Culex quinquefasciatus Say, a widely distributed mosquito in tropical and subtropical areas, is the most important vector of the filarial parasite Wuchereria bancrofti, the causative agent of lymphatic filariasis. In India, filariasis is endemic in 17 States and six Union Territories, putting about 553 million people at risk of infection. Vector control, which aims to prevent pathogen transmission through interventions targeting adult mosquito vectors, is a significant component of control of the disease. Chemical-based control represents a chief strategy in the management of mosquito vectors; however, continuous application of insecticides has led to the development of resistance in many mosquito vectors around the world. The current study aims to observe the variability of expression of carboxylesterase isozymes that play a role in detoxifying insecticides into non-toxic compounds, in different life stages of Culex mosquitoes, to understand levels of insecticide susceptibility that may be used in integrated mosquito management for efficient vector control. C. quinquefasciatus were collected from different localities of sub-Himalayan West Bengal, India, and adult and larval bioassays were performed against one organophosphate insecticide (chlorpyrifos) and two synthetic pyrethroid insecticides (deltamethrin and lambda-cyhalothrin). The activity of α- and β-carboxylesterases (quantitative assay) were measured in larvae and adults of C. quinquefasciatus using a microplate assay, and measured qualitative expression by native polyacrylamide gel electrophoresis. The study shows a differential activity of α- and β-carboxylesterases both in quantitative and qualitative assays. The quantitative assay reveals that larvae exhibit a 12.2-fold higher level activity of α-carboxylesterase and about 5.0-fold higher level of activity of β-carboxylesterase than adults. Some carboxylesterase isozymes, i.e., α-Est I-IV, α-Est VII and α-Est XI-XV were exclusively expressed in larvae, whereas α-Est V-VI and α-Est IX were expressed only in adults. In larvae, all β-Est I-IX were expressed, while in adults only β-Est IV-V was expressed. The results of adult and larval insecticide bioassay are also as per the above findings showing an LC90 value of 0.017 ppm, 0.097 ppm and 0.072 ppm in the larva, and LC90 value of 0.0015 ppm, 0.721 ppm, 0.364 ppm in adults against chlorpyrifos, deltamethrin and lambda-cyhalothrin, respectively.

Mosquito communities across the globe frequently comprise a mix of native and cosmopolitan species. New Zealand's mosquito communities are no exception. Here we describe the abundance, distribution and phenological patterns for a community of six mosquito taxa resident across the Kaipara Harbour region of northern New Zealand. Adult mosquitoes were sampled using baited light traps, serviced biweekly for 3½ years. Seasonal fluctuations in abundance of adults were examined for correlations with temperature and rainfall over the preceding weeks. Four endemic species comprised over 98% of the total catch, with Coquillettidia iracunda being the most abundant. Two introduced species, Aedes notoscriptus and Culex quinquefasciatus were widely distributed, but each comprised <1% of the total catch. Culiseta tonnoiri was the only species that appeared geographically restricted, occurring at one-third of the sites. Distinct temporal peaks in adult abundance were evident: Aedes antipodeus was most abundant in spring, Ae. notoscriptus and Cq. iracunda were most abundant in summer and Cx. quinquefasciatus was most abundant in autumn. Culiseta tonnoiri and Culex pervigilans were of variable abundance throughout the year. For all species examined, temporal variations in abundance were more strongly associated with temperature in the preceding weeks than with preceding rainfall. A better knowledge of the factors driving patterns of spatial and temporal abundance will allow an improved understanding of how non-native species may integrate themselves into resident mosquito communities.

Mosquito larvae have been shown to respond to water-borne kairomones from nearby predators by reducing their activity, and thus visibility. If they can identify the predator, they can then alter their response depending upon the associated predation risk. No studies have shown that mosquito larva may also detect water-borne vibrations from the predator. Final instar larvae of three mosquitoes: Culiseta longiareolata, Culex perexiguus and C. quinquefasciatus, were exposed to recorded vibrations from feeding dragonfly nymphs, to dragonfly kairomones and the combined effect of both. Predator vibrations caused C. longiareolata to significantly reduce bottom feeding and instead increased the more passive surface filter feeding. The larvae also significantly increased escape swimming activity. These behavioural changes were not significantly different from the effect of dragonfly kairomones, and there was no synergistic or additional effect of the two. C. perexiguus gave a smaller (but still significant) response to both dragonfly vibrations and to kairomones, probably due to a different feeding behaviour: when lying on the bottom, it was an inactive filter feeder. C. quinquefasciatus did not respond to either vibrations or kairomones and during these experiments was entirely an inactive surface filter feeder. Both C. longiareolata and C. perexiguus were thus able to detect and identify vibrations from feeding dragonfly nymphs as an anti-predator strategy. The lack of response in C. quinquefasciatus is probably a result of living in water that is highly polluted with organic material, where few predators can survive.

The circulatory system in insects is formed by a dorsal vessel (heart) that is a tubular structure that pumps haemolymph in the insect body cavity. Up until now, much is known about the structural organization of the heart in certain Brachycera (Diptera) (e.g. Drosophila). In contrast, little information is available regarding members of the Nematocera suborder (e.g. mosquitoes), in spite of their relevance to human health. Considering their importance, details of the heart morphology of six mosquito species (Aedes albopictus, Ae. aegypti, Ae. fluviatilis, Culex quinquefasciatus, Anopheles darlingi and An. aquasalis) were investigated by scanning electron microscopy (SEM). The heart of the adult mosquitoes, both males and females, consists of a dorsal tubular structure in association with pericardial cells located alongside the heart and alary muscles displaying ramifications that extend from the body wall to the heart surface. The SEM analysis also revealed in detail the organization of the heart, including paired valves on the heart wall (ostia). This study provides a detailed analysis of the mosquito heart microanatomy and, in our view, represents a significant contribution towards the understanding of structural–functional relationships associated with the heart of mosquito.

Oviposition is a major event in the life history of mosquitoes, shaping both individual fitness and vectorial capacity. Several exogenous factors have been shown as important for the dynamic forcing of oviposition at finely (hourly) and coarsely (monthly or season to season) grained temporal scales. However, field studies addressing the interplay of weather factors on oviposition dynamics at the intermediate (days to weeks) time scale are missing. Here, we present the results from a field study that showed the oviposition dynamics of the southern house mosquito, Culex quinquefasciatus Say (Diptera: Culicidae), to be: (i) primarily dictated by relative humidity; and (ii) disrupted by rainfall events that resulted in a modified sensitivity to relative humidity. Rainfall changed the concentration of ammonia, a major limiting resource of microbes used as food by mosquito larvae. Following major rainfall events, the importance of relative humidity in forcing the oviposition dynamics also changed. Finally, our results indicate that qualitative changes in oviposition habitats modify the importance of weather variables as predictors of mosquito oviposition dynamics.

Following observations by a service engineer (mid-2007), 12 of the hundreds of installed packaged plant (PP) sewage systems were producing relatively large numbers of Culex quinquefasciatus (Say) and a variety of filth flies in George Town, Grand Cayman. Due to the vector potential of C. quinquefasciatus in the Caribbean, we explored the efficacy of industry-standard insecticides against C. quinquefasciatus. Since PP systems contain an organic biofilm on the water surface, we devised a modified technique for collecting immatures and for the application of insecticides. We treated functioning and non-functioning PP systems with Bacillus sphaericus (VectoLex® WDG), Bacillus thuringiensis var. israelensis (Bti; VectoBac® CG), temephos (Abate® 4-E), monomolecular film or ethyoxylated alcohol surfactant (Agnique® MMF) and (S)-methoprene (Altosid® Pro-G). B. thuringiensis var. israelensis gave control for 35 and 48 days for functioning and non-functioning systems, respectively, with less control from B. sphaericus (high label rate) (c. 25 and 35 days) and temephos (suggested label rate) (c. 27 and 33 days). B. sphaericus (low label rate), monomolecular film and (S)-methoprene gave limited control of immatures (i.e. no mortality detected after 24 h). Treatment options for PP systems are discussed with regard to economics, operational feasibility, and within the context of integrated mosquito management. Functioning systems were recolonized at a faster rate than those that were not functioning, but the level of infestation in the non-functioning systems was considerably greater.

The laboratory studies were conducted to uncover the correlation between the levels of pyrethroid resistance and the reproductive potential of parent (SS) and resistant strains of Culex quinquefasciatus (RR) originating from Delhi, India and selected with deltamethrin (RDL) or the combination of deltamethrin and PBO (1:5) (RDP) at the larval stage and selected with deltamethrin at the adult stage (RDA). The reproductive potential was evaluated in terms of fecundity, fertility, egg hatchability and longevity of gonotrophic cycles. The RR strains exhibited 68–74% reduced duration of the gonotrophic cycles when compared with that of SS strain. The considerable decrease in the egg production, ranging from 45.4% to 61.6%, observed in the selected strains as compared to the SS strain, indicates the possible positive correlation between the levels of deltamethrin resistance and the reproduction disadvantage. This correlation was further confirmed by 24.6% to 53.6% decrease in the hatchability of eggs of the selected strains with respect to that of the parent strain. A worth-mentioning observation of the reduced reproductive fitness in RDP strains suggests the effectiveness of synergized deltamethrin selections in reducing the frequency of resistant individuals. The reproductive disadvantage in adult-selected strains possessing negligible resistance to deltamethrin implicates the efficacy of deltamethrin as an adulticide rather than as a larvicide against Cx. quinquefasciatus. The results suggest that the reduced reproductive fitness of resistant genotypes in the population can eliminate heterozygotes and resistant homozygotes by implementing different resistance-management strategies against Cx. quinquefasciatus.

Mosquitoes such as Culex quinquefasciatus Say (Diptera: Culicidae) are important vectors of organisms that cause disease in humans. Research into the development of effective standardized odour baits for blood-fed females (oviposition attractants), to enable entomological monitoring of vector populations, is hampered by complex protocols for extraction of physiologically active volatile chemicals from natural breeding site water samples, which have produced inconsistent results. Air entrainment and solvent extraction are technically demanding methods and are impractical for use in resource poor environments where mosquito-borne disease is most prevalent. This study reports the first use of a simple, robust extraction technique, stir bar sorptive extraction (SBSE), to extract behaviourally active small lipophilic molecules (SLMs) present in water samples collected from Cx. quinquefasciatus breeding sites in Tanzania. Extracts from a pit latrine and from a cess pool breeding site attracted more gravid Cx. quinquefasciatus in pair choice bioassays than control extracts, and coupled gas chromatography-electroantennography (GC-EAG) allowed tentative identification of 15 electrophysiologically active chemicals, including the known oviposition attractant, skatole (3-methylindole). Here, we have demonstrated, using simple pair choice bioassays in controlled laboratory conditions, that SBSE is effective for the extraction of behaviourally and electrophysiologically active semiochemicals from mosquito breeding site waters. Further research is required to confirm that SBSE is an appropriate technique for use in field surveys in the search for oviposition cues for Cx. quinquefasciatus.

Bacillus sphaericus (Bs) is a potential mosquito larvicide especially against Culex quinquefasciatus (Say), the vector of bancroftian filariasis. It is a gram-positive, aerobic and endospore-forming bacterium. During sporulation, it synthesizes binary endotoxins (molecular weight 42 and 51 kDa proteins) that are highly toxic to mosquito species. The mode of action of the binary toxin of this biolarvicide in the alimentary canal and the ultrastructural events in the tissues of the affected larvae have been demonstrated. Lysosomal components are the most important organelles involved in the metabolism of the foreign molecules encountered by the cells. In this paper, we report the ultrastructural changes in the midgut epithelial cells, with special emphasis on lysosomes (L), in untreated Cx. quinquefasciatus larvae and those treated with the Bs-IAB59 bacterial strain. In the Bs-treated larvae, the size of the L gradually increased, and within 16 h, fine filaments appeared and compartmentalized into small lamellar bodies, within the L. After 36 h, these lamellar bodies appeared to be collapsed, and later disintegrated in the 48th hour. In the untreated larvae, such ultrastructural changes in the L were not seen. These observations suggested that, though the target site of action of the Bs toxin is the midgut epithelial cells, ultrastructural changes in the L compartments play a vital role in the mortality of the mosquito larvae.

An acetone extract of Solanum trilobatum leaves was evaluated for its ovicidal activity on the mosquito species Culex quinquefasciatus and Culex tritaeniorhynchus, by exposing eggs ranging in age from 0 to 18 h to concentrations of 50–200 ppm of the extract, and assessing their percent hatchability. A 100-ppm dose of the extract killed all of the eggs from both species aged between 0 and 6 h. The 50- and 75-ppm concentrations were also highly effective against young eggs; the effect declined in older eggs. The extract was more ovicidal towards C. quinquefasciatus than C. tritaeniorhynchus. On a testé l'activité ovicide d'un extrait à l'acétone de feuilles de Solanum trilobatum sur les deux espèces de moustiques, Culex quinquefasciatus et Culex tritaeniorhynchus, en exposant des œufs âgés de 0 à 18h à des concentrations de l'extrait compris entre 50 et 200ppm et en évaluant le pourcentage d'éclosions. La concentration à 100ppm de l'extrait tue tous les œufs d'âge compris entre 0 et 6h des deux espèces de moustique. Les concentrations à 50 et 75ppm sont également très efficaces contre les jeunes œufs, mais l'effet diminue avec l'âge des œufs. L'extrait est plus efficace vis à vis de C. quinquefasciatus que de C. tritaeniorhynchus.

This paper investigates a cohort of 2187 laboratory reared Culex quinquefasciatus fed on 69 human volunteers, including 59 persons with different levels of Wuchereria bancrofti microfilariae and 10 without microfilaria. Mosquitoes were followed until death. Mosquito survival was analysed in relation to the level of microfilaria in the human and larval count in the dead mosquito. Vector mortality during the extrinsic incubation period (12 days post-engorgement) was significantly higher in mosquitoes fed on microfilaraemic volunteers (50%) than in those fed on amicrofilaraemics (29%). Both the percentage infected and the geometric mean parasite density was significantly higher among mosquitoes which died before 13 days (45% infected and 10 larvae per infected mosquito) than those surviving beyond 13 days (39% and 2·2), suggesting a parasite loss of more than 80% during the extrinsic incubation period. A large proportion (62%) of the mosquitoes that died during the early of phase of parasite development were infected (36% in low, 26% in medium and 90% in high human Mf-density). Survival analysis showed that the parasite load in mosquitoes and the human Mf-density for a given parasite load are independent risk factors of vector survival. Overall, the hazard of dying was found to be 11–15 times higher among mosquitoes fed on microfilaraemic volunteers than those fed on amicrofilaraemics. The hazard doubles for every increase of about 60–70 parasites in the vector. As a consequence of the parasite-induced reduction in vector survival, the transmission success of the parasite is reduced. The implication of the results on control/elimination of lymphatic filariasis using mass-drug administration is discussed.

This paper presents a model-based analysis of longitudinal data describing the impact of integrated vector management on the intensity of Wuchereria bancrofti infection in Pondicherry, India. The aims of this analysis were (1) to gain insight into the dynamics of infection, with emphasis on the possible role of immunity, and (2) to develop a model that can be used to predict the effects of control. Using the LYMFASIM computer simulation program, two models with different types of immunity (anti-L3 larvae or anti-adult worm fecundity) were compared with a model without immunity. Parameters were estimated by fitting the models to data from 5071 individuals with microfilaria-density measurement before and after cessation of a 5-year vector management programme. A good fit, in particular of the convex shape of the age-prevalence curve, required inclusion of anti-L3 or anti-fecundity immunity in the model. An individual's immune-responsiveness was found to halve in ~10 years after cessation of boosting. Explanation of the large variation in Mf-density required considerable variation between individuals in exposure and immune responsiveness. The mean life-span of the parasite was estimated at about 10 years. For the post-control period, the models predict a further decline in Mf prevalence, which agrees well with observations made 3 and 6 years after cessation of the integrated vector management programme.

Laboratory reared Culex quinquefasciatus Say, 1823 originating from the vicinity of Belem, in northern Brazil, were allowed to engorge on caimans (Caiman c. crocodilus) infected with Hepatozoon caimani (Carini, 1909) and boas (Boa constrictor) infected with H. cf. terzii (Sambon and Seligmann, 1907) both from Para State. Engorged mosquitoes killed on successive days post-feeding (p.f.) were studied by transmission electron microscopy. Images of oocysts from 13 days p.f., caiman-fed mosquitoes were also examined by scanning electron microscopy. The Hepatozoon spp. from the respective hosts differed in their ability to develop in C. quinquefasciatus. Most female mosquitoes fed on caimans, became fully engorged, and survived beyond 22 days p.f., whereas those engorged on boa became debilitated and did not survive beyond 9 days p.f. In boa-fed mosquitoes oocysts were found on the 6th day p.f. The few mosquitoes surviving to the 9th day p.f. contained either undivided oocysts or those that had already commenced sporogenic division. By 8–10 days p.f. caiman-fed mosquitoes contained uninucleate oocysts. Sporogonic divisions were observed from day 12 p.f. onwards. Although sporogenic development conformed in general with the previously reported accounts, the study allowed a more detailed examination of the plasmalemmal endocytotic system, and the consolidation of the crystalline body in specialized ‘factories’ of cystalline material. Sporozoite differentiation occasionally started on the 18th day p.f., but otherwise was observed only on day 22 p.f.

—Bioassays were conducted with Bacillus sphaericus (Neide) 1593M (Bsph) and a neem based biopesticide formulation, Neemtox® (0.03% azadirachtin), independently and in different combinations, to evaluate any synergistic effects on Culex quinquefasciatus Say (Diptera: Culicidae) larvae susceptible to Bsph. The results indicated that the two biopesticides have no synergistic interaction on the larvae. These results are discussed in light of earlier experiments with resistant C. quinquefasciatus, in which Bspfc-Neemtox synergism was seen.

—Organophosphorus-derived pesticides are commonly used to control Culex quinquefasciatus, the principal vector of filariasis in India. This paper reports on the susceptibility of C. quinquefasciatus from Madurai city, Tamil Nadu and its environs, to the organophosphate Malathion. It was observed that both larval and adult mosquitoes had low levels of resistance to the pesticide, with resistance ratios at LC50, LC90, and LC95 varying from 0.94 to 3.07 in larvae, and 0.93 to 34.68 in adults. This observation indicates the possibility of higher resistance developing in C. quinquefasciatus populations, the limitation of organophosphorus compounds as larvicides in mosquito breeding sites as a measure to control filariasis, and the importance of research into alternative measures for managing C. quinquefasciatus.

Experiments were carried out to determine the factors that influence the feeding behaviour of Culex tigripes, a mosquito whose larvae are predators of other mosquito larvae. The results indicated that the efficiency of predatory activities of Cx tigripes larvae increased as they developed from 1st to 4th instar with regard to the number of mosquito prey larvae they consumed in a given period of time. Fourth instars of Cx tigripes are the most voracious of all the stages and are better adapted for catching and consuming all stages of mosquito larvae. The mean number of mosquito larvae consumed in 24 hours increased with increasing prey density. When offered a mixture of different prey species and larval stages, Cx tigripes larvae consistently selected 4th instars of mosquitoes over pupae and preferred Aedes aegypti larvae to the larvae of Cx quinquefasciatus and Anopheles gambiae. Prey size, density and mobility were also found to influence prey selection by Cx tigripes.

To study the effect of temperature on the development and predatory behaviour of Culex (Lutzia) tigripes, immature stages of the predatory mosquito Culex (Lutzia) tigripes were reared at temperatures ranging from 12–37°C and provided Culex quinquefasciatus larvae as prey. Larval developmental duration decreased with an increase in rearing temperature until an optimum temperature of 30°C was reached. Above this temperature, the immatures developed slower. In contrast, pupal developmental duration decreased at temperatures above 30°C, being shortest at 32°C. The lower and upper threshold temperatures for larval development were around 12°C and 34°C respectively. Fourth instars were the most voracious and had the longest developmental time. The daily rate of predation increased with temperature, with more prey larvae being consumed at 30°C. Although they consumed more prey, Cx. tigripes larvae and pupae were smaller at high temperature. The increase in prey consumption during the entire larval developmental period at 20°C was attributed to a longer larval duration at this temperature. Developmental period and growth of male and female larvae reared at a particular temperature were not significantly different. Depending on temperature, each larva consumed between 160 and 229 Cx. quinquefasciatus larvae during its development. The implications of these findings to the possible use of Cx. tigripes for mosquito control are discussed.

Out of 85 Bacillus thuringiensis strains isolated from Nigerian soils, 18 were larvicidal to Aedes aegypti, Culex quinquefasciatus and Anopheles gambiae. At 10−6 dilution of the final whole culture (FWC), the 11 most active strains, code-named GSC1, GSC3, GNA13, GNA14, OGL8, BUS4, BUS5, OBG1, OBG4, OBG8 and BAR3 produced mortality of 11.7–61.7% and 3.3–48.3% in Ae. aegypti and in C. quinquefasciatus fourth instars respectively. At 0.5 × 10−5 dilution of the FWC, the B.t. strains caused mortality in An. gambiae larvae ranging from 31.7 to 94.1%. All the 18 mosquitocidal isolates belonged to the subspecies israelensis, i.e. serotype 14. Microscopic examination revealed all the isolates to be typically Bacillus, with irregular or amorphous crystals of varying sizes.

The uptake of Wuchereria bancrofti microfilariae (Mf) by Culex quinquefasciatus and their development in relation to human Mf density were quantified by allowing a total of 1096 wild mosquitoes to feed on 13 volunteers sleeping under partially open bed-nets. For each volunteer, each hour between 18.00 and 06.00 h the Mf density in finger-prick blood was determined and engorged mosquitoes collected. Each hourly collection of mosquitoes was kept separately. Half of them was dissected within 18 h post-feeding for the presence of ingested Mf, the other half was reared for 12 days to allow for the development of L3 larvae. About 20% of the latter mosquitoes died during these 12 days and these harboured significantly more larvae than the surviving ones, which could be an indication of excess-mortality among heavily infected mosquitoes. Assuming that variability in Mf uptake and in the number of developed L3 larvae can be described by a negative binomial distribution, a maximum-likelihood procedure was applied to estimate the relationship between human Mf density and both the arithmetic mean Mf uptake and L3 development. Both were adequately described by a saturating hyperbolic function that significantly differed from linearity. The saturation level for Mf was estimated at 29 (CI: 20–54) and for L3 larvae at 6·6 (CI: 4·3–17·0). Next, the L3 yield was related to Mf uptake indicating that the W. bancrofti–C. quinquefasciatus complex shows ‘limitation’, i.e. a decreasing yield for an increasing uptake. Both the number of Mf ingested and the number of L3 larvae developing per mosquito were found to be highly aggregated, with the level of aggregation decreasing in a non-linear way with human Mf density.

Acute toxicity tests were conducted to determine the biological effects of partially purified extracts of four different plants on the juveniles of Culex quinquefasciatus. The active ethyl acetate extract of Solarium suratense leaf produced a 24h LC50 of between 23.53 ppm for the second instars and 46.04 ppm for the third instars. This was followed by the defatted methanol fraction of Abrus precatorius seed coat extract with the LC50 values ranging from 59.82 ppm for the second instar to 77.34 ppm for the third instar. The petroleum ether fraction of Solatium trilobatum and the ethyl acetate fraction of Lencas aspera were less toxic to the larvae. The active fractions of the plant extracts disrupted moulting and metamorphosis, induced malformation, extended the larval duration and inhibited adult emergence. At concentrations of less than 37.64 ppm, they inhibited emergence of 50% of the larvae. The insecticidal activity of these extracts persisted for up to four days.