Symbiosis and insect diversification: an ancient symbiont of sap-feeding insects from the bacterial phylum Bacteroidetes

Several insect groups have obligate, vertically transmitted bacterial symbionts that provision hosts with nutrients that are limiting in the diet. Some of these bacteria have been shown to descend from ancient infections. Here we show that the large group of related insects including cicadas, leafhoppers, treehoppers, spittlebugs, and planthoppers host a distinct clade of bacterial symbionts. This newly described symbiont lineage belongs to the phylum Bacteroidetes. Analyses of 16S rRNA genes indicate that the symbiont phylogeny is completely congruent with the phylogeny of insect hosts as currently known. These results support the ancient acquisition of a symbiont by a shared ancestor of these insects, dating the original infection to at least 260 million years ago. As visualized in a species of spittlebug (Cercopoidea) and in a species of sharpshooter (Cicadellinae), the symbionts have extraordinarily large cells with an elongate shape, often more than 30 mum in length; in situ hybridizations verify that these correspond to the phylum Bacteroidetes. "Candidatus Sulcia muelleri" is proposed as the name of the new symbiont.     

Intracellular symbionts of sharpshooters (Insecta: Hemiptera: Cicadellinae) form a distinct clade with a small genome

The leafhoppers (Insecta: Hemiptera: Cicadellidae) are the most species-rich group of invertebrates in which intracellular symbionts are usual. Here we present the first molecular characterization of bacteriome-associates in the leafhoppers, with focus on the subfamily Cicadellinae (sharpshooters). Phylogenetic analyses of 16S rDNA sequences from intracellular symbionts residing in the bacteriomes of five host species indicate that these symbionts form a well-defined clade within the gamma-3 Proteobacteria, consistent with an ancient colonization and strict vertical transmission. More extensive gene sequence information is reported for the symbiont of Homalodisca coagulata (Say). The genome size, as determined by pulsed field gel electrophoresis, is approximately 680 kb. This finding, when combined with published results for symbionts of aphids, ants, psyllids and tsetse flies, adds to an emerging pattern which suggests that bacteriome associates often descend from ancient infections by gamma Proteobacteria, and that these lineages have undergone pronounced genome reduction. A new genus and species name, 'Candidatus Baumannia cicadellinicola' (sp. nov.) is proposed for this newly characterized clade of symbiotic bacteria.     

Symbiosis and Insect Diversification: an Ancient Symbiont of Sap-Feeding Insects from the Bacterial Phylum Bacteroidetes

Several insect groups have obligate, vertically transmitted bacterial symbionts that provision hosts with nutrients that are limiting in the diet. Some of these bacteria have been shown to descend from ancient infections. Here we show that the large group of related insects including cicadas, leafhoppers, treehoppers, spittlebugs, and planthoppers host a distinct clade of bacterial symbionts. This newly described symbiont lineage belongs to the phylum Bacteroidetes. Analyses of 16S rRNA genes indicate that the symbiont phylogeny is completely congruent with the phylogeny of insect hosts as currently known. These results support the ancient acquisition of a symbiont by a shared ancestor of these insects, dating the original infection to at least 260 million years ago. As visualized in a species of spittlebug (Cercopoidea) and in a species of sharpshooter (Cicadellinae), the symbionts have extraordinarily large cells with an elongate shape, often more than 30 μm in length; in situ hybridizations verify that these correspond to the phylum Bacteroidetes. “Candidatus Sulcia muelleri” is proposed as the name of the new symbiont.     

Bacteriome-associated endosymbionts of the green rice leafhopper <Emphasis Type="Italic">Nephotettix cincticeps</Emphasis> (Hemiptera: Cicadellidae)

The green rice leafhopper Nephotettix cincticeps (Uhler) is a commonly distributed pest of rice in East Asia. Early histological studies describe the presence of two bacteriome-associated symbionts and a rickettsial microorganism in N. cincticeps, but their microbiological affiliations have been elusive. We identified these bacterial symbionts using modern microbiological techniques. Cloning and sequencing of the 16S ribosomal RNA gene from dissected bacteriomes yielded two major and a minor bacterial sequences: a major sequence was placed in the Bacteroidetes clade of Sulcia muelleri, an ancient symbiont lineage associated with diverse hemipteran insects; another major sequence was allied to a β-proteobacterial sequence from a leafhopper Matsumuratettix hiroglyphicus; the minor sequence fell in the α-proteobacterial genus Rickettsia. In situ hybridization and transmission electron microscopy showed that the Sulcia symbiont and the β-proteobacterial symbiont are harbored within different types of bacteriocytes that constitute the outer and inner regions of the bacteriome, respectively. Oral administration of tetracycline to nymphal N. cincticeps resulted in retarded growth, high mortality rates, and failure in adult emergence, suggesting important biological roles of the symbionts for the host insect. The designation Candidatus Nasuia deltocephalinicola is proposed for the β-proteobacterial symbiont clade associated with N. cincticeps and allied leafhoppers of the subfamily Deltocephalinae.     

Two ancient bacterial endosymbionts have coevolved with the planthoppers (Insecta: Hemiptera: Fulgoroidea)

ABSTRACT: BACKGROUND: Members of the hemipteran suborder Auchenorrhyncha (commonly known as planthoppers, tree- and leafhoppers, spittlebugs, and cicadas) are unusual among insects known to harbor endosymbiotic bacteria in that they are associated with diverse assemblages of bacterial endosymbionts. Early light microscopic surveys of species representing the two major lineages of Auchenorrhyncha (the planthopper superfamily Fulgoroidea; and Cicadomorpha, comprising Membracoidea [tree- and leafhoppers], Cercopoidea [spittlebugs], and Cicadoidea [cicadas]), found that most examined species harbored at least two morphologically distinct bacterial endosymbionts, and some harbored as many as six. Recent investigations using molecular techniques have identified multiple obligate bacterial endosymbionts in Cicadomorpha; however, much less is known about endosymbionts of Fulgoroidea. In this study, we present the initial findings of an ongoing PCR-based survey (sequencing 16S rDNA) of planthopper-associated bacteria to document endosymbionts with a long-term history of codiversification with their fulgoroid hosts. RESULTS: Results of PCR surveys and phylogenetic analyses of 16S rDNA recovered a monophyletic clade of Betaproteobacteria associated with planthoppers; this clade included Vidania fulgoroideae, a recently described bacterium identified in exemplars of the planthopper family Cixiidae. We surveyed 77 planthopper species representing 18 fulgoroid families, and detected Vidania in 40 species (representing 13 families). Further, we detected the Sulcia endosymbiont (identified as an obligate endosymbiont of Auchenorrhyncha in previous studies) in 30 of the 40 species harboring Vidania. Concordance of the Vidania phylogeny with the phylogeny of the planthopper hosts (reconstructed based on sequence data from five genes generated from the same insect specimens from which the bacterial sequences were obtained) was supported by statistical tests of codiversification. Codiversification tests also supported concordance of the Sulcia phylogeny with the phylogeny of the planthopper hosts, as well as concordance of planthopper-associated Vidania and Sulcia phylogenies. CONCLUSIONS: Our results indicate that the Betaproteobacterium Vidania is an ancient endosymbiont that infected the common ancestor of Fulgoroidea at least 130 million years ago. Comparison of our findings with the early light-microscopic surveys conducted by Muller suggests that Vidania is Muller's x-symbiont, which he hypothesized to have codiversified with most lineages of planthoppers and with the Sulcia endosymbiont.     

Candidates for symbiotic control of sugarcane white leaf disease

The leafhopper Matsumuratettix hiroglyphicus (Matsumura) is the most important vector of a phytoplasma pathogen causing sugarcane white leaf (SCWL) disease. The purpose of this study was to evaluate candidate bacterial symbionts for possible use as vehicles in the control of the disease. 16S rRNA bacterial genes were amplified from whole bodies of M. hiroglyphicus leafhoppers and analyzed by cloning and sequencing. Two dominant groups were found: one belonged to the Betaproteobacteria that did not closely match any sequences in the database and was named bacterium associated with M. hiroglyphicus (BAMH). Another one found to be abundant in this leafhopper is "Candidatus Sulcia muelleri" in the order Bacteroidetes, which was previously reported in the insect members of the Auchenorrhyncha. Most M. hiroglyphicus leafhoppers carry both BAMH and "Ca. Sulcia muelleri." Fluorescent in situ hybridization showed that BAMH and "Ca. Sulcia muelleri" colocalized in the same bacteriomes. BAMH was present in the midgut and ovaries of the leafhopper and was found in all developmental stages, including eggs, nymphs, and adults. Because BAMH appears to be specific for the SCWL vector, we evaluated it as a candidate for symbiotic control of sugarcane white leaf disease.     

New bacterium symbiont in the bacteriome of the leafhopper Yamatotettix flavovittatus Matsumura

The leafhopper Yamatotettix flavovittatus Matsumura is the vector of the phytoplasma pathogen that causes white leaf disease in sugarcane crops. This study aimed to identify the bacterial symbionts associated with Y. flavovittatus by amplifying, cloning, and sequencing their 16S rRNA genes. Two types of bacteria were present; one is Candidatus Sulcia muelleri (Bacteroidetes), a well-known ancient primary symbiont found in a diverse range of insects in Auchenorrhyncha suborder. The other is a member of Gammaproteobacteria that differed from all other members deposited in the GenBank database and was therefore named Candidatus Yamatotia cicadellidicola. These bacteria were present throughout the leafhopper life cycle and were found in 100% of the natural host populations examined. Fluorescent in situ hybridization analysis revealed that these bacteria were co-localized in the same bacteriome and present in the full-grown oocyte. Our main finding suggests the Ca. Y. cicadellidicola is a new type of symbiont that co-occurs with Ca. S. muelleri in the leafhopper Y. flavovittatus (Deltocephalinae subfamily).     

Metabolic complementarity and genomics of the dual bacterial symbiosis of sharpshooters

Mutualistic intracellular symbiosis between bacteria and insects is a widespread phenomenon that has contributed to the global success of insects. The symbionts, by provisioning nutrients lacking from diets, allow various insects to occupy or dominate ecological niches that might otherwise be unavailable. One such insect is the glassy-winged sharpshooter (Homalodisca coagulata), which feeds on xylem fluid, a diet exceptionally poor in organic nutrients. Phylogenetic studies based on rRNA have shown two types of bacterial symbionts to be coevolving with sharpshooters: the gamma-proteobacterium Baumannia cicadellinicola and the Bacteroidetes species Sulcia muelleri. We report here the sequencing and analysis of the 686,192–base pair genome of B. cicadellinicola and approximately 150 kilobase pairs of the small genome of S. muelleri, both isolated from H. coagulata. Our study, which to our knowledge is the first genomic analysis of an obligate symbiosis involving multiple partners, suggests striking complementarity in the biosynthetic capabilities of the two symbionts: B. cicadellinicola devotes a substantial portion of its genome to the biosynthesis of vitamins and cofactors required by animals and lacks most amino acid biosynthetic pathways, whereas S. muelleri apparently produces most or all of the essential amino acids needed by its host. This finding, along with other results of our genome analysis, suggests the existence of metabolic codependency among the two unrelated endosymbionts and their insect host. This dual symbiosis provides a model case for studying correlated genome evolution and genome reduction involving multiple organisms in an intimate, obligate mutualistic relationship. In addition, our analysis provides insight for the first time into the differences in symbionts between insects (e.g., aphids) that feed on phloem versus those like H. coagulata that feed on xylem. Finally, the genomes of these two symbionts provide potential targets for controlling plant pathogens such as Xylella fastidiosa, a major agroeconomic problem, for which H. coagulata and other sharpshooters serve as vectors of transmission.     

Characterization and evolution of two bacteriome‐inhabiting symbionts in cixiid planthoppers (Hemiptera: Fulgoromorpha: Pentastirini)

Like other plant sap‐sucking insects, planthoppers within the family Cixiidae (Insecta: Hemiptera: Fulgoromorpha) host a diversified microbiota. We report the identification and first molecular characterization of symbiotic bacteria in cixiid planthoppers (tribe: Pentastirini). Using universal eubacterial primers we first screened the eubacterial 16S rRNA sequences in Pentastiridius leporinus (Linnaeus) with PCR amplification, cloning, and restriction fragment analysis. We identified three main 16S rRNA sequences that corresponded to a Wolbachia bacterium, a plant pathogenic bacterium, and a novel gammaproteobacterial symbiont. A fourth bacterial species affiliated with ‘Candidatus Sulcia muelleri’ was detected in PCR assays using primers specific for the Bacteroidetes. Within females of two selected cixiid planthoppers, P. leporinus and Oliarus filicicola, fluorescence In situ hybridization analysis and transmission electron microscopy observations showed that ‘Ca. Sulcia muelleri’ and the novel gammaproteobacterial symbiont were housed in separate bacteriomes. Phylogenetic analysis revealed that both of these symbionts occurred in at least four insect genera within the tribe Pentastirini. ‘Candidatus Purcelliella pentastirinorum’ was proposed as the novel gammaproteobacterial symbiont.     

Band‐aids for Buchnera and B vitamins for all

Evolution lacks foresight, and hence, key adaptations may produce major challenges over the long run. The natural world is rife with examples of long‐term ‘side effects’ associated with quick‐fix tinkering, including blind spots in vertebrate eyes. An important question is how nature compensates for imperfections once evolution has set a course. The symbioses associated with sap‐feeding insects present a fascinating opportunity to address this issue. On one hand, the substantial diversity and biomass of sap‐feeding insects are largely due to ancient acquisitions of nutrient‐provisioning bacterial symbionts. Yet, the insularity and small population sizes enforced by intracellular life and strict maternal transfer inevitably result in the degradation of symbiont genomes and, often, the beneficial services that symbionts provide. Stabilization through lateral transfer of bacterial genes into the host nucleus (often from exogenous sources) or replacement of the long‐standing symbiont with a new partner are potential solutions to this evolutionary dilemma (Bennett & Moran 2015 ). A third solution is adoption of a cosymbiont that compensates for specific losses in the original resident. Ancient ‘co‐obligate’ symbiont pairs in mealybugs, leafhoppers, cicadas and spittlebugs show colocalization, codiversification, metabolite exchange and generally nonredundant nutrient biosynthesis (Bennett & Moran 2015 ). But in this issue, Meseguer et al. ( 2017 ) report on a different flavour of cosymbiosis among conifer‐feeding Cinara aphids.     

Host-plants shape insect diversity: Phylogeny, origin, and species diversity of native Hawaiian leafhoppers (Cicadellidae: Nesophrosyne)

Herbivorous insects and the plants on which they specialize, represent the most abundant terrestrial life on earth, yet their inter-specific interactions in promoting species diversification remains unclear. This study utilizes the discreet geologic attributes of Hawai'i and one of the most diverse endemic herbivore radiations, the leafhoppers (Hemiptera: Cicadellidae: Nesophrosyne), as a model system to understand the role of host-plant use in insect diversification. A comprehensive phylogeny is reconstructed to examine the origins, species diversification, and host-plant use of the native Hawaiian leafhoppers. Results support a monophyletic Nesophrosyne, originating from the Western Pacific basin, with a sister-group relationship to the genus Orosius. Nesophrosyne is characterized by high levels of endemicity according to individual islands, volcanoes, and geologic features. Clades demonstrate extensive morphologically cryptic diversity among allopatric species, utilizing widespread host-plant lineages. Nesophrosyne species are host-plant specific, demonstrating four dominant patterns of specialization that shape species diversification: (1) diversification through host switching; (2) specialization on widespread hosts with allopatric speciation; (3) repeated, independent shifts to the same hosts; and, (4) absence or low abundance on some host. Finally, evidence suggests competing herbivore radiations limit ecological opportunity for diversifying insect herbivores. Results provide evolutionary insights into the mechanisms that drive and shape this biodiversity.     

Influence of host phylogeographic patterns and incomplete lineage sorting on within-species genetic variability in Wigglesworthia species, obligate symbionts of tsetse flies

Vertical transmission of obligate symbionts generates a predictable evolutionary history of symbionts that reflects that of their hosts. In insects, evolutionary associations between symbionts and their hosts have been investigated primarily among species, leaving population-level processes largely unknown. In this study, we investigated the tsetse (Diptera: Glossinidae) bacterial symbiont, Wigglesworthia glossinidia, to determine whether observed codiversification of symbiont and tsetse host species extends to a single host species (Glossina fuscipes fuscipes) in Uganda. To explore symbiont genetic variation in G. f. fuscipes populations, we screened two variable loci (lon and lepA) from the Wigglesworthia glossinidia bacterium in the host species Glossina fuscipes fuscipes (W. g. fuscipes) and examined phylogeographic and demographic characteristics in multiple host populations. Symbiont genetic variation was apparent within and among populations. We identified two distinct symbiont lineages, in northern and southern Uganda. Incongruence length difference (ILD) tests indicated that the two lineages corresponded exactly to northern and southern G. f. fuscipes mitochondrial DNA (mtDNA) haplogroups (P = 1.0). Analysis of molecular variance (AMOVA) confirmed that most variation was partitioned between the northern and southern lineages defined by host mtDNA (85.44%). However, ILD tests rejected finer-scale congruence within the northern and southern populations (P = 0.009). This incongruence was potentially due to incomplete lineage sorting that resulted in novel combinations of symbiont genetic variants and host background. Identifying these novel combinations may have public health significance, since tsetse is the sole vector of sleeping sickness and Wigglesworthia is known to influence host vector competence. Thus, understanding the adaptive value of these host-symbiont combinations may afford opportunities to develop vector control methods.     

Microbiome responses during virulence adaptation by a phloem‐feeding insect to resistant near‐isogenic rice lines

The microbiomes of phloem‐feeding insects include functional bacteria and yeasts essential for herbivore survival and development. Changes in microbiome composition are implicated in virulence adaptation by herbivores to host plant species or host populations (including crop varieties). We examined patterns in adaptation by the green leafhopper, Nephotettix virescens, to near‐isogenic rice lines (NILs) with one or two resistance genes and the recurrent parent T65, without resistance genes. Only the line with two resistance genes was effective in reducing leafhopper fitness. After 20 generations on the resistant line, selected leafhoppers attained similar survival, weight gain, and egg laying to leafhoppers that were continually reared on the susceptible recurrent parent, indicating that they had adapted to the resistant host. By sequencing the 16s rRNA gene, we described the microbiome of leafhoppers from colonies associated with five collection sites, and continually reared or switched between NILs. The microbiomes included 69–119 OTUs of which 44 occurred in ≥90% of samples. Of these, 14 OTUs were assigned to the obligate symbiont Candidatus sulcia clade. After 20 generations of selection, collection site had a greater effect than host plant on microbiome composition. Six bacteria genera, including C. sulcia, were associated with leafhopper virulence. However, there was significant within‐treatment, site‐related variability in the prevalence of these taxa such that the mechanisms underlying their association with virulence remain to be determined. Our results imply that these taxa are associated with leafhopper nutrition. Ours is the first study to describe microbiome diversity and composition in rice leafhoppers. We discuss our results in light of the multiple functions of herbivore microbiomes during virulence adaptation in insect herbivores.     

Symbiont-mediated adaptation by planthoppers and leafhoppers to resistant rice varieties

For over 50 years, host plant resistance has been the principal focus of public research to reduce planthopper and leafhopper damage to rice in Asia. Several resistance genes have been identified from native varieties and wild rice species, and some of these have been incorporated into high-yielding rice varieties through conventional breeding. However, adaptation by hoppers to resistant rice has been phenomenally rapid, and hopper populations with virulence against several resistance genes are now widespread. Directional genetic selection for virulent hoppers seems unlikely given the rapid pace of adaptation reported from field and laboratory studies. Among the alternative explanations for rapid hopper adaptation are changes (genetic, epigenetic, or community structure) in endosymbiont communities that become advantageous for planthoppers and leafhoppers that feed on resistant rice varieties. This review examines the nature of these symbiont communities and their functions in planthoppers and leafhoppers—focusing on their likely roles in mediating adaptation to plant resistance. Evidence from a small number of experimental studies suggests that bacterial and eukaryotic (including yeast-like) symbionts can determine or mediate hopper virulence on rice plants and that symbiont functions could change over successive generations of selection on both resistant and susceptible plants. The review highlights the potential complexity of rice hopper–symbiont interactions and calls for a more careful choice of research materials and methods to help reduce this complexity. Finally, the consequences of symbiont-mediated virulence adaptation for future rice breeding programs are discussed.     

Host selection by Homalodisca vitripennis: the interplay between feeding, egg maturation, egg load, and oviposition

For some phytophagous insects, egg maturation may be dependent on adult feeding. Accordingly, rates of egg maturation may be dependent on the quality and quantity of available food sources. In turn, oviposition behavior could be affected by diet quality via changes in egg load (number of mature eggs carried by a female). Experiments were conducted to determine whether adult feeding may affect oviposition behavior of the glassy-winged sharpshooter, Homalodisca vitripennis. No-choice tests demonstrated that eggs accumulated in glassy-winged sharpshooter abdomens as time since last oviposition increased largely as a function of feeding plant species. In choice tests, glassy-winged sharpshooter females were observed most frequently on the plant species that imparted the greatest egg maturation rate in no-choice tests. Direct tests of the effects of egg load on glassy-winged sharpshooter oviposition behavior found that females were more likely to deposit eggs as egg load increased. Similarly, acceptance of a low-ranked oviposition plant species by female glassy-winged sharpshooters increased with egg load and time since last oviposition. The results indicate that adult feeding affected glassy-winged sharpshooter egg maturation, plant species varied in quality for providing nutrients for egg maturation, and egg load affected oviposition behavior. Thus, the quantity and quality of available feeding plant species may affect glassy-winged sharpshooter egg maturation rates, which in turn may affect the plant species female glassy-winged sharpshooters select for oviposition.     

A specific mix of generalists: bacterial symbionts in Mediterranean Ircinia spp

Microbial symbionts form abundant and diverse components of marine sponge holobionts, yet the ecological and evolutionary factors that dictate their community structure are unresolved. Here, we characterized the bacterial symbiont communities of three sympatric host species in the genus Ircinia from the NW Mediterranean Sea, using electron microscopy and replicated 16S rRNA gene sequence clone libraries. All Ircinia host species harbored abundant and phylogenetically diverse symbiont consortia, comprised primarily of sequences related to other sponge-derived microorganisms. Community-level analyses of bacterial symbionts revealed host species-specific genetic differentiation and structuring of Ircinia-associated microbiota. Phylogenetic analyses of host sponges showed a close evolutionary relationship between Ircinia fasciculata and Ircinia variabilis, the two host species exhibiting more similar symbiont communities. In addition, several bacterial operational taxonomic units were shared between I.?variabilis and Ircinia oros, the two host species inhabiting semi-sciophilous communities in more cryptic benthic habitats, and absent in I.?fasciculata, which occurs in exposed, high-irradiance habitats. The generalist nature of individual symbionts and host-specific structure of entire communities suggest that: (1) a 'specific mix of generalists' framework applies to bacterial symbionts in Ircinia hosts and (2) factors specific to each host species contribute to the distinct symbiont mix observed in Ircinia hosts.     

Auchenorrhyncha-host plant interactions: leafhoppers and grasses

ABSTRACT.

• 1 Grass nutrient levels differed considerably between the grass species and with time.
• 2 Most species of leafhopper (Homoptera, Auchenorrhyncha) were present on all the grasses sampled but each grass had a different dominant leaf-hopper fauna.
• 3 The leafhopper—plant association varied depending on the leafhopper species. Species that were strongly associated with one host were rare. Other more oligophagous species were associated with a particular nitrogen level in the grass. These species were found on grasses that had nitrogen concentrations within a narrow range. As the plant nitrogen levels altered (associated with flowering, seed setting, and senescence) leafhoppers switched onto other food plants that had a suitable nitrogen level. An intermediate group of leafhoppers showed little specificity and little association with plant nitrogen levels.

     

Swapping symbionts in spittlebugs: evolutionary replacement of a reduced genome symbiont

Bacterial symbionts that undergo long-term maternal transmission experience elevated fixation of deleterious mutations, resulting in massive loss of genes and changes in gene sequences that appear to limit efficiency of gene products. Potentially, this dwindling of symbiont functionality impacts hosts that depend on these bacteria for nutrition. One evolutionary escape route is the acquisition of a novel symbiont with a robust genome and metabolic capabilities. Such an acquisition has occurred in an ancestor of Philaenus spumarius, the meadow spittlebug (Insecta: Cercopoidea), which has replaced its ancient association with the tiny genome symbiont Zinderia insecticola (Betaproteobacteria) with an association with a symbiont related to Sodalis glossinidius (Gammaproteobacteria). Spittlebugs feed exclusively on xylem sap, a diet that is low both in essential amino acids and in sugar or other substrates for energy production. The new symbiont genome has undergone proliferation of mobile elements resulting in many gene inactivations; nonetheless, it has selectively maintained genes replacing functions of its predecessor for amino-acid biosynthesis. Whereas ancient symbiont partners typically retain perfectly complementary sets of amino-acid biosynthetic pathways, the novel symbiont introduces some redundancy as it retains some pathways also present in the partner symbionts (Sulcia muelleri). Strikingly, the newly acquired Sodalis-like symbiont retains genes underlying efficient routes of energy production, including a complete TCA cycle, potentially relaxing the severe energy limitations of the xylem-feeding hosts. Although evolutionary replacements of ancient symbionts are infrequent, they potentially enable evolutionary and ecological novelty by conferring novel metabolic capabilities to host lineages.     

Population fluctuation of sharpshooters vectors of Xylella fastidiosa Wells et al. in commercial citrus groves in northwestern Paraná State

The citrus variegated chlorosis (CVC), an important disease of citrus in Brazil, is caused by the bacterium Xylella fastidiosa Wells et al. and transmitted by xylem-feeding sharpshooters (Hemiptera: Cicadellidae). This study evaluated the fluctuation of populations of species of sharpshooters belonging to the tribes Cicadellini and Proconiini, from subfamily Cicadelinae, in a commercial sweet orange [Citrus sinensis (L.) Osb.] grove, located in the Northwest Region of Paraná State, Brazil, in four varieties: Valência, Natal, Pêra, and Folha Murcha. Sharpshooters population was monitored using yellow stick traps sampled at 15 day-intervals, in 24 traps, from November of 1999 to March of 2004. The most abundant species were Dilobopterus costalimai Young (tribe Cicadellini) and Acrogonia citrina Marucci & Cavichioli (tribe Proconiini). Both species were detected during the complete period studied, which is important because they have great potential for transmitting CVC. Thus, since more than a sharpshooter species were detected, more efforts are recommended to monitor and control these insects in citrus groves, aiming to reduce the dissemination of CVC.     

Do assortative mating and immigrant inviability help maintain population genetic structuring of an herbivore on a crop and a wild relative?

Population genetic structuring is common among herbivorous insects and frequently is associated with divergent host plants, such as crops and their wild relatives. Previous studies showed population genetic structuring in corn leafhopper Dulbulus maidis in Mexico, such that the species consists of two sympatric, host plant-associated populations: an abundant and widespread "pestiferous” population on maize (Zea mays mays), and a small and localized "wild" population on perennial teosinte (Zea diploperennis). a maize wild relative with a limited distribution. This study addressed whether assortative mating and immigrant inviability mediate genetic structuring of corn leafliopper by comparing the mating and reproductive successes of pestiferous and wild females that colonize their nonassociated host plants against the successes of females colonizing their associated host plants. Assortative mating was assessed by comparing mating frequencies and premating and mating times among females of each population on each host plant: immigrant inviability was assessed by comparing, across two generations, the fecundity, survival, development time, sex ratio, and population growth rate among leafhopper populations and host plants. Our results showed that on maize, and compared to resident, pestiferous females, wild females were more likely to mate, and greater proportions of their offspring survived to adult stage and were daughters;consequently, the per-generation population growth rate on maize was greater for immigrant, wild leafhoppers compared to resident, pestiferous leafhoppers. Our results suggested that wild leafhoppers emigrating to maize have a fitness advantage over resident, pestiferous leafhoppers, while immigrant pestiferous and resident wild leafhoppers on teosinte have similar fitnesses.