Mosquito Fecundity Research Articles

Anopheline Orthologs of the Human Erythroid Heme Exporter, FLVCR, Export Heme: Potential Targets to Inhibit Plasmodium Transmission

AbstractAbstract 2Heme, a complex of iron and protoporphyrin IX, is ubiquitous in aerobic cells, serving as the prosthetic group for essential hemoproteins. However, an excess of intracellular “free” heme is toxic to cells, promoting lipid peroxidation, membrane injury, reactive oxygen species (ROS) production, and ultimately apoptosis, necessitating tight regulation. FLVCR is a human erythroid progenitor cell membrane transporter that exports heme from the cytosol, thereby protecting cells from heme toxicity (Quigley et al. Cell, 2004). It is also highly expressed at sites of heme trafficking including the liver, gut, kidney and erythrophagocytic macrophages. In accordance with its function and expression pattern, our knockout mouse model demonstrates that FLVCR is important both for erythropoiesis and for systemic iron homeostasis (Keel et al. Science 2008). Female mosquitoes ingest ∼10 times their weight in blood in a single meal, thus large quantities of heme are released into the midgut lumen, a source of toxic ROS. Notably, hematophagy also represents a major bottleneck in the Plasmodium lifecycle. Gametes egressing from disintegrating RBCs are fertilized within the midgut lumen, forming small numbers of ookinetes that are susceptible to ROS as they traverse the mosquito midgut epithelial cells (to develop into oocysts). Indeed, numerous studies demonstrate that mosquitoes with increased midgut oxidative stress are resistant to Plasmodium transmission. We hypothesize that dysregulation of anopheline FLVCR–mediated heme export by the mosquito midgut epithelium will increase epithelial cell oxidative stress and impact Plasmodium transmission at its weakest point.Using genomic approaches, we isolated anopheline orthologs of FLVCR from the prevalent malaria transmission vectors, Anopheles gambiae and A. stephensi. The AgFLVCR cDNA predicts a 51kDa protein of 474 aa; the sequence of AsFLVCR (474 aa) is 97% identical. Like FLVCR, both genes are predicted to encode Major Facilitator Superfamily transporter proteins containing 12 TM domains, with the N– and C–termini in the cytosol. Overexpression of AgFLVCR cDNA in (rat) NRK cells results in an increase in export of ZnMP (a fluorescent heme analog) comparable to that observed with NRK cells overexpressing human FLVCR—a rate significantly greater (∼2–fold) than that of control NRK cells, as measured by quantitative microscopy (n=4, p<0.001). Similar increases in heme export relative to controls are observed when (insect) Sf9 cells are transduced with Asflvcr or Agflvcr and ZnMP export analyzed using flow cytometry. The increase is blocked by specific siRNA against Asflvcr or Agflvcr. As expected, incubation with exogenous heme (20 μ M) reduces viability of NRK cells. However, overexpression of AsFLVCR in NRK cells, by reducing intracellular ROS levels by ∼ 40%, improves their viability 3–fold (n=3, p<0.001). In studies of A. stephensi mosquitoes, we demonstrate robust upregulation of AsFLVCR mRNA (Fig. A, left) and protein (right) at 24 h after hematophagy, while confocal fluorescence immunolocalization studies with an antibody (Ab) generated against an intracellular epitope of AsFLVCR show cell membrane targeting in midgut epithelial cells following a blood meal (Fig. B; blue, DAPI; green, AsFLVCR). Importantly, dsRNA-mediated knockdown of AsFLVCR in mosquitoes decreases midgut Asflvcr mRNA by 85%, resulting in a 30% reduction in protein levels post-hematophagy. A polyclonal Ab (α-AsFLVCR) was also generated against an extracellular epitope. Preliminary studies indicate it impairs heme export from Sf9 cells overexpressing AsFLVCR. At present we are evaluating the effects of α-AsFLVCR– or dsRNA–mediated blockade of AsFLVCR heme export function on Plasmodium oocyst survival, salivary gland sporozoite development, mosquito midgut ROS production and mosquito fecundity. If these results validate our hypothesis, modulation of anopheline FLVCR–like proteins may serve as a means of controlling malaria. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Influence of Multiple Blood Meals on Gonotrophic Dissociation and Fecundity in Aedes albopictus

Gonotrophic dissociation and fecundity in adult female Aedes albopictus affect the transmission of arbovirus and mosquito population dynamics. Female Ae. albopictus bloodfed on guinea pig and human hosts produced significantly (P < 0.05) higher number of eggs (80 and 82/female, respectively) than females fed on chicken (67 eggs/female). Fecundity in mosquitoes that took a double blood meal (chicken and guinea pig), a triple blood meal (3 separate guinea pigs), or mixed blood meals (chicken, guinea pig, and human) was significantly (P < 0.001) higher than in females fed on a single chicken or on 2 separate chickens (refeeding). Gonotrophic dissociation in laboratory colony of Ae. albopictus was first observed and its frequency decreased with multiple blood meals with triple feeding or mixed feeding (3 meals on 3 host types). Blood meal source did not significantly influence gonotrophic dissociation in Ae. albopictus.

Age modifies the effect of body size on fecundity in Culex quinquefasciatus Say (Diptera: Culicidae)

Fecundity of mosquitoes can vary with many factors and can have a strong effect on population growth. This study reports the effects of body size, blood meal size, and age on the reproductive output of nulliparous Culex quinquefasciatus, a vector of arboviruses and other pathogens. Mated adult female mosquitoes from a colony were reared under standard conditions and fed on chickens at different ages post-eclosion. Blood meal size and wing length were recorded, as well as the number of eggs in the first-cycle egg raft. Each of these factors had a significant influence on fecundity considered in a simple regression context. Multiple regression analysis revealed a significant interaction effect between age and body size on fecundity. Up to 13 days of age, fecundity was positively correlated with body size, but in mosquitoes older than 13 days, this relationship was not significantly different from zero. These results are discussed in terms of the known physiology of this and other species.

Toxicity of bloodmeals from ivermectin-treated cattle toAnopheles gambiaes.l.

Two anthelmintic drugs used as cattle dewormers, ivermectin and moxidectin, were tested for their lethal and sublethal effects on the malarial vectors Anopheles gambiae s.s. and An. arabiensis. In the laboratory, direct addition of ivermectin to bovine blood reduced the survivorship and fecundity of mosquitoes fed on the blood. The median lethal concentration (LC(50)) of ivermectin in the bloodmeal, for the laboratory populations of An. gambiae s.l., was 19.8 ppb. In the field, commercially available formulations containing ivermectin or moxidectin were injected into cattle at three times the recommended dose. Most (90%) of the An. gambiae s.s. that fed on the ivermectin-treated cattle within 2 weeks of treatment failed to survive more than 10 days post-bloodmeal. No eggs were deposited by An. gambiae s.s. that fed on ivermectin-treated cattle within 10 days of treatment. In contrast, the survivorship and egg production of the mosquitoes that fed on the moxidectin-treated cattle were no different from those feeding on untreated cattle. These results indicate that treatment of cattle with ivermectin could be used, as part of an integrated control programme, to reduce the zoophilic vector populations that contribute to the transmission of the parasites responsible for human malaria.

Effect of CI‐976 on ferritin secretion and viability in Aedes aegypti

In mammals, iron taken into somatic cells is stored in ferritin or incorporated into iron containing proteins. Very little ferritin is found circulating in mammalian blood; most is retained in the cytoplasm. Ferritin is a multimer of 24 subunits of heavy and light chains. Female mosquitoes, such as Aedes aegypti (yellow fever mosquito), require a blood meal for oogenesis. Mosquitoes receive a potentially toxic level of iron in the blood meal which must be processed and stored to prevent oxidative damage. We are studying how mosquitoes and mosquito cells deal with this iron load. Iron treatment of A. aegypti larval CCL‐125 cells induces ferritin co‐localization with the Golgi apparatus and discrete vesicles within the cytoplasm. When these cells are exposed to high levels of iron, iron accumulates in the membranes. In contrast to mammalian cells, mosquito cells secrete ferritin into the culture medium in response to iron treatment. In addition, a 59Fe pulse‐chase experiment showed that both membrane and secreted ferritin were loaded with iron. To evaluate the effects of preventing ferritin secretion in the presence of iron load, we tested several known secretory inhibitors. Treatment of CCL‐125 cells with CI‐976 and iron disrupts ferritin secretion and decreases cell viability. Studies are underway to determine the effects of CI‐976 and RNAi on mosquito viability and fecundity following the iron load of a blood meal. This work was supported by funds from the National Institutes of Health (GM056812), the Agricultural Experiment Station, the College of Agriculture and Life Sciences and the BIO5 Institute for Collaborative Bioresearch at The University of Arizona.

West Nile Virus Infection Decreases Fecundity ofCulex tarsalisFemales

West Nile virus (family Flaviviridae, genus Flavivirus, WNV) persistently infects many mosquito tissues, and it has been associated with cytopathological changes in midgut muscles and salivary glands. However, the effects of WNV infection on mosquito fitness (survival and reproduction) are not known. We conducted a life table study of individually housed female Culex tarsalis Coquillett. After an initial bloodmeal from a WNV-infected or uninfected chicken, mosquitoes were provided sucrose and offered weekly opportunities to feed on a hanging blood drop. WNV transmission status was determined by testing the remaining blood drop for virus after mosquito feeding. Dead mosquitoes and eggs were collected daily. Mosquito legs and bodies were tested for WNV, and eggs were counted and allowed to hatch. Two replicates of this experiment were performed, with a total of 62 mosquitoes that fed on a WNV-infected chicken (of which 21 became infected) and 43 mosquitoes that fed on an uninfected chicken. Fecundity of WNV-infected mosquitoes was significantly lower than that of uninfected mosquitoes, especially during the first oviposition. WNV infection was associated with smaller egg rafts, whereas increasing wing length and WNV titer in the legs had a positive effect on egg raft size. Additionally, infected mosquitoes had lower egg hatch rates than did uninfected mosquitoes. There were no significant differences in survival between infected and uninfected mosquitoes. Blood feeding rates were higher in infected mosquitoes than in uninfected mosquitoes. A small amount of virus (average, 378; range, 5–5,000 plaque-forming units) was transmitted to the blood drops fed upon by infected mosquitoes. Although WNV infection negatively impacts mosquito reproduction, facets of mosquito biology that are critical to virus transmission success were either not affected (survival) or changed in such a way as to result in enhanced vectorial capacity (blood feeding).

West Nile Virus Infection Decreases Fecundity of &lt;I&gt;Culex tarsalis&lt;/I&gt; Females

West Nile virus (family Flaviviridae, genus Flavivirus, WNV) persistently infects many mosquito tissues, and it has been associated with cytopathological changes in midgut muscles and salivary glands. However, the effects of WNV infection on mosquito fitness (survival and reproduction) are not known. We conducted a life table study of individually housed female Culex tarsalis Coquillett. After an initial bloodmeal from a WNV-infected or uninfected chicken, mosquitoes were provided sucrose and offered weekly opportunities to feed on a hanging blood drop. WNV transmission status was determined by testing the remaining blood drop for virus after mosquito feeding. Dead mosquitoes and eggs were collected daily. Mosquito legs and bodies were tested for WNV, and eggs were counted and allowed to hatch. Two replicates of this experiment were performed, with a total of 62 mosquitoes that fed on a WNV-infected chicken (of which 21 became infected) and 43 mosquitoes that fed on an uninfected chicken. Fecundity of WNV-infected mosquitoes was significantly lower than that of uninfected mosquitoes, especially during the first oviposition. WNV infection was associated with smaller egg rafts, whereas increasing wing length and WNV titer in the legs had a positive effect on egg raft size. Additionally, infected mosquitoes had lower egg hatch rates than did uninfected mosquitoes. There were no significant differences in survival between infected and uninfected mosquitoes. Blood feeding rates were higher in infected mosquitoes than in uninfected mosquitoes. A small amount of virus (average, 378; range, 5-5000 plaque-forming units) was transmitted to the blood drops fed upon by infected mosquitoes. Although WNV infection negatively impacts mosquito reproduction, facets of mosquito biology that are critical to virus transmission success were either not affected (survival) or changed in such a way as to result in enhanced vectorial capacity (blood feeding).

Effect of discriminative plant-sugar feeding on the survival and fecundity of Anopheles gambiae.

BackgroundA previous study showed for Anopheles gambiae s.s. a gradation of feeding preference on common plant species growing in a malaria holoendemic area in western Kenya. The present follow-up study determines whether there is a relationship between the mosquito's preferences and its survival and fecundity.MethodsGroups of mosquitoes were separately given ad libitum opportunity to feed on five of the more preferred plant species (Hamelia patens, Parthenium hysterophorus, Ricinus communis, Senna didymobotrya, and Tecoma stans) and one of the less preferred species (Lantana camara). The mosquitoes were monitored daily for survival. Sugar solution (glucose 6%) and water were used as controls. In addition, the fecundity of mosquitoes on each plant after (i) only one blood meal (number of eggs oviposited), and (ii) after three consecutive blood meals (proportion of females ovipositing, number of eggs oviposited and hatchability of eggs), was determined. The composition and concentration of sugar in the fed-on parts of each plant species were determined using gas chromatography. Using SAS statistical package, tests for significant difference of the fitness values between mosquitoes exposed to different plant species were conducted.Results and ConclusionAnopheles gambiae that had fed on four of the five more preferred plant species (T. stans, S. didymobotrya, R. communis and H. patens, but not P. hysterophorus) lived longer and laid more eggs after one blood meal, when compared with An. gambiae that had fed on the least preferred plant species L. camara. When given three consecutive blood-meals, the percentage of females that oviposited, but not the number of eggs laid, was significantly higher for mosquitoes that had previously fed on the four more preferred plant species. Total sugar concentration in the preferred plant parts was significantly correlated with survival and with the proportion of females that laid eggs. This effect was associated mainly with three sugar types, namely glucose, fructose, and gulose. Except for P. hysterophorus, the results suggest that feeding by mosquitoes on preferred plant species under natural conditions results in higher fitness-related benefits, and that the sugar content in preferred plant parts is largely responsible for these effects.

Laboratory evaluation of pyriproxifen treated bednets on mosquito fertility and fecundity. A preminary study

The study evaluated the effect of pyriproxifen treated bednets on mosquito fertility and fecundity in the laboratory. Pyriproxyfen (insect growth regulator) has been considered as a possible tool for management of pyrethroid resistance in mosquitoes. There are documentations of the effectiveness of pyriproxifen in controlling larval development when applied directly to breeding site. Considerations have been given to the use of pyriproxyfen on bed nets for sterilizing effect on mosquitoes resistant to pyrethroids. Groups of mosquitoes (Anopheles stephensi Beech) were exposed to bednet treated with 2% Pyriproxyfen and untreated netting 24 hrs after blood feeding. After oviposition, egg counts were done for each mosquito in the two groups. Larvae emerging from the laid eggs by each mosquito were counted. Three sets of experiments were successful. There was no significant difference in number of eggs laid between the two treatment groups (p=0.177). There was statistically significant difference in the number of laid eggs that hatched between the treatment types (p=0.0061). There was also statistically significant difference in the mean number of eggs that hatched between the experiments (p=0.0013). The mean number of eggs retained in the pyriproxyfen group was higher (70.3) than in the control group (41.6). This difference was not statistically significant with the small sample tested (p=0.08). The results suggest that 2% pyriproxyfen on bed nets has no effect on An. stephensi fecundity. Reduced fertility of eggs laid by mosquitoes exposed to pyriproxyfen treated bed nets was observed.

Sugar digestion in mosquitoes: Identification and characterization of three midgut α-glucosidases of the neo-tropical malaria vector Anopheles aquasalis (Diptera: Culicidae)

Dietary carbohydrates provide an important source of energy for flight, and contribute to longevity and fecundity of mosquitoes. The most common sugar mosquitoes ingest is sucrose, and digestion of this substance is carried out mainly by alpha-glucosidases. In the current work, we tested the efficiency of sucrose on Anopheles aquasalis female diet. The best longevity (days) was reached when sugar was available in the diet, whereas most only blood fed females were dead 6 days after emergence. Three alpha-glucosidase isoforms were detected in the adult female midgut, named alphaGlu1, alphaGlu2 and alphaGlu3. These are acidic alpha-glucosidases with optima pH around pH 5.5. alphaGlu1 and alphaGlu2 are present in both secreted and membrane-bound forms, whereas alpha-Glu3 only in anchored to membranes. The alpha-glucosidase activity is concentrated mainly in the posterior midgut (70%), both in non-fed or 10% sucrose fed females. The single form of these alpha-glucosidases seemed to be approximately 70 kDa polypeptides, although alphaGlu2 is presented in >or=600 kDa self-aggregates. Km values of alphaGlu1, alphaGlu2 and alphaGlu3 differed significantly from each other, supporting the statement that three alpha-glucosidases are produced in the female midgut. Together, all data suggest that sugar is an essential component of A. aquasalis female diet. In addition, alpha-glucosidases are synthesized in the same place where sucrose is digested and absorbed, the midgut.

Effects of in vivo exposure to DEET on blood feeding behavior and fecundity in Anopheles quadrimaculatus (Diptera: Culicidae)

This study determined the effects of contact with DEET on guinea pig skin on mortality, probing time, blood feeding rate, engorgement time, and fecundity responses in female Anopheles quadrimaculatus Say. Exposure, in this manner, to 10% DEET (in ethanol) for 5 min, resulted in 98% mortality in mosquitoes after 24 h. The median probing time (PT 50) required by females, when exposed to 0.1%, 1.0%, and 10% DEET, was significantly ( P < 0.0001) longer (12.5, 12.1, and 19.1 s, respectively) than the 6.8 s required by females to probe ethanol-treated skin (control). Similarly, mean blood feeding rates in populations of females exposed to 1.0% DEET for ⩽5 min (14.4%) was 6× lower ( P < 0.001) (85.5%) than in females exposed to ethanol-treated skin, whereas the mean engorgement time on skin treated with 1.0% DEET (66.3 s) was significantly shorter ( P < 0.0001) than for females feeding on the control guinea pigs (105.9 s). The mean number of mature oöcytes per female (fecundity) in treatment (1.0% DEET) and control mosquitoes was not significantly different. The responses to DEET observed in this study suggest that repeated exposure of female A. quadrimaculatus populations to this repellent, in laboratory bioassays, could result in confounding of toxicant and repellent effects and inaccurate estimates of DEET repellency.

EVALUATING THE COSTS OF MOSQUITO RESISTANCE TO MALARIA PARASITES

Abstract Costly resistance mechanisms have been cited as an explanation for the widespread occurrence of parasitic infections, yet few studies have examined these costs in detail. A malaria-mosquito model has been used to test this concept by making a comparison of the fitness of highly susceptible lines of mosquitoes with lines that are resistant to infection. Malaria infection is known to cause a decrease in fecundity and fertility of mosquitoes; were thus predicted to be fitter than susceptible ones. >o?Anopheles gambiae were selected for refractoriness/resistance or for increased susceptibility to infection by Plasmodium yoelii nigeriensis. Additional lines that acted as controls for inbreeding depression were raised in parallel but not exposed to selection pressure. Selections were made in triplicate so that founder effects could be detected. Resistance mechanisms that were selected included melanotic encapsulation of parasites within 24 h postinfection and the complete disappearance of parasites from the gut. Costs of immune surveillance were assessed after an uninfected feed, and costs of immune deployment were assessed after exposure to infection and to infection and additional stresses. Mosquito survivorship was unaffected by either resistance to infection or by an increased burden of infection when compared with low levels of infection. In most cases reproductive fitness was equally affected by refractoriness or by infection. Resistant mosquitoes did not gain a fitness advantage by eliminating the parasites. Costs were consistently associated with larval production and egg hatch rate but rarely attributed to changes in blood feeding and never to changes in mosquito size. No advantages appeared to be gained by the offspring of resistant mosquitoes. Furthermore, we were unable to select for refractoriness in groups of mosquitoes in which 100% or 50% of the population were exposed to infection every generation for 22 generations. Under these selection pressures, no population had become completely refractory and only one became more resistant. Variations in fitness relative to control lines in different groups were attributed to founder effects. Our conclusion from these findings is that refractoriness to malaria is as costly as tolerance of infection.

EVALUATING THE COSTS OF MOSQUITO RESISTANCE TO MALARIA PARASITES

Costly resistance mechanisms have been cited as an explanation for the widespread occurrence of parasitic infections, yet few studies have examined these costs in detail. A malaria-mosquito model has been used to test this concept by making a comparison of the fitness of highly susceptible lines of mosquitoes with lines that are resistant to infection. Malaria infection is known to cause a decrease in fecundity and fertility of mosquitoes; resistant mosquitoes were thus predicted to be fitter than susceptible ones. Anopheles gambiae were selected for refractoriness/resistance or for increased susceptibility to infection by Plasmodium yoelii nigeriensis. Additional lines that acted as controls for inbreeding depression were raised in parallel but not exposed to selection pressure. Selections were made in triplicate so that founder effects could be detected. Resistance mechanisms that were selected included melanotic encapsulation of parasites within 24 h postinfection and the complete disappearance of parasites from the gut. Costs of immune surveillance were assessed after an uninfected feed, and costs of immune deployment were assessed after exposure to infection and to infection and additional stresses. Mosquito survivorship was unaffected by either resistance to infection or by an increased burden of infection when compared with low levels of infection. In most cases reproductive fitness was equally affected by refractoriness or by infection. Resistant mosquitoes did not gain a fitness advantage by eliminating the parasites. Costs were consistently associated with larval production and egg hatch rate but rarely attributed to changes in blood feeding and never to changes in mosquito size. No advantages appeared to be gained by the offspring of resistant mosquitoes. Furthermore, we were unable to select for refractoriness in groups of mosquitoes in which 100% or 50% of the population were exposed to infection every generation for 22 generations. Under these selection pressures, no population had become completely refractory and only one became more resistant. Variations in fitness relative to control lines in different groups were attributed to founder effects. Our conclusion from these findings is that refractoriness to malaria is as costly as tolerance of infection.

The influence of malaria parasite genetic diversity and anaemia on mosquito feeding and fecundity.

Studies of invertebrate-parasite interactions frequently report that infection reduces host fecundity. The extent of the reduction is likely to be determined by a wide range of host and parasite factors. We conducted a laboratory experiment to evaluate the role of parasite genetics and infection genetic diversity on the fecundity of mosquitoes carrying malaria parasites. The malaria vector Anopheles stephensi was infected with either of 2 different genotypes of the rodent malaria parasite Plasmodium chabaudi, or by a mixture of both. Mixed genotype infections reduced mosquito fecundity by 20%, significantly more than either of the 2 single genotype infections. Mixed genotype infections were associated with high gametocyte densities and anaemia in mice, both of which were correlated with reduced bloodmeal size in mosquitoes. Bloodmeal size was the most important predictor of mosquito fecundity; the presence and number of parasites had no direct effect. Parasite density influenced the propensity of mosquitoes to feed on infected mice, with a higher percentage of mosquitoes taking a meal as asexual parasite and gametocyte density increased. Thus mosquitoes may preferentially feed on hosts who will most impair their fecundity.

Blocking of malaria parasite development in mosquito and fecundity reduction by midgut antibodies in Anopheles stephensi (Diptera: Culicidae).

Rabbits were immunized three times with extracts of Anopheles stephensi midgut. Immunized rabbits showed a high titer of antibodies when characterized by ELISA. We investigated the effect of anti-mosquito midgut antibodies on mosquito fecundity, longevity, mortality, engorgement, and the development of the malaria parasite in mosquitoes. Fecundity was reduced significantly (38%) and similarly hatchability by about 43.5%. There was no statistically significant effect on mortality, longevity, and engorgement. When the mosquito blood meal contained anti-midgut antibodies, fewer oocysts of Plasmodium vivax developed in the mosquito midgut and the proportion of mosquitoes becoming infected was significantly reduced. We also found that the midgut antibodies inhibit the development and/or translocation of the sporozoites. Antisera raised against midgut of A. stephensi recognized eight polypeptides (110, 92, 70, 45, 38, 29, 15, 13 kDa) by Western blotting. Cross-reactive antigens/epitopes present in other tissues of A. stephensi were also examined both by Western blotting and in vivo ELISA. Together, these observations open an avenue for research toward the development of a vector-based malaria parasite transmission blocking vaccine and/or anti-mosquito vaccine.

Induced immunity against the mosquito Anopheles stephensi (Diptera: Culicidae): effects of cell fraction antigens on survival, fecundity, and plasmodium berghei (Eucoccidiida: Plasmodiidae) transmission.

Two subeellular fractions from the midgut of the malaria mosquito Anopheles stephensi (Liston) were used to immunize BALB/c mice. Mice were subsequently infected with the rodent malaria parasite Plasmodium berghei (Vineke & Lips), and the effects of anti-mosquito immunity on mosquito survival and fecundity and on parasite transmission were investigated. Mosquitoes were infected directly from mice (in vivo) or by feeding cultured ookinetes through a membrane (in vitro). Infections were monitored by counting oocysts on the midgut wall. Microvilli extracts induced a strong and partially specific antibody reaction against the midgut, which was manifest as decreased survival in in vivo fed mosquitoes and reduced fecundity in both kinds of feeding. Antisera against microvilli reduced the mean intensity of P. berghei oocysts when fed in vitro, while mosquitoes fed antiserum against basolateral plasma membranes in vivo, showed higher oocyst burdens.

A kick in the guts for malaria.

Mosquito midgut-based antibodies have recently been recognized as a new means by which the transmission of malaria might be interrupted. Altaf A. Lal et al. (2001) (Proc. Natl. Acad. Sci. U. S. A. 98, 5228–5233) found that polyclonal sera raised against mosquito midgets blocked the passage of Plasmodium falciparum ookinetes across the midgut, leading to a significant reduction of infections in mosquitoes. The antibodies displayed broad-spectrum activity, blocking parasite development of both P. falciparum and P. vivax in five different mosquito species. In addition to their antiparasitic effects, the antibodies also reduced mosquito survivorship and fecundity. If applied in the field, such antibodies could restrict malaria transmission by reducing mosquito viability and reproduction, and by preventing their infection by Plasmodium spp. parasites. SHK

Anti-mosquito midgut antibodies block development of Plasmodium falciparum and Plasmodium vivax in multiple species of Anopheles mosquitoes and reduce vector fecundity and survivorship.

The mosquito midgut plays a central role in the sporogonic development of malaria parasites. We have found that polyclonal sera, produced against mosquito midguts, blocked the passage of Plasmodium falciparum ookinetes across the midgut, leading to a significant reduction of infections in mosquitoes. Anti-midgut mAbs were produced that display broad-spectrum activity, blocking parasite development of both P. falciparum and Plasmodium vivax parasites in five different species of mosquitoes. In addition to their parasite transmission-blocking activity, these mAbs also reduced mosquito survivorship and fecundity. These results reveal that mosquito midgut-based antibodies have the potential to reduce malaria transmission in a synergistic manner by lowering both vector competence, through transmission-blocking effects on parasite development, and vector abundance, by decreasing mosquito survivorship and egg laying capacity. Because the intervention can block transmission of different malaria parasite species in various species of mosquitoes, vaccines against such midgut receptors may block malaria transmission worldwide.

Effects of plant extracts on fecundity and fertility of mosquitoes

Rearing of Culex quinquefasciatus, Anopheles stephensi and Aedes aegypti larvae in water at concentrations less than the critical concentration for inhibition of adult emergence in 50% of treated larvae (EC50) of the ethyl acetate fractions of Calophyllum inophyllum seed and leaf, Solanum suratense and Samadera indica leaf extracts and the petrol ether fraction of Rhinocanthus nasutus leaf extract, from hatching to emergence significantly decreased the fecundity of the mosquitoes and the hatchability of their eggs. At the highest concentration of 50% EC50 of the extracts, the decrease in the fecundity over the control ranged between 62.4 and 87.4%. Sterility index of the mosquitoes reared in the media with the different extracts at this concentration ranged between 82.8 and 93.3%.

Effects of plant extracts on fecundity and fertility of mosquitoes

Effects of plant extracts on fecundity and fertility of mosquitoes