Chromosome-level genome assembly of the horned-gall aphid, Schlechtendalia chinensis (Hemiptera: Aphididae: Erisomatinae)

The horned gall aphid Schlechtendalia chinensis, is an economically important insect that induces galls valuable for medicinal and chemical industries. S. chinensis manipulates its host plant to form well-organized horned galls during feeding. So far, more than twenty aphid genomes have been reported; however, all of those are derived from free-living aphids. Here we generated a high-quality genome assembly of S. chinensis, representing the first genome sequence of a galling aphid. The final genome assembly was 280.43 Mb, with 97% of the assembled sequences anchored into thirteen chromosomes. S. chinensis presents the smallest aphid genome size among available aphid genomes to date. The contig and scaffold N50 values were 3.39 Mb and 20.58 Mb, respectively. The assembly included 96.4% of conserved arthropod and 97.8% of conserved Hemiptera single-copy orthologous genes based on BUSCO analysis. A total of 13,437 protein-coding genes were predicted. Phylogenomic analysis showed that S. chinensis formed a single clade between the Eriosoma lanigerum clade and the Aphidini+Macrosiphini aphid clades. In addition, salivary proteins were found to be differentially expressed when S. chinensis underwent host alternation, indicating their potential roles in gall formation and plant defense suppression. A total of 36 cytochrome P450 genes were identified in S. chinensis, considerably fewer compared to other aphids, probably due to its small host plant range. The high-quality S. chinensis genome assembly and annotation provide an essential genetic background for future studies to reveal the mechanism of gall formation and to explore the interaction between aphids and their host plants.

Impact of ploidy and pathogen life cycle on resistance durability

The breeding of resistant hosts based on the gene-for-gene interaction is crucial to address epidemics of plant pathogens in agroecosystems. Resistant host deployment strategies are developed and studied worldwide to decrease the probability of resistance breakdown and increase the resistance durability in various pathosystems. A major component of deployment host strategies is the proportion of resistant hosts in the landscape. However, the impact of this proportion on resistance durability remains unclear for diploid pathogens with complex life cycles. In this study, we modelled pathogen population dynamics and genetic evolution at the virulence locus to assess the impact of the ploidy (haploid or diploid) and the pathogen's life cycle (with or without host alternation) on resistance durability. Ploidy has a strong impact on evolutionary trajectories, with much greater stochasticity and delayed times of resistance breakdown for diploids. This result emphasizes the importance of genetic drift in this system: as the virulent allele is recessive, positive selection on resistant hosts only applies to homozygous (virulent) individuals, which may lead to population collapses at low frequencies of the virulent allele. We also observed differences in the effect of host deployment depending on the pathogen's life cycle. With host alternation, the probability that the pathogen population collapses strongly increases with the proportion of resistant hosts in the landscape. Therefore, resistance breakdown events occurring at high proportions of resistant hosts frequently amount to evolutionary rescue. Last, life cycles correspond to two selection regimes: without host alternation (soft selection) the resistance breakdown is mainly driven by the migration rate. Conversely, host alternation (hard selection) resembles an all-or-nothing game, with stochastic trajectories caused by the recurrent allele redistributions on the alternate host.

Microbiome diversity of cotton aphids (Aphis gossypii) is associated with host alternation

Aphids are infected by a series of bacteria that can help them survive on specific host plants. However, the associations between aphids and these bacteria are not clear, and the bacterial communities in many aphid species are poorly characterized. Here, we investigated the bacterial communities of cotton aphids (Aphis gossypii) on 2 representative winter host plants and transferred to 3 summer host plants by 16S rDNA sequencing using the Illumina MiSeq platform. Our results revealed that the bacterial communities varied among cotton aphids on hibiscus, cotton aphids on pomegranate, cotton aphids on cotton transferred from hibiscus, cotton aphids on muskmelon transferred from hibiscus, cotton aphids on cucumber transferred from hibiscus,. The diversity and richness of the bacterial communities were significantly higher in aphids on muskmelon and aphids on cucumber than in the other treatments. There were two main factors influencing the distribution of internal bacterial OTUs revealed by principal component analysis, including the differences among Punicaceae, Malvaceae and Cucurbitaceae. There were 28 bacterial communities with significant differences between two arbitrary treatments, which could be grouped into 6 main clusters depending on relative abundance. Moreover, our results indicated that in addition to the obligate endosymbiont Buchnera, with a dominant position (> 52%), A. gossypii also harbored 3 facultative endosymbiotic bacteria (Serratia, Arsenophonus, and Wolbachia) and 3 possibly symbiotic bacteria (Acinetobacter, Pantoea, and Flavobacterium). There were several correspondences between the symbiotic bacteria in cotton aphids and the specific host plants of the aphids. This study provides a better understanding of the interactions among symbiotic bacteria, aphids and host plants, suggesting that the selection pressure on aphid bacterial communities is likely to be exerted by the species of host plants.

Chromosome-level genome assembly of the horned-gall aphid, Schlechtendalia chinensis (Hemiptera: Aphididae: Erisomatinae)

The horned gall aphid Schlechtendalia chinensis, is an economically important insect that induces galls valuable for medicinal and chemical industries. S. chinensis manipulates its host plant to form well-organized horned galls during feeding. So far, more than twenty aphid genomes have been reported; however, all of those are derived from free-living aphids. Here we generated a high-quality genome assembly of S. chinensis, representing the first genome sequence of a galling aphid. The final genome assembly was 280.43 Mb, with 97% of the assembled sequences anchored into thirteen chromosomes. S. chinensis presents the smallest aphid genome size among available aphid genomes to date. The contig and scaffold N50 values were 3.39 Mb and 20.58 Mb, respectively. The assembly included 96.4% of conserved arthropod and 97.8% of conserved Hemiptera single-copy orthologous genes based on BUSCO analysis. A total of 13,437 protein-coding genes were predicted. Phylogenomic analysis showed that S. chinensis formed a single clade between the Eriosoma lanigerum clade and the Aphidini+Macrosiphini aphid clades. In addition, salivary proteins were found to be differentially expressed when S. chinensis underwent host alternation, indicating their potential roles in gall formation and plant defense suppression. A total of 36 cytochrome P450 genes were identified in S. chinensis, considerably fewer compared to other aphids, probably due to its small host plant range. The high-quality S. chinensis genome assembly and annotation provide an essential genetic background for future studies to reveal the mechanism of gall formation and to explore the interaction between aphids and their host plants.

Gymnosporangium species on Malus: species delineation, diversity and host alternation

Gymnosporangium species (Pucciniaceae, Pucciniales, Basidiomycota) are the causal agents of cedarapple rust diseases, which can lead to significant economic losses to apple cultivars. Currently, the genus contains 17 described species that alternate between spermogonial/aecial stages on Malus species and telial stages on Juniperus or Chamaecyparis species, although these have yet to receive a modern systematic treatment. Furthermore, prior studies have shown that Gymnosporangium does not belong to the Pucciniaceae sensu stricto (s.str.), nor is it allied to any currently defined rust family. In this study we examine the phylogenetic placement of the genus Gymnosporangium. We also delineate interspecific boundaries of the Gymnosporangium species on Malus based on phylogenies inferred from concatenated data of rDNA SSU, ITS and LSU and the holomorphic morphology of the entire life cycle. Based on these results, we propose a new family, Gymnosporangiaceae, to accommodate the genus Gymnosporangium, and recognize 22 Gymnosporangium species parasitic on Malus species, of which G. lachrymiforme, G. shennongjiaense, G. spinulosum, G. tiankengense and G. kanas are new. Typification of G. asiaticum, G. fenzelianum, G. juniperi-virginianae, G. libocedri, G. nelsonii, G. nidus-avis and G. yamadae are proposed to stabilize the use of names. Morphological and molecular data from type materials of 14 Gymnosporangium species are provided. Finally, morphological characteristics, host alternation and geographical distribution data are provided for each Gymnosporangium species on Malus.

Seasonal Migration in the Aphid Genus Stomaphis (Hemiptera: Aphididae): Discovery of Host Alternation Between Woody Plants in Subfamily Lachninae

About 10% of aphid species show host alternation. These aphids migrate between primary and secondary host plant species in spring and autumn. Host alternation has not been observed in subfamily Lachninae, although it has been suggested on the basis of circumstantial evidence that Stomaphis japonica (Takahashi) may alternate its host between Quercus serrata (Murray) and Quercus acutissima (Carruth). However, a molecular phylogenetic study has indicated that the Stomaphis individuals feeding on these two plant species belong to two different lineages and aphids feeding on Q. acutissima and Pinus densiflora (Sieb. & Zucc.) belong to the same lineage. Here, we examined host alternation in Stomaphis species by comparing molecular phylogenetic identities, morphological features, and life cycles. The molecular analysis and morphological examination showed that aphids feeding on Q. acutissima were the same as those feeding on P. densiflora, whereas aphids feeding on Q. serrata were different from those feeding on Q. acutissima or on P. densiflora. Furthermore, winged aphids were observed on both Q. acutissima and P. densiflora in autumn, but we did not observe winged aphids on Q. serrata. These results indicate that Stomaphis (Walker) individuals feeding on Q. serrata and Q. acutissima belong to two species, one that feeds year-round on Q. serrata, and another, heteroecious species that feeds on P. densiflora as a primary host and on Q. acutissima as a secondary host. This study documents host alternation in subfamily Lachninae for the first time and discusses the acquisition of host alternation by Stomaphis from evolutionary and ecological perspectives.

Extensive transcriptional changes in the aphid species Myzus cerasi under different host environments associated with detoxification genes

Aphids are phloem-feeding insects that cause yield losses to crops globally. These insects feature complex life cycles, which in the case of many agriculturally important species involves the use of primary and secondary host plant species. Whilst host alternation between primary and secondary host can occur in the field depending on host availability and the environment, aphid populations maintained as laboratory stocks generally are kept under conditions that allow asexual reproduction by parthenogenesis on secondary hosts. Here, we used Myzus cerasi (black cherry aphid) to assess aphid transcriptional differences between populations collected from primary hosts in the field and those adapted to secondary hosts under controlled environment conditions. Adaptation experiments of M. cerasi collected from local cherry tress to reported secondary host species resulted in low survival rates. Moreover, aphids were unable to survive on secondary host Land cress, unless first adapted to another secondary host, cleavers. Transcriptome analyses of populations collected from primary host cherry in the field and the two secondary host plant species in a controlled environment showed extensive transcriptional plasticity to a change in host environment, with predominantly genes involved in redox reactions differentially regulated. Most of the differentially expressed genes across the M. cerasi populations from the different host environments were duplicated and we found evidence for differential exon usage. In contrast, we observed only limited transcriptional to a change in secondary host plant species.

Parasite performance and host alternation: is there a negative effect in host-specific and host-opportunistic parasites?

SUMMARYEnvironmental fluctuations are expected to require special adaptations only if they are associated with a decrease in fitness. We compared reproductive performance between fleas fed on alternating (preferred and non-preferred) hosts and fleas fed solely on either a preferred or a non-preferred host to determine whether (1) host alternation incurs an immediate negative effect, and, if yes, then (2) whether this effect is greater in a host specialist (Parapulex chephrenis) than in host generalists (Xenopsylla conformisandSynosternus cleopatrae). We also compared flea performance under alternating host regimes with different host order (initial feeding on either a preferred or a non-preferred host). An immediate negative effect of alternating hosts on reproductive performance was found inP. chephrenisonly. These fleas produced 44·3% less eggs that were 3·6% smaller when they fed on alternating hosts as compared with a preferred host. In contrast,X. conformisandS. cleopatraeappeared to be able to adapt their reproductive strategy to host alternation by producing higher quality offspring (on average, 3·1% faster development and 2·1% larger size) without compromising offspring number. However, the former produced eggs that were slightly, albeit significantly, smaller when it fed on alternating hosts as compared with a preferred host. Moreover, host order affected reproductive performance in host generalists (e.g. 2·8% larger eggs when the first feeding was performed on a non-preferred host), but not in a host specialist. We conclude that immediate effects of environmental fluctuation on parasite fitness depend on the degree of host specialization.

Some bioecological aspects of the rose aphid, Macrosiphum rosae (Hemiptera: Aphididae) and its natural enemies

The rose aphid, Macrosiphum rosae, is one of the most important pests on roses in the world and it causes economic damage. In this study, biology, seasonal population dynamics, and status of natural enemies of the rose aphid were studied. Seasonal population dynamics was studied by randomly sampling 10 shoots every week in two locations of Isfahan, Iran. Rose aphid with a high population density, both in spring (April and May) and in autumn (November), was observed on roses. The results showed that the rose aphid overwinters as parthenogenetic females and nymphs. This aphid migrates to a secondary host, Dipsacus fullonum (Dipsacaceae), in summer due to poor food quality of rose plants. Since sexual form and egg of the rose aphid were not observed in Isfahan, it is probably anholocyclic species with host alternation in this area. Natural enemies of the rose aphid include four species of Coccinellidae, three species of Syrphidae, two species of Chamaemyiidae, one species of Chrysopidae, a few species of Anthocoridae and Miridae, and one species of Cantharidae. One species of ectoparasite mite of Erythraeidae was also collected. In addition, four species of parasitoid wasps, Braconidae, were collected.