Evidence for the establishment of aphid-eubacterium endosymbiosis in an ancestor of four aphid families.

Aphids (superfamily Aphidoidea) contain eubacterial endosymbionts localized within specialized cells (mycetocytes). The endosymbionts are essential for the survival of the aphid hosts. Sequence analyses of the 16S rRNAs from endosymbionts of 11 aphid species from seven tribes and four families have indicated that the endosymbionts are monophyletic. Furthermore, phylogenetic relationships within the symbiont clade parallel the relationships of the corresponding aphid hosts. Our findings suggest that this endocytobiotic association was established in a common ancestor of the four aphid families with subsequent diversification into the present species of aphids and their endosymbionts.     

Infection dynamics of coexisting beta- and gammaproteobacteria in the nested endosymbiotic system of mealybugs

We investigated the infection dynamics of endosymbiotic bacteria in the developmental course of the mealybugs Planococcus kraunhiae and Pseudococcus comstocki. Molecular phylogenetic analyses identified a betaproteobacterium and a gammaproteobacterium from each of the mealybug species. The former bacterium was related to the beta-endosymbionts of other mealybugs, i.e., "Candidatus Tremblaya princeps," and formed a compact clade in the Betaproteobacteria. Meanwhile, the latter bacterium was related to the gamma-endosymbionts of other mealybugs but belonged to distinct clades in the Gammaproteobacteria. Whole-mount in situ hybridization confirmed the peculiar nested formation in the endosymbiotic system of the mealybugs: the beta-endosymbiont cells were present in the cytoplasm of the bacteriocytes, and the gamma-endosymbiont cells were located in the beta-endosymbiont cells. In nymphal and female development, a large oval bacteriome consisting of a number of bacteriocytes was present in the abdomen, wherein the endosymbionts were harbored. In male development, strikingly, the bacteriome progressively degenerated in prepupae and pupae and became almost unrecognizable in adult males. In the degeneration process, the gamma-endosymbionts disappeared more rapidly than the beta-endosymbionts did. Quantitative PCR analyses revealed that (i) the population dynamics of the endosymbionts in female development reflected the reproductive activity of the insects, (ii) the population dynamics of the endosymbionts were strikingly different between female development and male development, (iii) the endosymbiont populations drastically decreased in male development, and (iv) the gamma-endosymbiont populations decreased more rapidly than the beta-endosymbiont populations in male development. Possible mechanisms underlying the uncoupled regulation of the beta- and gamma-endosymbiont populations are discussed in relation to the establishment and evolution of this unique prokaryote-prokaryote endosymbiotic system.     

Phylogenetic characterization and molecular evolution of bacterial endosymbionts in psyllids (Hemiptera: Sternorrhyncha)

Most sternorrhynchan insects harbor endosymbiotic bacteria in specialized cells (bacteriocytes) near the gut which provide essential nutrients for hosts. In lineages investigated so far with molecular methods (aphids, mealybugs, whiteflies), endosymbionts apparently have arisen from independent infections of common host ancestors and co-speciated with their hosts. Some endosymbionts also exhibit putatively negative genetic effects from their symbiotic association. In this study, the identity of endosymbionts in one major sternorrhynchan lineage, psyllids (Psylloidea), was investigated to determine their position in eubacterial phylogeny and their relationship to other sternorrhynchan endosymbionts. Small-subunit ribosomal RNA genes (16S rDNA) from bacteria in three psyllid species (families Psyllidae and Triozidae) were sequenced and incorporated into an alignment including other insect endosymbionts and free-living bacteria. In phylogenetic analysis, all sequences were placed within the gamma subdivision of the Proteobacteria. Three sequences, one from each psyllid species, formed a highly supported monophyletic group whose branching order matched the host phylogeny, and also exhibited accelerated rates of evolution and mutational bias toward A and T nucleotides. These attributes, characteristic of primary (P) bacteriocyte-dwelling endosymbionts, suggested that these sequences were from the putative psyllid P endosymbiont. Two other sequences were placed within the gamma-3 subgroup of Proteobacteria and were hypothesized to be secondary endosymbionts. The analysis also suggested a sister relationship between P endosymbionts of psyllids and whiteflies. Thus, a continuous mutualistic association between bacteria and insects may have existed since the common ancestor of psyllids and whiteflies. Calculations using a universal substitution rate in bacteria corrected for endosymbiont rate acceleration support the idea that this common ancestor was also the ancestor of all Sternorrhyncha. Compared with other P endosymbiont lineages, the genetic consequences of intracellular life for some psyllid endosymbionts have been exaggerated, indicating possible differences in population structures of bacteria and/or hosts.     

Development of a multiplex PCR for identification of vineyard mealybugs

A simple molecular tool was developed and tested to identify seven mealybug species found in North American vineyards: Pseudococcus maritimus Ehrhorn, Pseudococcus viburni (Signoret), Pseudococcus longispinus (Targioni-Tozzeti), Pseudococcus calceolariae (Maskell), Planococcus ficus (Signoret), Planococcus citri (Risso), and Ferrisia gilli Gullan. The developed multiplex PCR is based on the mitochondrial cytochrome c oxidase subunit one gene. In tests, this single-step multiplex PCR correctly identified 95 of 95 mealybug samples, representing all seven species and collected from diverse geographic regions. To test the sensitivity, single specimen samples with different Pl. ficus developmental stages (egg to adult female and adult male) were processed PCR and the resulting output provided consistent positive identification. To test the utility of this protocol for adult males caught in sex baited pheromone traps, Pl. ficus adult males were placed in pheromone traps, aged at a constant temperature of 26±2°C, and processed with the multiplex each day thereafter for 8 d. Results showed consistent positive identification for up to 6 d (range, 6-8 d). Results are discussed with respect to the usefulness of this molecular tool for the identification of mealybugs in pest management programs and biosecurity of invasive mealybugs.     

Molecular systematics of aphids and their primary endosymbionts

Aphids constitute a monophyletic group within the order Homoptera (i.e., superfamily Aphidoidea). The Aphidoidea originated in the Jurassic about 150 my ago from some aphidiform ancestor whose origin can be traced back to about 250 my ago. They exhibit a mutualistic association with intracellular bacteria (Buchnera sp.) related to Escherichia coli. Buchnera is usually considered the aphids' primary endosymbiont. The association is obligate for both partners. The 16S rDNA-based phylogeny of Buchnera from four aphid families showed complete concordance with the morphology-based phylogeny of their aphid hosts, which pointed to a single original infection in a common ancestor of aphids some 100-250 my ago followed by cospeciation of aphids and Buchnera. This study concentrated on the molecular phylogeny of both the aphids and their primary endosymbionts of five aphid families including for the first time representatives of the family Lachnidae. We discuss results based on two Buchnera genes (16S rDNA and the beta subunit of the F-ATPase complex) and on one host mitochondrial gene (the subunit 6 of the F-ATPase complex). Although our data do not allow definitive evolutionary relationships to be established among the different aphid families, some traditionally accepted groupings are put into question from both bacterial and insect data. In particular, the Lachnidae and the Aphididae, which from morphological data are considered recently evolved sister groups, do not seem to be as closely related as is usually accepted. Finally, we discuss our results in the light of the proposed parallel evolution of aphids and their endosymbionts.     

中国进境水果携带粉蚧疫情分析(2013—2016)

【目的】中国是水果生产大国和进口大国。水果是最容易携带虫害的产品之一,粉蚧是口岸水果检疫过程中常发现的害虫类群,中国口岸每年从进境水果截获大量粉蚧。通过分析中国进境水果携带粉蚧疫情,可为一线口岸检疫查验提供指导,为相关部门开展产地检疫和口岸监测提供依据,以防止危险性粉蚧的传入,保障中国水果生产安全,促进国际水果贸易健康发展。【方法】通过FAO网站、动植物检验检疫信息资源共享服务平台、中国知网等收集中国进境水果贸易数据及其携带粉蚧疫情,统计分析了中国水果进口贸易情况、粉蚧截获情况以及截获粉蚧的种类、来源地、截获口岸和寄主。【结果】2013—2016年,中国口岸从进境水果上截获的昆虫中粉蚧科昆虫截获量最大,占47.31%;其中截获量前十的粉蚧种类为杰克贝尔氏粉蚧、木槿曼粉蚧、双条拂粉蚧、大洋臀纹粉蚧、南洋臀纹粉蚧、柑橘棘粉蚧、甘蔗簇粉蚧、康氏粉蚧、菠萝灰粉蚧和李比利氏灰粉蚧;而这些有害生物的主要来源地为越南和泰国;粉蚧的主要截获口岸为广西、深圳和云南;而火龙果、榴莲、龙眼和山竹是截获粉蚧最多的进境水果。【结论】中国进境水果粉蚧疫情与水果的贸易量和贸易方式、输出国有害生物发生和检疫除害处理措施、口岸关注度和能力建设等情况相关。     

Molecular and histological characterization of primary (betaproteobacteria) and secondary (gammaproteobacteria) endosymbionts of three mealybug species

Microscopic localization of endosymbiotic bacteria in three species of mealybug (Pseudococcus longispinus, the long-tailed mealybug; Pseudococcus calceolariae, the citrophilus mealybug; and Pseudococcus viburni, the obscure mealybug) showed these organisms were confined to bacteriocyte cells within a bacteriome centrally located within the hemocoel. Two species of bacteria were present, with the secondary endosymbiont, in all cases, living within the primary endosymbiont. DNA from the dissected bacteriomes of all three species of mealybug was extracted for analysis. Sequence data from selected 16S rRNA genes confirmed identification of the primary endosymbiont as "Candidatus Tremblaya princeps," a betaproteobacterium, and the secondary endosymbionts as gammaproteobacteria closely related to Sodalis glossinidius. A single 16S rRNA sequence of the primary endosymbiont was found in all individuals of each mealybug species. In contrast, the presence of multiple divergent strains of secondary endosymbionts in each individual mealybug suggests different evolutionary and transmission histories of the two endosymbionts. Mealybugs are known vectors of the plant pathogen Grapevine leafroll-associated virus 3. To examine the possible role of either endosymbiont in virus transmission, an extension of the model for interaction of proteins with bacterial chaperonins, i.e., GroEL protein homologs, based on mobile-loop amino acid sequences of their GroES homologs, was developed and used for analyses of viral coat protein interactions. The data from this model are consistent with a role for the primary endosymbiont in mealybug transmission of Grapevine leafroll-associated virus 3.     

Parasitoids of obscure mealybug,Pseudococcus viburni (Hem.: Pseudococcidae) in California: establishment of Pseudaphycus flavidulus (Hym.: Encyrtidae) and discussion of related parasitoid species

To improve natural suppression of the obscure mealybug, Pseudococcus viburni (Signoret), the parasitoids Pseudaphycus flavidulus (Brèthes) and Leptomastix epona (Walker) (Hymenoptera: Encyrtidae) of Chilean origin were released in California's Central Coast vineyards from 1997 to 1999. A survey for parasitoids of P. viburni was conducted in the Edna Valley appellation wine grape region from 2005 to 2007, 6–8 years after classical biological control releases were discontinued. Two survey methods were used. First, field collections of obscure mealybugs from commercial vineyard blocks (2005–2007) and, second, placement of “sentinel mealybugs” on potted (1 L) grape vines (2006 only). From both survey methods, P. flavidulus was recovered, albeit levels of parasitism were low (less than 0.6%). We also placed longtailed mealybug, Pseudococcus longispinus (Targioni Tozzetti), on potted plants concurrent with placement of sentinel obscure mealybugs in the vineyard in order to measure parasitoid activity on this closely-related mealybug species. No P. flavidulus were recovered from P. longispinus. Other encyrtid parasitoids reared from either P. viburni or P. longispinus were Anagyrus pseudococci (Girault), Leptomastix dactylopii Howard, Leptomastidea abnormis (Girault), Coccidoxenoides perminutus Girault, and Tetracnemoidea peregrina (Compere). A hyperparasitoid, Chaetocerus sp., was also reared. The data are discussed with respect to biological control of vineyard mealybugs and newly developed controls for the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae). Because Pseudaphycus species reared from mealybugs are superficially very similar a taxonomic key and discussion of host relationships for selected Pseudaphycus species are provided.     

Hundred and sixty years of Australian lady bird beetle Crypotolaemus montrouzieri Mulsant – a global view

ABSTRACT

The Australian lady bird beetle Cryotolaemus montrouzieri Mulsant was first discovered in 1853 in Queensland and New South Wales of Eastern Australia and New Caledonia. It has provided very good control of the sucking insect pests, particularly soft scales and mealybugs at different locations in more than 60 countries since its introduction in 1892 from Australia to California. Besides, C. montrouzieri is also known to feed on whiteflies, aphids, hard scales, dactylopiids, eriococcids, margorodids, psyllids, etc. Cryptolaemus montrouzieri takes 30 days to complete life cycle at 30°C. Pupae of C. montrouzieri are stored for about 20 days without having any adverse effect on the fecundity of the resulting adults. Potato sprouts or ripe pumpkins have been used as laboratory hosts for multiplication of mealybugs and C. montrouzieri. Cryptolaemus montrouzieri provided very good control of mealybugs and soft scales in the absence of ants. It plays a great role in the suppression of soft scales belonging to the genus Pulvinaria and the mealybugs Planococcus citri, Ferrisia virgata, Maconellicoccus hirsutus, Nipaecoccus viridis, Pseudococcus jackbeardsleyi, Coccidihystrix insolita, Pseudococcus comstocki, Pseudococcus obscures, Pseudococcus aurilanatus, etc. Botanicals, biopesticide mineral oils, insecticidal soaps, conventional insecticides dichlorvos and chlorpyriphos and the new molecules spirotetramat, imidacloprid, abamectin, fluvalinate, profenophos, ethnfenprox, flufenoxuron, spinosad and bufrofezin appear to be safer to the adults and grubs of C. montrouzieri. Therefore, these chemicals are to be integrated cautiously in the management of mealybugs and soft scales.     

Pre‐release host range determination of the parasitoid Allotropa burrelli for the biocontrol of Pseudococcus comstocki in France

We performed “no‐choice” tests to study the host range of the parasitoid Allotropa burrelli (Muesebeck) (Hymenoptera: Platygastridae) for use against the Comstock mealybug, Pseudococcus comstocki (Kuwana) (Hemiptera: Pseudococcidae), in Southern France. We tested three Pseudococcidae species as potential non‐target hosts: two species from the same genus (Pseudococcus longispinus and Pseudococcus viburni) and Planococcus citri. Allotropa burrelli did not parasitize any of the non‐target mealybug species tested. No attempt of oviposition was recorded for the three species tested during the first 20 min of parasitoid release and no parasitism occurred in 6–8 hr of exposure of the mealybugs to the parasitoid.     

Pheromone-baited traps for assessment of seasonal activity and population densities of mealybug species (Hemiptera: Pseudococcidae) in nurseries producing ornamental plants

Operational parameters of traps baited with the pheromones of three mealybug species were optimized in nurseries producing ornamental plants. All pheromone doses (1-320 microg) attracted Pseudococcus longispinus (Targioni Tozzetti) and Pseudococcus viburni (Signoret) males, with the lowest dose (1 microg) attracting the fewest males for both species. Doses of 3.2-100 microg were as attractive to male P. longispinus as the highest dose (320 microg); doses from 10 to 320 microg were equally attractive for P. viburni males. Lures containing 25-microg doses of either pheromone had effective field lifetimes of at least 12 wk. Experiments were performed to test the efficacy of combining multiple pheromones to attract several species of mealybugs simultaneously. Lures loaded with a mixture of the pheromones of P. longispinus, P. viburni, and Planococcus citri (Risso) were as attractive to P. viburni and P. citri as lures with their individual pheromones. Response of P. longispinus to the blend was decreased by 38% compared with its pheromone as a single component. A subsequent trial with two-component blends showed that the pheromone ofP. citri was responsible for this modest decrease in P. longispinus response. This should not affect the overall efficacy of using these lures for monitoring the presence of all three mealybug species simultaneously. Pheromone traps were used to detect infestations of P. longispinus throughout the season and to track population cycles. When pheromone-baited traps for P. longispinus were compared with manual sampling, trap counts of male mealybugs were significantly correlated with mealybugs counted on plants in the vicinity of the traps.     

The genetic properties of the primary endosymbionts of mealybugs differ from those of other endosymbionts of plant sap-sucking insects

Mealybugs (Hemiptera, Coccoidea, Pseudococcidae), like aphids and psyllids, are plant sap-sucking insects that have an obligate association with prokaryotic endosymbionts that are acquired through vertical, maternal transmission. We sequenced two fragments of the genome of Tremblaya princeps, the endosymbiont of mealybugs, which is a member of the beta subdivision of the Proteobacteria. Each of the fragments (35 and 30 kb) contains a copy of 16S-23S-5S rRNA genes. A total of 37 open reading frames were detected, which corresponded to putative rRNA proteins, chaperones, and enzymes of branched-chain amino acid biosynthesis, DNA replication, protein translation, and RNA synthesis. The genome of T. princeps has a number of properties that distinguish it from the genomes of Buchnera aphidicola and Carsonella ruddii, the endosymbionts of aphids and psyllids, respectively. Among these properties are a high G+C content (57.1 mol%), the same G+C content in intergenic spaces and structural genes, and similar G+C contents of the genes encoding highly and poorly conserved proteins. The high G+C content has a substantial effect on protein composition; about one-third of the residues consist of four amino acids with high-G+C-content codons. Sequence analysis of DNA fragments containing the rRNA operon and adjacent regions from endosymbionts of several mealybug species suggested that there was a single duplication of the rRNA operon and the adjacent genes in an ancestor of the present T. princeps. Subsequently, in one mealybug lineage rpS15, one of the duplicated genes, was retained, while in another lineage it decayed. These results extend the diversity of the types of endosymbiotic associations found in plant sap-sucking insects.     

Aphid populations are frequently infected with facultative endosymbionts

The occurrence of facultative endosymbionts has been studied in many commercially important crop pest aphids, but their occurrence and effects in non-commercial aphid species in natural populations have received less attention. We screened 437 aphid samples belonging to 106 aphid species for the eight most common facultative aphid endosymbionts. We found one or more facultative endosymbionts in 53% (56 of 106) of the species investigated. This likely underestimates the situation in the field because facultative endosymbionts are often present in only some colonies of an aphid species. Oligophagous aphid species carried facultative endosymbionts significantly more often than monophagous species. We did not find a significant correlation between ant tending and facultative endosymbiont presence. In conclusion, we found that facultative endosymbionts are common among aphid populations. This study is, to our knowledge, the first of its kind in the Netherlands and provides a basis for future research in this field. For instance, it is still unknown in what way many of these endosymbionts affect their hosts, which is important for determining the importance of facultative endosymbionts to community dynamics.     

The eubacterial endosymbionts of whiteflies (homoptera: Aleyrodoidea) constitute a lineage distinct from the endosymbionts of aphids and mealybugs

Whiteflies (superfamily Aleyrodoidea) contain eubacterial endosymbionts localized within host cells known as mycetocytes. Sequence analysis of the genes for the 16S rRNA of the endosymbionts ofBemisia tabaci, Siphoninus phillyreae, andTrialeurodes vaporariorum indicates that these organisms are closely related and constitute a distinct lineage within the -subdivision of theProteobacteria. The endosymbionts of whiteflies are unrelated to the endosymbionts of aphids and mealybugs, which are in two separate lineages.     

Diversity,frequency, and geographic distribution of facultative bacterial endosymbionts in introduced aphid pests

Facultative bacterial endosymbionts in insects have been under intense study during the last years. Endosymbionts can modify the insect's phenotype, conferring adaptive advantages under environmental stress. This seems particularly relevant for a group of worldwide agricultural aphid pests, because endosymbionts modify key fitness‐related traits, including host plant use, protection against natural enemies and heat tolerance. Aimed to understand the role of facultative endosymbionts on the success of introduced aphid pests, the distribution and abundance of 5 facultative endosymbionts (Hamiltonella defensa, Regiella insecticola, Serratia symbiotica, Rickettsia and Spiroplasma) were studied and compared in 4 cereal aphids (Sitobion avenae, Diuraphis noxia, Metopolophium dirhodum and Schizaphis graminium) and in the pea aphid Acyrthosiphon pisum complex from 2 agroclimatic zones in Chile. Overall, infections with facultative endosymbionts exhibited a highly variable and characteristic pattern depending on the aphid species/host race and geographic zone, which could explain the success of aphid pest populations after their introduction. While S. symbiotica and H. defensa were the most frequent endosymbionts carried by the A. pisum pea‐race and A. pisum alfalfa‐race aphids, respectively, the most frequent facultative endosymbiont carried by all cereal aphids was R. insecticola. Interestingly, a highly variable composition of endosymbionts carried by S. avenae was also observed between agroclimatic zones, suggesting that endosymbionts are responding differentially to abiotic variables (temperature and precipitations). In addition, our findings constitute the first report of bacterial endosymbionts in cereal aphid species not screened before, and also the first report of aphid endosymbionts in Chile.     

Evaluating hypotheses for the origin of eukaryotes

Numerous scenarios explain the origin of the eukaryote cell by fusion or endosymbiosis between an archaeon and a bacterium (and sometimes a third partner). We evaluate these hypotheses using the following three criteria. Can the data be explained by the null hypothesis that new features arise sequentially along a stem lineage? Second, hypotheses involving an archaeon and a bacterium should undergo standard phylogenetic tests of gene distribution. Third, accounting for past events by processes observed in modern cells is preferable to postulating unknown processes that have never been observed. For example, there are many eukaryote examples of bacteria as endosymbionts or endoparasites, but none known in archaea. Strictly post‐hoc hypotheses that ignore this third criterion should be avoided. Applying these three criteria significantly narrows the number of plausible hypotheses. Given current knowledge, our conclusion is that the eukaryote lineage must have diverged from an ancestor of archaea well prior to the origin of the mitochondrion. Significantly, the absence of ancestrally amitochondriate eukaryotes (archezoa) among extant eukaryotes is neither evidence for an archaeal host for the ancestor of mitochondria, nor evidence against a eukaryotic host. BioEssays 29: 74–84, 2007. © 2006 Wiley Periodicals, Inc.     

Occurrence of Chaperonin 60 and Chaperonin 10 in primary and secondary bacterial symbionts of aphids: Implications for the evolution of an endosymbiotic system in aphids

Summary All aphids harbor symbiotrophic prokaryotes (primary symbionts) in a specialized-abdominal cell, the bacteriocyte. Chaperonin 60 (Cpn60, symbionin) and chaperonin 10 (Cpn10), which are high and low molecular weight heatshock proteins, were sought in tissues of more than 60 aphid species. The endosymbionts were compared immunologically and histologically. It was demonstrated that (1) there are two types of aphids in terms of the endosymbiotic system: some with only primary symbionts and others with, in addition, secondary symbionts; (2) the primary symbionts of various aphids are quite similar in morphology whereas the secondary symbionts vary; and (3) irrespective of the aphid species, Cpn60 is abundant in both the primary and secondary symbionts, while Cpn10 is abundant in the secondary symbionts but present in small amounts in the primary ones. Based on these results, we suggest that the primary symbionts have been derived from a prokaryote that was acquired by the common ancestor of aphids whereas the secondary symbionts have been acquired by various aphids independently after divergence of the aphid species. In addition, we point out the possibility that the prokaryotes under intracellular conditions have been subject to some common evolutionary pressures, and as a result, have come to resemble cell organelles.     

The Genetic Properties of the Primary Endosymbionts of Mealybugs Differ from Those of Other Endosymbionts of Plant Sap-Sucking Insects

Mealybugs (Hemiptera, Coccoidea, Pseudococcidae), like aphids and psyllids, are plant sap-sucking insects that have an obligate association with prokaryotic endosymbionts that are acquired through vertical, maternal transmission. We sequenced two fragments of the genome of Tremblaya princeps, the endosymbiont of mealybugs, which is a member of the β subdivision of the Proteobacteria. Each of the fragments (35 and 30 kb) contains a copy of 16S-23S-5S rRNA genes. A total of 37 open reading frames were detected, which corresponded to putative rRNA proteins, chaperones, and enzymes of branched-chain amino acid biosynthesis, DNA replication, protein translation, and RNA synthesis. The genome of T. princeps has a number of properties that distinguish it from the genomes of Buchnera aphidicola and Carsonella ruddii, the endosymbionts of aphids and psyllids, respectively. Among these properties are a high G+C content (57.1 mol%), the same G+C content in intergenic spaces and structural genes, and similar G+C contents of the genes encoding highly and poorly conserved proteins. The high G+C content has a substantial effect on protein composition; about one-third of the residues consist of four amino acids with high-G+C-content codons. Sequence analysis of DNA fragments containing the rRNA operon and adjacent regions from endosymbionts of several mealybug species suggested that there was a single duplication of the rRNA operon and the adjacent genes in an ancestor of the present T. princeps. Subsequently, in one mealybug lineage rpS15, one of the duplicated genes, was retained, while in another lineage it decayed. These results extend the diversity of the types of endosymbiotic associations found in plant sap-sucking insects.     

Happens in the best of subfamilies: establishment and repeated replacements of co‐obligate secondary endosymbionts within Lachninae aphids

Virtually all aphids maintain an obligate mutualistic symbiosis with bacteria from the Buchnera genus, which produce essential nutrients for their aphid hosts. Most aphids from the Lachninae subfamily have been consistently found to house additional endosymbionts, mainly Serratia symbiotica. This apparent dependence on secondary endosymbionts was proposed to have been triggered by the loss of the riboflavin biosynthetic capability by Buchnera in the Lachninae last common ancestor. However, an integral large‐scale analysis of secondary endosymbionts in the Lachninae is still missing, hampering the interpretation of the evolutionary and genomic analyses of these endosymbionts. Here, we analysed the endosymbionts of selected representatives from seven different Lachninae genera and nineteen species, spanning four tribes, both by FISH (exploring the symbionts’ morphology and tissue tropism) and 16S rRNA gene sequencing. We demonstrate that all analysed aphids possess dual symbiotic systems, and while most harbour S. symbiotica, some have undergone symbiont replacement by other phylogenetically‐distinct bacterial taxa. We found that these secondary associates display contrasting cell shapes and tissue tropism, and some appear to be lineage‐specific. We propose a scenario for symbiont establishment in the Lachninae, followed by changes in the symbiont's tissue tropism and symbiont replacement events, thereby highlighting the extraordinary versatility of host‐symbiont interactions.