Molecular phylogeny reveals the existence of two sibling species in the aphid pest Brachycaudus helichrysi (Hemiptera: Aphididae)

Piffaretti, J., Vanlerberghe‐Masutti, F., Tayeh, A., Clamens, A.‐L., C?ur d’Acier, A. & Jousselin E. (2012). Molecular phylogeny reveals the existence of two sibling species in the aphid pest Brachycaudus helichrysi (Hemiptera: Aphididae). —Zoologica Scripta, 41, 266–280. Brachycaudus helichrysi is a worldwide polyphagous aphid pest that seriously damages its primary hosts (Prunus spp.) and the various cultivated plants among its secondary hosts (e.g. sunflower). A recent study of the Brachycaudus genus suggested that this species might encompass two differentiated lineages. We tested this hypothesis, by carrying out a phylogenetic study of this aphid pest based on worldwide sampling and the evaluation of mitochondrial, nuclear and Buchnera aphidicola DNA markers. We show that this species is actually an amalgamation of two sibling taxa, B. helichrysi H1 and B. helichrysi H2, that seem to have overlapping geographic ranges and herbaceous host plant preferences. These two taxa displayed levels of genetic divergence as great as those generally found between sister species in the Brachycaudus genus, suggesting that they actually correspond to two distinct species. Our phylogenetic reconstructions revealed a degree of incongruence between the topologies obtained with the aphid gene data set and with data for a DNA marker from its primary endosymbiont. We identified possible reasons for this observation and discuss the ecological and genotypic data suggesting that B. helichrysi H1 and B. helichrysi H2 have different life cycles.     

Genetic evidence from mitochondrial, nuclear, and endosymbiont markers for the evolution of host plant associated species in the aphid genus Hyalopterus (Hemiptera: Aphididae)

Over the past several decades biologists' fascination with plant-herbivore interactions has generated intensive research into the implications of these interactions for insect diversification. The study of closely related phytophagous insect species or populations from an evolutionary perspective can help illuminate ecological and selective forces that drive these interactions. Here we present such an analysis for aphids in the genus Hyalopterus (Hemiptera: Aphididae), a cosmopolitan group that feeds on plants in the genus Prunus (Rosaceae). Hyalopterus currently contains two recognized species associated with different Prunus species, although the taxonomy and evolutionary history of the group is poorly understood. Using mitochondrial COI sequences, 16S rDNA sequences from the aphid endosymbiont Buchnera aphidicola, and nine microsatellite loci we investigated population structure in Hyalopterus from the most commonly used Prunus host species throughout the Mediterranean as well as in California, where the species H. pruni is an invasive pest. We found three deeply divergent lineages structured in large part by specific associations with plum, almond, and peach trees. There was no evidence that geographic or temporal barriers could explain the overall diversity in the genus. Levels of genetic differentiation are consistent with that typically attributed to aphid species and indicate divergence times older than the domestication of Prunus for agriculture. Interestingly, in addition to their typical hosts, aphids from each of the three lineages were frequently found on apricot trees. Apricot also appears to act as a resource mediated hybrid zone for plum and almond associated lineages. Together, results suggest that host plants have played a role in maintaining host-associated differentiation in Hyalopterus for as long as several million years, despite worldwide movement of host plants and the potential for ongoing hybridization.     

Aphids (Hemiptera: Aphidoidea) on cultivated and self-sown plants in Greece

The present work covers original information on aphids (Hemiptera: Aphidoidea) from Greece during 1995–2005. The individual aphid taxa were collected from their host plants and identified. The plant taxa were classified in two major categories: cultivated and self-sown. The cultivated ones were classified as: herbaceous, climbing and trees. The selfsown ones were classified as: annual herbaceous, annual or biennial herbaceous, biennial or perennial herbaceous, perennial herbaceous, shrubby and trees Two hundred twelve plant taxa were identified on which 105 aphid taxa were recorded. We report 391 plant taxa-aphid taxa associations from which, 190 are referred to cultivated and 201 to self-shown plant taxa. Aphis gossypii was found to infest the widest spectrum of cultivated plant taxa whereas Brachycaudus helichrysi was found to infest the widest spectrum of self-sown plant taxa. Myzus persicae was found to infest the widest spectrum of the total number of plant taxa. Information for several economically unimportant aphid taxa in the area are also presented.     

Host Plant Specialization in the Sugarcane Aphid Melanaphis sacchari

Most aphids are highly specialized on one or two related plant species and generalist species often include sympatric populations adapted to different host plants. Our aim was to test the hypothesis of the existence of host specialized lineages of the aphid Melanaphis sacchari in Reunion Island. To this end, we investigated the genetic diversity of the aphid and its association with host plants by analyzing the effect of wild sorghum Sorghum bicolor subsp. verticilliflorum or sugarcane as host plants on the genetic structuring of populations and by performing laboratory host transfer experiments to detect trade-offs in host use. Genotyping of 31 samples with 10 microsatellite loci enabled identification of 13 multilocus genotypes (MLG). Three of these, Ms11, Ms16 and Ms15, were the most frequent ones. The genetic structure of the populations was linked to the host plants. Ms11 and Ms16 were significantly more frequently observed on sugarcane, while Ms15 was almost exclusively collected in colonies on wild sorghum. Laboratory transfer experiments demonstrated the existence of fitness trade-offs. An Ms11 isofemale lineage performed better on sugarcane than on sorghum, whereas an Ms15 lineage developed very poorly on sugarcane, and two Ms16 lineages showed no significant difference in performances between both hosts. Both field and laboratory results support the existence of host plant specialization in M. sacchari in Reunion Island, despite low genetic differentiation. This study illustrates the ability of asexual aphid lineages to rapidly undergo adaptive changes including shifting from one host plant to another.     

Intraspecific variation in host plant quality: the aphid Cinara cupressi on the Mexican cypress, Cupressus lusitanica

Abstract.

• 1 In Kenya, the aphid Cinara cupressi (Buckton) has an aggregated distribution across individuals of its host plant, the Mexican cypress, Cupressus lusitanica (Mill).
• 2 There are significant differences in host plant quality: C.cupressi nymphs transplanted onto cypress trees with low aphid infestations are significantly less likely to establish than aphids transplanted onto trees with high aphid infestations.
• 3 Given that some transplanted nymphs establish, the previous level of infestation does not influence aphid survival.
• 4 Evidence for local adaptation to individual plants was not found: nymphs transplanted to the trees from which their parents were collected neither established more readily nor showed lower mortality than those transplanted to other trees with similar levels of infestation. Therefore the variation in host plant quality has not led to the development of local adaptation to particular host plants.

     

The life-history of the leaf-curling plum aphid Brachycaudus helichrysi in Northern Ireland and its ability to transmit potato virus YC(AB)

The life-history of leaf-curling plum aphid, Brachycaudus helichrysi was studied in Northern Ireland from 1977–1980. It was shown that the life cycle differed in several respects from those of geographically distinct populations, reported by other authors, especially with regard to the timing of egg hatch. Body length and antennal segment measurements of the adult stages on Prunus spinosa and Trifolium pratense correlated well with published dimensions for the species. Virological studies showed B. helichrysi to be capable of transmitting potato virus Y^C(AB) with a vector efficiency of 34%. This value is higher than previous estimates and enhances the significance of the species as a virus vector in potato crops early in the growing season.     

Host preference of the plum curculio

We assessed host preference of adult plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), based on the total number of mark‐released and wild adults recovered and the total distance moved by mark‐released adults in an orchard whose layout was designed to specifically allow foraging plum curculios to choose among host tree species. Host trees included apple, Malus domestica Borkh.; pear, Pyrus communis (L.); peach, Prunus persica (L.) Batsch; apricot, Prunus armeniaca L.; tart cherry, Prunus cerasus L.; sweet cherry, Prunus avium (L.); European plum, Prunus domestica L.; and Japanese plum, Prunus salicina Lindl. (all Rosaceae). We released 2900 marked adults and recovered 17.7%. We used screen traps to provide a measure of the number of adults that arrived at and climbed up particular host trees and found that significantly greater numbers of marked adults and the greatest number of wild adults were recovered from screen traps attached to Japanese plum. We sampled host tree canopies by tapping limbs to provide a measure of the number of adults within a tree canopy at a particular moment. Again, significantly greater numbers of marked and wild adults were recovered from plum species, with no difference between Japanese and European plum cultivars for marked individuals, but with significantly greater numbers of wild individuals recovered from Japanese plum. The preference index (PI) for Japanese plum based on total distances moved by all marked adults recovered on Japanese plum divided by the total distance moved by marked adults recovered on other host trees indicated that Japanese plum was the most highly preferred host, followed by European plum, peach, sweet cherry, tart cherry, apricot, apple, and pear, respectively.     

Pine pest aphids of the genus Eulachnus (Hemiptera: Aphididae: Lachninae): how far can their range extend?

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Effects of habitat fragmentation on the three-way interaction among ants,aphids and larvae of the giant purple emperor, <Emphasis Type="Italic">Sasakia charonda</Emphasis> (Hewitson), a near-threatened butterfly

Survival rates of both early and middle instar larvae of the nymphalid butterfly, Sasakia charonda, were estimated to be lowest on test trees planted in a meadow (site A), intermediate in a small, narrow secondary deciduous broadleaf forest (small patch, site B) and highest in a large secondary deciduous broadleaf forest (large forest, site C). The larval mortality rates due to predation by tree-climbing predators from the ground (tree climbing predator) such as ants and the larvae of carabids were estimated to be greater at sites A and B than those at site C. The number of predatory ants climbing test trees was significantly greater at sites A and B than at site C, and the ants harvested honeydew from aphids living on tree leaves at those two sites. Aphid densities were significantly higher on trees at sites A and B than at site C, and aphid densities and numbers of predatory ants were significantly and positively correlated at sites A and B. In an experiment controlling aphid density per branch on test trees, the numbers of ants and the mortality rates of S. charonda larvae were greater on branches with high aphid densities than on those with low aphid densities at both sites A and B. These results suggest that the aphid density per host tree was higher in the meadow and the small patch than in the large forest; at both sites these higher aphid densities attracted higher numbers of predatory ants to test trees, and as a result, mortality rates of S. charonda larvae were increased.     

Do ecological niches differ between sexual and asexual lineages of an aphid species?

According to environmental-based theories on the maintenance of sexual reproduction, sexual and asexual populations may coexist if they occupy different ecological niches. The aphid Rhopalosiphum padi offers a good opportunity to test this hypothesis since sexual and asexual lineages show local coexistence during a large part of their respective life-cycles. Because these two reproductive variants are morphologically identical but genetically distinct, we first characterized them using genetic markers in populations of R. padi in areas where sexual and asexual lineages may occur in sympatry. We then inferred the natal host plant of sexual and asexual genotypes by analysing stable isotopic ratios and showed that sexual ones mostly originated from C₃ Poaceae while asexual ones originated from C₃ and C₄ plants, although the majority came from C₄ Poaceae. These findings indicate that ecological niches of sexual and asexual lineages of R. padi differ, offering a plausible explanation for the local coexistence of the two reproductive modes in this species through habitat specialisation.     

How does a Psittacanthus robustus Mart. population structure relate to a Vochysia thyrsoidea Pohl. host population?

Distribution of parasitic plants is directly linked with the distribution of host species and behavioral patterns of seed dispersers. Psittacanthus robustus (Loranthaceae) is a neotropical hemiparasite that mainly colonizes species of the family Vochysiaceae. Vochysia thyrsoidea is the main host of P. robustus and is commonly found in areas of cerrado rupestre (rocky savanna), an abundant vegetation in our study site. We conducted the study in the ecological park Parque Ecológico Quedas do Rio Bonito (PEQRB), over an area of 2.82 ha of cerrado rupestre. The objective of this work was to investigate population structure, parasitic behavior (mistletoe grip height and circumference of host branch), and spatial distribution of Psittacanthus robustus on a population of Vochysia thyrsoidea. We sampled 267 V. thyrsoidea individuals and found that the population had a random distribution pattern. Seventy-nine individuals (29.6% of the sample population) hosted the hemiparasite, to a total of 193 P. robustus individuals. The number of mistletoe individuals per host plant ranged between 1 and 12. The V. thyrsoidea individuals most infested with mistletoes were those reaching greater heights. The correlation between height of host plant and preferred grip height was highly significant, with the preferred grip height being the uppermost portions of host plants. The crown size of P. robustus individuals ranged between 10 and 230 cm. The main disperser of P. robustus fruit was found to be swallow-tanager Tersina viridis viridis. Its activities led to a clumped pattern of spatial distribution of the hemiparasite along with higher infestation in larger trees.     

Low Genetic Diversity in Melanaphis sacchari Aphid Populations at the Worldwide Scale

Numerous studies have examined the genetic diversity and genetic structure of invading species, with contrasting results concerning the relative roles of genetic diversity and phenotypic plasticity in the success of introduced populations. Increasing evidence shows that asexual lineages of aphids are able to occupy a wide geographical and ecological range of habitats despite low genetic diversity. The anholocyclic aphid Melanaphis sacchari is a pest of sugarcane and sorghum which originated in the old world, was introduced into the Americas, and is now distributed worldwide. Our purpose was to assess the genetic diversity and structuring of populations of this species according to host and locality. We used 10 microsatellite markers to genotype 1333 individuals (57 samples, 42 localities, 15 countries) collected mainly on sugarcane or sorghum. Five multilocus lineages (MLL) were defined, grouping multilocus genotypes (MLG) differing by only a few mutations or scoring errors. Analysis of a 658 bp sequence of mitochondrial COI gene on 96 individuals revealed five haplotypes, with a mean divergence of only 0.19 %. The distribution of MLL appeared to be strongly influenced by geography but not by host plant. Each of the five MLL grouped individuals from (A) Africa, (B) Australia, (C) South America, the Caribbean and the Indian Ocean including East Africa, (D) USA, and (E) China. The MLL A and C, with a wide geographic distribution, matched the definition of superclone. Among aphids, M. sacchari has one of the lowest known rates of genetic diversity for such a wide geographical distribution.     

Analyzing the Spatial Structure of Broughtonia cubensis (Orchidaceae) Populations in the Dry Forests of Guanahacabibes,Cuba

A current key issue in ecology is the role of spatial effects on population and community dynamics. In this paper, we test several hypotheses related to spatial structures and coexistence of epiphytic tropical orchid species with special emphasis on the endemic species Broughtonia cubensis. More specifically, we explored the spatial structure of orchid–host plant communities at three different levels of organization (occupied vs. nonoccupied host trees, trees with B. cubensis vs. other orchids, and reproductive vs. nonreproductive B. cubensis plants). We mapped all potential host trees and orchids at three 20 × 20 m plots and applied techniques of spatial point pattern analysis such as mark connection and mark correlation functions to evaluate departures from randomized communities. We found spatial aggregation of trees with epiphytic orchids and segregation between trees with and without epiphytic orchids, and that there was an intraspecific spatial aggregation of B. cubensis in relation to the other seven epiphytic orchid species. Furthermore, we found spatial aggregation of reproductive B. cubensis individuals and segregation between reproductive and nonreproductive individuals on their phorophytes. Thus, orchid–host plant communities show hierarchical spatial structuring with aggregation and segregation at different levels of organization. Our results point to an enhancement of local species in the coexistence of tropical epiphytic orchid communities, by reducing competition through niche differentiation.     

An Experimental Test of whether the Defensive Phenotype of an Aphid Facultative Symbiont Can Respond to Selection within a Host Lineage

An experiment was conducted to test whether parasitoid resistance within a single clonal line of pea aphid (Acyrthosiphon pisum) might increase after exposure to the parasitoid wasp Aphidius ervi. Any change in resistance was expected to occur through an increase in the density of protective symbiotic bacteria rather than genetic change within the aphid or the bacterial symbiont. Six aphid lineages were exposed to high parasitoid attack rates over nine generations, each line being propagated from individuals that had survived attack; a further six lineages were maintained without parasitoids as a control. At the end of the experiment the strength of resistance of aphids from treatment and control lines were compared. No differences in resistance were found.     

Patch size of gall-forming aphids: deme formation revisited

Plants of the genus Pistacia (Anacardiaceae) serve as obligate hosts for a group of specialized gall-forming aphids (Homoptera: Fordinae). The aphids regularly migrate between the Pistacia (primary) host plants and the roots of non-specific grasses and cereals (secondary hosts). Gall density varies considerably between trees and sites. The intimate relationships between the aphids and their primary host, the natural variation of host susceptibility, and the heterogeneous geographical environment may promote local adaptation and deme formation in the aphid populations. Indeed, previous analyses of the genetic structure of the aphid Baizongia pistaciae, which forms large galls on the deciduous P. palaestina trees, suggested deme formation (Martinez et al. 2005). In this study, we analyzed the genetic structure of the B. pistaciae population at eight sites and 78 trees throughout Israel and a single population in Turkey, using two molecular markers (AFLP fingerprints and COI sequencing). The genetic distance between the Israeli populations was found to be low (D = 0.01–0.02), and there was no genetic differentiation found between any population pairs. In five of the Israeli populations, we also compared the genetic identity between aphids forming galls on the same tree and between galls on neighboring trees. The analysis indicated that the genetic identity of different galls within a tree resembles the correspondence between trees within a population. Our results showed no indication of deme formation or any hierarchical genetic substructuring within B. pistaciae populations in Israel. The extensive gene flow between aphid colonies may be explained by their dispersal abilities and the potential bridging role of the secondary hosts.     

Local adaptation and host race formation of a gall-forming aphid in relation to environmental heterogeneity

Summary The process of host race formation in the aphid Tetraneura yezoensis is examined in relation to its population structure. T. yezoensis induces pouch galls on new leaves of Ulmus davidiana and U. laciniata. Its populations on the two host species are often sympatric. Fundatrices found on one elm species, when reciprocally transplanted to the other, suffered greatly reduced average fitness. This shows that aphid populations associated with the two elm species are genetically differentiated in physiological traits. Individual trees of each elm species showed large differences in susceptibility to gall formation and in bud burst time, and such between-tree variations were consistent over years. Overwintered eggs taken in early spring from four trees (two from each species) were incubated under the same temperature conditions. The average hatching time differed significantly even between populations from conspecific trees, and the sequence of egg hatching paralleled that of the leafing of those four trees. This between-tree difference in hatching time was consistent over years and was found to be genetic, showing that gene flow between aphid populations on separate trees is often restricted. The heterogeneity in host traits may have promoted the evolution of philopatry in this aphid. Of the fundatrices that hatched on a tree of one elm species, a few precent were preadapted to gall formation on the other elm species. This suggests that the formation of a new host race proceeds parapatrically under disruptive selection and at a low level of gene flow. Evidence was actually obtained that a small fraction of Tetraneura alates are passively transported and land on non-host plants.     

Diversity in symbiont consortia in the pea aphid complex is associated with large phenotypic variation in the insect host

Virtually all eukaryotes host microbial symbionts that influence their phenotype in many ways. In a host population, individuals may differ in their symbiotic complement in terms of symbiont species and strains. Hence, the combined expression of symbiont and host genotypes may generate a range of phenotypic diversity on which selection can operate and influence host population ecology and evolution. Here, we used the pea aphid to examine how the infection with various symbiotic complements contributes to phenotypic diversity of this insect species. The pea aphid hosts an obligate symbiont (Buchnera aphidicola) and several secondary symbionts among which is Hamiltonella defensa. This secondary symbiont confers a protection against parasitoids but can also reduce the host’s longevity and fecundity. These phenotypic effects of H. defensa infection have been described for a small fraction of the pea aphid complex which encompasses multiple plant-specialized biotypes. In this study, we examined phenotypic differences in four pea aphid biotypes where H. defensa occurs at high frequency and sometimes associated with other secondary symbionts. For each biotype, we measured the fecundity, lifespan and level of parasitoid protection in several aphid lineages differing in their symbiotic complement. Our results showed little variation in longevity and fecundity among lineages but strong differences in their protection level. These differences in protective levels largely resulted from the strain type of H. defensa and the symbiotic consortium in the host. This study highlights the important role of symbiotic complement in the emergence of phenotypic divergence among host populations of the same species.     

Diversity of the Most Commonly Reported Facultative Symbionts in Two Closely-Related Aphids with Different Host Ranges

Richness and abundance of facultative symbionts vary strongly with aphid species and genotype, symbiont strain, host plant, biogeography, and a number of abiotic factors. Despite indications that aphids in the same ecological niche show similar levels of facultative symbiont richness, existing reports do not consider the potential role of host plants on aphid microbial community. Little is known about how oligophagy and polyphagy may be influenced by secondary symbiont distribution, mainly because studies on secondary symbiont diversity are biased towards polyphagous aphids from the Northern Hemisphere. Here, we demonstrate the richness and abundance of the most common aphid-associated facultative symbionts in two tropical aphid species, the oligophagous Aphis (Toxoptera) citricidus (Kirkaldy) (Hemiptera: Aphididae) and the polyphagous Aphis aurantii (Boyer de Fonscolombe) (Hemiptera: Aphididae). Aphis citricidus is restricted to Citrus sp. host plants and closely related genera, whereas A. aurantii successfully exploits a wide variety of host plants from different families. Both were collected in the same ecological niche and our data basically indicated the same richness of secondary symbionts, but the abundance at which secondary symbionts occurred was very distinct between the two species. Spiroplasma was the most abundant facultative symbiont associated with A. citricidus and A. aurantii in the ecological niche studied. Single and multiple secondary symbiont infections were observed, but diversity of multiple infections was particularly high in A. citricidus. We discuss our findings and suggest hypotheses to explain causes and consequences of the differences in secondary symbiont diversity observed between these two aphid species.     

Molecular biological properties of new isolates of plum pox virus strain Winona

Plum pox virus (PPV, genus Potyvirus, family Potyviridae) is the most important virus pathogen of stone fruit cultures of the genus Prunus from an economical standpoint. Winona strain (PPV-W) is the most variable of nine known virus strains and one of the most widespread in the European part of Russia. Six new PPV-W isolates were first discovered in green plantations of Moscow (Kp2U, Avang, Pulk, Pulk-1), in Taldomsky district of Moscow region (Karm), and in Kovrovsky district of Vladimir region (Vlad-4) on wild trees of plum Prunus domestica. 3’-Terminal segment of genome of new isolates was notable for high variability level. The study on the relationship with other isolates of this strain by means of phylogenetic analysis of gene sequence of the coat protein showed the lack of clusterization of Russian PPV-W isolates according to geographical principle. Inoculation of Nicotiana benthamiana plants by hop plant louse Phorodon humili from plum trees infected with Avang and Pulk isolates and by thistle aphid Brachycaudus cardui from the tree infected with Kp2U isolate led to the systemic viral infection in indicator plants, suggesting the possibility of PPV-W spread by both aphid species in nature. Transmission of PPV-W through seeds was not observed.     

Host range limitation caused by incomplete host regulation in an aphid parasitoid

Defining host ranges in parasitoid insects is important both from a theoretical and an applied point of view. Based on the literature, some species seem able to use a wide range of hosts, while field studies indicate possible local host specialization. In koinobiont endoparasitoid species, such specialization could involve physiological processes. We tested the ability of two strains of the cosmopolitan and polyphagous parasitoid Diaeretiella rapae, to develop in three of its recorded aphid host species. Both strains produced high parasitism rates on the cabbage aphid Brevicoryne brassicae and the green peach aphid Myzus persicae but almost no progeny on the cherry-oat aphid Rhopalosiphum padi. This last species was less attacked by female parasitoids. Moreover, parasitoid eggs and larvae were smaller than in the two other host aphid species and their development was delayed. This abnormal development appeared to be due to an incomplete host regulation process, probably related to the low number and the size of teratocytes produced by D. rapae in R. padi individuals. Such a failure as far as gaining control of the host's metabolism is concerned could play an important role in shaping the host range of parasitoid insects, leading to local variation of the host spectrum in populations from various geographical areas.