Younger Mosquitoes Research Articles

Long-term impacts of egg quiescence and Wolbachia infection on lipid profiles in Aedes aegypti: Ovarian roles in lipid synthesis during reproduction

Wolbachia, an endosymbiotic bacterium, relies on nutrients from its host to complete its life cycle. The presence of Wolbachia strain wAlbB in the mosquito Aedes aegypti during egg or larval stages affects the host’s development, leading to the absence of developed and visible ovaries in adult mosquito females. In this study, we investigated the impacts of egg quiescence and Wolbachia infection on lipid profiles of adult Ae. aegypti females, and discerned the role of ovaries in lipid synthesis in the reproductive process. The lipidomes of Wolbachia infected and uninfected female individuals at various developmental stages were quantitatively analyzed by LC-MS/MS. Lipidomic change patterns were systematically further investigated in wAlbB-infected fertile females and infertile females following blood feeding. Prolonged egg quiescence induced a shortage of acyl-carnitine (CAR) and potentially impacted some molecules of diacyl-phospholipid (diacyl-PL) and sphingolipid (SL) in young adult mosquitoes. After the first gonotrophic cycle, infertile females accumulated more CAR and lyso-phospholipid (lyso-PL) than fertile females. Then in the second gonotrophic cycle, the patterns of different lipid groups remained similar between fertile and infertile females. Only a small proportion of molecules of triglyceride (TG), phospholipid (lyso-PL and diacyl-PL) and ceramide (Cer) increased exclusively in fertile females from 0 h to 16 h post blood meal, suggesting that the generation or prescence of these lipids rely on ovaries. In addition, we found cardiolipins (CL) might be impacted by Wolbachia infection at the egg stage, and infected mosquitoes also showed distinct patterns between fertile and infertile females at their second gonotrophic cycle. Our study provides new insights into the long-term influence of Wolbachia on lipid profiles throughout various life stages of mosquitoes. Additionally, it suggests a role played by ovaries in lipid synthesis during mosquito reproduction.

Mosquito ageing modulates the development, virulence and transmission potential of pathogens.

Host age variation is a striking source of heterogeneity that can shape the evolution and transmission dynamic of pathogens. Compared with vertebrate systems, our understanding of the impact of host age on invertebrate-pathogen interactions remains limited. We examined the influence of mosquito age on key life-history traits driving human malaria transmission. Females of Anopheles coluzzii, a major malaria vector, belonging to three age classes (4-, 8- and 12-day-old), were experimentally infected with Plasmodium falciparum field isolates. Our findings revealed reduced competence in 12-day-old mosquitoes, characterized by lower oocyst/sporozoite rates and intensities compared with younger mosquitoes. Despite shorter median longevities in older age classes, infected 12-day-old mosquitoes exhibited improved survival, suggesting that the infection might act as a fountain of youth for older mosquitoes specifically. The timing of sporozoite appearance in the salivary glands remained consistent across mosquito age classes, with an extrinsic incubation period of approximately 13 days. Integrating these results into an epidemiological model revealed a lower vectorial capacity for older mosquitoes compared with younger ones, albeit still substantial owing to extended longevity in the presence of infection. Considering age heterogeneity provides valuable insights for ecological and epidemiological studies, informing targeted control strategies to mitigate pathogen transmission.

Developing methods for chilling, compacting, and sterilizing adult Aedes aegypti (Diptera: Culicidae) and comparing mating competitiveness between males sterilized as adults versus pupae for sterile male release.

The yellow fever mosquito, Aedes aegypti L., can transmit several pathogens responsible for human diseases. With insecticide resistance development becoming a concern, alternative control strategies are needed for Ae. aegypti. Sterile insect technique (SIT) is an increasingly popular option being explored. However, logistical issues in mass production and sterilization make it difficult to maintain a SIT program. Male mosquitoes are typically irradiated as pupae because this is the earliest developmental point at which females can be separated from males, but asynchrony in pupation and high variability in pupal responses to irradiation based on pupal age make it difficult to sterilize mass quantities of pupae on a regular schedule in a rearing facility. Young adult mosquitoes have wider windows for irradiation sterilization than pupae, which can allow facilities to have fixed schedules for irradiation. We produced a workflow for adult Ae. aegypti irradiation in a mosquito control district with an operational SIT program that currently irradiates pupae. The impacts of chilling, compaction, and radiation dose on survival were all assessed before combining them into a complete adult irradiation protocol. Males chilled up to 16 h prior to compaction and compacted to 100 males/cm3 during radiation resulted in low mortality. Males irradiated as adults had increased longevity and similar sterility compared to males irradiated as pupae. Additionally, males sterilized as adults were more sexually competitive than males sterilized as pupae. Thus, we have shown that irradiating adult males can be a viable option to increase the efficiency of this operational mosquito SIT program.

Age-dependence of susceptibility to single and repeated deltamethrin exposure in pyrethroid-resistant Aedes aegypti strains

Monitoring insecticide resistance is crucial in disease-transmitting mosquitoes to allow assessment of viable candidate insecticides to use for control and to provide indication of changes in resistance. Insecticide resistance bioassays are typically performed on young female mosquitoes, yet disease is transmitted by older females, which may also have encountered insecticide multiple times during their adult life. If insecticide mortality rates increase with age directly, or indirectly via cumulative toxicity from repeated exposure, the strategy of testing young mosquitoes as the least susceptible cohort would be supported. We tested three hypotheses via examination of how age and cumulative exposure impact mortality rates to the pyrethroid deltamethrin in strains of Aedes aegypti from Jeddah, Saudi Arabia and the Cayman Islands, which show differences in resistance mechanisms. Females of different ages (5, 7, 10 and 14 days-old) were exposed using WHO tube assays to either a single dose of insecticide, or in a second experiment females (initially 5 days-old) were exposed daily over 10 days. Age only increased mortality in the Jeddah strain at 14 days-old and had no impact on the Cayman strain. This is consistent with greater impact linked to metabolic resistance in the Jeddah strain, though results from qPCR of four candidate genes, failed to provide evidence for a candidate underpinning an age-dependent change in resistance. With repeated exposure, mortality rates of surviving females decreased to very low levels, suggesting that surviving older cohorts of females may exhibit substantially lower susceptibility than young females in single exposure assays. Our results indicate that testing young females with a single insecticide exposure should capture minimum susceptibility for the majority of the population, but a small fraction of older females may prove particularly unresponsive to pyrethroid-based control measures.

Increased insulin signaling in the Anopheles stephensi fat body regulates metabolism and enhances the host response to both bacterial challenge and Plasmodium falciparum infection

In vertebrates and invertebrates, the insulin/insulin-like growth factor 1 (IGF1) signaling (IIS) cascade is highly conserved and plays a vital role in many different physiological processes. Among the many tissues that respond to IIS in mosquitoes, the fat body has a central role in metabolism, lifespan, reproduction, and innate immunity. We previously demonstrated that fat body specific expression of active Akt, a key IIS signaling molecule, in adult Anopheles stephensi and Aedes aegypti activated the IIS cascade and extended lifespan. Additionally, we found that transgenic females produced more vitellogenin (Vg) protein than non-transgenic mosquitoes, although this did not translate into increased fecundity. These results prompted us to further examine how IIS impacts immunity, metabolism, growth and development of these transgenic mosquitoes. We observed significant changes in glycogen, trehalose, triglycerides, glucose, and protein in young (3–5 d) transgenic mosquitoes relative to non-transgenic sibling controls, while only triglycerides were significantly changed in older (18 d) transgenic mosquitoes. More importantly, we demonstrated that enhanced fat body IIS decreased both the prevalence and intensity of Plasmodium falciparum infection in transgenic An. stephensi. Additionally, challenging transgenic An. stephensi with Gram-positive and Gram-negative bacteria altered the expression of several antimicrobial peptides (AMPs) and two anti-Plasmodium genes, nitric oxide synthase (NOS) and thioester complement-like protein (TEP1), relative to non-transgenic controls. Increased IIS in the fat body of adult female An. stephensi had little to no impact on body size, growth or development of progeny from transgenic mosquitoes relative to non-transgenic controls. This study both confirms and expands our understanding of the critical roles insulin signaling plays in regulating the diverse functions of the mosquito fat body.

Effect of wall type, delayed mortality and mosquito age on the residual efficacy of a clothianidin-based indoor residual spray formulation (SumiShield™ 50WG) in southern Mozambique.

Indoor residual spraying (IRS) is one of the main malaria vector control strategies in Mozambique alongside the distribution of insecticide treated nets. As part of the national insecticide resistance management strategy, Mozambique introduced SumiShield™ 50WG, a third generation IRS product, in 2018. Its residual efficacy was assessed in southern Mozambique during the 2018–2019 malaria season. Using a susceptible Anopheles arabiensis strain, residual efficacy was assessed on two different wall surfaces, cement and mud-plastered walls, using standard WHO (World Health Organization) cone bioassay tests at three different heights. Female mosquitoes of two age groups (2–5 and 13–26 day old) were exposed for 30 minutes, after which mortality was observed 24h, 48h, 72h, and 96h and 120h post-exposure to assess (delayed) mortality. Lethal times (LT) 90, LT50 and LT10 were estimated using Bayesian models. Mortality 24h post exposure was consistently below 80%, the current WHO threshold value for effective IRS, in both young and old mosquitoes, regardless of wall surface type. Considering delayed mortality, residual efficacies (mosquito mortality equal or greater than 80%) ranged from 1.5 to ≥12.5 months, with the duration depending on mortality time post exposure, wall type and mosquito age. Looking at mortality 72h after exposure, residual efficacy was between 6.5 and 9.5 months, depending on wall type and mosquito age. The LT50 and LT10 (i.e. 90% of the mosquitoes survive exposure to the insecticides) values were consistently higher for older mosquitoes (except for LT10 values for 48h and 72h post-exposure mortality) and ranged from 0.9 to 5.8 months and 0.2 to 7.8 months for LT50 and LT10, respectively. The present study highlights the need for assessing mosquito mortality beyond the currently recommended 24h post exposure. Failure to do so may lead to underestimation of the residual efficacy of IRS products, as delayed mortality will lead to a further reduction in mosquito vector populations and potentially negatively impact disease transmission. Monitoring residual efficacy on relevant wall surfaces, including old mosquitoes that are ultimately responsible for malaria transmission, and assessing delayed mortalities are critical to provide accurate and actionable data to guide vector control programmes.

Multiple blood feeding in mosquitoes shortens the Plasmodium falciparum incubation period and increases malaria transmission potential.

Many mosquito species, including the major malaria vector Anopheles gambiae, naturally undergo multiple reproductive cycles of blood feeding, egg development and egg laying in their lifespan. Such complex mosquito behavior is regularly overlooked when mosquitoes are experimentally infected with malaria parasites, limiting our ability to accurately describe potential effects on transmission. Here, we examine how Plasmodium falciparum development and transmission potential is impacted when infected mosquitoes feed an additional time. We measured P. falciparum oocyst size and performed sporozoite time course analyses to determine the parasite's extrinsic incubation period (EIP), i.e. the time required by parasites to reach infectious sporozoite stages, in An. gambiae females blood fed either once or twice. An additional blood feed at 3 days post infection drastically accelerates oocyst growth rates, causing earlier sporozoite accumulation in the salivary glands, thereby shortening the EIP (reduction of 2.3 ± 0.4 days). Moreover, parasite growth is further accelerated in transgenic mosquitoes with reduced reproductive capacity, which mimic genetic modifications currently proposed in population suppression gene drives. We incorporate our shortened EIP values into a measure of transmission potential, the basic reproduction number R0, and find the average R0 is higher (range: 10.1%-12.1% increase) across sub-Saharan Africa than when using traditional EIP measurements. These data suggest that malaria elimination may be substantially more challenging and that younger mosquitoes or those with reduced reproductive ability may provide a larger contribution to infection than currently believed. Our findings have profound implications for current and future mosquito control interventions.

Leaf Extract of Dillenia indica as a Source of Selenium Nanoparticles with Larvicidal and Antimicrobial Potential toward Vector Mosquitoes and Pathogenic Microbes

Chikungunya, dengue, Zika, malaria, Japanese encephalitis, filariasis, West Nile, etc. are mosquito transmitted diseases that have killed millions of people worldwide, and millions of people are at risk of these diseases. Control of the mosquitoes, such as Aedes aegypti and Culex quinquefasciatus, is challenging due to their development of resistance to synthetic insecticides. The habitats of the young mosquitoes are also the habitats for foodborne pathogens like Staphylococcus aureus (MTCC96) and Serratia marcescens (MTCC4822). The present study was aimed at synthesizing eco-friendly green nanoparticles using Dillenia indica leaf broth and analyzing its efficacy in controlling the vector mosquitoes A. aegypti and C. quinquefasciatus, as well as the microbial pathogens St. aureus and Se. marcescens. The formation of selenium nanoparticles (SeNps) was confirmed using UV-Vis spectroscopy (absorption peak at 383.00 nm), Fourier transform infrared radiation (FTIR spectrum peaks at 3177, 2114, 1614, 1502, 1340, 1097, 901, 705, and 508 cm−1), X-ray diffraction (diffraction peaks at 23.3 (100), 29.6 (101), 43.5 (012), and 50.05 (201)), and scanning electron microscopy (oval shaped). The size of the nanoparticles and their stability were analyzed using dynamic light scattering (Z-Average value of 248.0 nm) and zeta potential (−13.2 mV). The SeNps disorganized the epithelial layers and have broken the peritrophic membrane. Histopathological changes were also observed in the midgut and caeca regions of the SeNPs treated A. aegypti and C. quinquefasciatus larvae. The SeNps were also active on both the bacterial species showing strong inhibitory zones. The present results will explain the ability of SeNps in controlling the mosquitoes as well as the bacteria and will contribute to the development of multi potent eco-friendly compounds.

Impact of Mosquito Age and Insecticide Exposure on Susceptibility of Aedes albopictus (Diptera: Culicidae) to Infection with Zika Virus.

Zika virus (ZIKV) is primarily transmitted to humans by Aedes aegypti and Ae. albopictus. Vector–virus interactions influencing vector competence vary and depend on biological and environmental factors. A mosquito’s chronological age may impact its immune response against virus infection. Insecticides, source reduction, and/or public education are currently the best defense against mosquitoes that transmit ZIKV. This study assessed the effects of a mosquito’s chronological age at time of infection on its response to ZIKV infection. We exposed young (6–7 d post-emergence) and old (11–12 d post-emergence) Ae. albopictus to a sublethal dose of bifenthrin prior to oral exposure to blood meals containing ZIKV (7-day incubation period). Old mosquitoes experienced a significantly (p < 0.01) higher rate of mortality than young mosquitoes. Significantly higher ZIKV body titers (p < 0.01) were observed in the old control group compared to the young control group. Significantly higher (p < 0.01) ZIKV dissemination rates and leg titers (p < 0.01) were observed in old bifenthrin-exposed mosquitoes compared to old control mosquitoes or young bifenthrin-exposed or control mosquitoes. Hence, bifenthrin exposure may increase the potential for virus transmission; however, the degree of these impacts varies with mosquito age. Impacts of insecticides should be considered in risk assessments of potential vector populations.

Optimizing Direct Membrane and Direct Skin Feeding Assays for Plasmodium falciparum Transmission-Blocking Vaccine Trials in Bancoumana, Mali.

Malaria transmission-blocking vaccines (TBV) have been evaluated in field trials in Mali since 2013. However, the assays currently used to measure serum antibody TB activity (TBA) after vaccination are highly variable, in part due to the lack of optimization and standardization for field assays in which mosquitoes feed on gametocytemic blood. Herein, we report a study conducted in Bancoumana village, Mali, where we identify and optimize the parameters that contribute to successful mosquito feeding outcomes in both direct skin feeds (DSFs) and direct membrane feeding assays (DMFA). These parameters include: 1) mosquito age, 2) duration of mosquito starvation prior to feeding, 3) membrane selection for DMFA, 4) anatomical location of DSF feeding (arm, calf, and ankle), and 5) time of day for DSF (dawn or dusk). We found that younger mosquitoes were significantly associated with higher feeding, survival, and infection rates. Longer starvation times were positively, but not significantly, associated with higher infection rates, but were negatively associated with feeding and survival. Membrane type and body location did not affect infection outcome significantly. Although dusk was found to be associated with higher infection rates, this may be confounded by the time from positive blood smear. Based on these findings, we make specific recommendations for optimal feeding parameters in the different assay types to maximize the chance of detecting parasite transmission in a standardized manner.

The effects of ingestion of hormonal host factors on the longevity and insecticide resistance phenotype of the major malaria vector Anopheles arabiensis (Diptera: Culicidae).

Exogenous vertebrate-derived factors circulating in the blood have the capacity to modulate the biology of haematophagous insects. These include insulin, insulin growth factor 1 (IGF) and transforming growth factor β1 (TGFβ). The effects of the consumption of these three proteins were examined on laboratory strains of Anopheles arabiensis. SENN, an insecticide susceptible strain and SENN DDT, a resistant strain selected from SENN, were fed with host factor-supplemented sucrose. Adult longevity was measured and insecticide resistance phenotype over time was assessed by WHO bioassay. Detoxification and oxidative stress defence enzyme activity was assessed calorimetrically. Insulin supplementation augmented insecticide resistance in young adult mosquitoes. This effect was due to the hormonal nature of the protein, as heat-denatured insulin did not elicit the same response. In contrast, IGF and TGFβ consumption generally reduced the expression of insecticide resistance. Insulin ingestion significantly reduced longevity in the insecticide susceptible strain. IGF elicited the same response in the susceptible strain, while TGF consumption had no effect on either strain. Consumption of all factors significantly decreased Glutathione S-transferase activity and increased cytochrome P450 and superoxide dismutase activity. This suggests that the altered detoxification phenotype is mediated primarily by cytochrome P450 activity, which would result in an increase in oxidative stress. The increased superoxide dismutase activity suggests that this enzyme class alleviates the oxidative stress as opposed to glutathione-based redox systems. Oxidative stress responses play a crucial role in insecticide resistance and longevity. These data show that ingested hormonal factors can affect mosquito longevity and insecticide susceptibility, both of which are important characteristics in terms of malaria transmission and control.

Decrease of larval and subsequent adult Anopheles sergentii populations following feeding of adult mosquitoes from Bacillus sphaericus-containing attractive sugar baits.

BackgroundBacillus sphaericus is a mosquito-larvae pathogen which proliferates in the host cadavers, spreading and preserving the infection within the larval habitats for prolonged periods. In this pilot field study, we presented B. sphaericus-containing attractive sugar baits (ASB) to wild Anopheles sergentii adults, with the assumption that bait-fed, B. sphaericus-carrying mosquitoes are able to efficiently transmit the pathogen to the larval habitats, causing larval mortality and leading to a decrease in the subsequent adult population.MethodsThe experiment was conducted over 75 days in two desert-surrounded streamlets. Blooming Ochradenus baccatus bushes were sprayed with bait solutions consisting of sugar and food dye marker solutions, with or without B. sphaericus at the experimental and control streamlets, respectively. Adult mosquito and larvae numbers were monitored before and after the treatment application, and the proportion of bait-fed adults was determined by visual inspection for dye presence.ResultsPresence of food dye confirmed a large fraction of the adult mosquito population (70%-75%) readily ingested Bacillus sphaericus- containing bait. By the end of the study period, the larval population at the experimental site was six-fold smaller than the concurrent larval population at the control site. The ensuing adult An. sergentii population was also reduced to about 60% at the experimental site, while the adult mosquito population at the control site had increased 2.4 fold over the same time-frame. The reduction in adult mosquito numbers became apparent after a lag time (10 days), suggesting the treatment had minimal effect on adult longevity, also indicated by the post-treatment increase in the proportion of old mosquitoes and concomitant decrease in the proportion of young mosquitoes.ConclusionsPresentation of B. sphaericus-containing ASB substantially impacts the larval population, which in turn leads to a significant reduction of the ensuing numbers of adult mosquitoes. Although such outcomes may be the result of other causes, these preliminary results raise the possibility that adult mosquitoes can efficiently transmit the pathogen into the larval habitats. The transfer of B. sphaericus via contaminated adult mosquito carriers may allow introduction of pathogens to breeding places which are dispersed, hard to find, or difficult to access.

Modelling the impact of declining insecticide resistance with mosquito age on malaria transmission.

The evolution of insecticide resistance can lead to an increase in the entomological indicators of malaria transmission, such as mosquito survival and blood feeding rates, thus threatening efforts to control malaria. Yet, there is little evidence from the field that malaria control programmes are failing due to insecticide resistance. One explanation for this apparent contradiction is the growing evidence that insecticide resistance declines with mosquito age. Once a mosquito is first infected by Plasmodium parasites, it will not be able to transmit those parasites until they have undergone development, which lasts around 10 days. Thus, although the evolution of resistance in a population will enhance the survival of young mosquitoes, the insecticide may still kill old, and thus potentially infectious, mosquitoes, and thereby maintaining its efficacy in controlling malaria. The current evidence for age-related insecticide resistance is reviewed. A mathematical model is then described that predicts how the decline of resistance with the age of a mosquito will affect the intensity of transmission of malaria. The model combines the behavioural response of the mosquitoes to insecticides with an epidemiological model of malaria. It was found that phenotypic resistance decreases between 1.37% to 9.71% per day, independent of the mosquito species or strain. The models suggest that a decline in resistance within this range strongly diminishes the predicted impact of insecticide resistance on the effectiveness of malaria transmission-controlling interventions. Our model can be used to assess the threat of insecticide-resistance for the control of malaria. The model confirms observations from the field suggesting that, even where genetically insecticide-resistant mosquitoes dominate populations, insecticides can substantially reduce the transmission of malaria.

Anopheles sinensis mosquito insecticide resistance: comparison of three mosquito sample collection and preparation methods and mosquito age in resistance measurements

BackgroundInsecticide resistance monitoring in malaria mosquitoes is essential for guiding the rational use of insecticides in vector control programs. Resistance bioassay is the first step for insecticide monitoring and it lays an important foundation for molecular examination of resistance mechanisms. In the literature, various mosquito sample collection and preparation methods have been used, but how mosquito sample collection and preparation methods affect insecticide susceptibility bioassay results is largely unknown. The objectives of this study were to determine whether mosquito sample collection and preparation methods affected bioassay results, which may cause incorrect classification of mosquito resistance status.MethodsThe study was conducted in Anopheles sinensis mosquitoes in two study sites in central China. Three mosquito sample collection and preparation methods were compared for insecticide susceptibility, kdr frequencies and metabolic enzyme activities: 1) adult mosquitoes collected from the field; 2) F1 adults from field collected, blood-fed mosquitoes; and 3) adult mosquitoes reared from field collected larvae.ResultsMosquito sample collection and preparation methods significantly affected mortality rates in the standard WHO tube resistance bioassay. Mortality rate of field-collected female adults was 10-15% higher than in mosquitoes reared from field-collected larvae and F1 adults from field collected blood-fed females. This pattern was consistent in mosquitoes from the two study sites. High kdr mutation frequency (85-95%) with L1014F allele as the predominant mutation was found in our study populations. Field-collected female adults consistently exhibited the highest monooxygenase and GST activities. The higher mortality rate observed in the field-collected female mosquitoes may have been caused by a mixture of mosquitoes of different ages, as older mosquitoes were more susceptible to deltamethrin than younger mosquitoes.ConclusionsFemale adults reared from field-collected larvae in resistance bioassays are recommended to minimize the effect of confounding factors such as mosquito age and blood feeding status so that more reliable and reproducible mortality may be obtained.

The microsporidian parasite Vavraia culicis as a potential late life-acting control agent of malaria.

Microsporidian parasites are being considered as alternatives to conventional insecticides for malaria control. They should reduce malaria transmission by shortening the lifespan of female mosquitoes and thus killing them before they transmit malaria. As the parasite replicates throughout the mosquito's life, it should have little detrimental effects on young mosquitoes, thus putting less selection pressure on the hosts to evolve resistance. Here, we examined these expectations for the microsporidian Vavraia culicis on Anopheles gambiae Giles sensu stricto mosquitoes under varying environmental conditions. Infection by the microsporidian delayed pupation by 10%, decreased fecundity by 23% and reduced adult lifespan by 27%, with higher infectious doses causing greater effects. The decrease of lifespan was mostly because of an increase of the mortality rate with age. Similarly, the parasite's effect on mosquito fecundity increased with the mosquitoes’ age. Neither infection nor food availability affected juvenile survival. Thus, as V. culicis reduced the longevity of A. gambiae (s.s.), yet affected mortality and fecundity of the young mosquitoes only slightly, the microsporidian is a promising alternative to insecticides for effective malaria control that will impose little evolutionary pressure for resistance.

The role of tryptophan and its derivatives for development of malaria parasite in vector mosquito

Xanthurenic acid (XA), a lateral reaction product of tryptophan metabolism in the omochrome pathway of eye pigment synthesis in insects, induces gametogenesis of malaria parasites. We have succeeded in measuring XA contents in the mosquito tissues using a high performance liquid chromatography with electrochemical detection system. XA content is not enough for activating gametocytes in the midgut where blood meal is taken. We have found that the salivary gland of mosquito contains a sufficient amount of XA for activating gametocytes and mosquito ingests saliva into the midgut during blood feeding. Taken together, it is likely that XA is discharged from salivary gland during blood feeding and is swallowed to the midgut where it affects malaria gametocytes. In the present study, we compared young mosquitoes (2–3 day-old after emergence) with old mosquitoes (12–14 day-old after emergence) in terms of transmission efficacy. XA contents in whole body and the salivary gland were larger in the young group. Numbers of oocyst developed on the midgut after taking blood from the same mouse with malaria were also higher in the young group. When both groups fed a blood meal with cultured ookinetes of malaria parasites, the numbers of oocyst were similar in both groups, suggesting that conditions for development from ookinetes to oocysts were similar in young and old mosquitoes. Taking these results together, we conclude that transmission efficacy is controlled by the amount of XA in the salivary gland.

MOSQUITOES DO SENESCE: DEPARTURE FROM THE PARADIGM OF CONSTANT MORTALITY

Although variation in mortality is considered by virtually all vector-borne disease specialists to be one of the most important determinants of an arthropod's capacity to transmit pathogens, the operational assumption often is that insect vector mortality is independent of age. Acceptance of the non-senescence assumption leads to the erroneous conclusion that mosquito age is unimportant, results in misleading predictions regarding disease reductions after vector control, and represses study of other aspects of mosquito biology that change with age. We brought large-scale laboratory life table techniques (N > 100,000) to bear on the question of age-dependent mortality in the mosquito vector of dengue virus, Aedes aegypti. Mortality was highly age dependent in both sexes. Mortality was low at young ages (< 10 days old), steadily increased at middle ages, and decelerated at older ages. A newly derived age-dependent model of pathogen transmission shows the importance of young mosquitoes and population age structure to transmission dynamics. Departure from the age-independent mortality paradigm encourages research on overlooked complexities in mosquito biology, the need for innovative methods to study mosquito population dynamics, and the need to study age-dependent changes for an accurate understanding of mosquito biology and pathogen transmission.

Paridade de Anopheles cruzii em Floresta Ombrófila Densa no Sul do Brasil

To determine the parity and ovarian development of Anopheles cruzii species during the seasons. Collections were carried out fortnightly in the morning in the Palmito State Park in the municipality of Paranaguá, Southern Brazil, between April 2004 and April 2005. Adult mosquitoes were captured using human landing rate. Dissections were performed using Detinova's and Polovodova's methods and follicular development was assessed following Christophers and Mer's criteria. A total of 208 specimens of Anopheles cruzii were dissected. Most females dissected were nulliparous in the seasons; 14.4% of them were found to be nulliparous above Christophers and Mer's stage II, which shows previous blood meal prior to the first oviposition. It was observed that Anopheles cruzii populations comprised young mosquitoes, probably due to high mortality among parous females. The likely gonotrophic discordance is epidemiologically relevant because female mosquitoes can search for more than one host to complete the maturation of their eggs.

Factors influencing the seasonal life history of the pitcher‐plant mosquito, Wyeomyia smithii

Abstract. 1. The effects of resource levels, thermal microclimate, and seasonal oviposition patterns on fecundity and survivorship in the pitcher‐plant mosquito, Wyeomyia smithii (Coq.), were examined at a northern Wisconsin bog over the course of 2 years. Wyeomyia smithii are bivoltine at this locality, thereby enabling the study of summer and overwintering generations separately.2. Nutrient resources of W. smithii were not limiting and there was no indication of density‐dependent survivorship or fecundity.3. Oviposition rates were highest in young, large pitchers and individual mosquitoes appeared to allocate only a few eggs to any one leaf.4. Winter was the harsh season, and the principal manifestation of seasonal harshness was reduced survivorship.5. Overwintering W. smithii that had been oviposited later in the summer had a higher odds of survival than those oviposited earlier in the summer.6. It was concluded that dispersal of eggs among many pitchers serves to spread the risk of encountering lethal winter temperatures among spatially unpredictable patches.

Nectar feeding by the early-spring mosquito Aedes provocans.

Nectar feeding by males and females of the mosquito Aedes provocans was studied at a site near Belleville, Ontario, Canada. Canada plum, Prunus nigra, and especially pin cherry, P. pensylvanica, bloomed contemporaneously with the emergence of Ae. provocans and were important nectar sources for adult mosquitoes during their first week of life. Blossoms of P. pensylvanica shielded for 24 h from foragers produced an average of 0.14 mg of sugar (approximately 2.3J). This nectar was avidly sought by both sexes of Ae. provocans; > 97% of the blossoms were visited by mosquitoes in the first few days of blooming. Young adult mosquitoes were found on blossoms at all hours of the day and night; feeding on P. nigra was strongly eocrepuscular, whereas on P. pensylvanica feeding was much less strongly periodic. Adults foraged for nectar in an energy-conserving, pedestrian strategy, devoting 56% (females) and 68% (males) of their time on blossoms to nectar feeding during foraging bouts that lasted a median of 5.3 min. Both sexes sought nectar soon after emergence--males before they had completed hypopygial rotation or swarmed, and females before mating or host seeking. Female Ae. provocans sought nectar in all stages of oogenesis, but primarily at the initiation of a gonotrophic cycle. Energy stores in the crop averaged 18J per female, with a distribution that depended on gonotrophic age and parity.