Females Of Culex Pipiens Research Articles

Clash of mosquito wings: Larval interspecific competition among the mosquitoes, Culex pipiens, Aedes albopictus and Aedes aegypti reveals complex population dynamics in shared habitats.

Globalisation, climate change and international trade are the factors contributing to the spread of Aedes albopictus (Diptera: Culicidae) and Ae. aegypti into new areas. In newly invaded habitats, these non-native species can serve as arbovirus disease vectors or increase the risk of disease spill over. These mosquitoes continue to emerge in new areas where they have or will have overlapping ranges with other resident mosquito species. The study investigates how invasive Aedes mosquitoes compete with the native Culex pipiens in Türkiye, which might affect the overall mosquito population dynamics and disease transmission risks. Both Aedes species exhibited contrasting responses to interspecific competition with Cx. pipiens. While Ae. albopictus suffers reduced emergence primarily in larger containers with abundant food, Ae. aegypti surprisingly thrives in mixed cultures under all food conditions. Adult Cx. pipiens emergence drops by half against Ae. albopictus and under specific conditions with Ae. aegypti. Competition influences mosquito size differently across species and life stages. Culex pipiens females grow larger when competing with Ae. aegypti, potentially indicating resource advantage or compensatory strategies. However, Ae. albopictus size shows more nuanced responses, suggesting complex interactions at play. Understanding how invasive and native mosquitoes interact with each other can provide insights into how they adapt and coexist in shared habitats. This knowledge can inform effective control strategies. The study highlights the differential responses of invasive Aedes species and the potential for managing populations based on their competitive interactions with the native Cx. pipiens. It can contribute to improved monitoring and prediction systems for the spread of invasive mosquitoes and the associated disease risks.

Larvicidal, biological, and histopathological alterations induced by pomegranate peel extract, Punica granatum against Culex pipiens L. (Diptera: Culicidae)

The insecticidal efficacy of agricultural waste pomegranate peel extract was determined according to the world health organization (WHO) against the Culex pipiens 3rd instar larvae. The mortality percentage of the treated larvae was the first indicator to evaluate the inhibition effect of the pomegranate peel extract. The median lethal concentrations (LC50) were (95.63, 62.55, 54.47 and 44.35) ppm at different times post-treatment (24, 48, 72, 96 hours), respectively. The tested extract showed repellent against Culex pipiens females. Phytochemical screening was carried out to detect the effective chemical groups in the tested extract then the extract was analyzed by GC-MS and HPLC. The used extract caused a reduction in some biological aspects of Culex pipiens. Several forms of morphological malformations were detected and many aberrations have been induced. The activities of enzymes, as well as total proteins, carbohydrates, and lipids of Culex pipiens larvae, were significantly reduced compared to the untreated. Electrophoretic analysis of protein revealed inhibitory action of the tested extract on the protein contents and fraction patterns. Ultrastructure studies showed a drastic effect on some larval tissues in response to the pomegranate peel petroleum ether extract.

Mosquitoes are attracted by the odour of Plasmodium-infected birds

Parasites can manipulate their hosts to increase their transmission success. Avian malaria parasites (Plasmodium) are thought to alter the cues such as host odour, used by host-seeking mosquitoes. Bird odour is affected by secretions from the uropygial gland and may play a role in modulating vector-host interactions. We tested the hypothesis that mosquitoes are more attracted to the uropygial secretions and/or whole-body odour (headspace) of Plasmodium-infected house sparrows (Passer domesticus) than to those of uninfected birds. We tested the attraction of nulliparous (e.g. uninfected mosquitoes without previous access to blood) Culex pipiens females towards these stimuli in a dual-choice olfactometer. We used Gas Chromatography-Mass Spectrometry (GC–MS) analyses to assess whether Plasmodium infection is associated with differences in the chemical composition of uropygial secretions. Mosquitoes were more attracted to the odours of infected than uninfected birds, regardless of sex. However, the significant interaction between infection status and the stimuli (uropygial secretion or headspace) showed that mosquitoes were more attracted to the headspace of infected birds; no differences were found in the case of uropygial secretions. The compounds in the volatile lipophilic fraction of the uropygial secretion did not differ between infected and uninfected birds. These results support the host manipulation hypothesis since avian Plasmodium parasites may be capable of altering their host’s body odour, thereby making infected individuals more attractive to mosquitoes.

Laboratory Evaluation of Some Local Components as Attractants to the Mosquito, Culex pipiens Females

Culex pipiens is a cosmopolitan mosquito species and is an important vector for periodic lymphatic filariasis, West Nile virus, and Rift Valley fever. Using newer technologies like the application of semiochemical-baited traps for mass trapping or killing of adult females of mosquito under integrated pest management (IPM) programs have been encouraged instead of intensive using of chemical insecticides to avoid hazardous effects to human, animals, and livestock in addition to environmental problems. The present study focused on the evaluation of the efficacy of attractive traps in trapping the mosquito, Culex pipiens females under laboratory conditions. The traps were supplied with some of safe components such as (1) sucrose, molasses and CAPL* (Central Agricultural Pesticides Laboratory) alone and mixed with Baker’s yeast granules that cause releasing of CO2 as an attractive material and (2) ammonium hydroxide (33%) and lactic acid alone and mixed with molasses or sucrose. The obtained results showed that the sugary solutions (sucrose, molasses, and CAPL* solutions) alone had lower attractive effect (46.7- 72.0% attraction after two days exposure) as compared with those that were mixed with Baker’s yeast granules (92-100% attraction). In addition CO2 emanation showed attraction and killing effects on tested mosquitoes. Ammonium hydroxide (33%) exhibited high attraction effect at low dilution (1 µl/100 ml water attracted 100% of mosquitoes after two days exposure) while lactic acid was weak attractant (1 µl/100 ml water attracted only 44% of mosquitoes). So lactic acid (5 µl/100 ml water) attraction (60% after two days) was augmented by adding of 50 gm molasses and 50 gm sucrose (96% and 92% attraction, respectively at day 2 post-exposure). It can be concluded that solutions showed ≥ 90% attraction after two days exposure (sucrose + yeast, molasses + yeast, CAPL* + yeast, ammonium hydroxide (33%) at 1 µl and lactic acid at 5 µl mixed with sucrose or molasses) are considered attractive materials, but for control purposes, solutions which cause complete death for the attracted mosquitoes are preferred such as sucrose + yeast, molasses + yeast, and CAPL* + yeast. However, further intensive studies are needed to test the efficacy of such materials as control agents under field conditions.

Multi‐scale oviposition site selection in two mosquito species

1. In organisms characterised by complex life cycles, habitat selection often occurs at multiple spatial scales. For instance, female mosquitoes searching for an appropriate aquatic habitat to oviposit their eggs should also consider the characteristics of the terrestrial landscape in which it is embedded.2. In this study, a field experiment was conducted to test for multi‐scale oviposition site selection in two mosquito species. Artificial pools were placed in two adjacent landscapes, olive plantations and a citrus orchard, mainly differing in their blooming periods and nectar availability. Pools were organised in three pairs: predatory caged fish were present in both pools, in one pool, or in none.3. Early during the season, most of the egg rafts were laid by Culiseta longiareolata females in pools located within the blooming citrus orchard. When blooming shifted to the olive plantation, C. longiareolata become opportunistic. Culex pipiens females appeared later on during the season, when egg rafts of C. longiareolata were scarce, and they exhibited a higher selectivity to the olive plantation, although its blooming ended. In addition, the selectivity of C. pipiens to fish‐free pools was stronger than that of C. longiareolata.4. Culex pipiens was more selective, possibly due to its high dispersal ability, which can lower movement cost and enhance the ability to gather environmental information. A trade‐off among gonotrophic cycles, combined with a shorter breeding season and limited recognition ability of the predatory fish may have reduced C. longiareolata selectivity. These differential oviposition patterns can strongly affect the population and community dynamics of both species.

Repellent and insecticidal efficacy of a combination of dinotefuran, pyriproxyfen and permethrin (Vectra® 3D) against Culex pipiens in dogs

Culex pipiens is an important vector of pathogens of substantial medical and veterinary importance such as Dirofilaria immitis and Dirofilaria repens or the West Nile Virus. The control of these mosquitoes is therefore essential to control the transmission of mosquito-borne agents to humans and animals. A combination of dinotefuran, permethrin and pyriproxyfen (Vectra® 3D) has already shown its efficacy against Aedes aegypti. The aim of this study was to confirm the efficacy of this combination in repelling and killing another species of mosquito, Culex pipiens, after a single topical application to dogs.Twelve adult Beagle dogs with an equal receptivity to mosquitoes were included in the study and divided in two groups of six dogs: an untreated control group and a group treated with a combination containing 54mg/mL dinotefuran +4.84mg/mL pyriproxyfen +397mg/mL permethrin (Vectra® 3D). All dogs were challenged with 80 Culex pipiens females for 90±5min on Days - 28, 1, 7, 14, 21 and 28. The treatment was applied once topically on Day 0. Count and engorgement determination of dead and live mosquitoes were performed after each exposure to treated and untreated dogs.Compared to control dogs, the spot-on formulation provided a repellent efficacy (anti-feeding effect) against mosquitoes of 98.9%, 98.8%, 98.6%, 96.7% and 97.9% on Days 1, 7, 14, 21 and 28 respectively. There was a significant difference (p≤0.05) between the treated and controlled groups on every assessment day. The insecticidal efficacy on treated dogs at 90min was 34.7%, 50.3%, 39.7%, 22.8% and 11.4% on Days 1, 7, 14, 21 and 28 respectively. There was a significant difference between the treated and controlled groups for live mosquitoes for all assessment days (p<0.05).A single topical application of a combination of dinotefuran, permethrin and pyriproxyfen showed a significant repellent effect (i.e. >96%) against Culex pipiens which lasted for 28days. The results suggest that the Vectra® 3D spot-on solution could be used as an effective mosquito control strategy in dogs and is therefore recommended for use in a dirofilariosis prevention programme.

A potential role for ribosomal protein S2 in the gene network regulating reproductive diapause in the mosquito Culex pipiens

We propose that a shut-down in expression of ribosomal protein S2 (rpS2) contributes to regulation of diapause in adult females of Culex pipiens. While this gene is expressed continuously in nondiapausing females reared under long-day conditions, it is strongly down-regulated 5-18 days after adult eclosion in females reared under the short-day conditions that induce diapause. The possibility that this shut-down in expression of rpS2 contributes to the arrest in ovarian development characteristic of diapause is bolstered by the diapause-like arrest in follicle growth observed when nondiapausing females are injected with dsrpS2. A control gene encoding another ribosomal protein, L19, is expressed equally in nondiapausing and diapausing females, and RNA interference directed against rpL19 did not arrest follicle growth, thus indicating that the response we observed in knocking down expression of rpS2 is not common to all ribosomal proteins. Diapause in C. pipiens is readily terminated with juvenile hormone (JH), and in this study we demonstrated that an exogenous application of JHIII can rescue the arrest in follicle growth caused by dsrpS2. Together, these results suggest that rpS2 plays a critical role in arresting the ovarian development associated with diapause in this mosquito.

Diapause-specific gene expression in the northern house mosquito, Culex pipiens L., identified by suppressive subtractive hybridization

In this study we probe the molecular events underpinning diapause observed in overwintering females of Culex pipiens. Using suppressive subtractive hybridization (SSH) we have identified 40 genes that are either upregulated or downregulated during this seasonal period of dormancy. Northern blot hybridizations have confirmed the expression of 32 of our SSH clones, including six genes that are upregulated specifically in early diapause, 17 that are upregulated in late diapause, and two upregulated throughout diapause. In addition, two genes are diapause downregulated and five remain unchanged during diapause. These genes can be categorized into eight functional groups: genes with regulatory functions, metabolically-related genes, those involved in food utilization, stress response genes, cytoskeletal genes, ribosomal genes, transposable elements, and genes with unknown functions.

Repellency of inseminated Culex pipiens (Diptera: Culicidae) females to various wing‐beat sound frequencies in modulated intensities in a flight chamber

AbstractWing‐beat sound frequencies at 370, 440, 493 and 554 Hz were evaluated for female mosquito repellency. One hundred inseminated females of Culex pipiens were introduced into a 30 cm × 30 cm × 3 m screened cage with an electronic device (cellular phone) emitting selected frequencies positioned at one end of the chamber. The mosquitoes were counted in areas of 0.0–0.5, 0.5–1.0, 1.0–2.0 and 2.0–3.0 m from the cellular phone. In a second test, 50 Cx. pipiens were released in the screened cage with a shaved rat as bait placed beside the cellular phone (370 Hz) at the center of the chamber. Statistical analysis (anova) showed that significantly fewer (P &lt; 0.05) mosquitoes rested near the cellular phone at 370 Hz, but not at the other frequencies. Similarly, there was significant reduction (mean 33.0%) in the number of mosquitoes taking a blood meal on the shaved rat when the cellular phone was turned on (P &lt; 0.01).

Repellent activity of five essential oils against Culex pipiens

Essential oils extracted from the seeds of anise ( Pimpinella anisum), dried fruits of eucalyptus ( Eucalyptus camaldulensis), dried foliage of mint ( Mentha piperita) and basil ( Ocimum basilicum) and fresh foliage of laurel ( Laurus nobilis) were tested for their repellency against the adult females of Culex pipiens. All essential oils showed repellency in varying degrees, eucalyptus, basil and anise being the most active.

The haemagglutination activity in the different developmental stages and changes of this activity caused by analogues of insect hormones in two members of the Culex pipiens complex of mosquitoes

. Haemagglutination activity was studied in last larval instars, pupae and adults of both sexes of the Culex pipiens mosquito complex. In females of Culex pipiens quinquefasciatus Say, an anautogenous member of C. pipiens complex, activity was detected in the homogenate of the head-thorax complex, gut and remaining abdomen (after removing the gut), before and after sucking water, glucose solution or blood. Similar investigations were made in females of autogenous Culex pipiens molestus Forskal, a member of the same mosquito complex. The results were compared with data obtained for males of these subspecies, plus the larvae and pupae. The results show that haemagglutination activity in adult females depends not on the sucking of blood, but on the age of the females. In newly emerged females, the level of activity was very low, but after 24 h or 48 h of activity was highly enhanced, even in females that had no possibility to suck water or other liquids including blood. Furthermore, in C. p. molestus, the haemagglutination activity does not change in hungry or engorged females, and a high level of activity was found in the gut of last larval instars, a developmental stage that never takes blood. Treatment with methoprene reduces haemagglutination activity in both sexes, but 20-hydroxycdysone application decreased activity in the gut of females. It is suggested that haemagglutination activity may be regulated indirectly by the endocrine system. The possibility that haemagglutination activity may depend on some aspect of the digestive system that has no direct connection to blood uptake is discussed. In addition, the activity may be important not only for the elimination of infections, but also for the processing of food and the utilization and transport of nutrients.

Induction of oogenesis in mosquitoes (Diptera: Culicidae) by infusion of the hemocoel with amino acids.

As done previously with adult females of Culex pipiens pallens Coquillett, a mixture of 17 amino acids was infused into the hemocoel of females of seven anautogenous and one autogenous mosquito species belonging to three genera. In Culex. p. quinquefasciatus Say, Cx. tritaeniorhynchus Giles, Cx. kyotoensis Yamaguti & LaCasse, Aedes albopictus (Skuse), Armigeres subalbatus (Coquillett), and Cx. p. molestus Forskal, which previously had laid autogenously matured first batch of eggs, ovarian development was stimulated and frequently continued to maturity. In most mosquitoes, the number of mature follicles nearly doubled when the period of infusion was extended from 24 to 48 h. Therefore, the two previously indicated roles of amino acids, one to initiate ovarian development and the other to regulate the number of maturing oocytes, were confirmed in these species. In Cx. halifaxii Theobald and Ae. japonicus (Theobald), however, the frequency of activation and maturation of ovaries was low compared with the other species, indicating that those species may require some factors other than an increase in amino acids for normal ovarian development after a blood meal.

Terpene-sensitive receptors in female Culex pipiens mosquitoes: Electrophysiology and behaviour

Mosquitoes feed on plants extensively and depend on them as a source of energy for flight and metabolic maintenance; yet little attention has been given to the cues that mosquitoes use to locate and choose appropriate host plants in their environment. This paper describes the electrophysiological characteristics of antennal olfactory receptors in Culex pipiens females that detect terpenes (constituents of essential plant oils) and the results of a behavioural assay that suggest a possible role for these compounds in the short-distance feeding behaviour of this species.

The susceptibility of a mosquito species (Culex pipiens quinquefasclatus) to the insecticides, malathion, DDT and UBMT in the Sudan savanna zone of Nigeria

The susceptibility of adult females of Culex pipiens quinquefasciatus to malathion, dichlorodiphenyl trichloroethane (DDT), and 1 – (- dimethylaminobenzylidene) – 3 -methylthiotriazene (DBMT) was assessed by residual application using the World Health Organisation’s (WHO) standard susceptibility test method on the Main Campus, Ahmadu Bello University, Zaria. Also the susceptibility and contact bioassay studies were carried out on the larvae of this species for malathion and DBMT. The results obtained indicate that DBMT has insecticidal property on both larval and adult C.p. quinquefasciatus. Of the three insecticides tested, malathion was the most effective at high concentration while DBMT was the most effective at low concentration. C.p. quinquefasciatus has high resistance to DDT. The larvae were more susceptible to malathion than DBMT, the latter being poorly larvicidal. The results of the residual application test on a concrete wall surface indicate that malathion is much more stable than DBMT.

Post-diapause sensory responsiveness in Culex pipiens

Adult Culex pipiens females do not host-seek and hence do not feed on blood during diapause. Such diapausing females do not possess the highly sensitive olfactory receptors for the host attractant lactic acid that are characteristic of nondiapausing host-seeking females. In this study single unit electrophysiological recordings coupled with quantitative odour-delivery techniques were employed to study sensory responsiveness in females that had terminated diapause (as evidenced by resumption of ovarian follicle growth). Such females display changes in peripheral receptor responsiveness that can be summarized as follows: (1) Highly sensitive lactic acid-excited cells associated with the sensilla basiconica type A3 are present in females that have terminated diapause. (2) The proportion of responsive (albeit nonspecific) cells associated with the sensilla trichodea type A2 increases whereas the proportion of nonresponsive cells decrease in post-diapause females; this change in sensory responsiveness is not accompanied by an increase in the number of cells specifically sensitive to ethyl propionate or by a change in receptor sensitivity. Resumption of post-diapause anautogenous reproductive activity in this mosquito thus involves resumption of ovarian follicle development, resumption of host-seeking behaviour, and changes in peripheral receptor responsiveness.

A behavioural and sensory analysis of host-seeking behaviour in the diapausing mosquito Culex pipiens

Diapausing Culex pipiens females maintained in diapause-inducing conditions fail to exhibit host-seeking behaviour for at least 30 days after adult emergence. This behavioural hiatus is characterized by the absence of high-sensitivity antennal receptor responses to the host attractant lactic acid. Non-diapausing females readily exhibit host seeking and invariably have antennal receptors with high lactic acid sensitivity. This difference in receptor sensitivity may be restricted to the lactic acid-sensitive receptors as other antennal receptors (specifically, those sensitive to putative oviposition-site attractants) are unaffected by the diapause state.

Experimental Hibernation Studies in Culex Pipiens (Diptera: Culicidae): Reactivation of Ovarian Development and Blood-Feeding in Prehibernating Females

Two characteristics of prehibemating adult Culex pipiens females are a reduction in the blood-feeding drive and the failure of ovarian follicles to mature following a full blood meal. This latter characteristic has great importance to our understanding of the role of overwintering Culex mosquitoes in the winter maintenance of certain arboviruses. New evidence is presented which offers an explanation of how prehibernating female Cx, pipiens mosquitoes may take a viremic blood meal, yet not undergo ovarian development. Females which had been subjected in the laboratory to short daily photophases and cool temperatures (L:D 9:15, 15°C) from the pupal stage to 7 days after emergence were warmed to 25°C for various periods of time, About 45% of those warmed for 72–84 h took full blood meals, and of these, 40% failed to develop mature follicles. We suggest that such warming periods are analogous to situations which may be encountered in nature by prehibernating female Cx. pipiens .

Untersuchungen zum Aminosäuren- und Proteinstoffwechsel während der autogenen und anautogenen Eireifung von Culex pipiens

Under the same larval dietary conditions newly emerged autogenous females of Culex pipiens pipiens L. are significantly heavier, have a distinctly higher total nitrogen content, and contain twice as much protein as anautogenous females of Culex pipiens fatigans Wiedem. After each gonotrophic cycle these values decline to a residual level which is the same in both types of mosquitoes (2·5 mg fresh weight, 50μg nitrogen and 0·1 mg protein per female). The residual values show a sharp increase of two to four times after each blood meal. This physiological periodicity has its morphological appearance in a parallel alteration of the volume of developing ovarian follicles. The absolute protein content of mature ovaries shortly before oviposition is significantly lower after autogenous maturation (without a previous blood meal) than after anautogenous maturation (after a previous blood meal), whereas the relative protein content per unit wet weight of the ovary is the same in both. In anautogenous females the protein content of the whole body shortly before egg-laying is the same as that of their ovaries. In contrast, the body of autogenous females contains at this time only half as much protein as the ovaries. It is concluded that during the period of autogenous maturation yolk protein is synthesized at the expense of protein reserve carried over from the larval life. Analyses of ovary hydrolysates demonstrated that the rate of deposition of yolk protein is different between the two types of egg maturation: autogenous females show the greatest increase of proteins in their ovaries between 48 and 72 hr after emergence, whereas in anautogenous females this takes place between 24 and 48 hr after a blood meal. During these periods there is also a maximal increase in the volume of ovarian follicles. The percentage distribution of amino acids in hydrolysates from ovaries at the resting stage differs distinctly between the two types of females but shows a remarkable similarity prior to oviposition. In female adult mosquitoes the free amino acids decrease at the time of yolk synthesis and increase in the course of digestion of a blood meal. In general, alanine, glutamic acid, methionine sulphoxide, and histidine show the highest concentrations, amounting to 5 to 30 per cent of the total. With the exception of methionine sulphoxide and taurine, the pattern of free amino acids in the two types of females is similar. Investigations of the content of the midgut at different intervals after a blood meal revealed that during the first day about 50 per cent of the ingested blood disappeared from the intestine. At 72 to 96 hr after a blood meal, i.e. at the time of oviposition, digestion is usually completed. In the excreta after a blood meal uric acid contributes to about 30 per cent of the dry weight in both mosquito types. About 64 per cent of the total nitrogen excreted is present as uric acid, 16 per cent as amino nitrogen, and 20 per cent as unknown residues. Excretion of amino acids has also been analysed. During the first day after blood-feeding free histidine contributes to about 80 per cent of all free amino acids excreted. Hydrolysis of the excreta demonstrated that during the second day 60 per cent of all peptide or protein-bound amino acids excreted is represented by glycine. Histamine and taurine could not be detected. In general, the excretion of uric acid and amino acids reaches a maximum between 24 and 48 hr after blood ingestion, at the time when anautogenous synthesis of yolk protein is most intensive. In anautogenous females of C. p. fatigans only two-thirds of all amino acids ingested with blood are utilized for egg production (42 eggs/mg blood). In autogenous females of C. p. pipiens the protein reserve carried over from the larval stage is only about half as much as the protein taken up from a blood meal, but apparently sufficient for the production of a first batch of eggs, which indeed is smaller than the subsequent ones. The present results are discussed in relation to the problem of autogeny in mosquitoes.