Fate of blood meal iron in mosquitoes

Identification of nectar sources foraged by female mosquitoes in Canada

For many mosquito species, the females must obtain vertebrate blood to complete a gonotrophic cycle. These blood meals are frequently supplemented by feeding on sugary plant nectar, which sustains energy reserves needed for flight, mating, and overall fitness. Our understanding of mosquito nectar foraging behaviors is mostly limited to laboratory experiments and direct field observations, with little research into natural mosquito-host plant relationships done in North America. In this study, we collected nectar-fed female mosquitoes over a 2-year period in Manitoba, Canada, and amplified a fragment of the chloroplast rbcL gene to identify the plant species fed upon. We found that mosquitoes foraged from diverse plant families (e.g., grasses, trees, ornamentals, and legumes), but preferred certain species, most notably soybean and Kentucky blue grass. Moreover, there appeared to be some associations between plant feeding preferences and mosquito species, date of collection, landscape, and geographical region. Overall, this study implemented DNA barcoding to identify nectar sources forage by mosquitoes in the Canadian Prairies.

Dietary calcium (Ca2+) impacts Ca2+ content and molecular expression of Ca2+-transporters in Malpighian tubules of the yellow fever mosquito, Aedes aegypti

The renal (Malpighian) tubules of insects play important roles in hemolymph Ca2+ regulation. Here we investigated how dietary Ca2+ loads from sucrose or blood meals affect the Ca2+ content and mRNA expression of Ca2+ transporters in Malpighian tubules of adult female mosquitoes. Using the yellow fever mosquito Aedes aegypti we found that feeding females 10% sucrose with elevated Ca2+ concentration ad libitum for 6 days led to increased Ca2+ content in Malpighian tubules. The increases of Ca2+ content correlated with up-regulations of mRNAs encoding intracellular Ca2+-ATPases (SERCA and SPCA), a plasma membrane Ca2+-ATPase (PMCA), and a K+-dependent Na+/Ca2+ exchanger (NCKX1). We also found that when adult females were fed blood, tubule Ca2+ content changed dynamically over the next 72 h in a manner consistent with redistribution of tubule Ca2+ stores to other tissues (e.g., ovaries). The changes in tubule Ca2+ were correlated with dynamic changes in mRNA abundances of SERCA, SPCA, PMCA, and NCKX1. Our results are the first to demonstrate that Malpighian tubules of adult female mosquitoes have a remarkable capacity to handle high dietary Ca2+ loads, most likely through the combination of storing excess Ca2+ within intracellular compartments and secreting it into the tubule lumen for excretion. Our results also suggest that the Malpighian tubules play key roles in supplying Ca2+ to other tissues during the processing of blood meals.

Effects of host blood on mosquito reproduction

Female mosquitoes require blood from their host for egg development. However, the relationship between the composition of host blood and mosquito reproduction, and whether and how this is linked to host selection, remain unclear. A better understanding of these issues is beneficial for mass-rearing of mosquitoes for vector control. This review provides an overview of the currently known effects of blood constituents on mosquito reproduction. Furthermore, it highlights knowledge gaps and proposes new avenues for investigation. We recommend that research efforts be focused on physiological differences between generalist and specialist mosquito species as models to investigate if and how host preference correlates with reproductive output.

Black queen cell virus detected in Canadian mosquitoes

Black queen cell virus (BQCV) is a ubiquitous honeybee virus and a significant pathogen to queen bee (Apis mellifera) larvae. However, many aspects of the virus remain poorly understood, including the transmission dynamics. In this study, we used next-generation sequencing to identify BQCV in Aedes vexans (n = 4,000) collected in 2019 and 2020 from Manitoba, Canada. We assembled de novo the nearly complete (>96%) genome sequence of the virus, which is the first available from North America and the first report of BQCV being harbored by mosquitoes. Phylogenetic tree reconstructions indicated that the genome had 95.5% sequence similarity to a BQCV isolate from Sweden. Sequences of a potential vector (Varroa destructor) and a microsporidian associated with BQCV (Nosema apis) were not identified in the mosquito samples, however, we did detect sequences of plant origin. We, therefore, hypothesize that the virus was indirectly acquired by mosquitoes foraging at the same nectar sources as honeybees.

Iron Homeostasis in Insects

Iron is an essential micronutrient for all types of organisms; however, iron has chemical properties that can be harmful to cells. Because iron is both necessary and potentially damaging, insects have homeostatic processes that control the redox state, quantity, and location of iron in the body. These processes include uptake of iron from the diet, intracellular and extracellular iron transport, and iron storage. Early studies of iron-binding proteins in insects suggested that insects and mammals have surprisingly different mechanisms of iron homeostasis, including different primary mechanisms for exporting iron from cells and for transporting iron from one cell to another, and subsequent studies have continued to support this view. This review summarizes current knowledge about iron homeostasis in insects, compares insect and mammalian iron homeostasis mechanisms, and calls attention to key remaining knowledge gaps.

Metal ions in insect reproduction: a crosstalk between reproductive physiology and immunity

Most insects exhibit high reproductive capacity, which demands large amounts of energy, including macronutrients and micronutrients. Interestingly, many proteins involved in oogenesis depend on metals ions, in particular iron (Fe), zinc (Zn), and copper (Cu). Mechanisms by which metal ions influence reproduction have been described in Drosophila melanogaster, but remain poorly understood in hematophagous insects where blood meals include significant ingestion of metal ions. Moreover, there is evidence that some proteins involved in reproduction and immunity could have dual function in both processes. This review highlights the importance of metal ions in the reproduction of non-hematophagous and hematophagous insects. In addition, we discuss how insects optimize physiological processes using proteins involved in crosstalk between reproductive physiology and immunity, which is a double-edge sword in allocating their functions to protect the insect and ensure reproduction.

Phenotypic analyses, protein localization, and bacteriostatic activity of Drosophila melanogaster transferrin-1

Transferrin-1 (Tsf1) is an extracellular insect protein with a high affinity for iron. The functions of Tsf1 are still poorly understood; however, Drosophila melanogaster Tsf1 has been shown to influence iron distribution in the fly body and to protect flies against some infections. The goal of this study was to better understand the physiological functions of Tsf1 in D. melanogaster by 1) investigating Tsf1 null phenotypes, 2) determining tissue-specific localization of Tsf1, 3) measuring the concentration of Tsf1 in hemolymph, 4) testing Tsf1 for bacteriostatic activity, and 5) evaluating the effect of metal and paraquat treatments on Tsf1 abundance. Flies lacking Tsf1 had more iron than wild-type flies in specialized midgut cells that take up iron from the diet; however, the absence of Tsf1 had no effect on the iron content of whole midguts, fat body, hemolymph, or heads. Thus, as previous studies have suggested, Tsf1 appears to have a minor role in iron transport. Tsf1 was abundant in hemolymph from larvae (0.4 μM), pupae (1.4 μM), adult females (4.4 μM) and adult males (22 μM). Apo-Tsf1 at 1 μM had bacteriostatic activity whereas holo-Tsf1 did not, suggesting that Tsf1 can inhibit microbial growth by sequestering iron in hemolymph and other extracellular environments. This hypothesis was supported by detection of secreted Tsf1 in tracheae, testes and seminal vesicles. Colocalization of Tsf1 with an endosome marker in oocytes suggested that Tsf1 may provide iron to developing eggs; however, eggs from mothers lacking Tsf1 had the same amount of iron as control eggs, and they hatched at a wild-type rate. Thus, the primary function of Tsf1 uptake by oocytes may be to defend against infection rather than to provide eggs with iron. In beetles, Tsf1 plays a role in protection against oxidative stress. In contrast, we found that flies lacking Tsf1 had a typical life span and greater resistance to paraquat-induced oxidative stress. In addition, Tsf1 abundance remained unchanged in response to ingestion of iron, cadmium or paraquat or to injection of iron. These results suggest that Tsf1 has a limited role in protection against oxidative stress in D. melanogaster.

Disturbance gradient and mosquito diversity pattern in areas surrounding Chini Lake - the second largest freshwater lake in Peninsular Malaysia

Malaysia is a tropical country that has consistently been facing a prevalent threat of mosquito-borne diseases. Amongst the plethora of diseases, the most common mosquito-borne disease in the country is dengue fever, transmitted by Aedes spp. mosquitoes. This study aims to examine the effects of human activity associated with different land use on mosquito population composition and diversity. Our study site is Chini Lake, a naturally occurring lake and the second-largest freshwater body in Malaysia. The areas surrounding the Lake have been subjected to various human activities, such as economic development and conversion into rubber plantations, while some areas remain pristine, making Chini Lake an ideal location to examine the gradient of human disturbances on mosquito composition and diversity. We sampled adult mosquitoes and larvae across a range of sites with different levels of human disturbance. As expected, in areas with high disturbance scores, the species richness of adult and larval mosquitoes were reduced while the abundance was higher. The results also revealed minimal overlap between species captured for adult and larval samplings, suggesting that land-use changes affect both life stages differently. Different resource requirements of adult and larval mosquitoes likely led to the observed diversity pattern in this small survey. We suggest future work to look into how habitat heterogeneity affects both life stages and sexes of mosquito diversity patterns and distribution.

Antiviral RNAi Mechanisms to Arboviruses in Mosquitoes: microRNA Profile of Aedes aegypti and Culex quinquefasciatus from Grenada, West Indies

Mosquito-borne arboviruses, such as dengue virus, West Nile virus, Zika virus and yellow fever virus, impose a tremendous cost on the health of populations around the world. As a result, much effort has gone into the study of the impact of these viruses on human infections. Comparatively less effort, however, has been made to study the way these viruses interact with mosquitoes themselves. As ingested arboviruses infect their midgut and subsequently other tissue, the mosquito mounts a multifaceted innate immune response. RNA interference, the central intracellular antiviral defense mechanism in mosquitoes and other invertebrates can be induced and modulated through outside triggers (small RNAs) and treatments (transgenesis or viral-vector delivery). Accordingly, modulation of this facet of the mosquito’s immune system would thereby suggest a practical strategy for vector control. However, this requires a detailed understanding of mosquitoes’ endogenous small RNAs and their effects on the mosquito and viral proliferation. This paper provides an up-to-date overview of the mosquito’s immune system along with novel data describing miRNA profiles for Aedes aegypti and Culex quinquefasiatus in Grenada, West Indies.

nAnopheles blood meal sources and entomological indicators related to Plasmodium transmission in malaria endemic areas of Colombia

Malaria is an important public health problem, caused by Plasmodium parasites which are transmitted by female Anopheles mosquitoes that bite humans to obtain blood. The aim of this work was to identify the blood feeding sources of Anopheles female mosquitoes and calculate their entomological indices in relation to Plasmodium transmission. Mosquitoes were collected in malaria endemic localities of the Bajo Cauca and Pacific regions of Colombia using human landing catch and barrier screens, from 18:00 - 24:00 hr, in 2018-2021. Animal censuses within a radius of ∼250 meters were carried out at each sampling site. A total of 2,018 Anopheles specimens were collected and the most abundant species were Anopheles (Nys.) darlingi and Anopheles (Nys.) nuneztovari. The highest human biting rate was 77.5 bites per person per night (b/p/n) for An. nuneztovari in Córdoba-Pacific and 17.5 b/p/n for An. darlingi in Villa Grande-Bajo Cauca. Both species were active mainly in indoor unwalled rooms of the houses. Only An. nuneztovari from Córdoba-Pacific was infected with Plasmodium, with an entomological inoculation rate of 91.25 infective bites per year. Detection of blood feeding sources demonstrate that humans were the most common host, however, An. nuneztovari showed a preference for feeding on dogs and An. darlingi on pigs, dogs and Galliformes, rather than humans. These results contribute to entomological surveillance information and provide valuable data that can be used to tailor effective control interventions to minimize human-vector contact in these malaria endemic regions.

Carica papaya Leaf Juice for Dengue: A Scoping Review

The potential therapeutic effect of Carica papaya leaf juice has attracted wide interest from the public and scientists in relieving dengue related manifestations. Currently, there is a lack of evaluated evidence on its juice form. Therefore, this scoping review aims to critically appraise the available scientific evidence related to the efficacy of C. papaya leaf juice in dengue. A systematic search was performed using predetermined keywords on two electronic databases (PubMed and Google Scholar). Searched results were identified, screened and appraised to establish the association between C. papaya and alleviating dengue associated conditions. A total of 28 articles (ethnobotanical information: three, in vitro studies: three, ex vivo studies: one, in vivo study: 13, clinical studies: 10) were included for descriptive analysis, which covered study characteristics, juice preparation/formulations, study outcomes, and toxicity findings. Other than larvicidal activity, this review also reveals two medicinal potentials of C. papaya leaf juice on dengue infection, namely anti-thrombocytopenic and immunomodulatory effects. C. papaya leaf juice has the potential to be a new drug candidate against dengue disease safely and effectively.

Shotgun and TMT-Labeled Proteomic Analysis of the Ovarian Proteins of an Insect Vector, Aedes aegypti (Diptera: Culicidae)

Aedes aegypti [Linnaeus in Hasselquist; yellow fever mosquito] transmits several viruses that infect millions of people each year, including Zika, dengue, yellow fever, chikungunya, and West Nile. Pathogen transmission occurs during blood feeding. Only the females blood feed as they require a bloodmeal for oogenesis; in the bloodmeal, holo-transferrin and hemoglobin provide the females with a high iron load. We are interested in the effects of the bloodmeal on the expression of iron-associated proteins in oogenesis. Previous data showed that following digestion of a bloodmeal, ovarian iron concentrations doubles by 72 hr. We have used shotgun proteomics to identify proteins expressed in Ae. aegypti ovaries at two oogenesis developmental stages following blood feeding, and tandem mass tag-labeling proteomics to quantify proteins expressed at one stage following feeding of a controlled iron diet. Our findings provide the first report of mosquito ovarian protein expression in early and late oogenesis. We identify proteins differentially expressed in the two oogenesis development stages. We establish that metal-associated proteins play an important role in Ae. aegypti oogenesis and we identify new candidate proteins that might be involved in mosquito iron metabolism. Finally, this work identified a unique second ferritin light chain subunit, the first reported in any species. The shotgun proteomic data are available via ProteomeXchange with identifier PXD005893, while the tandem mass tag-labeled proteomic data are available with identifier PXD028242.

Two ferritins from Dermanyssus gallinae: characterization and in vivo assessment as protective antigens

BACKGROUND

The poultry red mite, Dermanyssus gallinae is recognized worldwide as the most important bloodsucking ectoparasite in layer and breeder flocks. In bloodsucking ectoparasites, ferritins (FERs), the iron-storage proteins, play a pivotal role in dealing with the challenge of large amounts of released iron during the digestion of blood meal. However, no information is available concerning FERs of D. gallinae. The aim of the present study was to investigate the characteristics, functions and the vaccine efficacy of FERs in D. gallinae.

RESULTS

Two heavy-chain FERs of D. gallinae were identified and characterized. Phylogenetic analysis indicated that Dg-FER1 may be a secretory FER and Dg-FER2 an intracellular one. RNAi results demonstrated that Dg-fers play key roles in mite survival, successful reproduction and blood digestion. Immunization with rDg-FER1 or rDg-FER2 successfully induced chickens to produce high levels of antigen-specific IgY, resulting in a significant increase in mite mortality (by 58.67% on Day 5) and decreases in oviposition (by 42.15%) and fecundity (by 68.97%) in the rDg-FER1 group, and a 13.73% increase in mite mortality and a 20.89% decrease in fecundity in the rDg-FER1 group. The overall immunization efficacy of rDg-FER1 was 93.51%.

CONCLUSION

Two Dg-FERs are crucial to the survival, reproduction and blood digestion of D. gallinae. This study has provided preliminary evidence demonstrating the potential of rDg-FER1 as a vaccine antigen for D. gallinae. © 2021 Society of Chemical Industry.

Mosquito metallomics reveal copper and iron as critical factors for Plasmodium infection

Iron and copper chelation restricts Plasmodium growth in vitro and in mammalian hosts. The parasite alters metal homeostasis in red blood cells to its favor, for example metabolizing hemoglobin to hemozoin. Metal interactions with the mosquito have not, however, been studied. Here, we describe the metallomes of Anopheles albimanus and Aedes aegypti throughout their life cycle and following a blood meal. Consistent with previous reports, we found evidence of maternal iron deposition in embryos of Ae. aegypti, but less so in An. albimanus. Sodium, potassium, iron, and copper are present at higher concentrations during larval developmental stages. Two An. albimanus phenotypes that differ in their susceptibility to Plasmodium berghei infection were studied. The susceptible white stripe (ws) phenotype was named after a dorsal white stripe apparent during larval stages 3, 4, and pupae. During larval stage 3, ws larvae accumulate more iron and copper than the resistant brown stripe (bs) phenotype counterparts. A similar increase in copper and iron accumulation was also observed in the susceptible ws, but not in the resistant bs phenotype following P. berghei infection. Feeding ws mosquitoes with extracellular iron and copper chelators before and after receiving Plasmodium-infected blood protected from infection and simultaneously affected follicular development in the case of iron chelation. Unexpectedly, the application of the iron chelator to the bs strain reverted resistance to infection. Besides a drop in iron, iron-chelated bs mosquitoes experienced a concomitant loss of copper. Thus, the effect of metal chelation on P. berghei infectivity was strain-specific.

To establish a life cycle between insect and mammalian hosts, the malaria parasite has evolved mechanisms to manage metal ions from the distinct microenvironments it encounters. Previous work has addressed how interference using metal chelation affects parasite development in human, primate, and rodent hosts. Similar studies in mosquito species that harbor Plasmodium have not been performed. Here, we address such micronutrient relationships in three steps. First, we characterized how the metallome fluctuates during development in two species of mosquito. Second, we asked whether susceptibility to Plasmodium infection correlated with a differential response in mosquito metal homeostasis. Third, we tested the effects of iron and copper chelation treatment of adult mosquitoes concerning propensity of infection and mosquito reproduction. Metal ions offer a promising target in the ongoing efforts to control the mosquito-borne disease.

Olfaction in Anopheles mosquitoes

As vectors of disease, mosquitoes are a global threat to human health. The Anopheles mosquito is the deadliest mosquito species as the insect vector of the malaria-causing parasite, which kills hundreds of thousands every year. These mosquitoes are reliant on their sense of smell (olfaction) to guide most of their behaviors, and a better understanding of Anopheles olfaction identifies opportunities for reducing the spread of malaria. This review takes a detailed look at Anopheles olfaction. We explore a range of topics from chemosensory receptors, olfactory neurons, and sensory appendages to behaviors guided by olfaction (including host-seeking, foraging, oviposition, and mating), to vector management strategies that target mosquito olfaction. We identify many research areas that remain to be addressed.

Aedes aegypti dyspepsia encodes a novel member of the SLC16 family of transporters and is critical for reproductive fitness

As a key vector for major arthropod-borne viruses (arboviruses) such as dengue, Zika and chikungunya, control of Aedes aegypti represents a major challenge in public health. Bloodmeal acquisition is necessary for the reproduction of vector mosquitoes and pathogen transmission. Blood contains potentially toxic amounts of iron while it provides nutrients for mosquito offspring; disruption of iron homeostasis in the mosquito may therefore lead to novel control strategies. We previously described a potential iron exporter in Ae. aegypti after a targeted functional screen of ZIP (zinc-regulated transporter/Iron-regulated transporter-like) and ZnT (zinc transporter) family genes. In this study, we performed an RNAseq-based screen in an Ae. aegypti cell line cultured under iron-deficient and iron-excess conditions. A subset of differentially expressed genes were analyzed via a cytosolic iron-sensitive dual-luciferase reporter assay with several gene candidates potentially involved in iron transport. In vivo gene silencing resulted in significant reduction of fecundity (egg number) and fertility (hatch rate) for one gene, termed dyspepsia. Silencing of dyspepsia reduced the induction of ferritin expression in the midgut and also resulted in delayed/impaired excretion and digestion. Further characterization of this gene, including a more direct confirmation of its substrate (iron or otherwise), could inform vector control strategies as well as to contribute to the field of metal biology.

The transmission-blocking effects of antimalarial drugs revisited: fitness costs and sporontocidal effects of artesunate and sulfadoxine-pyrimethamine

Assays used to evaluate the transmission-blocking activity of antimalarial drugs are largely focused on their potential to inhibit or reduce the infectivity of gametocytes, the blood stages of the parasite that are responsible for the onward transmission to the mosquito vector. For this purpose, the drug is administered concomitantly with gametocyte-infected blood, and the results are evaluated as the percentage of reduction in the number of oocysts in the mosquito midgut. We report the results of a series of experiments that explore the transmission-blocking potential of two key antimalarial drugs, artesunate and sulfadoxine-pyrimethamine, when administered to mosquitoes already infected from a previous blood meal. For this purpose, uninfected mosquitoes and mosquitoes carrying a 6 day old Plasmodium relictum infection (early oocyst stages) were allowed to feed either on a drug-treated or an untreated host in a fully factorial experiment. This protocol allowed us to bypass the gametocyte stages and establish whether the drugs have a sporontocidal effect, i.e. whether they are able to arrest the ongoing development of oocysts and sporozoites, as would be the case when a mosquito takes a post-infection treated blood meal. In a separate experiment, we also explored whether a drug-treated blood meal impacted key life history traits of the mosquito relevant for transmission, and if this depended on their infection status. Our results showed that feeding on an artesunate- or sulfadoxine-pyrimethamine-treated hosts has no epidemiologically relevant effects on the fitness of infected or uninfected mosquitoes. In contrast, when infected mosquitoes fed on an sulfadoxine-pyrimethamine-treated host, we observed both a significant increase in the number of oocysts in the midgut, and a drastic decrease in both sporozoite prevalence (-30%) and burden (-80%) compared with the untreated controls. We discuss the potential mechanisms underlying these seemingly contradictory results and contend that, provided the results are translatable to human malaria, the potential epidemiological and evolutionary consequences of the current preventive use of sulfadoxine-pyrimethamine in malaria-endemic countries could be substantial.

The direct and indirect effects of copper on vector-borne disease dynamics

Metal pollution is a growing concern that affects the health of humans and animals globally. Copper is an essential insect micronutrient required for respiration, pigmentation and oxidative stress protection but can also act as a potentially toxic trace element. While several studies have focused on the negative fitness effects of copper on the aquatic larvae of mosquitoes, the effects of larval copper exposure on adult mosquito fitness (i.e., survival and fecundity) and their ability to transmit parasites (i.e., vector competence) remains unclear. Here, using a well-studied model vector-parasite system, the mosquito Aedes aegypti and parasite Dirofilaria immitis, we show that sublethal copper exposure in larval mosquitoes alters adult female fecundity and vector competence. Specifically, mosquitoes exposed to copper had a hormetic fecundity response and mosquitoes exposed to 600 μg/L of copper had significantly fewer infective parasite larvae than control mosquitoes not exposed to copper. Thus, exposure of mosquito larvae to copper levels far below EPA-mandated safe drinking water limits (1300 μg/L) can impact vector-borne disease dynamics not only by reducing mosquito abundance (through increased larval mortality), but also by reducing parasite transmission risk. Our results also demonstrated that larval copper is retained through metamorphosis to adulthood in mosquitoes, indicating that these insects could transfer copper from aquatic to terrestrial foodwebs, especially in urban areas where they are abundant. To our knowledge this is the first study to directly link metal exposure with vector competence (i.e., ability to transmit parasites) in any vector-parasite system. Additionally, it also demonstrates unequivocally that mosquitoes can transfer contaminants from aquatic to terrestrial ecosystems. These results have broad implications for public health because they directly linking contaminants and vector-borne disease dynamics, as well as linking mosquitoes and contaminant dynamics.

Cancer and mosquitoes - An unsuspected close connection

Cancer is a major public health issue and represents a significant burden in countries with different levels of economic wealth. In parallel, mosquito-borne infectious diseases represent a growing problem causing significant morbidity and mortality worldwide. Acknowledging that these two concerns are both globally distributed, it is essential to investigate whether they have a reciprocal connection that can fuel their respective burdens. Unfortunately, very few studies have examined the link between these two threats. This review provides an overview of the possible links between mosquitoes, mosquito-borne infectious diseases and cancer. We first focus on the impact of mosquitoes on carcinogenesis in humans including the transmission of oncogenic pathogens through mosquitoes, the immune reactions following mosquito bites, the presence of non-oncogenic mosquito-borne pathogens, and the direct transmission of cancer cells. The second part of this review deals with the direct or indirect consequences of cancer in humans on mosquito behaviour. Thirdly, we discuss the potential impacts that natural cancers in mosquitoes can have on their life history traits and therefore on their vector capacity. Finally, we discuss the most promising research avenues on this topic and the integrative public health strategies that could be envisioned in this context.

Wolbachia's Deleterious Impact on Aedes aegypti Egg Development: The Potential Role of Nutritional Parasitism

Simple Summary

Mosquito-borne viral diseases such as dengue, Zika and chikungunya cause a significant global health burden and are currently increasing in outbreak frequency and geographical reach. Wolbachia pipientis, an endosymbiotic bacterium, offers a solution to this. When Wolbachia is introduced into the main mosquito vector of these viruses, Aedes aegypti, it alters the mosquito’s reproductive biology, as well as reducing the ability of the mosquitoes to transmit viruses. These traits can be leveraged to reduce virus transmission within a community by mass releasing Wolbachia-infected mosquitoes. However, Wolbachia has some negative effects on Aedes aegypti fitness, particularly egg longevity, and the reason behind this remains ambiguous. Insect fitness is very important for the success for Wolbachia-biocontrol strategies as they rely on the released insects being competitive with the wild mosquito population. This review summarises the fitness effects of Wolbachia on Aedes aegypti and investigates the possible contribution of Wolbachia as a nutritional parasite in lowering host fitness. It proposes the next stages of research that can be conducted to address nutritional parasitism to aid in the expansion of Wolbachia-based disease management programs worldwide.

Abstract

The artificial introduction of the endosymbiotic bacterium, Wolbachia pipientis, into Aedes (Ae.) aegypti mosquitoes reduces the ability of mosquitoes to transmit human pathogenic viruses and is now being developed as a biocontrol tool. Successful introgression of Wolbachia-carrying Ae. aegypti into native mosquito populations at field sites in Australia, Indonesia and Malaysia has been associated with reduced disease prevalence in the treated community. In separate field programs, Wolbachia is also being used as a mosquito population suppression tool, where the release of male only Wolbachia-infected Ae. aegypti prevents the native mosquito population from producing viable eggs, subsequently suppressing the wild population. While these technologies show great promise, they require mass rearing of mosquitoes for implementation on a scale that has not previously been done. In addition, Wolbachia induces some negative fitness effects on Ae. aegypti. While these fitness effects differ depending on the Wolbachia strain present, one of the most consistent and significant impacts is the shortened longevity and viability of eggs. This review examines the body of evidence behind Wolbachia’s negative effect on eggs, assesses nutritional parasitism as a key cause and considers how these impacts could be overcome to achieve efficient large-scale rearing of these mosquitoes.

Anopheles metabolic proteins in malaria transmission, prevention and control: a review

The increasing resistance to currently available insecticides in the malaria vector, Anopheles mosquitoes, hampers their use as an effective vector control strategy for the prevention of malaria transmission. Therefore, there is need for new insecticides and/or alternative vector control strategies, the development of which relies on the identification of possible targets in Anopheles. Some known and promising targets for the prevention or control of malaria transmission exist among Anopheles metabolic proteins. This review aims to elucidate the current and potential contribution of Anopheles metabolic proteins to malaria transmission and control. Highlighted are the roles of metabolic proteins as insecticide targets, in blood digestion and immune response as well as their contribution to insecticide resistance and Plasmodium parasite development. Furthermore, strategies by which these metabolic proteins can be utilized for vector control are described. Inhibitors of Anopheles metabolic proteins that are designed based on target specificity can yield insecticides with no significant toxicity to non-target species. These metabolic modulators combined with each other or with synergists, sterilants, and transmission-blocking agents in a single product, can yield potent malaria intervention strategies. These combinations can provide multiple means of controlling the vector. Also, they can help to slow down the development of insecticide resistance. Moreover, some metabolic proteins can be modulated for mosquito population replacement or suppression strategies, which will significantly help to curb malaria transmission.

Transcriptomic analyses of Aedes aegypti cultured cells and ex vivo midguts in response to an excess or deficiency of heme: a quest for transcriptionally-regulated heme transporters

Background

Aedes aegypti is the principle vector of many arboviruses, including dengue virus and Zika virus, which are transmitted when an infected female mosquito takes a blood meal in order to initiate vitellogenesis. During blood digestion, ~ 10 mM heme-iron is ingested into the midgut lumen. While heme acts as both a nutrient and signaling molecule during blood digestion, it can also be highly toxic if left unchaperoned. Both signaling by, and degradation of, heme are intracellular processes, occurring in the nucleus and cytoplasm, respectively. However, the precise mechanism of heme uptake into the midgut epithelium is not currently known.

Results

We used next generation RNA sequencing with the goal to identify genes that code for membrane bound heme import protein(s) responsible for heme uptake into the midgut epithelium. Heme deprivation increased uptake of a heme fluorescent analog in cultured cells, while treatment of midguts with an excess of heme decreased uptake, confirming physiological changes were occurring in these heme-sensitive cells/tissues prior to sequencing. A list of candidate genes was assembled for each of the experimental sample sets, which included Aag2 and A20 cultured cells as well as midgut tissue, based on the results of a differential expression analysis, soft cluster analysis and number of predicted transmembrane domains. Lastly, the functions related to heme transport were examined through RNAi knockdown.

Conclusions

Despite a large number of transmembrane domain containing genes differentially expressed in response to heme, very few were highly differentially expressed in any of the datasets examined. RNAi knockdown of a subset of candidates resulted in subtle changes in heme uptake, but minimal overall disruption to blood digestion/egg production. These results could indicate that heme import in Ae. aegypti may be controlled by a redundant system of multiple distinct transport proteins. Alternatively, heme membrane bound transport in Ae. aegypti could be regulated post-translationally.

Supply and demand-heme synthesis, salvage and utilization by Apicomplexa

The Apicomplexa phylum groups important human and animal pathogens that cause severe diseases, encompassing malaria, toxoplasmosis, and cryptosporidiosis. In common with most organisms, apicomplexans rely on heme as cofactor for several enzymes, including cytochromes of the electron transport chain. This heme derives from de novo synthesis and/or the development of uptake mechanisms to scavenge heme from their host. Recent studies have revealed that heme synthesis is essential for Toxoplasma gondii tachyzoites, as well as for the mosquito and liver stages of Plasmodium spp. In contrast, the erythrocytic stages of the malaria parasites rely on scavenging heme from the host red blood cell. The unusual heme synthesis pathway in Apicomplexa spans three cellular compartments and comprises enzymes of distinct ancestral origin, providing promising drug targets. Remarkably given the requirement for heme, T. gondii can tolerate the loss of several heme synthesis enzymes at a high fitness cost, while the ferrochelatase is essential for survival. These findings indicate that T. gondii is capable of salvaging heme precursors from its host. Furthermore, heme is implicated in the activation of the key antimalarial drug artemisinin. Recent findings established that a reduction in heme availability corresponds to decreased sensitivity to artemisinin in T. gondii and Plasmodium falciparum, providing insights into the possible development of combination therapies to tackle apicomplexan parasites. This review describes the microeconomics of heme in Apicomplexa, from supply, either from de novo synthesis or scavenging, to demand by metabolic pathways, including the electron transport chain.

Understanding Tick Biology and Its Implications in Anti-tick and Transmission Blocking Vaccines Against Tick-Borne Pathogens

Ticks are obligate blood-feeding ectoparasites that transmit a wide variety of pathogens to animals and humans in many parts of the world. Currently, tick control methods primarily rely on the application of chemical acaricides, which results in the development of resistance among tick populations and environmental contamination. Therefore, an alternative tick control method, such as vaccines have been shown to be a feasible strategy that offers a sustainable, safe, effective, and environment-friendly solution. Nevertheless, novel control methods are hindered by a lack of understanding of tick biology, tick-pathogen-host interface, and identification of effective antigens in the development of vaccines. This review highlights the current knowledge and data on some of the tick-protective antigens that have been identified for the formulation of anti-tick vaccines along with the effects of these vaccines on the control of tick-borne diseases.

Elizabethkingia anophelis: Physiologic and Transcriptomic Responses to Iron Stress

In this study, we investigated the global gene expression responses of Elizabethkingia anophelis to iron fluxes in the midgut of female Anopheles stephensi mosquitoes fed sucrose or blood, and in iron-poor or iron-rich culture conditions. Of 3,686 transcripts revealed by RNAseq technology, 218 were upregulated while 112 were down-regulated under iron-poor conditions. Hemolysin gene expression was significantly repressed when cells were grown under iron-rich or high temperature (37°C) conditions. Furthermore, hemolysin gene expression was down-regulated after a blood meal, indicating that E. anophelis cells responded to excess iron and its associated physiological stress by limiting iron loading. By contrast, genes encoding respiratory chain proteins were up-regulated under iron-rich conditions, allowing these iron-containing proteins to chelate intracellular free iron. In vivo studies showed that growth of E. anophelis cells increased 3-fold in blood-fed mosquitoes over those in sucrose-fed ones. Deletion of siderophore synthesis genes led to impaired cell growth in both iron-rich and iron-poor media. Mutants showed more susceptibility to H2O2 toxicity and less biofilm formation than did wild-type cells. Mosquitoes with E. anophelis experimentally colonized in their guts produced more eggs than did those treated with erythromycin or left unmanipulated, as controls. Results reveal that E. anophelis bacteria respond to varying iron concentration in the mosquito gut, harvest iron while fending off iron-associated stress, contribute to lysis of red blood cells, and positively influence mosquito host fecundity.

The male mosquito contribution towards malaria transmission: Mating influences the Anopheles female midgut transcriptome and increases female susceptibility to human malaria parasites

Mating causes dramatic changes in female physiology, behaviour, and immunity in many insects, inducing oogenesis, oviposition, and refractoriness to further mating. Females from the Anopheles gambiae species complex typically mate only once in their lifetime during which they receive sperm and seminal fluid proteins as well as a mating plug that contains the steroid hormone 20-hydroxyecdysone. This hormone, which is also induced by blood-feeding, plays a major role in activating vitellogenesis for egg production. Here we show that female Anopheles coluzzii susceptibility to Plasmodium falciparum infection is significantly higher in mated females compared to virgins. We also find that mating status has a major impact on the midgut transcriptome, detectable only under sugar-fed conditions: once females have blood-fed, the transcriptional changes that are induced by mating are likely masked by the widespread effects of blood-feeding on gene expression. To determine whether increased susceptibility to parasites could be driven by the additional 20E that mated females receive from males, we mimicked mating by injecting virgin females with 20E, finding that these females are significantly more susceptible to human malaria parasites than virgin females injected with the control 20E carrier. Further RNAseq was carried out to examine whether the genes that change upon 20E injection in the midgut are similar to those that change upon mating. We find that 79 midgut-expressed genes are regulated in common by both mating and 20E, and 96% (n = 76) of these are regulated in the same direction (up vs down in 20E/mated). Together, these findings show that male Anopheles mosquitoes induce changes in the female midgut that can affect female susceptibility to P. falciparum. This implies that in nature, males might contribute to malaria transmission in previously unappreciated ways, and that vector control strategies that target males may have additional benefits towards reducing transmission.

Malaria mosquitoes must successfully mate and bloodfeed in order to reproduce. The impact of bloodfeeding on malaria transmission is clear given that all transmission is caused by female mosquitoes that have fed at least twice: once leading to an initial infection, and again 10–14 days later resulting in parasite transmission. The impact of mating on malaria transmission is less clear. Here we show that mating status significantly enhances transmission, such that mated females are more likely to transmit malaria parasites than virgin females. We further examine whether a hormone transferred by mating might cause this enhanced susceptibility, and we find that indeed the receipt of this hormone is also correlated with enhanced susceptibility. The results of this study imply that efforts to target male mosquitoes might not only suppress mosquito populations, but also act to decrease vector competence among residual females.

Iron and Ferritin Deposition in the Ovarian Tissues of the Yellow Fever Mosquito (Diptera: Culicidae)

Dengue, yellow fever, and Zika are viruses transmitted by yellow fever mosquito, Aedes aegypti [Linnaeus (Diptera: Culicidae)], to thousands of people each year. Mosquitoes transmit these viruses while consuming a blood meal that is required for oogenesis. Iron, an essential nutrient from the blood meal, is required for egg development. Mosquitoes receive a high iron load in the meal; although iron can be toxic, these animals have developed mechanisms for dealing with this load. Our previous research has shown iron from the blood meal is absorbed in the gut and transported by ferritin, the main iron transport and storage protein, to the ovaries. We now report the distribution of iron and ferritin in ovarian tissues before blood feeding and 24 and 72 h post-blood meal. Ovarian iron is observed in specific locations. Timing post-blood feeding influences the location and distribution of the ferritin heavy-chain homolog, light-chain homolog 1, and light-chain homolog 2 in ovaries. Understanding iron deposition in ovarian tissues is important to the potential use of interference in iron metabolism as a vector control strategy for reducing mosquito fecundity, decreasing mosquito populations, and thereby reducing transmission rates of vector-borne diseases.

Does differential iron supply to algae affect Daphnia life history? An ionome-wide study

The availability of iron (Fe) varies considerably among diet items, as well as ecosystems. Availability of Fe has also changed due to anthropogenic environmental changes in oceanic as well as inland ecosystems. We know little about its role in the nutrition of ecologically important consumers, particularly in inland ecosystems. Physiological studies in several taxa indicate marked effects of dietary Fe on oogenesis. We predicted that differential Fe supply to algae will impact algal Fe concentration with consequences on the life history of the freshwater grazer, Daphnia magna. We found that algal Fe concentration increased with Fe supply, but did not affect algal growth, indicating that the majority of experimental Fe additions were likely adsorbed to, or stored in algal cells. Regardless, data indicate that algal Fe impacted the reproductive traits (age and size at maturity) but not juvenile growth rate of Daphnia. A subsequent experiment revealed that Fe concentration in eggs was significantly higher than the rest of Daphnia. These results indicate that the concentration of Fe in or on algal cells may vary considerably among ecosystems overlying distinct geological formations differing in Fe, possibly with important implications for zooplankton life histories. Understanding the mechanisms underlying this response is unlikely to be accomplished by a strict focus on Fe because we found correlated shifts in the algal ionome, with concomitant ionome-wide adjustments in Daphnia. Information on ionome-wide responses may be useful in better understanding the responses of biota to changes in the supply of any one element.

Mosquito adaptations to hematophagia impact pathogen transmission

Mosquito-borne diseases such as Dengue fever, Chikungunya, and Malaria are critical threats to public health in many parts of the world. Female mosquitoes have evolved multiple adaptive mechanisms to hematophagy, including the ability to efficiently draw and digest blood, as well as the ability to eliminate excess fluids and toxic by-products of blood digestion. Pathogenic agents enter the mosquito digestive tract with the blood meal and need to travel through the midgut and into the hemocele in order to reach the salivary glands and infect a new host. Pathogens need to adjust to these hostile gut, hemocele, and salivary gland environments, and when possible influence the physiology and behavior of their hosts to enhance transmission.

Haem Biology in Metazoan Parasites - 'The Bright Side of Haem'

Traditionally, host haem has been recognized as a cytotoxic molecule that parasites need to eliminate or detoxify in order to survive. However, recent evidence indicates that some lineages of parasites have lost genes that encode enzymes involved specifically in endogenous haem biosynthesis. Such lineages thus need to acquire and utilize haem originating from their host animal, making it an indispensable molecule for their survival and reproduction. In multicellular parasites, host haem needs to be systemically distributed throughout their bodies to meet the haem demands in all cell and tissue types. Host haem also gets deposited in parasite eggs, enabling embryogenesis and reproduction. Clearly, a better understanding of haem biology in multicellular parasites should elucidate organismal adaptations to obligatory blood-feeding.

Mosquito Innate Immunity

Mosquitoes live under the endless threat of infections from different kinds of pathogens such as bacteria, parasites, and viruses. The mosquito defends itself by employing both physical and physiological barriers that resist the entry of the pathogen and the subsequent establishment of the pathogen within the mosquito. However, if the pathogen does gain entry into the insect, the insect mounts a vigorous innate cellular and humoral immune response against the pathogen, thereby limiting the pathogen's propagation to nonpathogenic levels. This happens through three major mechanisms: phagocytosis, melanization, and lysis. During these processes, various signaling pathways that engage intense mosquito⁻pathogen interactions are activated. A critical overview of the mosquito immune system and latest information about the interaction between mosquitoes and pathogens are provided in this review. The conserved, innate immune pathways and specific anti-pathogenic strategies in mosquito midgut, hemolymph, salivary gland, and neural tissues for the control of pathogen propagation are discussed in detail.

The Effect of SkitoSnack, an Artificial Blood Meal Replacement, on Aedes aegypti Life History Traits and Gut Microbiota

Public health research and vector control frequently require the rearing of large numbers of vector mosquitoes. All target vector mosquito species are anautogenous, meaning that females require vertebrate blood for egg production. Vertebrate blood, however, is costly, with a short shelf life. To overcome these constraints, we have developed SkitoSnack, an artificial blood meal replacement for the mosquito Aedes aegypti, the vector of dengue, Zika and chikungunya virus. SkitoSnack contains bovine serum albumin and hemoglobin as protein source as well as egg yolk and a bicarbonate buffer. SkitoSnack-raised females had comparable life history traits as blood-raised females. Mosquitoes reared from SkitoSnack-fed females had similar levels of infection and dissemination when orally challenged with dengue virus type 2 (DENV-2) and significantly lower infection with DENV-4. When SkitoSnack was used as a vehicle for DENV-2 delivery, blood-raised and SkitoSnack-raised females were equally susceptible. The midgut microbiota differed significantly between mosquitoes fed on SkitoSnack and mosquitoes fed on blood. By rearing 20 generations of Aedes exclusively on SkitoSnack, we have proven that this artificial diet can replace blood in mosquito mass rearing.

Characterisation of Anopheles gambiae heme oxygenase and metalloporphyrin feeding suggests a potential role in reproduction

The mosquito Anopheles gambiae is the principal vector for malaria in sub-Saharan Africa. The ability of A. gambiae to transmit malaria is strictly related to blood feeding and digestion, which releases nutrients for oogenesis, as well as substantial amounts of highly toxic free heme. Heme degradation by heme oxygenase (HO) is a common protective mechanism, and a gene for HO exists in the An. gambiae genome HO (AgHO), although it has yet to be functionally examined. Here, we have cloned and expressed An. gambiae HO (AgHO) in E. coli. Purified recombinant AgHO bound hemin stoichiometrically to form a hemin-enzyme complex similar to other HOs, with a K_D of 3.9 ± 0.6 μM; comparable to mammalian and bacterial HOs, but 7-fold lower than that of Drosophila melanogaster HO. AgHO also degraded hemin to biliverdin and released CO and iron in the presence of NADPH cytochrome P450 oxidoreductase (CPR). Optimal AgHO activity was observed at 27.5 °C and pH 7.5. To investigate effects of AgHO inhibition, adult female A. gambiae were fed heme analogues Sn- and Zn-protoporphyrins (SnPP and ZnPP), known to inhibit HO. These led to a dose dependent decrease in oviposition. Cu-protoporphyrin (CuPP), which does not inhibit HO had no effect. These results demonstrate that AgHO is a catalytically active HO and that it may play a key role in egg production in mosquitoes. It also presents a potential target for the development of compounds aimed at sterilising mosquitoes for vector control.

Biochemical Comparison of dsRNA Degrading Nucleases in Four Different Insects

Double stranded RNAs (dsRNA) degrading nuclease is responsible for the rapid degradation of dsRNA molecules, and thus accounts for variations in RNA interference (RNAi) efficacy among insect species. Here, the biochemical properties and tissue-specific activities of dsRNA degrading nucleases in four insects (Spodoptera litura, Locusta migratoria, Periplaneta americana, and Zophobas atratus) from different orders were characterized using a modified assay method. The results revealed that all insect dsRNA degrading nucleases tested showed high activity in alkaline environments at optimal Mg2+ concentrations and elevated temperatures. We also found that enzymes from different insects varied in terms of their optimal reaction conditions and kinetic parameters. Whole body enzyme activity differed dramatically between insect species, although enzymes with higher substrate affinities (lower Km) were usually balanced by a smaller Vmax to maintain a proper level of degradative capacity. Furthermore, enzyme activities varied significantly between the four tested tissues (whole body, gut, hemolymph, and carcass) of the insect species. All the insects tested showed several hundred-fold higher dsRNA degrading activity in their gut than in other tissues. Reaction environment analysis demonstrated that physiological conditions in the prepared gut fluid and serum of different insects were not necessarily optimal for dsRNA degrading nuclease activity. Our data describe the biochemical characteristics and tissue distributions of dsRNA degrading activities in various insects, not only explaining why oral delivery of dsRNA often produces lower RNAi effects than injection of dsRNA, but also suggesting that dsRNA-degrading activities are regulated by physiological conditions. These results allow for a better understanding of the properties of dsRNA degrading nucleases, and will aid in the development of successful RNAi strategies in insects.

Transcriptome profiling of the honeybee parasite Varroa destructor provides new biological insights into the mite adult life cycle

Background

The parasite Varroa destructor represents a significant threat to honeybee colonies. Indeed, development of Varroa infestation within colonies, if left untreated, often leads to the death of the colony. Although its impact on bees has been extensively studied, less is known about its biology and the functional processes governing its adult life cycle and adaptation to its host. We therefore developed a full life cycle transcriptomic catalogue in adult Varroa females and included pairwise comparisons with males, artificially-reared and non-reproducing females (10 life cycle stages and conditions in total).

Results

Extensive remodeling of the Varroa transcriptome was observed, with an upregulation of energetic and chitin metabolic processes during the initial and final phases of the life cycle (e.g. phoretic and post-oviposition stages), whereas during reproductive stages in brood cells genes showing functions related to transcriptional regulation were overexpressed. Several neurotransmitter and neuropeptide receptors involved in behavioural regulation, as well as active compounds of salivary glands, were also expressed at a higher level outside the reproductive stages. No difference was detected between artificially-reared phoretic females and their counterparts in colonies, or between females who failed to reproduce and females who successfully reproduced, indicating that phoretic individuals can be reared outside host colonies without impacting their physiology and that mechanisms underlying reproductive failure occur before oogenesis.

Conclusions

We discuss how these new findings reveal the remarkable adaptation of Varroa to its host biology and notably to the switch from living on adults to reproducing in sealed brood cells. By spanning the entire adult life cycle, our work captures the dynamic changes in the parasite gene expression and serves as a unique resource for deciphering Varroa biology and identifying new targets for mite control.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4668-z) contains supplementary material, which is available to authorized users.

Identification of Candidate Iron Transporters From the ZIP/ZnT Gene Families in the Mosquito Aedes aegypti

Mosquito-transmitted viral pathogens, such as dengue and Zika, afflict tens of thousands of people every year. These viruses are transmitted during the blood-feeding process that is required for mosquito reproduction, the most important vector being Aedes aegypti. While vertebrate blood is rich in protein, its high iron content is potentially toxic to mosquitoes. Although iron transport and sequestration are essential in the reproduction of vector mosquitoes, we discovered that culicine mosquitoes lack homologs of the common iron transporter NRAMP. Using a novel cell-based screen, we identified two ZIP and one ZnT genes as candidate iron transporters in the mosquito A. aegypti, the vector of dengue, Zika, and chikungunya. We determined the organ-specific expression pattern of these genes at critical time points in early reproduction. The result indicates modulation of these genes upon blood feeding, especially a ZIP13 homolog that is highly up-regulated after blood feeding, suggesting its importance in iron mobilization during blood digestion and reproduction. Gene silencing resulted in differential iron accumulation in the midgut and ovaries. This study sets a foundation for further investigation of iron transport and control strategies of this viral vector.

Modulation of mitochondrial metabolism as a biochemical trait in blood feeding organisms: the redox vampire hypothesis redux

Hematophagous organisms undergo remarkable metabolic changes during the blood digestion process, increasing fermentative glucose metabolism, and reducing respiratory rates, both consequence of functional mitochondrial remodeling. Here, we review the pathways involved in energy metabolism and mitochondrial functionality in a comparative framework across different hematophagous species, and consider how these processes regulate redox homeostasis during blood digestion. The trend across distinct species indicate that a switch in energy metabolism might represent an important defensive mechanism to avoid the potential harmful interaction of oxidants generated from aerobic energy metabolism with products derived from blood digestion. Indeed, in insect vectors, blood feeding transiently reduces respiratory rates and oxidant production, irrespective of tissue and insect model. On the other hand, a different scenario is observed in several unrelated parasite species when exposed to blood digestion products, as respiratory rates reduce and mitochondrial oxidant production increase. The emerging picture indicates that re-wiring of energy metabolism, through reduced mitochondrial function, culminates in improved tolerance to redox insults and seems to represent a key step for hematophagous organisms to cope with the overwhelming and potentially toxic blood meal.

Silencing of Iron and Heme-Related Genes Revealed a Paramount Role of Iron in the Physiology of the Hematophagous Vector Rhodnius prolixus

Iron is an essential element for most organisms However, free iron and heme, its complex with protoporphyrin IX, can be extremely cytotoxic, due to the production of reactive oxygen species, eventually leading to oxidative stress. Thus, eukaryotic cells control iron availability by regulating its transport, storage and excretion as well as the biosynthesis and degradation of heme. In the genome of Rhodnius prolixus, the vector of Chagas disease, we identified 36 genes related to iron and heme metabolism We performed a comprehensive analysis of these genes, including identification of homologous genes described in other insect genomes. We observed that blood-meal modulates the expression of ferritin, Iron Responsive protein (IRP), Heme Oxygenase (HO) and the heme exporter Feline Leukemia Virus C Receptor (FLVCR), components of major pathways involved in the regulation of iron and heme metabolism, particularly in the posterior midgut (PM), where an intense release of free heme occurs during the course of digestion. Knockdown of these genes impacted the survival of nymphs and adults, as well as molting, oogenesis and embryogenesis at different rates and time-courses. The silencing of FLVCR caused the highest levels of mortality in nymphs and adults and reduced nymph molting. The oogenesis was mildly affected by the diminished expression of all of the genes whereas embryogenesis was dramatically impaired by the knockdown of ferritin expression. Furthermore, an intense production of ROS in the midgut of blood-fed insects occurs when the expression of ferritin, but not HO, was inhibited. In this manner, the degradation of dietary heme inside the enterocytes may represent an oxidative challenge that is counteracted by ferritins, conferring to this protein a major antioxidant role. Taken together these results demonstrate that the regulation of iron and heme metabolism is of paramount importance for R. prolixus physiology and imbalances in the levels of these key proteins after a blood- meal can be extremely deleterious to the insects in their various stages of development.

Ironing out the Details: Exploring the Role of Iron and Heme in Blood-Sucking Arthropods

Heme and iron are essential molecules for many physiological processes and yet have the ability to cause oxidative damage such as lipid peroxidation, protein degradation, and ultimately cell death if not controlled. Blood-sucking arthropods have evolved diverse methods to protect themselves against iron/heme-related damage, as the act of bloodfeeding itself is high risk, high reward process. Protective mechanisms in medically important arthropods include the midgut peritrophic matrix in mosquitoes, heme aggregation into the crystalline structure hemozoin in kissing bugs and hemosomes in ticks. Once heme and iron pass these protective mechanisms they are presumed to enter the midgut epithelial cells via membrane-bound transporters, though relatively few iron or heme transporters have been identified in bloodsucking arthropods. Upon iron entry into midgut epithelial cells, ferritin serves as the universal storage protein and transport for dietary iron in many organisms including arthropods. In addition to its role as a nutrient, heme is also an important signaling molecule in the midgut epithelial cells for many physiological processes including vitellogenesis. This review article will summarize recent advancements in heme/iron uptake, detoxification and exportation in bloodfeeding arthropods. While initial strides have been made at ironing out the role of dietary iron and heme in arthropods, much still remains to be discovered as these molecules may serve as novel targets for the control of many arthropod pests.

Description of a Second Ferritin Light Chain Homologue From the Yellow Fever Mosquito (Diptera: Culicidae)

Ferritin is required for iron storage in vertebrates and for iron transport and storage in invertebrates, specifically insects. Classical ferritins consist of 24 subunits configured as a polyhedron wherein iron is held. The 24 subunits include light and heavy chains, each with specific functions. Several homologues of the light and heavy chains have been sequenced and studied in insects. In addition to iron transport and storage, ferritin has a role in dietary iron absorption, and functions as a protective agent preventing iron overload, decreasing oxidative stress, and reducing infection in these animals. The expression profile and regulation of a second ferritin light chain homologue (LCH2) in Aedes aegypti [Linnaeus (Diptera: Culicidae), yellow fever mosquito] was characterized in cells, animal developmental stages, and tissues post bloodmeal (PBM) by real-time PCR and immunoblot. Two previously studied ferritin subunits from Ae. aegypti, HCH and LCH1, along with LCH2 were immunoprecipitated and analyzed by mass spectrometry. The three Ae. aegypti ferritin subunits, HCH, LCH1, and LCH2, have different expression profiles and regulation with iron exposure, developmental stage, and tissue response PBM. Ae. aegypti expresses multiple and unique ferritin light chain subunits. Ae. aegypti, the vector for Zika, Dengue, and yellow fever, requires iron for oogenesis that is transported and stored in ferritin; this vector expresses a second light chain ferritin subunit homologue unlike any other species in which ferritin has been studied to date.

How micronutrients influence the physiology of mosquitoes

Micronutrients or non-energetic nutrients (NEN) are needed in reduced amounts, but are essential for many mosquito physiological processes that influence biological traits from vector competence to reproductive capacity. The NEN include amino acids (AA), vitamins, salts, metals and sterols. Free AA plays critical roles controlling most physiological processes, from digestion to reproduction. Particularly proline connects metabolic pathways in energy production, flight physiology and ammonia detoxification. Metal, in particular iron and calcium, salts, sterol and vitamin homeostasis are critical for cell signaling, respiration, metabolism and reproduction. Micronutrient homeostasis influence the symbiotic relationships with microorganisms, having important implications in mosquitoes' nutrition, physiology and behavior, as well as in mosquito immunity and vector competence.

Iron availability affects West Nile virus infection in its mosquito vector

Background

Mosquitoes are responsible for transmission of viruses, including dengue, West Nile and chikungunya viruses. Female mosquitoes are infected when they blood-feed on vertebrates, a required step for oogenesis. During this process, mosquitoes encounter high iron loads. Since iron is an essential nutrient for most organisms, including pathogens, one of the defense mechanisms for the host includes sequestration of iron away from the invading pathogen. Here, we determine whether iron availability affects viral replication in mosquitoes.

Methods

To elucidate effect of iron availability on mosquito cells during infection, Culex cells were treated with either ferric ammonium citrate (FAC) or the iron chelator, deferoxamine (DFX). Real time RT-PCR was performed using ferritin (heavy chain) and NRAMP as a measure of iron homeostasis in cells. To determine iron requirement for viral replication, Culex cells were knocked down for NRAMP using dsRNA. Finally, the results were validated in Culex mosquito-infection model, by treating infected mosquitoes with DFX to reduce iron levels.

Results

Our results show that infection of Culex cells led to induction in levels of ferritin (heavy chain) and NRAMP mRNAs in time-dependent manner. Results also showed that treatment of cells with FAC, reduced expression of NRAMP (iron transporter) and increase levels of ferritin (heavy chain). Interestingly, increasing iron levels increased viral titers; while reducing intracellular iron levels, either by NRAMP knock-down or using DFX, reduced viral titers. The results from Culex mosquito infection showed that mosquitoes treated with DFX had reduced viral titers compared with untreated controls in midgut as well as carcass 8 days pi. Saliva from mosquitoes treated with DFX also showed reduced viral titers compared with untreated controls, indicating low viral transmission capacity.

Conclusions

Our results indicate that iron is required for viral replication in mosquito cells. Mosquitoes respond to viral infection, by inducing expression of heavy chain ferritin, which sequesters available iron, reducing its availability to virus infected cells. The data indicates that heavy chain ferritin may be part of an immune mechanism of mosquitoes in response to viral infections.

Proteomic analysis in the Dufour's gland of Africanized Apis mellifera workers (Hymenoptera: Apidae)

The colony of eusocial bee Apis mellifera has a reproductive queen and sterile workers performing tasks such as brood care and foraging. Chemical communication plays a crucial role in the maintenance of sociability in bees with many compounds released by the exocrine glands. The Dufour’s gland is a non-paired gland associated with the sting apparatus with important functions in the communication between members of the colony, releasing volatile chemicals that influence workers roles and tasks. However, the protein content in this gland is not well studied. This study identified differentially expressed proteins in the Dufour’s glands of nurse and forager workers of A. mellifera through 2D-gel electrophoresis and mass spectrometry. A total of 131 spots showed different expression between nurse and forager bees, and 28 proteins were identified. The identified proteins were categorized into different functions groups including protein, carbohydrate, energy and lipid metabolisms, cytoskeleton-associated proteins, detoxification, homeostasis, cell communication, constitutive and allergen. This study provides new insights of the protein content in the Dufour’s gland contributing to a more complete understanding of the biological functions of this gland in honeybees.

The Dose Makes the Poison: Nutritional Overload Determines the Life Traits of Blood-Feeding Arthropods

Vertebrate blood composition is heavily biased towards proteins, and hemoglobin, which is a hemeprotein, is by far the most abundant protein. Typically, hematophagous insects ingest blood volumes several times their weight before the blood meal. This barbarian feast offers an abundance of nutrients, but the degradation of blood proteins generates toxic concentrations of amino acids and heme, along with unparalleled microbiota growth. Despite this challenge, hematophagous arthropods have successfully developed mechanisms that bypass the toxicity of these molecules. While these adaptations allow hematophagous arthropods to tolerate their diet, they also constitute a unique mode of operation for cell signaling, immunity, and metabolism, the study of which may offer insights into the biology of disease vectors and may lead to novel vector-specific control methods.

Sweet waste extract uptake by a mosquito vector: Survival, biting, fecundity responses, and potential epidemiological significance

In nature, adult mosquitoes typically utilize nectar as their main energy source, but they can switch to other as yet unidentified sugary fluids. Contemporary lifestyles, with their associated unwillingness to consume leftovers and improper disposal of waste, have resulted in the disposal of huge amounts of waste into the environment. Such refuse often contains unfinished food items, many of which contain sugar and some of which can collect water from rain and generate juices. Despite evidence that mosquitoes can feed on sugar-rich suspensions, semi-liquids, and decaying fruits, which can be abundant in garbage sites, the impacts of sweet waste fluids on dengue vectors are unknown. Here, we investigated the effects of extracts from some familiar sweet home waste items on key components of vectorial capacity of Aedes aegypti. Adult mosquitoes were fed one of five diets in this study: water (WAT); sucrose (SUG); bakery product (remnant of chocolate cake, BAK); dairy product (yogurt, YOG); and fruit (banana (BAN). Differences in survival, response time to host, and egg production were examined between groups. For both males and females, maintenance on BAK extract resulted in marked survival levels that were similar to those seen with SUG. Sweet waste extracts provided better substrates for survival compared to water, but this superiority was mostly seen with BAK. Females maintained on BAK, YOG, and BAN exhibited shorter response times to a host compared to their counterparts maintained on SUG. The levels of egg production were equivalent in waste extract- and SUG-fed females. The findings presented here illustrate the potential of sweet waste-derived fluids to contribute to the vectorial capacity of dengue vectors and suggest the necessity of readdressing the issue of waste disposal, especially that of unfinished sweet foods. Such approaches can be particularly relevant in dengue endemic areas where rainfall is frequent and waste collection infrequent.

The impact of metagenomic interplay on the mosquito redox homeostasis

Mosquitoes are exposed to oxidative challenges throughout their life cycle. The primary challenge comes from a blood meal. The blood digestion turns the midgut into an oxidative environment, which imposes pressure not only on mosquito fecundity and other physiological traits but also on the microbiota in the midgut. During evolution, mosquitoes have developed numerous oxidative defense mechanisms to maintain redox homeostasis in the midgut. In addition to antioxidants, SOD, catalase, and glutathione system, sufficient supply of the reducing agent, NADPH, is vital for a successful defense against oxidative stress. Increasing evidence indicates that in response to oxidative stress, cells reconfigure metabolic pathways to increase the generation of NADPH through NADP-reducing networks including the pentose phosphate pathway and others. The microbial homeostasis is critical for the functional contributions to various host phenotypes. The symbiotic microbiota is regulated largely by the Duox-ROS pathway in Drosophila. In mosquitoes, Duox-ROS pathway, heme-mediated signaling, antimicrobial peptide production and C-type lectins work in concert to maintain the dynamic microbial community in the midgut. Microbial mechanisms against oxidative stress in this context are not well understood. Emerging evidence that microbial metabolites trigger host oxidative response warrants further study on the metagenomic interplay in an oxidative environment like mosquito gut ecosystem. Besides the classical Drosophila model, hematophagous insects like mosquitoes provide an alternative model system to study redox homeostasis in a symbiotic metagenomic context.

Artificial Diets for Mosquitoes

Mosquito-borne diseases are responsible for more than a million human deaths every year. Modern mosquito control strategies such as sterile insect technique (SIT), release of insects carrying a dominant lethal (RIDL), population replacement strategies (PR), and Wolbachia-based strategies require the rearing of large numbers of mosquitoes in culture for continuous release over an extended period of time. Anautogenous mosquitoes require essential nutrients for egg production, which they obtain through the acquisition and digestion of a protein-rich blood meal. Therefore, mosquito mass production in laboratories and other facilities relies on vertebrate blood from live animal hosts. However, vertebrate blood is expensive to acquire and hard to store for longer times especially under field conditions. This review discusses older and recent studies that were aimed at the development of artificial diets for mosquitoes in order to replace vertebrate blood.

The reproductive ecology of iron in women

Reproductive ecology focuses on the sensitivity of human reproduction to environmental variation. While reproductive ecology has historically focused on the relationship between energy status and reproductive outcomes, iron status is equally critical to women's reproductive health, given the wide-ranging detrimental effects of iron-deficiency anemia on maternal and infant well-being. This review interprets the vast literature on iron status and women's reproduction through an evolutionary framework. First, it will critique the evidence for iron deficiency caused by blood loss during menstruation, reinterpreting the available data as ecological variation in menses within and between populations of women. Second, it will highlight the scant but growing evidence that iron status is implicated in fertility, a relationship that has deep evolutionary roots. Third, this review proposes a new hypothesis for the transfer of iron from mother to infant via pregnancy and breastfeeding: reproductive iron withholding. In this hypothesis, mothers transfer iron to infants in a manner that helps infants avoid iron-mediated infection and oxidative stress, but trades off with potential risk of maternal and infant iron deficiency. Finally, this review explores two main factors that can modify the relationship between iron status and the gestation-lactation cycle: (1) the relationship between long-term reproductive effort (parity) and iron status and (2) supplementation schemes before and during pregnancy. The review concludes by suggesting continued research into iron homeostasis in women using evolutionary, ecological, and biocultural frameworks.