

Discovery of a bromeliad-inhabiting Culex (micraedes) sp. in south Florida.

Immatures of a Culex (Micraedes) sp. were collected from bromeliads at 6 sites in Dade County, FL. This discovery represents the first time a member of this subgenus has been detected in the continental United States. The Cx (Micraedes) sp. was found in both native and exotic bromeliads, and at some sites this Culex occurred in these plants as frequently as Wyeomyia spp.

Animals↗
PubMed1997

Esterase gene amplification in Culex pipiens.

In the mosquito Culex pipiens one of the major resistance mechanisms to organophosphorous pesticides (OPs) is increased detoxification of insecticide. This resistance is the consequence of overproduction of two types of esterases, esterases A and B, coded at two loci, Est-3 (A esterase) and Est-2 (B esterase). We have analysed the genomic structure of these genes in different strains resistant to OPs and have attempted to characterize the different types of mutations leading to the resistant phenotypes. It is shown that, concerning the more frequent resistant phenotypes, mutations leading to resistance are of two main types. First, overproduction of one A esterase present in Southern France results from a regulatory mechanism. The second type of mutation is gene amplification which involves events that have initially generated the duplication of both the A and B esterase or only the B esterase locus. We report the point that the most frequent esterase overproductions are the results of eight different mutations and that, given the range of distribution of these genotypes, mutation leading to an efficient resistance gene is one of the most limiting factors for the evolution toward resistance in Culex pipiens.

Animals↗
PubMed1997

Study on the flying height of Aedes caspius and Culex pipiens females in the Po Delta area, Italy.

We have studied the vertical distribution of Culicidae in the "Ancona di Bellocchio" protected area (Regional Park of the Po Delta, Emilia-Romagna, Italy) by means of nonilluminated CDC traps baited with CO2. Traps were placed at heights of 1.5, 3, 4, and 5 m from the ground in open areas and at 1.5, 3, 4, 5, 6, and 7 m in wooded areas. We calculated the average flying height of the species caught, i.e., in order of decreasing flying height, Culex pipiens Linnaeus s.l., Culex modestus Ficalbi, Coquillettidia richiardii (Ficalbi), Aedes detritus (Haliday), Aedes caspius (Pallas). We also calculated the linear regression lines for both sites and found that 90% of Ae. caspius flew within a height of 1.64 m from the ground level, 95% within 2.68 m, and 99% at a height not exceeding 4 m; whereas 90% of Cx. pipiens moved within 3.45 m from the ground level, 95% within 4.02 m, and 99% within 4.76 m. The vertical distributions of Ae. caspius and Cx. pipiens did not vary significantly over the seasons and were not affected by the presence of trees or variations in temperature and wind velocity within the range of measurements obtained. The data obtained provide useful information for planning Ae. caspius control measures based on a mechanical barrier capable of preventing mosquitoes from moving toward residential settlements and tourist resorts bordering on the protected area as an alternative to aerial treatment with the larvicide Bacillus thuringiensis subsp. israelensis.

Aedes↗
PubMed1997

[Determination of insecticide resistance and its biochemical mechanisms in 2 strains of Culex quinquefasciatus from Santiago de Cuba].

It was analyzed the behavior of the resistance of 3 organophosphated insecticides (malathion, clorpirifos and methyl-pyrimifos), 3 pyrethroids (deltamethrin, lambda-cyhalothrin and cypermethrin), and 1 carbamate (propuxur) in populations of Culex quinquefasciatus from 2 municipalities of the province of Santiago de Cuba. The values of the resistance factor proved that there is resistance to malathion and clorpirifos. However, in spite of the existence of a high frequency of the mechanisms of elevated esterases and altered acetylcholinesterase no resistance to methylpymirifos, was observed which demonstrated that this insecticide is not affected by these mechanisms selected in our populations of Culex quinquefasciatus. There was resistence to deltamethrin, and lambda-cyhalothrin in Santiago de Cuba, whereas it was moderate to cypermethrin in Santiago and San Luis. Resistance to deltamethrin was also found in San Luis, but it was mild to lambda-cyhalothrin. The results obtained from the use of the synergists S,S,S tributyl phosphotritiade (DBF) and piperonyl butoxide (PB) indicated that the mechanisms of resistance of unspecific esterases and oxidases of multiple function are involved in the resistance to pyrethroids in both strains from Santiago de Cuba and San Luis. It was determined by the biochemical tests that there existed a high frequency of the mechanisms of esterases and altered acetylcholinesterase. The results of the polyacrylamide gel electrophoresis (PAGE) showed that esterase B1 appears more frequently associated with esterases A6 and B6. It was inferred that this association could be connected with the resistance to pyrethroids.

Acetylcholinesterase↗
PubMed1998

Insecticidal properties of citrus oils against Culex pipiens and Musca domestica.

Peel oils of lemon, grapefruit and navel orange were tested for insecticidal activities against larvae and adults of Culex pipiens and Musca domestica. Lemon peel oil was the most effective against larvae and adults of C. pipiens. Grapefruit peel oil was more toxic to adults of M. domestica while lemon oil, was more toxic Musca larvae. On the other hand, the orange peel oil was the least effective against larvae and adults of both species. The toxicity of oils applied to larval stages was extended to pupal and adult stages. C. pipiens adults appeared with paralyzed legs, while M domestica adults appeared normal. The weights of pupae treated as larvae were generally less than that of the control. All oils produced deleterious effects on fecundity of survivors of sublethal doses. The effect was obviously recorded in treated adults. Treatment of Culex & Musca with oils caused serious latent effect.

Animals↗
PubMed1991

[Esterase patterns in Culex (C.) quinquefasciatus Say, 1823, and its relation to malathion organophosphate insecticide resistance].

This paper describes the esterase patterns found in a wild strain of Culex quinquefasciatus which was known to bear resistance genes and the existence of genetic polymorphism for such esterases is demonstrated. The most frequent polymorphisms found were Est-1, Est-2, and Est-3; Est-2 was possibly responsible for Culex quinquefasciatus resistance. The frequency of potentially resistant females was significantly higher as compared to males: in addition, the hypothesis was proposed that heterozygotie Est-3 is selected as a genotype which may contribute to resistance in neotropical areas.

Animals↗
PubMed1995

[The association of resistance to organophosphate, carbamate and pyrethroid insecticides with the mechanisms of resistance observed in Culex quinquefasciatus strains from Ciudad de La Habana province].

The mechanisms of resistance in Culex quinquefasciatus from 6 municipalities of Havana City were studied in order to determine their genetic frequency. Increased esterases and altered acetylcholinesterase are still being the major resistance mechanisms in Havana City. The mechanisms of esterases is of high frequency, followed by altered acetylcholinestenase. Resistance to cholorpirifos was found for the first time in Culex quinquefasciatus, while resistance of malathion and carbamate propoxur is maintained, and deterioration to pyrethroid susceptibility is being detected. The synergistic effect of S.S.S. trubutyl phosphotritiade (DEF) and piperonil butoxide (PB) was analysed, and it was proven that esterases enzymes and multifunction oxidases are involved in the resistance to pyrethroids. By electrophoresis in polyerylamide gel, it was determined that the combination of esterases that seems to be associated with the resistance to perythroids is B1-A6-B6, which appeared with the greatest percentage. Valves of genetic frequency in the 6 municipalities were found to be high, for both esterase genes and acetylcholinesterase genes (Ache).

Animals↗
PubMed2005

Evolution of resistance toward Bacillus sphaericus or a mixture of B. sphaericus+Cyt1A from Bacillus thuringiensis, in the mosquito, Culex quinquefasciatus (Diptera: Culicidae).

The 2362 strain of Bacillus sphaericus (Bs) Neide is a highly mosquitocidal bacterium used in commercial bacterial larvicides primarily to control mosquitoes of the genus Culex. Unfortunately, Bs is at high risk for selecting resistance in mosquito populations, because its binary toxin apparently only binds to a single receptor type on midgut microvilli. A potential key strategy for delaying resistance to insecticidal proteins is to use mixtures of toxins that act at different targets within the insect, especially mixtures that interact synergistically. We tested this hypothesis for delaying the phenotypic expression of resistance by exposing Culex quinquefasciatus Say larvae to Bs alone or in combination with Cyt1A from Bacillus thuringiensis subsp. israelensis. Two laboratory lines of Cx. quinquefasciatus, one sensitive to Bs and the other containing Bs resistance alleles, were subjected to intensive selection pressure for 20 generations with either Bs 2362 or a 3:1 mixture of Bs 2362+Cyt1A. At the end of the study, the sensitive line had evolved >1000-fold resistance when selected with Bs alone, whereas the parallel line selected with Bs+Cyt1A exhibited only low resistance toward this mixture (RR95, 1.4). Similar results were observed in the lines containing Bs resistance alleles. Both lines selected with Bs+Cyt1A exhibited substantial resistance to Bs in the absence of Cyt1A. Although selection with Bs+Cyt1A did not prevent the underlying evolution of resistance to Bs, these results suggest that a mixture of Bs with other endotoxins, particularly one like Bs+Cyt1A in which the components interact synergistically, will provide longer lasting and more effective mosquito control than Bs alone.

Animals↗
PubMed1995

Kinetic and molecular differences in the amplified and non-amplified esterases from insecticide-resistant and susceptible Culex quinquefasciatus mosquitoes.

Two non-amplified esterases were purified from the insecticide-susceptible Pel SS strain of Culex quinquefasciatus. These were the two major esterase activity peaks in this strain. The two corresponding amplified carboxylesterases, Est alpha 2 and Est beta 2, involved in organophosphate sequestration were purified from two resistant C. quinquefasciatus strains. The Pel SS esterases were significantly less reactive with the organophosphates than those from the resistant strains. One of the Pel SS esterases was electrophoretically identical to amplified Culex Est beta 1. However, it differed kinetically, and in its nucleotide and predicted amino acid sequences from the two characterized amplified Est beta 1s, it is classified as Est beta 1(3). Restriction fragment analysis suggested Pel SS has only one Est alpha and one Est beta gene, while the resistant Pel RR has both amplified and non-amplified forms of Est alpha and Est beta. The EcoRI fragments for both Pel SS esterases were distinct from those of the amplified Est alpha 2(1), Est beta 2(1), or Est beta 1(1&2). An esterase with the same size EcoRI fragment as Est beta 1(3) was also present in Pel RR. This and restriction enzyme fragment analysis of C. quinquefasciatus field populations suggest that variability of the susceptible alleles may be lower than previously suggested. A non-amplified Est alpha with a unique EcoRI band was present in Pel RR. The previous esterase purification procedures may not have separated these amplified and non-amplified alleles. Hence, the small differences between the purified esterases from resistant strains may reflect mixtures of identical amplified alleles with different non-amplified alleles, which have significantly different k alpha values.

Animals↗
PubMed1993

Endosymbiotic relationship between a rickettsia-like microorganism and the male germ-cells of Culex tigripes.

The male mosquitoes of the species Culex tigripes possess endosymbionts localized in the cytoplasm of the germ-cells. The somatic cells of the testis do not exhibit this particularity. The spermatogonia, spermatocytes and spermatids all possess a few symbionts. They are eliminated in the residual body at the end of spermiogenesis when the spermatozoon matures. They are absent from the seminal vesicles. A few spermatocytes and spermatids show a proliferation of the endosymbionts. This seems to be associated with an abnormal spermiogenesis. These symbionts are comparable to the Wolbachia described in two other species of mosquitoes: Culex pipiens and Aedes scutellaris.

Animals↗
PubMed2026

ChIP-seq profiling identifies diapause-regulated H3K27me3 targets in the fat body of Culex pipiens.

Culex pipiens, a principal vector of significant arboviruses, survives winter through diapause, a hormonally controlled inactive phase that enhances endurance under severe cold circumstances. Recent data suggests that epigenetic processes, namely histone post-translational modifications (hPTMs), play a crucial role in regulating seasonal dormancy. Prior studies from our laboratory indicated a decrease in the methylation of Histone 3 (H3K27me3) in diapausing fat body tissue, associated with elevated expression of the histone demethylase UTX. Nonetheless, the precise genomic areas impacted by these chromatin alterations remained unidentified. We used chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-seq) to delineate the genome-wide distribution of H3K27me3 across fat body chromatin in diapausing (D) and non-diapausing (ND) female Cx. pipiens. Notably, the higher signal at transcription start sites (TSSs) reflects localized redistribution rather than a global decrease, as diapausing fat bodies retain less H3K27me3 overall but concentrate it at promoters. To investigate the functional significance of these chromatin alterations, we confirmed a number of target loci via ChIP-qPCR and assessed gene expression with qRT-PCR. We identified many critical genes that were markedly increased in diapausing mosquitoes, exhibiting an inverse relation to H3K27me3 enrichment. Our data demonstrates different H3K27me3 chromatin landscapes between diapausing and non-diapausing Cx. pipiens, corroborating a hypothesis of selective, locus-specific repression in the non-diapause state and its targeted removal during diapause to permit activation of dormancy-associated genes. These results suggest that chromatin remodeling is a core driver of the diapause switch.

Animals↗