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Tsetse flies are the sole vectors of human African trypanosomiasis throughout sub-Saharan Africa. Both sexes of adult tsetse feed exclusively on blood and contribute to disease transmission. Notable differences between tsetse and other disease vectors include obligate microbial symbioses, viviparous reproduction, and lactation. Here, we describe the sequence and annotation of the 366-megabase Glossina morsitans morsitans genome. Analysis of the genome and the 12,308 predicted protein–encoding genes led to multiple discoveries, including chromosomal integrations of bacterial (Wolbachia) genome sequences, a family of lactation-specific proteins, reduced complement of host pathogen recognition proteins, and reduced olfaction/chemosensory associated genes. These genome data provide a foundation for research into trypanosomiasis prevention and yield important insights with broad implications for multiple aspects of tsetse biology.

Both Aedes aegytpi and Ae. albopictus are major vectors of 5 important arboviruses (namely chikungunya virus, dengue virus, Rift Valley fever virus, yellow fever virus, and Zika virus), making these mosquitoes an important factor in the worldwide burden of infectious disease. Vector control using insecticides coupled with larval source reduction is critical to control the transmission of these viruses to humans but is threatened by the emergence of insecticide resistance. Here, we review the available evidence for the geographical distribution of insecticide resistance in these 2 major vectors worldwide and map the data collated for the 4 main classes of neurotoxic insecticide (carbamates, organochlorines, organophosphates, and pyrethroids). Emerging resistance to all 4 of these insecticide classes has been detected in the Americas, Africa, and Asia. Target-site mutations and increased insecticide detoxification have both been linked to resistance in Ae. aegypti and Ae. albopictus but more work is required to further elucidate metabolic mechanisms and develop robust diagnostic assays. Geographical distributions are provided for the mechanisms that have been shown to be important to date. Estimating insecticide resistance in unsampled locations is hampered by a lack of standardisation in the diagnostic tools used and by a lack of data in a number of regions for both resistance phenotypes and genotypes. The need for increased sampling using standard methods is critical to tackle the issue of emerging insecticide resistance threatening human health. Specifically, diagnostic doses and well-characterised susceptible strains are needed for the full range of insecticides used to control Ae. aegypti and Ae. albopictus to standardise measurement of the resistant phenotype, and calibrated diagnostic assays are needed for the major mechanisms of resistance.

Most pathogens require a relatively long period of development in their mosquito vector before they can be transmitted to a new human host; hence, only older insects are of epidemiological importance. The successful transfer of a life-shortening strain of the inherited bacterial symbiont, Wolbachia, into the major mosquito vector of dengue, Aedes aegypti, halved adult life span under laboratory conditions. The association is stable, and the Wolbachia strain is maternally inherited at high frequency. It is capable of inducing complete cytoplasmic incompatibility, which should facilitate its invasion into natural field populations and its persistence over time. Our data suggest that targeting mosquito age with inherited Wolbachia infections may be a viable strategy to reduce the transmission of pathogens such as dengue viruses.

Background The Russian wheat aphid, Diuraphis noxia Kurdjumov, is one of the most important pests of small grains throughout the temperate regions of the world. This phytotoxic aphid causes severe systemic damage symptoms in wheat, barley, and other small grains as a direct result of the salivary proteins it injects into the plant while feeding. Results We sequenced and de novo assembled the genome of D. noxia Biotype 2, the strain most virulent to resistance genes in wheat. The assembled genomic scaffolds span 393 MB, equivalent to 93% of its 421 MB genome, and contains 19,097 genes. D. noxia has the most AT-rich insect genome sequenced to date (70.9%), with a bimodal CpG( O/E ) distribution and a complete set of methylation related genes. The D. noxia genome displays a widespread, extensive reduction in the number of genes per ortholog group, including defensive, detoxification, chemosensory, and sugar transporter groups in comparison to the Acyrthosiphon pisum genome, including a 65% reduction in chemoreceptor genes. Thirty of 34 known D. noxia salivary genes were found in this assembly. These genes exhibited less homology with those salivary genes commonly expressed in insect saliva, such as glucose dehydrogenase and trehalase, yet greater conservation among genes that are expressed in D. noxia saliva but not detected in the saliva of other insects. Genes involved in insecticide activity and endosymbiont-derived genes were also found, as well as genes involved in virus transmission, although D. noxia is not a viral vector. Conclusions This genome is the second sequenced aphid genome, and the first of a phytotoxic insect. D. noxia ’s reduced gene content of may reflect the influence of phytotoxic feeding in shaping the D. noxia genome, and in turn in broadening its host range. The presence of methylation-related genes, including cytosine methylation, is consistent with other parthenogenetic and polyphenic insects. The D. noxia genome will provide an important contrast to the A. pisum genome and advance functional and comparative genomics of insects and other organisms.

In this review, we explore the state-of-the-art of sand fly relationships with microbiota, viruses and Leishmania, with particular emphasis on the vector immune responses. Insect-borne diseases are a major public health problem in the world. Phlebotomine sand flies are proven vectors of several aetiological agents including viruses, bacteria and the trypanosomatid Leishmania, which are responsible for diseases such as viral encephalitis, bartonellosis and leishmaniasis, respectively. All metazoans in nature coexist intimately with a community of commensal microorganisms known as microbiota. The microbiota has a fundamental role in the induction, maturation and function of the host immune system, which can modulate host protection from pathogens and infectious diseases. We briefly review viruses of public health importance present in sand flies and revisit studies done on bacterial and fungal gut contents of these vectors. We bring this information into the context of sand fly development and immune responses. We highlight the immunity mechanisms that the insect utilizes to survive the potential threats involved in these interactions and discuss the recently discovered complex interactions among microbiota, sand fly, Leishmania and virus. Additionally, some of the alternative control strategies that could benefit from the current knowledge are considered.

Here, we show that the major mosquito vector for dengue virus uses the JAK-STAT pathway to control virus infection. Dengue virus infection in Aedes aegypti mosquitoes activates the JAK-STAT immune signaling pathway. The mosquito's susceptibility to dengue virus infection increases when the JAK-STAT pathway is suppressed through RNAi depletion of its receptor Domeless (Dome) and the Janus kinase (Hop), whereas mosquitoes become more resistant to the virus when the negative regulator of the JAK-STAT pathway, PIAS, is silenced. The JAK-STAT pathway exerts its anti-dengue activity presumably through one or several STAT-regulated effectors. We have identified, and partially characterized, two JAK-STAT pathway-regulated and infection-responsive dengue virus restriction factors (DVRFs) that contain putative STAT-binding sites in their promoter regions. Our data suggest that the JAK-STAT pathway is part of the A. aegypti mosquito's anti-dengue defense and may act independently of the Toll pathway and the RNAi-mediated antiviral defenses.

Cucumber mosaic virus (CMV) often accompanies a short RNA molecule called a satellite RNA (satRNA). When infected with CMV in the presence of Y-satellite RNA (Y-sat), tobacco leaves develop a green mosaic, then turn yellow. Y-sat has been identified in the fields in Japan. Here, we show that the yellow leaf colour preferentially attracts aphids, and that the aphids fed on yellow plants, which harbour Y-sat-derived small RNAs (sRNAs), turn red and subsequently develop wings. In addition, we found that leaf yellowing did not necessarily reduce photosynthesis, and that viral transmission was not greatly affected despite the low viral titer in the Y-sat-infected plants. Y-sat-infected plants can therefore support a sufficient number of aphids to allow for efficient virus transmission. Our results demonstrate that Y-sat directly alters aphid physiology via Y-sat sRNAs to promote wing formation, an unprecedented survival strategy that enables outward spread via the winged insect vector. The cucumber mosaic virus is accompanied by short RNA molecules, satellite RNAs. This study shows that leaves infected with Y-satellite RNA preferentially attract aphids and manipulate aphid physiology to promote their spread to neighbouring plants.

Wolbachia used to counter dengue fever The mosquito-borne viral disease dengue fever is an increasing problem in tropical and subtropical regions. Traditional control measures aimed at reducing populations of the main transmission vector, Aedes aegypti , have had little success. Two papers in this issue report an alternative approach to mosquito population control using the bacterium Wolbachia pipientis , natural insect symbionts that facilitate their own transmission through a process called cytoplasmic incompatibility. In the first paper, Scott O'Neill and colleagues describe a Wolbachia strain derived from fruitflies that significantly reduces dengue virus carriage in mosquitoes without imposing a fitness cost. In the second paper, they demonstrate in a controlled field trial that the release of colonized mosquitoes leads to successful invasion of natural mosquito populations. These results suggest a viable strategy to control dengue fever. Genetic manipulations of insect populations for pest control have been advocated for some time, but there are few cases where manipulated individuals have been released in the field and no cases where they have successfully invaded target populations 1 . Population transformation using the intracellular bacterium Wolbachia is particularly attractive because this maternally-inherited agent provides a powerful mechanism to invade natural populations through cytoplasmic incompatibility 2 . When Wolbachia are introduced into mosquitoes, they interfere with pathogen transmission and influence key life history traits such as lifespan 3 , 4 , 5 , 6 . Here we describe how the w Mel Wolbachia infection, introduced into the dengue vector Aedes aegypti from Drosophila melanogaster 7 , successfully invaded two natural A. aegypti populations in Australia, reaching near-fixation in a few months following releases of w Mel-infected A. aegypti adults. Models with plausible parameter values indicate that Wolbachia -infected mosquitoes suffered relatively small fitness costs, leading to an unstable equilibrium frequency <30% that must be exceeded for invasion. These findings demonstrate that Wolbachia -based strategies can be deployed as a practical approach to dengue suppression with potential for area-wide implementation.

In the last decade there have been marked reductions in malaria incidence in sub-Saharan Africa. Sustaining these reductions will rely upon insecticides to control the mosquito malaria vectors. We report that in the primary African malaria vector, Anopheles gambiae sensu stricto, a single enzyme, CYP6M2, confers resistance to two classes of insecticide. This is unique evidence in a disease vector of cross-resistance associated with a single metabolic gene that simultaneously reduces the efficacy of two of the four classes of insecticide routinely used for malaria control. The gene-expression profile of a highly DDT-resistant population of A. gambiae s.s. from Ghana was characterized using a unique whole-genome microarray. A number of genes were significantly overexpressed compared with two susceptible West African colonies, including genes from metabolic families previously linked to insecticide resistance. One of the most significantly overexpressed probe groups (false-discovery rate-adjusted P < 0.0001) belonged to the cytochrome P450 gene CYP6M2. This gene is associated with pyrethroid resistance in wild A. gambiae s.s. populations) and can metabolize both type I and type II pyrethroids in recombinant protein assays. Using in vitro assays we show that recombinant CYP6M2 is also capable of metabolizing the organochlorine insecticide DDT in the presence of solubilizing factor sodium cholate.

Wolbachia used to counter dengue fever The mosquito-borne viral disease dengue fever is an increasing problem in tropical and subtropical regions. Traditional control measures aimed at reducing populations of the main transmission vector, Aedes aegypti , have had little success. Two papers in this issue report an alternative approach to mosquito population control using the bacterium Wolbachia pipientis , natural insect symbionts that facilitate their own transmission through a process called cytoplasmic incompatibility. In the first paper, Scott O'Neill and colleagues describe a Wolbachia strain derived from fruitflies that significantly reduces dengue virus carriage in mosquitoes without imposing a fitness cost. In the second paper, they demonstrate in a controlled field trial that the release of colonized mosquitoes leads to successful invasion of natural mosquito populations. These results suggest a viable strategy to control dengue fever. Dengue fever is the most important mosquito-borne viral disease of humans with more than 50 million cases estimated annually in more than 100 countries 1 , 2 . Disturbingly, the geographic range of dengue is currently expanding and the severity of outbreaks is increasing 2 , 3 , 4 . Control options for dengue are very limited and currently focus on reducing population abundance of the major mosquito vector, Aedes aegypti 5 , 6 . These strategies are failing to reduce dengue incidence in tropical communities and there is an urgent need for effective alternatives. It has been proposed that endosymbiotic bacterial Wolbachia infections of insects might be used in novel strategies for dengue control 7 , 8 , 9 . For example, the w MelPop-CLA Wolbachia strain reduces the lifespan of adult A. aegypti mosquitoes in stably transinfected lines 8 . This life-shortening phenotype was predicted to reduce the potential for dengue transmission. The recent discovery that several Wolbachia infections, including w MelPop-CLA, can also directly influence the susceptibility of insects to infection with a range of insect and human pathogens 9 , 10 , 11 has markedly changed the potential for Wolbachia infections to control human diseases. Here we describe the successful transinfection of A. aegypti with the avirulent w Mel strain of Wolbachia , which induces the reproductive phenotype cytoplasmic incompatibility with minimal apparent fitness costs and high maternal transmission, providing optimal phenotypic effects for invasion. Under semi-field conditions, the w Mel strain increased from an initial starting frequency of 0.65 to near fixation within a few generations, invading A. aegypti populations at an accelerated rate relative to trials with the w MelPop-CLA strain. We also show that w Mel and w MelPop-CLA strains block transmission of dengue serotype 2 (DENV-2) in A. aegypti , forming the basis of a practical approach to dengue suppression 12 .