Life cycle of Culex quinquefasciatus Say (Diptera: Culicidae) under uncontrolled conditions

Aspects of the growth and development were described for immature stages of Culex quinquefasciatus Say, 1826 (Diptera: Culicidae), an antropophilic mosquito species found frequently in Bogotá, Colombia. Two experiments were carried out during January-February and September-October of 2001 under ambient environmental conditions. Oviposition occured 5-8 days after blood ingestion. Females laid eggs in plastic containers filled with pooled water with high organic material content. The number of eggs per raft varied between 152 and 203. For the 2 trials, the hatch rate was 50% and 75%. The asynchronous egg hatch, the short duration of the pupal stage (11% of the total development time, and the high efficiency of adult emergence from the pupal stage (98.6%) were noted. In general, these development times were shorter compared to those reported by other authors. Moreover, the high percentages of hatch (83.6%), pupation (86.6%) and emergence (98.6%) under the average temperature conditions of 14.8 degrees C and 15.1 degrees C, and average relative humidity of 72.5% and 74.1%, respectively) demonstrated adaptation of C. quinquefasciatus to Bogotá's cool, high altitude environment. These characteristics, together with its vectorial capacity and the resistance to chemical control methods, could make this species become a risk for the health of human populations.     

The salivary gland chromosomes of Culex (Culex) vishnui (Culicidae: Diptera)

Culex vishnui is a member of the vishnui group comprising six closely resembling species. The salivary gland chromosomes are longer than those found in Anopheles, more fragile and spread with difficulty. The banding pattern is compared with that of Culex pipiens pipiens and Culex pipiens fatigans. Homologies are closest between vishnui and fatigans. The incidence of asynapsis between the homologues is very high.     

Genetic differentiation of Culex pipiens (Diptera: Culicidae) in China

The population genetic structures of Culex pipiens Linnaeus were evaluated in China over a 2000 km transect that encompasses the two subspecies, C. p. pallens and C. p. quinquefasciatus. Four polymorphic allozyme loci were investigated in 1376 mosquitoes sampled from 20 populations across four provinces. These loci were not statistically dependent with no apparent heterozygote deficit or excess. On a regional scale (intra-province), a low (Fst=0.007-0.016) and significant genetic differentiation was found, with no clear geographical pattern. On a wider scale (inter-province), the genetic differentiation was higher (Fst=0.059), and an isolation by distance emerged. The results are compared with previous population genetic surveys of this mosquito species in different geographic areas over the world. The overall pattern suggests that Culex pipiens requires considerable distance (500-1000 km) to show isolation by distance, irrespective of the subspecies (C. p. pipiens, C. p. quinquefasciatus and C. p. pallens) or the geographic location.     

Existence of Two Acetylcholinesterases in the Mosquito Culex pipiens (Diptera: Culicidae)

Abstract: Two acetylcholinesterases (AChEs), AChE1 and AChE2, differing in substrate specificity and in some aspects of inhibitor sensitivity, have been characterized in the mosquito Culex pipiens . The results of ultracentrifugation in sucrose gradients and nondenaturing gel electrophoresis of AChE activity peak fractions show that each AChE is present as two molecular forms: one amphiphilic dimer possessing a glycolipid anchor and one hydrophilic dimer that does not interact with nondenaturing detergents. Treatment by phosphatidylinositol-specific phospholipase C converts each type of amphiphilic dimer into the corresponding hydrophilic dimer. Molecular forms of AChE1 have a lower electrophoretic mobility than those of AChE2. However, amphiphilic dimers and hydrophilic dimers have similar sedimentation coefficients (5.5S and 6.5S, respectively). AChE1 and AChE2 dimers, amphiphilic or hydrophilic, resist dithiothreitol reduction under conditions that allow reduction of Drosophila AChE dimers. In the insecticide-susceptible strain S-LAB, AChE1 is inhibited by 5 × 10⁻⁴ M propoxur (a carbamate insecticide), whereas AChE2 is resistant. All animals are killed by this concentration of propoxur, indicating that only AChE1 fulfills the physiological function of neurotransmitter hydrolysis at synapses. In the insecticide-resistant strain, MSE, there is no mortality after exposure to 5 × 10⁻⁴ M propoxur: AChE2 sensitivity to propoxur is unchanged, whereas AChE1 is now resistant to 5 × 10⁻⁴ M propoxur. The possibility that AChE1 and AChE2 are products of tissue-specific posttranslational modifications of a single gene is discussed, but we suggest, based on recent results obtained at the molecular level in mosquitoes, that they are encoded by two different genes.     

The Effect of Sucrose Concentration on Olfactory-Based Associative Learning in Culex quinquefasciatus Say (Diptera: Culicidae)

A classical conditioning approach was used to examine the ability of Culex quinquefasciatus Say (Diptera: Culicidae) to associate odor with a sugar-meal of varying quality. The objectives of this study were to investigate the impact of different sucrose concentrations (5 %, 10 %, or 50 %) on positive response to conditioning and to examine sucrose concentration preference following exposure to a 10 % solution. Mosquitoes conditioned in conjunction with all three sucrose concentrations showed evidence of learning; including the concentration of the conditioning stimulus, and the sex of the mosquito. Using colored solutions to determine feeding patterns of experienced mosquitoes indicated male mosquitoes showed no preference but females showed a preference for 10 % over 5 % sucrose but not between 10 % and 50 % sucrose solutions.     

Description of immature stages of Culex ocossa Dyar & Knab, Culex delpontei Duret and Culex pereyrai Duret of the Melanoconion subgenus (Diptera: Culicidae).

The larva and pupa of Culex (Melanoconion) ocossa Dyar & Knab are redescribed and those of Culex (Melanoconion) delpontei Duret and Culex (Melanoconion) pereyrai Duret are described from specimens collected in the states of S?o Paulo and Paraná, Brazil. The pupa of Cx. ocossa differs from those of the other two species in having seta 5-IV-VI dark with strongly aciculated branches, and caudolateral angle of segment VIII produced into sharp point, and seta 1-P present; Cx. delpontei can be distinguished from Cx. pereyrai in possessing paddle lightly tanned, trumpet flared, and wing and leg cases lightly tanned, without pattern of dark spots; Cx. pereyrai can be recognized by having wing case with pattern of dark, discontinuously pigmented, longitudinal lines, and trumpet cylindrical, not flared. The larvae of the three species share the presence of seta 2-C placed medially to seta 1-C.     

Identification and classification of detoxification enzymes from Culex quinquefasciatus (Diptera: Culicidae)

Molecular characterization of the insecticide resistance has become a hot research topic ever since the first disease transmitting arthropod (Anopheles gambiae) genome sequence has unveiled in 2002. A recent publication of the Culex quinquefasciatus genome sequence has opened up new opportunities for molecular and comparative genomic analysis of multiple mosquito genomes to characterize the insecticide resistance. Here, we utilized a whole genome sequence of Cx. quinquefasciatus to identify putatively active members of the detoxification supergene families, namely cytochrome P450s (P450s), glutathione-S-transferases (GSTs), and choline/carboxylesterases (CCEs). The Culex genome analysis revealed 166 P450s, 40 GSTs, and 62 CCEs. Further, the comparative genomic analysis shows that these numbers are considerably higher than the other dipteran mosquitoes. These observed speciesspecific expansions of the detoxification super gene family members endorse the popular understanding of the involvement of these gene families in protecting the organism against multitudinous classes of toxic substances during its complex (aquatic and terrestrial) life cycle. Thus, the generated data set may provide an initial point to start with to characterize the insecticide resistance at a molecular level which could then lead the development of an easy to use molecular marker to monitor the incipient insecticide resistance in field environs.     

Association of esterases with insecticide resistance in Culex quinquefasciatus (Diptera: Culicidae)

The southern house mosquito, Culex quinquefasciatus Say, is a competent vector of human disease and an important target of mosquito abatement programs. However, these management programs have been compromised by development of insecticide resistance. In the current study, susceptibilities to naled and resmethrin, two adulticides used in mosquito abatement, were monitored using a topical and contact bioassay, respectively, in five field- collected populations of C. quinquefasciatus (MARC, HOOD1, HOOD2, MINLOVE, and THIB). Frequencies of resistance, measured as survival after treatment with discriminating concentrations (i.e., sufficient to kill > 90% of a reference susceptible strain) were high (88.0-96.8%) in all field collections treated with naled, but were variable (3.3-94.2%) with resmethrin. In addition, esterase activities in mosquitoes from these collections were quantified using alpha-naphthyl acetate and ranged from 1.08 to 3.39 micromol alpha-naphthol produced min(-1) mg prot(-1). Heightened activities were associated with decreased insecticide susceptibility in HOOD1, THIB, and MINLOVE but not HOOD2. Esterases were visualized using native polyacrylamide gel electrophoresis, and intra- and interstrain differences in banding patterns were detected. In addition, esterases from MINLOVE mosquitoes were more numerous and intensely staining when compared with those from a laboratory-susceptible strain. Finally, naled synergized the toxicity of resmethrin in populations with decreased insecticide susceptibility and increased esterase activity by 2.5-(MINLOVE) to three-fold (THIB). Results from this study will allow management strategies for populations of C. quinquefasciatus to be optimized, and provide a foundation for further studies exploring use of esterase inhibitors as synergists of pyrethroid toxicity.     

The relationship between photoperiod and autogeny in Culex tarsalis (Diptera, Culicidae)

The effect of day length on autogenous expression was tested with a non-selected Washington strain, and an autogeny-selected California strain of Culex tarsalis. When conducted at 2-hour increments, a plateau of maximum response was seen between 10 and 16 hours, with a decline below and above this range. Using paired comparisons at 8 and 16 hours, the long photoperiod group nearly always had a higher proportion of autogeny as well as increased numbers of mature oocytes per autogenous female. This response was also noted when only adults were exposed to diverse photoperiods. Photoperiod is discussed as a significant factor in rate of increase of populations, in addition to the well known effect of higher temperature.

---

Zusammenfassung Die Wirkung der Tageslänge auf die Expressivität der Autogenie wurde an einem nicht selektieren Washingtoner Stamm und an einem auf Autogenie ausgelesenen Kalifornischen Stamm von Culex tarsalis untersucht. Bei Prüfung in zweistündigen Abständen ergab sich ein Gleichbleiben der maximalen Reaktion zwischen 10 und 16 Stunden Licht je Tag und eine Abnahme unterhalb und oberhalb dieses Bereichs. Bei paarweisem Vergleich von 8 und 16 Stunden Licht ergaben die langen Photoperioden fast immer einen höheren Prozentsatz an Autogenie sowie eine gesteigerte Anzahl reifer Oocyten in den autogenen Weibchen. Diese Reaktion wurde auch beobachtet, wenn nur die Imagines den verschiedenen Photoperioden ausgestzt wurden. Die Tageslänge wird als entscheidender Faktor bei der Zuwachsrate der Populationen behandelt, zusätzlich zu der wohlbekannten Wirkung höherer Temperatur.

---

---

Scientific Paper 2721, Project 1592, College of Agriculture, Washington State University.     

Spacing behaviour in resting Culex pipiens (Diptera, Culicidae): a computer modelling approach

Abstract. We compared two models based on Monte Carlo simulations with the spacing patterns of resting adults of the mosquito Cx pipiens L. (form molestus ) (Diptera, Culicidae). The comparison with the first model which assumed a distribution of complete spatial randomness showed that there was a tendency for mosquitoes to repel other mosquitoes which were too close, resulting in high local regularity. The second model took this repulsion into account. A final test of global patchiness using Model 2 indicated that the spacing behaviour of Cx pipiens was not sufficiently described by local regularity only, but also required a gregarious element. This supports the hypothesis that the molestus form of Cx pipiens shows spaced-out gregariousness in the sense of Kennedy & Crawley (1967).     

Lectin binding sites on head structures of the spermatid and spermatozoon of the mosquito Culex quinquefasciatus (Diptera, Culicidae).

The presence of intranuclear and acrosomal lectin binding sites in spermatids and spermatozoa of the mosquito Culex quinquefasciatus was analysed. Direct and indirect lectin-gold techniques were used on LR White-embedded cells. The nuclear compartment was the structure most intensely labelled. Early spermatid nucleus showed moderate labelling for peanut agglutinin (PNA), Griffonia simplicifolia IB4 (GS-IB4) and Ricinus communis agglutinin (RCA), and light labelling for the other lectins tested. The sperm nucleus was intensely labelled by all lectins. The acrosome, an enzyme-containing structure, was labelled by some lectins. The anterior acrosomal region was labelled by PNA, while the proximal acrosomal region was labelled by PNA and G. simplicifolia II (GS II) lectins, and showed the presence of fucose residues with the use of Ulex europaeus I (UEA-I) lectin. The spermatozoa stored in the spermatheca showed the same pattern of labelling as that observed in spermatozoa localized in testis and seminal vesicles for all lectins tested. Carbohydrate residues in the nuclear compartment may be involved with the process of chromatin condensation. In the acrosomal region these residues may play a role in the process of sperm-oocyte interaction.     

Laboratory evaluation of lactic acid on attraction of Culex spp. (Diptera: Culicidae)

The role of lactic acid was evaluated for attraction of Culex nigripalpus, Culex quinquefasciatus, Culex tarsalis, and Aedes aegypti in the laboratory using a dual‐port olfactometer. When lactic acid was combined with chicken odor, attraction was increased for Cx. quinquefasciatus compared to chicken odor alone but not for Cx. nigripalpus, Cx. tarsalis, and Ae. aegypti. Lactic acid combined with hand odor did not change attraction of Cx. tarsalis and Ae. aegypti but decreased attraction of Cx. nigripalpus and Cx. quinquefasciatus. The addition of lactic acid to CO₂ increased attraction of Ae. aegypti and Cx. quinquefasciatus but reduced attraction of Cx. nigripalpus and Cx. tarsalis. Use of commercial lactic acid baits with CO₂ resulted in a similar trend except for Cx. nigripalpus which showed no difference. A blend of lactic acid, acetone, and dimethyl disulfide was attractive to Ae. aegypti (63.4%) but elicited low responses by all Culex spp. (1.3–26.8%). Addition of the blend to CO₂ increased attraction of Ae. aegypti and Cx. quinquefasciatus but reduced attraction of Cx. nigripalpus and Cx. tarsalis. The mixture of compounds plus CO₂ was as attractive as a hand for Cx. quinquefasciatus, Cx. tarsalis, and Ae. aegypti.     

Ovipositional and ovicidal effects of the microbial agent Bacillus thuringiensis israelensis on Culex quinquefasciatus say (Diptera: Culicidae).

The magnitude of oviposition as well as the size, shape and the number of eggs per of egg rafts egg raft were determined after gravid Culex quinquefasciatus Say oviposited on water treated with water dispersible granules (WDG) of Bacillus thuringiensis ssp. israelensis (Bti) and on untreated water. The mean number of eggs/raft was lower in the treated than in the untreated water. Bti concentrations from 0.5 to 2.0mg/L affected the shape of egg rafts and number of eggs in each raft. As the concentration of Bti increased from 0.5 to 2.0 mg/L the shape of egg rafts became more irregular with fewer eggs in each raft. Exposure to Bti at 2- and 26-h reduced the hatching rates, and fewer eggs hatched at 26-h of exposure to Bti. As the concentration of Bti WDG increased from 0.5 to 2.0 mg/L, the hatching rate decreased. Eggs exposed for 2-h to 2.0mg/ L Bti had a hatch of 30% after 24 h, the rate increasing to 57% after 72 h. In contrast, in 26-h exposed eggs to 2.0 mg/L Bti, the hatching rate after 24 h was only 12% and this rate increased to 39% after 72 h. In larvae from eggs exposed for 2 h, the survival rate was 40% at 2.0 mg/L Bti and 87% in untreated controls. In contrast, the survival rates of larvae from 26-h exposed eggs was 91% in controls while it was 30% at 2.0 mg/L Bti. As the concentration of Bti increased from 0.5 to 2.0 mg/ 1 the survival rates of larvae decreased. The combined effects of reductions of egg rafts, low number of eggs per egg raft, and reduced hatching and survival rates could have significant cumulative effects on the yield of adult mosquitoes, and this could result in a greater control potential of this microbial agent.     

Checklist of Iranian mosquitoes (Diptera: Culicidae).

The mosquito fauna of Iran includes seven genera, 64 species, and three subspecies. The records of 12 other species should be verified. There are 24 species in the most recent checklist of Iranian Anopheles. Two species, An. peditaeniatus and An. fluviatilis species V, have been reported since. An. atroparvus, An. labranchiae, and An. martinius of the Maculipennis Group, and An. cinereus, An. nigerrimus, and An. rhodesiensis rupicola were recorded previously but are not included in the checklist. The checklist of Iranian Culicinae includes ten species of the tribe Aedini, but there are some records of four other species: Aedes aegypti, Ochlerotatus berlandi, Oc. chelli, and Oc. dorsalis. The genus Culex includes 19 species, excluding Cx. impudicus, which has not been collected recently, and some doubtful records of Cx. univittatus, Cx. vishnui, and Cx. vagans. The genus Culiseta includes five species and the genera Coquillettidia and Uranotaenia each include one species in Iran. No information is available for the An. subpictus, Oc. caspius, Oc. detritus, and Oc. pulcritaris species complexes in Iran. The An. claviger and Cx. pipiens complexes and the An. hyrcanus group require review.     

Characterization of Culex pipiens Complex (Diptera: Culicidae) Populations in Colorado,USA Using Microsatellites

Mosquitoes such as those in the Culex pipiens complex are important vectors of disease. This study was conducted to genetically characterize Cx. pipiens complex populations in the state of Colorado, USA, and to determine the number of genetic clusters represented by the data. Thirteen populations located among four major river basins were sampled (n = 597 individuals) using a panel of 14 microsatellites. The lowest-elevation sites had the highest Expected Heterozygosity (H_E) values (range 0.54–0.65). AMOVA results indicated the presence of statistically significant amounts of variation within each level when populations were analyzed as one group or when they were grouped either by river basin or by their position on the east or west side of the Rocky Mountains. Most pairwise F_ST values were significant via permutation test (range 0–0.10), with the highest values from comparisons with Lamar, in southeast CO. A neighbor joining tree based on Cavalli–Sforza and Edwards’s chord distances was consistent with the geographic locations of populations, as well as with the AMOVA results. There was a significant isolation by distance effect, and the cluster analysis resolved five groups. Individuals were also assayed with an additional microsatellite marker, Cxpq78, proposed to be monomorphic in Cx. pipiens but polymorphic in the closely related but biologically distinct species Cx. quinquefasciatus. Low frequencies (≤3%) of Cx. quinquefasciatus alleles for this marker were noted, and mostly confined to populations along the Interstate 25 corridor. Pueblo was distinct in that it had 10% Cx. quinquefasciatus alleles, mostly of one allele size. The degree of population genetic structure observed in this study is in contrast with that of Cx. tarsalis, the other major vector of WNV in the western U.S., and likely reflects the two species’ different dispersal strategies.     

Chromosomal Evidence on the Sporogony of Amblyospora californica (Microspora: Amblyosporidae) in Culex tarsalis (Diptera: Culicidae)

ABSTRACT. Amblyospora californica is a polymorphic, eukaryotic microsporidian. Three types of sporogony producing three types of spores occur in male larvae and female adults of its mosquito host, Culex tarsalis , and an alternate copepod host, Acanthocyclops vernalis. Development of A. californica in male larvae includes merogony and sporogony. Karyogamy and meiosis was observed in sporogony in male larvae but not in the female adult or in the copepod. Chromosomal evidence showed that sporogony included two consecutive meiotic divisions and a subsequent mitosis forming an octosporont, ultimately containing eight haploid, uninucleate mature spores. In this species, the haploid number of chromosomes is nine. Macrosporoblasts and macrospores, containing 1, 2 or more nuclei, can be seen in infected male larvae. The stage of sporogony in which cytokinesis was arrested seems to determine the number of nuclei. Those with only one nucleus, we believe are due to failed nuclear division at meiosis. Although A. californica displayed a process of karyogamy and meiosis similar to that of the species from Cx. salinarius , they may not be the same species because of the difference in their chromosome numbers.