Diversity of secondary endosymbionts among different putative species of the whitefly Bemisia tabaci

Abstract Endosymbionts are important components of arthropod biology. The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex composed of ≥ 28 putative species. In addition to the primary endosymbiont Portiera aleyrodidarum, six secondary endosymbionts (S‐endosymbionts), Hamiltonella, Rickettsia, Wolbachia, Cardinium, Arsenophonus and Fritschea, have been identified in B. tabaci thus far. Here, we tested five of the six S‐endosymbiont lineages (excluding Fritschea) from 340 whitely individuals representing six putative species from China. Hamiltonella was detected only in the two exotic invaders, Middle East‐Asia Minor 1 (MEAM1) and Mediterranean (MED). Rickettsia was absent in Asia II 1 and MED, scarce in Asia II 3 (13%), but abundant in Asia II 7 (63.2%), China 1 (84.7%) and MEAM1 (100%). Wolbachia, Cardinium and Arsenophonus were absent in the invasive MEAM1 and MED but mostly abundant in the native putative species. Furthermore, phylogenetic analyses revealed that some S‐endosymbionts have several clades and different B. tabaci putative species can harbor different clades of a given S‐endosymbiont, demonstrating further the complexity of S‐endosymbionts in B. tabaci. All together, our results demonstrate the variation and diversity of S‐endosymbionts in different putative species of B. tabaci, especially between invasive and native whiteflies.     

Species and endosymbiont diversity of Bemisia tabaci (Homoptera: Aleyrodidae) on vegetable crops in Senegal

Bemisia tabaci‐transmitted geminiviruses are one of the major threats on cassava and vegetable crops in Africa. However, to date, few studies are available on the diversity of B. tabaci and their associated endosymbionts in Africa. More than 28 species have been described in the complex of B. tabaci cryptic species; among them, 2 are invasive pests worldwide: MED and MEAM1. In order to assess the species diversity of B. tabaci in vegetable crops in Senegal, several samplings in different localities, hosts and seasons were collected and analyzed with nuclear (microsatellite) and mitochondrial (COI) markers. The bacterial endosymbiont community was also studied for each sample. Two species were detected: MED Q1 and MEAM1 B. Patterns of MED Q1 (dominance on most of the samples and sites, highest nuclear and mitochondrial diversity and broader secondary endosymbiont community: Hamiltonella, Cardinium, Wolbachia and Rickettsia), point toward a predominant resident begomovirus vector group for MED Q1 on market gardening crops. Furthermore, the lower prevalence of the second species MEAM1 B, its lower nuclear and mitochondrial diversity and a narrower secondary endosymbiont community (Hamiltonella/Rickettsia), indicate that this genetic group is exotic and results from a recent invasion in this area.     

Identification of biotypes and secondary endosymbionts of Bemisia tabaci in Korea and relationships with the occurrence of TYLCV disease

Bemisia tabaci is a species complex that consists of at least 24 genetically diverse biotypes. Here, we determined the biotypes of 27 populations collected in 17 different regions of Korea. Nucleotide sequence comparisons of cytochrome oxidase showed that 26 populations were Q biotype and that one population, the Goyang population, was B biotype. Further subgroup analysis of the Q biotype showed that all populations belonged to the Q1 subgroup, which originates from Western Mediterranean countries. Five endosymbiotic bacteria from various B. tabaci populations were analyzed by comparing rDNA sequences. Hamiltonella was detected in all the populations tested regardless of biotype. Cardinium was detected in all Q biotype populations but not in the B biotype population, while Rickettsia was detected in the B biotype population but not in Q biotype populations. Arsenophonus and Wolbachia were detected in 35% and 58% of Q biotype populations, respectively, but not in the B biotype population. Our results show that the endosymbiont profile is strongly associated with each biotype and with subgroups of the Q biotype. Survey of TYLCV disease from 2008 to 2010 indicated that this disease is widely spread in Korea. This study suggests that the rapid spread of TYLCV may be associated with endosymbiont infection, particularly Hamiltonella infection of B. tabaci.     

Identification and Localization of a Rickettsia sp. in Bemisia tabaci (Homoptera: Aleyrodidae)

Whiteflies (Homoptera: Aleyrodidae) are sap-sucking insects that harbor “Candidatus Portiera aleyrodidarum,” an obligatory symbiotic bacterium which is housed in a special organ called the bacteriome. These insects are also home for a diverse facultative microbial community which may include Hamiltonella, Arsenophonus, Fritchea, Wolbachia, and Cardinium spp. In this study, the bacteria associated with a B biotype of the sweet potato whitefly Bemisia tabaci were characterized using molecular fingerprinting techniques, and a Rickettsia sp. was detected for the first time in this insect family. Rickettsia sp. distribution, transmission and localization were studied using PCR and fluorescence in situ hybridizations (FISH). Rickettsia was found in all 20 Israeli B. tabaci populations screened but not in all individuals within each population. A FISH analysis of B. tabaci eggs, nymphs, and adults revealed a unique concentration of Rickettsia around the gut and follicle cells, as well as a random distribution in the hemolymph. We postulate that the Rickettsia enters the oocyte together with the bacteriocytes, leaves these symbiont-housing cells when the egg is laid, multiplies and spreads throughout the egg during embryogenesis and, subsequently, disperses throughout the body of the hatching nymph, excluding the bacteriomes. Although the role Rickettsia plays in the biology of the whitefly is currently unknown, the vertical transmission on the one hand and the partial within-population infection on the other suggest a phenotype that is advantageous under certain conditions but may be deleterious enough to prevent fixation under others.     

Selective and stable elimination of endosymbionts from multiple‐infected whitefly Bemisia tabaci by feeding on a cotton plant cultured in antibiotic solutions

The maternally heritable endosymbiont provides many ecosystem functions. Antibiotic elimination of a specific symbiont and establishment of experimental host lines lacking certain symbionts enable the roles of a given symbiont to be explored. The whitefly Bemisia tabaci (Gennadius) in China harbors obligate symbiont Portiera infecting each individual, as well as facultative symbionts, such as Hamiltonella, Rickettsia and Cardinium, with co‐infections occurring relatively frequently. So far no studies have evaluated the selectivity and efficacy of a specific symbiont elimination using antibiotics in whiteflies co‐infected with different symbionts. Furthermore, no success has been achieved in establishing certain symbiont‐free B. tabaci lines. In this study, we treated Hamiltonella‐infected B. tabaci line, Hamiltonella‐Rickettsia‐co‐infected line and Hamiltonella‐Cardinium co‐infected line by feeding B. tabaci adults with cotton plants cultured in water containing rifampicin, ampicillin or a mixture of them, aiming to selectively curing symbiont infections and establishing stable symbiont‐free lines. We found ampicillin selectively eliminated Cardinium without affecting Portiera, Hamiltonella and Rickettsia, although they coexisted in the same host body. Meanwhile, all of the symbionts considered in our study can be removed by rifampicin. The reduction of facultative symbionts occurred at a much quicker pace than obligate symbiont Portiera during rifampicin treatment. Also, we measured the stability of symbiont elimination in whitefly successive generations and established Rickettsia‐infected and Cardinium‐infected lines which are absent in natural populations. Our results provide new protocols for selective elimination of symbionts co‐existing in a host and establishment of different symbiont‐infected host lines.     

Diversity of symbiotic bacteria associated with Bemisia tabaci (Homoptera: Aleyrodidae) in cassava mosaic disease pandemic areas of Tanzania

All Bemisia tabaci individuals harbour an obligate bacterial symbiont (Portiera aleyrodidarum), and many also harbour non‐essential facultative symbionts. The association of symbiotic bacteria with the various genetic groups of B. tabaci remains unknown for East Africa. This study aimed to assess any association between the various whitefly genetic groups and the endosymbionts they harbour; to investigate if a unique endosymbiont is associated with super‐abundant whiteflies, and to provide baseline information on endosymbionts of whiteflies for a part of East Africa. Whiteflies collected during surveys in Tanzania were genotyped and screened for the presence of the obligate and six secondary symbionts (SS): Rickettsia (R), Hamiltonella (H), Arsenophonus (A), Wolbachia (W), Cardinium (C) and Fritschea (F). The results revealed the presence of Mediterranean (MED), East Africa 1 (EA1), Indian Ocean (IO) and Sub‐Saharan Africa 1 (SSA1) genetic groups of Bemisia tabaci, with SSA1 further clustered into four sub‐groups: SSA1‐SG1, SSA1‐SG2, SSA1‐SG1/2 and SSA1‐SG3. F was completely absent from all of the whiteflies tested while R was always found in double or multiple infections. In general, no particular symbiont appeared to be associated with the super‐abundant SSA1‐SG1 B. tabaci, although A or AC infections were common among infected individuals. The most striking feature of these super‐abundant whiteflies, dominating cassava mosaic disease pandemic areas, was the high prevalence of individuals uninfected by any of the six SS tested. This study of the endosymbionts of B. tabaci in East Africa showed contrasting patterns of infection in crop and weed hosts.     

Detection of symbionts and virus in the whitefly <Emphasis Type="Italic">Bemisia tabaci</Emphasis> (Hemiptera: Aleyrodidae), vector of the <Emphasis Type="Italic">Mungbean yellow mosaic India virus</Emphasis> in Central India

Legume crops in Central India, the main soybean production area of the country, may suffer from yellow mosaic disease caused by the Mungbean yellow mosaic India virus (MYMIV). MYMIV is transmitted by the sweet potato whitefly, Bemisia tabaci (Gennadius), which is a species complex composed of various genetic groups. This vector species harbors different endosymbionts among regional strains and among individuals. To elucidate fundamental aspects of this virus vector in the state of Madhya Pradesh, the infection status of the symbionts and the virus in whiteflies was studied. A polymerase chain reaction (PCR) survey of the whiteflies collected in Madhya Pradesh found four secondary endosymbionts, Arsenophonus, Hemipteriphilus, Wolbachia, and Cardinium, in addition to the primary endosymbiont Portiera. Arsenophonus and Hemipteriphilus were highly infected but the infection rates of Wolbachia and Cardinium were low. MYMIV was detected in whitefly populations collected from various host plants in Madhya Pradesh. The whitefly populations belonged to the Asia I and II genetic groups; several different Asia II populations were also distributed. Specific relations were not observed among symbiont infection status, virus infection, and the whitefly genetic groups in the populations of Madhya Pradesh, though Cardinium was highly detected in the Asia II-1 group. New primers, which can be used for PCR template validation and for discriminating two phylogenetically close endosymbionts, were designed.     

Lysine provisioning by horizontally acquired genes promotes mutual dependence between whitefly and two intracellular symbionts

Horizontal gene transfer is widespread in insects bearing intracellular symbionts. Horizontally transferred genes (HTGs) are presumably involved in amino acid synthesis in sternorrhynchan insects. However, their role in insect-symbiont interactions remains largely unknown. We found symbionts Portiera, Hamiltonella and Rickettsia possess most genes involved in lysine synthesis in the whitefly Bemisia tabaci MEAM1 although their genomes are reduced. Hamiltonella maintains a nearly complete lysine synthesis pathway. In contrast, Portiera and Rickettsia require the complementation of whitefly HTGs for lysine synthesis and have lysE, encoding a lysine exporter. Furthermore, each horizontally transferred lysine gene of ten B. tabaci cryptic species shares an evolutionary origin. We demonstrated that Hamiltonella did not alter the titers of Portiera and Rickettsia or lysine gene expression of Portiera, Rickettsia and whiteflies. Hamiltonella also did not impact on lysine levels or protein localization in bacteriocytes harboring Portiera and ovaries infected with Rickettsia. Complementation with whitefly lysine synthesis HTGs rescued E. coli lysine gene knockout mutants. Silencing whitefly lysA in whiteflies harboring Hamiltonella reduced lysine levels, adult fecundity and titers of Portiera and Rickettsia without influencing the expression of Hamiltonella lysA. Furthermore, silencing whitefly lysA in whiteflies lacking Hamiltonella reduced lysine levels, adult fecundity and titers of Portiera and Rickettsia in ovarioles. Therefore, we, for the first time, demonstrated an essential amino acid lysine synthesized through HTGs is important for whitefly reproduction and fitness of both obligate and facultative symbionts, and it illustrates the mutual dependence between whitefly and its two symbionts. Collectively, this study reveals that acquisition of horizontally transferred lysine genes contributes to coadaptation and coevolution between B. tabaci and its symbionts.     

Evidence for Horizontal Transmission of Secondary Endosymbionts in the Bemisia tabaci Cryptic Species Complex

Bemisia tabaci (Hemiptera: Aleyrodidae) is a globally distributed pest composed of at least 34 morphologically indistinguishable cryptic species. At least seven species of endosymbiont have been found infecting some or all members of the complex. The origin(s) of the associations between specific endosymbionts and their whitefly hosts is unknown. Infection is normally vertical, but horizontal transmission does occur and is one way for new infections to be introduced into individuals. The relationships between the different members of the cryptic species complex and the endosymbionts have not been well explored. In this study, the phylogenies of different cryptic species of the host with those of their endosymbionts were compared. Of particular interest was whether there was evidence for both coevolution and horizontal transmission. Congruence was observed for the primary endosymbiont, Portiera aleyrodidarum, and partial incongruence in the case of two secondary endosymbionts, Arsenophonus and Cardinium and incongruence for a third, Wolbachia. The patterns observed for the primary endosymbiont supported cospeciation with the host while the patterns for the secondary endosymbionts, and especially Wolbachia showed evidence of host shifts and extinctions through horizontal transmission rather than cospeciation. Of particular note is the observation of several very recent host shift events in China between exotic invader and indigenous members of the complex. These shifts were from indigenous members of the complex to the invader as well as from the invader to indigenous relatives.     

Bemisia tabaci in Iraq: Population structure,endosymbiont diversity and putative species

Whiteflies (Hemiptera: Aleyrodidae) are major pests of many crops worldwide. Bemisia tabaci is a cryptic species complex composed of more than 39 putative species. Understanding which putative species of B. tabaci are predominant in an area is vital for effective pest management since they may vary considerably with respect to insecticide resistance, host plant range and virus transmission. Here, for the first time, the genetic diversity, the symbiont diversity and population structure of B. tabaci in Iraq were studied. Fourteen populations were analysed using mitochondrial cytochrome C oxidase subunit 1 (mtCO1) sequencing and microsatellite genotyping. Symbiotic bacteria were identified using 16S rRNA and 23S rRNA sequencing. MtCO1 sequencing detected two putative species of B. tabaci. The predominant putative species in Iraq was Middle East-Asia Minor (MEAM) 1 subcladeB2. In addition, one individual was MEAM1-subcladeB. The second putative species was a single individual of MEAM2. The microsatellite data indicated low genetic diversity, with no biologically informative clustering. All MEAM1 individuals harboured one primary symbiont, Portiera aleyrodidarum, and most (96%) have two secondary symbionts: Hamiltonella sp. and Rickettsia sp. This study has identified the genetic diversity and population structure of B. tabaci in Iraq. Further investigation is needed to update the pest status of B. tabaci in this region. The current data, combined with investigations into the capacity of the various putative species to transmit plant viruses, especially tomato yellow leaf curl virus, will aid pest management and horticultural production.     

Genetic diversity of Bemisia tabaci cryptic species in Nigeria and their relationships with endosymbionts and acquired begomoviruses

Bemisia tabaci is a species complex of at least 44 cryptic species with a worldwide distribution. It is a serious pest of many crop plants as well as a successful vector of at least 100 begomoviruses. Using B. tabaci collected from cassava and tomato fields in the southwestern and north central regions of Nigeria, we determined nucleotide sequences from the mitochondrial cytochrome c oxidase subunit I (COI) of 23 B. tabaci samples, the 16S and 23S ribosomal DNA of endosymbionts, and the coat protein gene of geminiviruses ingested by the whiteflies. The COI analysis identified three different genetic groups including the indigenous Sub-Saharan Africa 1 subgroup 1 (SSA1-SG1) and 5 (SSA1-SG5, which was most prevalent), and an invasive cryptic species (Mediterranean). SSA1 was infected by five known secondary endosymbionts, Arsenophonus, Cardinium, Hamiltonella, Rickettsia, and Wolbachia, and co-infections with two or three endosymbionts were common. Five begomoviruses, okra enation leaf curl virus, squash leaf curl China virus, tobacco curly shoot virus, tomato leaf curl New Delhi virus, and tomato yellow leaf curl virus, were detected from 43.5% of the B. tabaci samples. However, cassava mosaic disease that causes devastating cassava yield losses was not detected in this study. This study improves the current understanding of the genetic diversity of B. tabaci cryptic species, and it reveals their relationships with endosymbionts and geminiviruses in the cassava and tomato fields of Nigeria.     

Genetic variability,community structure,and horizontal transfer of endosymbionts among three Asia II‐Bemisia tabaci mitotypes in Pakistan

Endosymbionts associated with the whitefly Bemisia tabaci cryptic species are known to contribute to host fitness and environmental adaptation. The genetic diversity and population complexity were investigated for endosymbiont communities of B. tabaci occupying different micro‐environments in Pakistan. Mitotypes of B. tabaci were identified by comparative sequence analysis of the mitochondria cytochrome oxidase I (mtCOI) gene sequence. Whitefly mitotypes belonged to the Asia II‐1, ‐5, and ‐7 mitotypes of the Asia II major clade. The whitefly–endosymbiont communities were characterized based on 16S ribosomal RNA operational taxonomic unit (OTU) assignments, resulting in 43 OTUs. Most of the OTUs occurred in the Asia II‐1 and II‐7 mitotypes (r² = .9, p < .005), while the Asia II‐5 microbiome was less complex. The microbiome OTU groups were mitotype‐specific, clustering with a basis in phylogeographical distribution and the corresponding ecological niche of their whitefly host, suggesting mitotype‐microbiome co‐adaptation. The primary endosymbiont Portiera was represented by a single, highly homologous OTU (0%–0.67% divergence). Two of six Arsenophonus OTUs were uniquely associated with Asia II‐5 and ‐7, and one occurred exclusively in Asia II‐1, two only in Asia II‐5, and one in both Asia II‐1 and ‐7. Four other secondary endosymbionts, Cardinium, Hemipteriphilus, Rickettsia, and Wolbachia OTUs, were found at ≤29% frequencies. The most prevalent Arsenophonus OTU was found in all three Asia II mitotypes (55% frequency), whereas the same strain of Cardinium and Wolbachia was found in both Asia II‐1 and ‐5, and a single Hemipteriphilus OTU occurred in Asia II‐1 and ‐7. This pattern is indicative of horizontal transfer, suggestive of a proximity between mitotypes sufficient for gene flow at overlapping mitotype ecological niches.     

Cover Caption

The whitefly vector of viruses Bemisia tabaci is one of the major threats on cassava and vegetable crops in Africa. More than 28 species have been described in the complex of B. tabaci cryptic species; among them, two are invasive pests worldwide (MEAM1 and MED), bearing a large and species specific endosymbiont community. To date, this is the first time that MEAM1and MED were described in Senegal together with their prevalence and associated endosymbiont community on vegetable crops (see pages 386–398). Photo by Antoine Franck, CIRAD, UMR PVBMT.     

Are ecological communities the seat of endosymbiont horizontal transfer and diversification? A case study with soil arthropod community

Maternally inherited endosymbionts of arthropods are one of the most abundant and diverse group of bacteria. These bacterial endosymbionts also show extensive horizontal transfer to taxonomically unrelated hosts and widespread recombination in their genomes. Such horizontal transfers can be enhanced when different arthropod hosts come in contact like in an ecological community. Higher rates of horizontal transfer can also increase the probability of recombination between endosymbionts, as they now share the same host cytoplasm. However, reports of community‐wide endosymbiont data are rare as most studies choose few host taxa and specific ecological interactions among the hosts. To better understand endosymbiont spread within host populations, we investigated the incidence, diversity, extent of horizontal transfer, and recombination of three endosymbionts (Wolbachia, Cardinium, and Arsenophonus) in a specific soil arthropod community. Wolbachia strains were characterized with MLST genes whereas 16S rRNA gene was used for Cardinium and Arsenophonus. Among 3,509 individual host arthropods, belonging to 390 morphospecies, 12.05% were infected with Wolbachia, 2.82% with Cardinium and 2.05% with Arsenophonus. Phylogenetic incongruence between host and endosymbiont indicated extensive horizontal transfer of endosymbionts within this community. Three cases of recombination between Wolbachia supergroups and eight incidences of within‐supergroup recombination were also found. Statistical tests of similarity indicated supergroup A Wolbachia and Cardinium show a pattern consistent with extensive horizontal transfer within the community but not for supergroup B Wolbachia and Arsenophonus. We highlight the importance of extensive community‐wide studies for a better understanding of the spread of endosymbionts across global arthropod communities.     

Antagonistic interaction between male-killing and cytoplasmic incompatibility induced by Cardinium and Wolbachia in the whitefly,Bemisia tabaci

Cardinium and Wolbachia are maternally inherited bacterial symbionts of arthropods that can manipulate host reproduction by increasing the fitness of infected females.Here,we report that Cardinium and Wolbachia coinfection induced male-killing and cytoplasmic incompatibility(CI)when they coexisted in a cryptic species of whitefly,Bemisia tabaci Asia II7.Cardinium and Wolbachia symbionts were either singly or simul-taneously localized in the bacteriocytes placed in the abdomen of B.tabaci nymphs and adults.Cardinium-Wolbachia coinfection induced male-killing and resulted in a higher female sex ratio in the intraspecific amphigenetic progeny of Asia II7 IcwH and IcwL lines;interestingly,male-illing induction was enhanced with increased Cardinium titer.Moreover,single infection of Wolbachia induced partial CI in the Asia II7 Iw line and resulted in reduced fecundity,higher embryonic mortality,and lower female sex ratio.The uninfected Asia II7 Iu line had significantly higher fecundity,lower embryonic and nymphal mortalities,and a lower level of CI than both the Wolbachia infected Asia II7 Iw line and the Cardinium--Wolbachia-coinfected Asia II7 IcwH line.Our findings indicate that Cardinium-Wolbachia coinfection induced male-killing,which may have had antag-onistic effects on Wolbachia-induced CI in the Asia II7 whiteflies.For the first time,our study revealed that B.tabaci Asia II7 reproduction is co-manipulated by Cardinium and Wolbachia endosymbionts.     

Inactivation of Wolbachia Reveals Its Biological Roles in Whitefly Host

Background

The whitefly Bemisia tabaci is cryptic species complex composed of numerous species. Individual species from the complex harbor a diversity of bacterial endosymbionts including Wolbachia. However, while Wolbachia is known to have a number of different roles, its role in B. tabaci is unclear. Here, the antibiotic rifampicin is used to selectively eliminate Wolbachia from B. tabaci so as to enable its roles in whitefly development and reproduction to be explored. The indirect effects of Wolbachia elimination on the biology of Encarsia bimaculata, a dominant parasitoid of B. tabaci in South China, were also investigated.

Methodology/Principal Finding

qRT-PCR and FISH were used to show that after 48 h exposure to 1.0 mg/ml rifampicin, Wolbachia was completely inactivated from B. tabaci Mediterranean (MED) without any significant impact on either the primary symbiont, Portiera aleyrodidarum or any of the other secondary endosymbionts present. For B. tabaci MED, Wolbachia was shown to be associated with decreased juvenile development time, increased likelihood that nymphs completed development, increased adult life span and increased percentage of female progeny. Inactivation was associated with a significant decrease in the body size of the 4^th instar which leads us to speculate as to whether Wolbachia may have a nutrient supplementation role. The reduction in nymph body size has consequences for its parasitoid, E. bimaculata. The elimination of Wolbachia lead to a marked increase in the proportion of parasitoid eggs that completed their development, but the reduced size of the whitefly host was also associated with a significant reduction in the size of the emerging parasitoid adult and this was in turn associated with a marked reduction in adult parasitoid longevity.

Conclusions/Significance

Wolbachia increases the fitness of the whitefly host and provides some protection against parasitization. These observations add to our understanding of the roles played by bacterial endosymbionts.     

The Facultative Symbiont Rickettsia Protects an Invasive Whitefly against Entomopathogenic Pseudomonas syringae Strains

Facultative endosymbionts can benefit insect hosts in a variety of ways, including context-dependent roles, such as providing defense against pathogens. The role of some symbionts in defense may be overlooked, however, when pathogen infection is transient, sporadic, or asymptomatic. The facultative endosymbiont Rickettsia increases the fitness of the sweet potato whitefly (Bemisia tabaci) in some populations through mechanisms that are not yet understood. In this study, we investigated the role of Rickettsia in mediating the interaction between the sweet potato whitefly and Pseudomonas syringae, a common environmental bacterium, some strains of which are pathogenic to aphids. Our results show that P. syringae multiplies within whiteflies, leading to host death, and that whiteflies infected with Rickettsia show a decreased rate of death due to P. syringae. Experiments using plants coated with P. syringae confirmed that whiteflies can acquire the bacteria at a low rate while feeding, leading to increased mortality, particularly when the whiteflies are not infected with Rickettsia. These results suggest that P. syringae may affect whitefly populations in nature and that Rickettsia can ameliorate this effect. This study highlights the possible importance of interactions among opportunistic environmental pathogens and endosymbionts of insects.     

Rickettsia influences thermotolerance in the whitefly Bemisia tabaci B biotype

Abstract The whitefly Bemisia tabaci harbors Portiera aleyrodidarum, an obligatory symbiotic bacterium, as well as several secondary symbionts, including Rickettsia, Hamiltonella, Wolbachia, Arsenophonus, Cardinium and Fritschea, the function of which is unknown. In Israel, Rickettsia is found in both the B and Q of B. tabaci biotypes, and while all other secondary symbionts are located in the bacteriomes, Rickettsia can occupy most of the body cavity of the insect. We tested whether Rickettsia influences the biology of B. tabaci and found that exposing a Rickettsia‐containing population to increasing temperatures significantly increases its tolerance to heat shock that reached 40°C, compared to a Rickettsia‐free population. This increase in tolerance to heat shock was not associated with specific induction of heat‐shock protein gene expression; however, it was associated with reduction in Rickettsia numbers as was assessed by quantitative real‐time polymerase chain reaction and fluorescence in situ hybridization analyses. To assess the causes for thermotolerance when Rickettsia is reduced, we tested whether its presence is associated with the induction of genes required for thermotolerance. We found that under normal 25°C rearing temperature, genes associated with response to stress such as cytoskeleton genes are induced in the Rickettsia‐containing population. Thus, the presence of Rickettsia in B. tabaci under normal conditions induces the expression of genes required for thermotolerance that under high temperatures indirectly lead to this tolerance.     

Independent cytoplasmic incompatibility induced by Cardinium and Wolbachia maintains endosymbiont coinfections in haplodiploid thrips populations

Cardinium and Wolbachia are common maternally inherited reproductive parasites that can coinfect arthropods, yet interactions between both bacterial endosymbionts are rarely studied. For the first time, we report their independent expression of complete cytoplasmic incompatibility (CI) in a coinfected host, and CI in a species of the haplodiploid insect order Thysanoptera. In Pezothrips kellyanus, Cardinium‐induced CI resulted in a combination of male development (MD) and embryonic female mortality (FM) of fertilized eggs. In contrast, Wolbachia‐induced CI resulted in FM together with postembryonic mortality not previously reported as a CI outcome. Both endosymbionts appeared to not influence fecundity but virgins produced more offspring than mated females. In coinfected individuals, Wolbachia density was higher than Cardinium. Wolbachia removal did not impact Cardinium density, suggesting a lack of competition within hosts. Maternal transmission was complete for Wolbachia and high for Cardinium. Our data support theoretical predictions and empirical detection of high endosymbiont prevalence in field populations of the native range of this pest thrips. However, previous findings of more frequent loss of Wolbachia than Cardinium, particularly in field populations of the host's invasive range, suggest that genetic diversity or varying environmental factors between field populations also play a role in shaping host‐endosymbiont dynamics.     

Quantification and Localization of Watermelon Chlorotic Stunt Virus and Tomato Yellow Leaf Curl Virus (Geminiviridae) in Populations of Bemisia tabaci (Hemiptera,Aleyrodidae) with Differential Virus Transmission Characteristics

Bemisia tabaci (Gennadius) is one of the economically most damaging insects to crops in tropical and subtropical regions. Severe damage is caused by feeding and more seriously by transmitting viruses. Those of the genus begomovirus (Geminiviridae) cause the most significant crop diseases and are transmitted by B. tabaci in a persistent circulative mode, a process which is largely unknown. To analyze the translocation and to identify critical determinants for transmission, two populations of B. tabaci MEAM1 were compared for transmitting Watermelon chlorotic stunt virus (WmCSV) and Tomato yellow leaf curl virus (TYLCV). Insect populations were chosen because of their high and respectively low virus transmission efficiency to compare uptake and translocation of virus through insects. Both populations harbored Rickettsia, Hamiltonella and Wolbachia in comparable ratios indicating that endosymbionts might not contribute to the different transmission rates. Quantification by qPCR revealed that WmCSV uptake and virus concentrations in midguts and primary salivary glands were generally higher than TYLCV due to higher virus contents of the source plants. Both viruses accumulated higher in insects from the efficiently compared to the poorly transmitting population. In the latter, virus translocation into the hemolymph was delayed and virus passage was impeded with limited numbers of viruses translocated. FISH analysis confirmed these results with similar virus distribution found in excised organs of both populations. No virus accumulation was found in the midgut lumen of the poor transmitter because of a restrained virus translocation. Results suggest that the poorly transmitting population comprised insects that lacked transmission competence. Those were selected to develop a population that lacks virus transmission. Investigations with insects lacking transmission showed that virus concentrations in midguts were reduced and only negligible virus amounts were found at the primary salivary glands indicating for a missing or modified receptor responsible for virus attachment or translocation.