The worldwide spread of Aedes albopictus: New insights from mitogenomes.

The tiger mosquito (Aedes albopictus) is one of the most invasive species in the world and a competent vector for numerous arboviruses, thus the study and monitoring of its fast worldwide spread is crucial for global public health. The small extra-nuclear and maternally-inherited mitochondrial DNA represents a key tool for reconstructing phylogenetic and phylogeographic relationships within a species, especially when analyzed at the mitogenome level. Here the mitogenome variation of 76 tiger mosquitoes, 37 of which new and collected from both wild adventive populations and laboratory strains, was investigated. This analysis significantly improved the global mtDNA phylogeny of Ae. albopictus, uncovering new branches and sub-branches within haplogroup A1, the one involved in its recent worldwide spread. Our phylogeographic approach shows that the current distribution of tiger mosquito mitogenome variation has been strongly affected by clonal and sub-clonal founder events, sometimes involving wide geographic areas, even across continents, thus shedding light on the Asian sources of worldwide adventive populations. In particular, different starting points for the two major clades within A1 are suggested, with A1a spreading mainly along temperate areas from Japanese and Chinese sources, and A1b arising and mainly diffusing in tropical areas from a South Asian source.

Impact of temperature on dengue and chikungunya transmission by the mosquito Aedes albopictus.

The mosquito Aedes albopictus is an invasive species first detected in Europe in Albania in 1979, and now established in 28 European countries. Temperature is a limiting factor in mosquito activities and in the transmission of associated arboviruses namely chikungunya (CHIKV) and dengue (DENV). Since 2007, local transmissions of CHIKV and DENV have been reported in mainland Europe, mainly in South Europe. Thus, the critical question is how far north transmission could occur. In this context, the Albanian infestation by Ae. albopictus is of interest because the species is present up to 1200 m of altitude; this allows using altitude as a proxy for latitude. Here we show that Ae. albopictus can transmit CHIKV at 28 °C as well as 20 °C, however, the transmission of DENV is only observed at 28 °C. We conclude that if temperature is the key environmental factor limiting transmission, then transmission of CHIKV, but not DENV is feasible in much of Europe.

Behavioural Responses of Male Aedes albopictus to Different Volatile Chemical Compounds.

The Asian tiger mosquito, Aedes albopictus, has become one of the most important invasive vectors for disease pathogens such as the viruses that cause chikungunya and dengue. Given the medical importance of this disease vector, a number of control programmes involving the use of the sterile insect technique (SIT) have been proposed. The identification of chemical compounds that attract males can be very useful for trapping purposes, especially for monitoring the makeup of the male population during control programmes, such as those involving the use of the SIT. Twenty-eight chemical compounds from different chemical classes were evaluated using a dual-port olfactometer assay. The compounds included known animal, fungal and plant host volatiles, and components of a putative Aedes aegypti pheromone. Many of the compounds were repellent for male mosquitoes, especially at the highest concentration. One compound, decanoic acid, acted as an attractant for males at an intermediate concentration. Decanoic acid did not elicit a significant response from female mosquitoes.

Viviparity and habitat restrictions may influence the evolution of male reproductive genes in tsetse fly (Glossina) species.

BACKGROUND: Glossina species (tsetse flies), the sole vectors of African trypanosomes, maintained along their long evolutionary history a unique reproductive strategy, adenotrophic viviparity. Viviparity reduces their reproductive rate and, as such, imposes strong selective pressures on males for reproductive success. These species live in sub-Saharan Africa, where the distributions of the main sub-genera Fusca, Morsitans, and Palpalis are restricted to forest, savannah, and riverine habitats, respectively. Here we aim at identifying the evolutionary patterns of the male reproductive genes of six species belonging to these three main sub-genera. We then interpreted the different patterns we found across the species in the light of viviparity and the specific habitat restrictions, which are known to shape reproductive behavior. RESULTS: We used a comparative genomic approach to build consensus evolutionary trees that portray the selective pressure acting on the male reproductive genes in these lineages. Such trees reflect the long and divergent demographic history that led to an allopatric distribution of the Fusca, Morsitans, and Palpalis species groups. A dataset of over 1700 male reproductive genes remained conserved over the long evolutionary time scale (estimated at 26.7 million years) across the genomes of the six species. We suggest that this conservation may result from strong functional selective pressure on the male imposed by viviparity. It is noteworthy that more than half of these conserved genes are novel sequences that are unique to the Glossina genus and are candidates for selection in the different lineages. CONCLUSIONS: Tsetse flies represent a model to interpret the evolution and differentiation of male reproductive biology under different, but complementary, perspectives. In the light of viviparity, we must take into account that these genes are constrained by a post-fertilization arena for genomic conflicts created by viviparity and absent in ovipositing species. This constraint implies a continuous antagonistic co-evolution between the parental genomes, thus accelerating inter-population post-zygotic isolation and, ultimately, favoring speciation. Ecological restrictions that affect reproductive behavior may further shape such antagonistic co-evolution.

Electrophysiological Responses of the Mediterranean Fruit Fly, Ceratitis capitata, to the Cera Trap® Lure: Exploring Released Antennally-Active Compounds.

The Mediterranean fruit fly (medfly), Ceratitis capitata, is a worldwide pest of agriculture able to use olfactory cues to locate habitat, food sources, mates and oviposition sites. The sensitivity of medfly olfaction has been exploited to develop olfactory-based attractants that are currently important tools for detection, control and eradication of its populations. Among these is Cera Trap® (BIOIBERICA, S.A.U.), a cost-effective bait. Here we used coupled gas chromatography/electroantennographic detection (GC-EAD) and GC/mass spectrometry (GC-MS) approaches to characterize the medfly antennally-active compounds released by this lure. We identified GC peaks corresponding to chemicals belonging to six different classes including heterocyclic aromatic compounds, aliphatic alcohols, aldehydes, esters, sesquiterpene hydrocarbons, and aromatic alcohols. We tested ten potential candidate volatiles belonging to these classes and predicted to be emitted by the lure and found that they were eliciting electroantennographic responses in medfly adults. These results will help in unravelling the physiological mechanisms of odor perception in both sexes, especially in relation to Cera Trap® attractant activity, which in the field has been shown to be female-specific. These findings and their developments will ultimately expand the toolbox for medfly control in the field.

Transcribed sex-specific markers on the Y chromosome of the oriental fruit fly, Bactrocera dorsalis.

BACKGROUND: The Oriental fruit fly, Bactrocera dorsalis, is a highly polyphagous invasive species with a high reproductive potential. In many tropical and subtropical parts of the world it ranks as one of the major pests of fruits and vegetables. Due to its economic importance, genetic, cytogenetic, genomic and biotechnological approaches have been applied to understand its biology and to implement the Sterile Insect Technique, currently a part of area-wide control programmes against this fly. Its chromosome complement includes five pairs of autosomes and the sex chromosomes. The X and Y sex chromosomes are heteromorphic and the highly heterochromatic and degenerate Y harbours the male factor BdMoY. The characterization of the Y chromosome in this fly apart from elucidating its role as primary sex determination system, it is also of crucial importance to understand its role in male biology. The repetitive nature of the Y chromosome makes it challenging to sequence and characterise. RESULTS: Using Representational Difference Analysis, fluorescent in situ hybridisation on mitotic chromosomes and in silico genome resources, we show that the B. dorsalis Y chromosome harbours transcribed sequences of gyf, (typo-gyf) a homologue of the Drosophila melanogaster Gigyf gene, and of a non-LTR retrotransposon R1. Similar sequences are also transcribed on the X chromosome. Paralogues of the Gigyf gene are also present on the Y and X chromosomes of the related species B. tryoni. Another identified Y-specific repetitive sequence linked to BdMoY appears to be specific to B. dorsalis. CONCLUSIONS: Our random scan of the Y chromosome provides a broad picture of its general composition and represents a starting point for further applicative and evolutionary studies. The identified repetitive sequences can provide a useful Y-marking system for molecular karyotyping of single embryos. Having a robust diagnostic marker associated with BdMoY will facilitate studies on how BdMoY regulates the male sex determination cascade during the embryonic sex-determination window. The Y chromosome, despite its high degeneracy and heterochromatic nature, harbours transcribed sequences of typo-gyf that may maintain their important function in post-transcriptional mRNA regulation. That transcribed paralogous copies of Gigyf are present also on the X and that this genomic distribution is maintained also in B. tryoni raises questions on the evolution of sex chromosomes in Bactrocera and other tephritids.

Interpreting Morphological Adaptations Associated with Viviparity in the Tsetse Fly Glossina morsitans (Westwood) by Three-Dimensional Analysis.

Tsetse flies (genus Glossina), the sole vectors of African trypanosomiasis, are distinct from most other insects, due to dramatic morphological and physiological adaptations required to support their unique biology. These adaptations are driven by demands associated with obligate hematophagy and viviparous reproduction. Obligate viviparity entails intrauterine larval development and the provision of maternal nutrients for the developing larvae. The reduced reproductive capacity/rate associated with this biology results in increased inter- and intra-sexual competition. Here, we use phase contrast microcomputed tomography (pcMicroCT) to analyze morphological adaptations associated with viviparous biology. These include (1) modifications facilitating abdominal distention required during blood feeding and pregnancy, (2) abdominal and uterine musculature adaptations for gestation and parturition of developed larvae, (3) reduced ovarian structure and capacity, (4) structural features of the male-derived spermatophore optimizing semen/sperm delivery and inhibition of insemination by competing males and (5) structural features of the milk gland facilitating nutrient incorporation and transfer into the uterus. Three-dimensional analysis of these features provides unprecedented opportunities for examination and discovery of internal morphological features not possible with traditional microscopy techniques and provides new opportunities for comparative morphological analyses over time and between species.

Transcriptional variation of sensory-related genes in natural populations of Aedes albopictus.

BACKGROUND: The Asian tiger mosquito, Aedes albopictus, is a highly dangerous invasive vector of numerous medically important arboviruses including dengue, chikungunya and Zika. In four decades it has spread from tropical Southeast Asia to many parts of the world in both tropical and temperate climes. The rapid invasion process of this mosquito is supported by its high ecological and genetic plasticity across different life history traits. Our aim was to investigate whether wild populations, both native and adventive, also display transcriptional genetic variability for functions that may impact their biology, behaviour and ability to transmit arboviruses, such as sensory perception. RESULTS: Antennal transcriptome data were derived from mosquitoes from a native population from Ban Rai, Thailand and from three adventive Mediterranean populations: Athens, Greece and Arco and Trento from Italy. Clear inter-population differential transcriptional activity was observed in different gene categories related to sound perception, olfaction and viral infection. The greatest differences were detected between the native Thai and the Mediterranean populations. The two Italian populations were the most similar. Nearly one million quality filtered SNP loci were identified. CONCLUSION: The ability to express this great inter-population transcriptional variability highlights, at the functional level, the remarkable genetic flexibility of this mosquito species. We can hypothesize that the differential expression of genes, including those involved in sensory perception, in different populations may enable Ae. albopictus to exploit different environments and hosts, thus contributing to its status as a global vector of arboviruses of public health importance. The large number of SNP loci present in these transcripts represents a useful addition to the arsenal of high-resolution molecular markers and a resource that can be used to detect selective pressure and adaptive changes that may have occurred during the colonization process.

Tracing temporal and geographic distribution of resistance to pyrethroids in the arboviral vector Aedes albopictus.

BACKGROUND: The arboviral vector Aedes albopictus became established on all continents except Antarctica in the past 50 years. A consequence of its rapid global invasion is the transmission of diseases previously confined to the tropics and subtropics occurring in temperate regions of the world, including the re-emergence of chikungunya and dengue in Europe. Application of pyrethroids is among the most widely-used interventions for vector control, especially in the presence of an arboviral outbreak. Studies are emerging that reveal phenotypic resistance and monitor mutations at the target site, the para sodium channel gene, primarily on a local scale. METHODS: A total of 512 Ae. albopictus mosquitoes from twelve geographic sites, including those from the native home range and invaded areas, were sampled between 2011 and 2018, and were analyzed at five codons of the para sodium channel gene with mutations predictive of resistance phenotype. Additionally, to test for the origin of unique kdr mutations in Mexico, we analyzed the genetic connectivity of southern Mexico mosquitoes with mosquitoes from home range, the Reunion Island, America and Europe. RESULTS: We detected mutations at all tested positions of the para sodium channel gene, with heterozygotes predominating and rare instance of double mutants. We observed an increase in the distribution and frequency of F1534C/L/S mutations in the ancestral China population and populations in the Mediterranean Greece, the appearance of the V1016G/I mutations as early as 2011 in Italy and mutations at position 410 and 989 in Mexico. The analyses of the distribution pattern of kdr alleles and haplotype network analyses showed evidence for multiple origins of all kdr mutations. CONCLUSIONS: Here we provide the most-up-to-date survey on the geographic and temporal distribution of pyrethroid-predictive mutations in Ae. albopictus by combining kdr genotyping on current and historical samples with published data. While we confirm low levels of pyrethroid resistance in most analyzed samples, we find increasing frequencies of F1534C/S and V1016G in China and Greece or Italy, respectively. The observed patterns of kdr allele distribution support the hypothesis that on site emergence of resistance has contributed more than spread of resistance through mosquito migration/invasions to the current widespread of kdr alleles, emphasizing the importance of local surveillance programs and resistance management.

Species-specific transcriptional profiles of the gut and gut microbiome of Ceratitis quilicii and Ceratitis rosa sensu stricto.

The fruit fly species, Ceratitis rosa sensu stricto and Ceratitis quilicii, are sibling species restricted to the lowland and highland regions, respectively. Until recently, these sibling species were considered as allopatric populations of C. rosa with distinct bionomics. We used deep Next Generation Sequencing (NGS) technology on intact guts of individuals from the two sibling species to compare their transcriptional profiles and simultaneously understand gut microbiome and host molecular processes and identify distinguishing genetic differences between the two species. Since the genomes of both species had not been published previously, the transcriptomes were assembled de novo into transcripts. Microbe-specific transcript orthologs were separated from the assembly by filtering searches of the transcripts against microbe databases using OrthoMCL. We then used differential expression analysis of host-specific transcripts (i.e. those remaining after the microbe-specific transcripts had been removed) and microbe-specific transcripts from the two-sibling species to identify defining species-specific transcripts that were present in only one fruit fly species or the other, but not in both. In C. quilicii females, bacterial transcripts of Pectobacterium spp., Enterobacterium buttiauxella, Enterobacter cloacae and Klebsiella variicola were upregulated compared to the C. rosa s.s. females. Comparison of expression levels of the host transcripts revealed a heavier investment by C. quilicii (compared with C. rosa s.s.) in: immunity; energy production; cell proliferation; insecticide resistance; reproduction and proliferation; and redox reactions that are usually associated with responses to stress and degradation of fruit metabolites.

Comparative genomic analysis of six Glossina genomes, vectors of African trypanosomes.

BACKGROUND: Tsetse flies (Glossina sp.) are the vectors of human and animal trypanosomiasis throughout sub-Saharan Africa. Tsetse flies are distinguished from other Diptera by unique adaptations, including lactation and the birthing of live young (obligate viviparity), a vertebrate blood-specific diet by both sexes, and obligate bacterial symbiosis. This work describes the comparative analysis of six Glossina genomes representing three sub-genera: Morsitans (G. morsitans morsitans, G. pallidipes, G. austeni), Palpalis (G. palpalis, G. fuscipes), and Fusca (G. brevipalpis) which represent different habitats, host preferences, and vectorial capacity. RESULTS: Genomic analyses validate established evolutionary relationships and sub-genera. Syntenic analysis of Glossina relative to Drosophila melanogaster shows reduced structural conservation across the sex-linked X chromosome. Sex-linked scaffolds show increased rates of female-specific gene expression and lower evolutionary rates relative to autosome associated genes. Tsetse-specific genes are enriched in protease, odorant-binding, and helicase activities. Lactation-associated genes are conserved across all Glossina species while male seminal proteins are rapidly evolving. Olfactory and gustatory genes are reduced across the genus relative to other insects. Vision-associated Rhodopsin genes show conservation of motion detection/tracking functions and variance in the Rhodopsin detecting colors in the blue wavelength ranges. CONCLUSIONS: Expanded genomic discoveries reveal the genetics underlying Glossina biology and provide a rich body of knowledge for basic science and disease control. They also provide insight into the evolutionary biology underlying novel adaptations and are relevant to applied aspects of vector control such as trap design and discovery of novel pest and disease control strategies.

The Nix locus on the male-specific homologue of chromosome 1 in Aedes albopictus is a strong candidate for a male-determining factor.

BACKGROUND: Global concern over the rapid expansion of the Asian tiger mosquito, Aedes albopictus, and its vector competence has highlighted an urgent need to improve currently available population control methods, like the Sterile Insect Technique. Knowledge of the sex determination cascade is a prerequisite for the development of early-stage sexing systems. To this end, we have characterised the putative sex determination gene, Nix, in this species. In Aedes species the chromosome complement consists of three pairs of chromosomes. The sex determination alleles are linked to the smallest homomorphic chromosome. RESULTS: We identified the male-specific chromosome 1 of Ae. albopictus that carries the putative male-determining gene Nix. We have also characterised the complete genomic sequence of the Nix gene which is composed of two exons and a short intron. The gene displays different levels of intron retention during development. Comparison of DNA sequences covering most of the Nix gene from individuals across the species range revealed no polymorphism. CONCLUSIONS: Our characterisation of the Nix gene in Ae. albopictus represents an initial step in the analysis of the sex determination cascade in this species. We found evidence of intron retention (IR) in Nix. IR might play a role in regulating the expression of Nix during development. Our results provide the basis for the development of new genetic control strategies.

Larval Diet Affects Male Pheromone Blend in a Laboratory Strain of the Medfly, Ceratitis capitata (Diptera: Tephritidae).

The Mediterranean fruit fly (medfly) Ceratitis capitata is a polyphagous pest of fruits and crops with a worldwide distribution. Its ability to use different larval hosts may have multiple effects, including impacts on adult reproductive biology. The male sex pheromone, which plays a key role in attracting both other males to lekking arenas and females for mating, is a mixture of chemical compounds including esters, acids, alkanes and terpenes known to differ between laboratory strains and wild-type populations. The relationship between larval diet and adult pheromone composition remains unexplored. Here, we investigated the effect of larval diet, including laboratory media and fresh fruits, on the composition of the male pheromone mixture. Using Headspace Solid Phase Microextraction we collected the pheromone emitted by males reared as larvae on different substrates and found both qualitative and quantitative differences. A number of alkanes appeared to be typical of the pheromone of males reared on wheat bran-based larval medium, and these may be cuticular hydrocarbons involved in chemical communication. We also detected differences in pheromone composition related to adult male age, suggesting that variations in hormonal levels and/or adult diet could also play a role in determining the chemical profile emitted. Our findings highlight the plasticity of dietary responses of C. capitata, which may be important in determining the interactions of this pest with the environment and with conspecifics. These results also have applied relevance to increase the mating competitiveness of mass-reared C. capitata used in Sterile Insect Technique programs.

Current source density mapping of antennal sensory selectivity reveals conserved olfactory systems between tephritids and Drosophila.

Ecological specialization of insects involves the functional and morphological reshaping of olfactory systems. Little is known about the degree to which insect sensitivity to odorant compounds is conserved between genera, tribes, or families. Here we compared the olfactory systems of six tephritid fruit fly species spanning two tribes and the distantly related Drosophila melanogaster at molecular, functional, and morphological levels. Olfaction in these flies is mediated by a set of olfactory receptors (ORs) expressed in different functional classes of neurons located in distinct antennal regions. We performed a phylogenetic analysis that revealed both family-specific OR genes and putative orthologous OR genes between tephritids and Drosophila. With respect to function, we then used a current source density (CSD) analysis to map activity across antennae. Functional maps mirrored the intrinsic structure of antennae observed with scanning electron microscopy. Together, the results revealed partial conservation of the olfactory systems between tephritids and Drosophila. We also demonstrate that the mapping of olfactory responses is necessary to decipher antennal sensory selectivity to olfactory compounds. CSD analysis can be easily applied to map antennae of other species and therefore enables the rapid deriving of olfactory maps and the reconstructing of the target organisms' history of evolution.

Genetic evidence for a worldwide chaotic dispersion pattern of the arbovirus vector, Aedes albopictus.

BACKGROUND: Invasive species represent a global concern for their rapid spread and the possibility of infectious disease transmission. This is the case of the global invader Aedes albopictus, the Asian tiger mosquito. This species is a vector of medically important arboviruses, notably chikungunya (CHIKV), dengue (DENV) and Zika (ZIKV). The reconstruction of the complex colonization pattern of this mosquito has great potential for mitigating its spread and, consequently, disease risks. METHODOLOGY/PRINCIPAL FINDINGS: Classical population genetics analyses and Approximate Bayesian Computation (ABC) approaches were combined to disentangle the demographic history of Aedes albopictus populations from representative countries in the Southeast Asian native range and in the recent and more recently colonized areas. In Southeast Asia, the low differentiation and the high co-ancestry values identified among China, Thailand and Japan indicate that, in the native range, these populations maintain high genetic connectivity, revealing their ancestral common origin. China appears to be the oldest population. Outside Southeast Asia, the invasion process in La Réunion, America and the Mediterranean Basin is primarily supported by a chaotic propagule distribution, which cooperates in maintaining a relatively high genetic diversity within the adventive populations. CONCLUSIONS/SIGNIFICANCE: From our data, it appears that independent and also trans-continental introductions of Ae. albopictus may have facilitated the rapid establishment of adventive populations through admixture of unrelated genomes. As a consequence, a great amount of intra-population variability has been detected, and it is likely that this variability may extend to the genetic mechanisms controlling vector competence. Thus, in the context of the invasion process of this mosquito, it is possible that both population ancestry and admixture contribute to create the conditions for the efficient transmission of arboviruses and for outbreak establishment.

The Worldwide Spread of the Tiger Mosquito as Revealed by Mitogenome Haplogroup Diversity.

In the last 40 years, the Asian tiger mosquito Aedes albopictus, indigenous to East Asia, has colonized every continent except Antarctica. Its spread is a major public health concern, given that this species is a competent vector for numerous arboviruses, including those causing dengue, chikungunya, West Nile, and the recently emerged Zika fever. To acquire more information on the ancestral source(s) of adventive populations and the overall diffusion process from its native range, we analyzed the mitogenome variation of 27 individuals from representative populations of Asia, the Americas, and Europe. Phylogenetic analyses revealed five haplogroups in Asia, but population surveys appear to indicate that only three of these (A1a1, A1a2, and A1b) were involved in the recent worldwide spread. We also found out that a derived lineage (A1a1a1) within A1a1, which is now common in Italy, most likely arose in North America from an ancestral Japanese source. These different genetic sources now coexist in many of the recently colonized areas, thus probably creating novel genomic combinations which might be one of the causes of the apparently growing ability of A. albopictus to expand its geographical range.

Genetic diversity and population structure in Bactrocera correcta (Diptera: Tephritidae) inferred from mtDNA cox1 and microsatellite markers.

Bactrocera correcta is one of the most destructive pests of horticultural crops in tropical and subtropical regions. Despite the economic risk, the population genetics of this pest have remained relatively unexplored. This study explores population genetic structure and contemporary gene flow in B. correcta in Chinese Yunnan Province and attempts to place observed patterns within the broader geographical context of the species' total range. Based on combined data from mtDNA cox1 sequences and 12 microsatellite loci obtained from 793 individuals located in 7 countries, overall genetic structuring was low. The expansion history of this species, including likely human-mediated dispersal, may have played a role in shaping the observed weak structure. The study suggested a close relationship between Yunnan Province and adjacent countries, with evidence for Western and/or Southern Yunnan as the invasive origin of B. correcta within Yunnan Province. The information gleaned from this analysis of gene flow and population structure has broad implications for quarantine, trade and management of this pest, especially in China where it is expanding northward. Future studies should concentrate effort on sampling South Asian populations, which would enable better inferences of the ancestral location of B. correcta and its invasion history into and throughout Asia.

Sperm-less males modulate female behaviour in Ceratitis capitata (Diptera: Tephritidae).

In the Mediterranean fruit fly, Ceratitis capitata (Wiedemann)(Diptera: Tephritidae), mating has a strong impact on female biology, leading to a decrease in sexual receptivity and increased oviposition and fecundity. Previous studies suggest that sperm transfer may play a role in inducing these behavioural changes. Here we report the identification of a medfly innexin gene, Cc-inx5, whose expression is limited to the germ-line of both sexes. Through RNA interference of this gene, we generated males without testes and, consequently, sperm, but apparently retaining all the other reproductive organs intact. These sperm-less males were able to mate and, like their wild-type counterparts, to induce in their partners increased oviposition rates and refractoriness to remating. Interestingly, matings to sperm-less males results in oviposition rates higher than those induced by copulation with control males. In addition, the observed female post-mating behavioural changes were congruent with changes in transcript abundance of genes known to be regulated by mating in this species. Our results suggest that sperm transfer is not necessary to reduce female sexual receptivity and to increase oviposition and fecundity. These data pave the way to a better understanding of the role/s of seminal components in modulating female post-mating responses. In the long term, this knowledge will be the basis for the development of novel approaches for the manipulation of female fertility, and, consequently, innovative tools to be applied to medfly control strategies in the field.

The whole genome sequence of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), reveals insights into the biology and adaptive evolution of a highly invasive pest species.

BACKGROUND: The Mediterranean fruit fly (medfly), Ceratitis capitata, is a major destructive insect pest due to its broad host range, which includes hundreds of fruits and vegetables. It exhibits a unique ability to invade and adapt to ecological niches throughout tropical and subtropical regions of the world, though medfly infestations have been prevented and controlled by the sterile insect technique (SIT) as part of integrated pest management programs (IPMs). The genetic analysis and manipulation of medfly has been subject to intensive study in an effort to improve SIT efficacy and other aspects of IPM control. RESULTS: The 479 Mb medfly genome is sequenced from adult flies from lines inbred for 20 generations. A high-quality assembly is achieved having a contig N50 of 45.7 kb and scaffold N50 of 4.06 Mb. In-depth curation of more than 1800 messenger RNAs shows specific gene expansions that can be related to invasiveness and host adaptation, including gene families for chemoreception, toxin and insecticide metabolism, cuticle proteins, opsins, and aquaporins. We identify genes relevant to IPM control, including those required to improve SIT. CONCLUSIONS: The medfly genome sequence provides critical insights into the biology of one of the most serious and widespread agricultural pests. This knowledge should significantly advance the means of controlling the size and invasive potential of medfly populations. Its close relationship to Drosophila, and other insect species important to agriculture and human health, will further comparative functional and structural studies of insect genomes that should broaden our understanding of gene family evolution.