Host Plant Species Research Articles

A new neopasiphaeine bee associated with flowers of Loasaceae (Hymenoptera: Colletidae: Actenosigynes).

The genus Actenosigynes includes two species, A. fulvoniger (Michener, 1989) and A. mantiqueirensis Silveira, 2009, both oligolectic on flowers of Blumenbachia (Loasaceae) in southern Brazil. We describe a third species, Actenosigynes silveirai Siriani-Oliveira, sp. n., and provide additional evidence to the suspected narrow host-plant specificity between bees of this genus and Loasaceae. This new species was only recorded to collect resources on flowers of Aosa, a genus closely related to Blumenbachia in the subfamily Loasoideae. We illustrate female and male specimens of the three species to offer a complete summary of the morphological variation within this modestly sized genus of Neopasiphaeinae, including photographs of male genitalia and associated metasomal sterna. Moreover, we provide an identification key for the three species of Actenosigynes and the first phylogenetic and dating estimate for these taxa. The genus diversified in southern South America during the Miocene-Pliocene, following a more ancient divergence associated with the orogenic events that separated its sister-genus, Torocolletes, west of the Andes. We dedicate this newly described species to Fernando A. Silveira for his contributions to research on Brazilian bee taxonomy and biology.

Assessing the applicability of nuclear 18S and ITS2-28S rRNA genes for diagnostics of Bactrocera dorsalis (Diptera: Tephritidae) in the Philippines

Fruit flies belonging to the Bactrocera dorsalis species complex pose a significant threat to mangoes and other crops in the Philippines and worldwide. Identifying cryptic species within this complex is challenging, particularly when relying solely on morphological analysis. In this study, we sequenced two fragments of the nuclear 18S and ITS2-28S rRNA genes from specimens of Bactrocera dorsalis Hendel collected in the Philippines to assess their applicability for species diagnostics. Subsequent sequencing and analysis revealed that the 18S and 28S rRNA gene fragments matched B. dorsalis sequences in NCBI but also displayed high similarity with other Bactrocera and insect species. On the other hand, sequences of the ITS2 segment showed hits specific to B. dorsalis. Further analysis of the 18S rRNA gene in fruit flies collected from various sources and host plants in the country suggests conserved sequences among Bactrocera samples, irrespective of collection site and host plant species. In conclusion, our findings suggest that, among the tested nuclear DNA fragments, only the ITS2 demonstrates sufficient species-level nucleotide variation for effective use as a molecular diagnostic marker for B. dorsalis identification.

Natural regulation of Helicoverpa armigera larvae by hymenopteran parasitoids in northern Cameroon: Is there scope for application of conservation biological control in cotton agroecosystems?

The conservation biological control (CBC) concept has been explored through research conducted in northern Cameroon on larval parasitism of Helicoverpa armigera, a major cotton pest, on different host plants year round, from early September 2008 to late December 2014. A total of 47,152 caterpillars were reared over the 6-year period. They were found regularly present on crops such as cotton and okra and on wild plants, including Corynandra viscosa and Hyptis spp. The overall percentages of nematode- and disease-infected caterpillars were very low (1.05% and 2.92%, respectively). Diptera species accounted for less than 0.1% of the parasitoids that had emerged from caterpillars. Total hymenopteran parasitism was 10.5%, and varied markedly depending on the host plants. Nine Hymenoptera species were identified, with Meteorus laphygmarum being the dominant one (almost 80% of all 2698 adult parasitoids obtained after rearing), followed by Schoenlandella variegata (16.42%) and Charops spinitarsis (<2%). Out of this total, 35%, 28% and 25% of the adults were obtained respectively on C. vicosa, cotton and Hyptis spp., i.e. < 5% on all other host plants. The analysis conducted on 237 collections showed that, after adjusting for year and month effects, a highly significant difference was found between the parasitism rates observed on the different host plant species. The plants most suitable for H. armigera parasitism were Acantospermum hispidum, C. viscosa and Hyptis spp. The proportion of M. laphygmarum among emerged hymenoptera was highest on C. viscosa, medium on cotton and Hyptis spp. and lowest on L. esculentum. Future studies that could be carried out are outlined in the discussion with the aim of facilitating the transfer of parasitoids from caterpillars present on one plant species to those infesting cotton crops.

Species swarms and their caterpillar colonisers: phylogeny and polyphenols determine host plant specificity in New Guinean Lepidoptera

The majority of multi-cellular terrestrial life is found in tropical forests and is either an invertebrate or a plant: for decades ecologists have sought to understand why. As global change erodes the list of extant species on our planet quantifying what species remain, along with their origins and ecology, contributes to our ability to preserve ecosystem functioning and resilience. Here we study three feeding guilds of caterpillars (Lepidoptera) and seek to understand the drivers of their diet breadth across four diverse tropical plant genera in Papua New Guinea. Host specificity is central to biodiversity estimates and the resilience of ecological networks. Specifically, we calculate distance-based host specificity in relation to plant phylogenetic relationships alongside chemical and mechanical traits of leaves. In terms of chemical defenses, we focus on the major polyphenol groups, a compound class shared across many plant species. We refine our data exploration using food webs and ordinations to pick out specific traits of relevance to insect host specificity. Our results showed that the degree of specialization for caterpillars took the following order: phylogenetic&amp;gt;polyphenol&amp;gt;mechanical, such that insect specificity was explained best by host phylogeny and polyphenol chemistry in our study system. Leaf mining insects had higher host specificity than those feeding externally. Of the traits studied hexahydroxydiphenoyl derivatives, galloyl derivatives, trichome density, quinic acid derivatives, myricetins and successional index explained the most variation in overall insect community structure. Our findings build on earlier studies of New Guinean rainforest communities and add a mechanistic explanation to previous findings that host genera are functional islands for insect herbivores. Further, we demonstrate that different plant genera combine different defensive traits that appear to drive associated insect diversity. Our approach integrates trait data and phylogeny to explore dimensions of specialization and we welcome metabolomic studies that will provide more detailed explanations for insect-herbivore host use. Finally, chemical diversity is directly linked to organismal diversity and by studying a range of insect herbivore guilds we make a connection between feeding ecology and specialization that will help to predict species interactions and, potentially, the persistence of ecological networks.

Evolution of realized niche breadth diversity driven by community dynamics.

Why many herbivorous insects are host plant specialists, with non-negligible exceptions, is a conundrum of evolutionary biology, especially because the host plants are not necessarily optimal larval diets. Here, I present a novel model of host plant preference evolution of two insect species. Because habitat preference evolution is contingent upon demographic dynamics, I integrate the evolutionary framework with the modern coexistence theory. The results show that the two insect species can evolve into a habitat specialist and generalist, when they experience both negative and positive frequency-dependent community dynamics. This happens because the joint action of positive and negative frequency dependence creates multiple (up to nine) eco-evolutionary equilibria. Furthermore, initial condition dependence due to positive frequency dependence allows specialization to poor habitats. Thus, evolved habitat preferences do not necessarily correlate with the performances. The model provides explanations for counterintuitive empirical patterns and mechanistic interpretations for phenomenological models of niche breadth evolution.

The impact of Elaeagnus angustifolia root exudates on Parafrankia soli NRRL B-16219 exoproteome.

Root exudates from host plant species are known to play a critical role in the establishment and maintenance of symbiotic relationships with soil bacteria. In this study, we investigated the impact of root exudates from compatible host plant species; Elaeagnus angustifolia on the exoproteome of Parafrankia soli strain NRRL B-16219. A total of 565 proteins were evidenced as differentially abundant, with 32 upregulated and 533 downregulated in presence of the plant exudates. Analysis of the function of these proteins suggests that the bacterial strain is undergoing a complex metabolic reprogramming towards a new developmental phase elicited in presence of host plant root exudates. The upregulation of Type II/IV secretion system proteins among the differentially expressed proteins indicates their possible role in infecting the host plant, as shown for some rhizobia. Additionally, EF-Tu, proteins upregulated in this study, may function as an effector for the T4SSs and trigger plant defense responses. These findings suggest that Parafrankia soli may use EF-Tu to infect the actinorhizal host plant and pave the way for further investigations of the molecular mechanisms underlying the establishment of symbiotic relationships.

A gap in the recognition of two mycorrhizal factors: new insights into two LysM-type mycorrhizal receptors.

Arbuscular mycorrhizal (AM) fungi are crucial components of the plant microbiota and can form symbioses with 72% of land plants. Researchers have long known that AM symbioses have dramatic effects on plant performance and also provide multiple ecological services in terrestrial environments. The successful establishment of AM symbioses relies on the host plant recognition of the diffusible mycorrhizal (Myc) factors, lipo-chitooligosaccharides (LCOs) and chitooligosaccharides (COs). Among them, the short-chain COs such as CO4/5 secreted by AM fungi are the major Myc factors in COs. In this review, we summarize current advances, develop the concept of mycorrhizal biceptor complex (double receptor complexes for Myc-LCOs and CO4/5 in the same plant), and provide a perspective on the future development of mycorrhizal receptors. First, we focus on the distinct perception of two Myc factors by different host plant species, highlighting the essential role of Lysin-Motif (LysM)-type mycorrhizal receptors in perceiving them. Second, we propose the underlying molecular mechanisms by which LysM-type mycorrhizal receptors in various plants recognize both the Myc-LCOs and -COs. Finally, we explore future prospects for studies on the biceptor complex (Myc-LCO and -CO receptors) in dicots to facilitate the utilization of them in cereal crops (particularly in modern cultivated rice). In conclusion, our understanding of the precise perception processes during host plant interacting with AM fungi, where LysM-type mycorrhizal receptors act as recruiters, provides the tools to design biotechnological applications addressing agricultural challenges.

Diversity and composition of the bacterial communities associated with the Australian spittlebugs Bathyllus albicinctus and Philagra parva (Hemiptera: Aphrophoridae).

Spittlebugs and froghoppers (Hemiptera: Cercopoidea) are insects feeding on xylem, which potentially can cause significant economic damage worldwide by transmitting plant pathogenic bacteria such as Xylella fastidiosa. Australia and New Zealand are currently free from X. fastidiosa, but they are home to at least 45 native spittlebug species. Among these, the Australian natives Bathyllus albicinctus (Erichson, 1842) and Philagra parva (Donovan, 1805) are particularly widespread and can be found across southern and eastern Australia, with B. albicinctus also in New Zealand. The potential that both species might be capable of vectoring Xylella fastidiosa poses a substantial biosecurity risk if the bacterium were to invade these regions. In this study, we examined 87 spittlebug nymphs collected across 12 different host plant species, in five locations in Victoria, Australia. Our objective was to explore the factors influencing bacterial communities within and between these widespread spittlebug species, considering geographic location, insect phylogenetics, and host plant associations. We employed COI barcoding to assess insect genetic variation and 16S high throughput sequencing (HTS) metabarcoding to analyse bacterial microbiome diversity across various host plants. Our findings revealed minimal genetic divergence among spittlebug individuals in the same species, highlighting conspecificity despite conspicuous morphological divergences. On the other hand, we recorded significant variation in bacterial communities harboured by Bathyllus albicinctus nymphs feeding on different plants, even when these were collected within close proximity to each other. Therefore, host plant association appeared to shape the bacterial communities of spittlebugs more than insect genetic divergence or geographical location. These diverse bacterial communities could potentially facilitate transmission of plant pathogenic bacteria, underscoring the risk of widespread transmission among numerous plant hosts through insect-plant interactions. This study emphasizes the critical need to understand these complex interactions, particularly in the context of biosecurity.

Taxonomic analysis of phytopathogenic micromycetes of landscape trees and shrubs (based on the example or Samarkand city)

The article provides information about phytopathogenic micromycetes of trees and shrubs common in the city of Samarkand. In the course of the research, it was established that 45 species of micromycete fungi are found in 32 plant species and are pathogenic. As a result of the analysis, it was established that 45 species of micromycete fungi belong to 3 divisions, 14 orders, 24 families and 28 genera. Herbarium data collected during the study were analyzed and it was found that 45 species of phytopathogenic micromycetes parasitize 32 species of host plants belonging to 28 genera and 21 families. The study identified 45 species of phytopathogenic micromycetes parasitizing 32 species of host plants. These 32 species of forage plants belong to 27 genera and 21 families, of which 21 species of trees and 11 species of shrubs were identified. Under the influence of fungal diseases caused by phytopathogenic micromycetes recorded in 32 species of ornamental trees and shrubs, the aesthetic properties of these plants decreased. Host plants were identified that were heavily infected with several species of phytopathogenic micromycetes.

New Host Plant Species of Grapevine Virus A Identified with Vector-Mediated Infections.

Grapevine virus A (GVA) is an economically important virus and a member of the genus Vitivirus (family Betaflexiviridae) that causes a range of symptoms with qualitative and quantitative effects on grape production. Wild and domesticated species of Vitis, including hybrids used as rootstocks, are considered important natural hosts of GVA. Mechanical transmission to some herbaceous plant species, graft transmission, and vector transmission from grape to grape by various mealybugs and soft scale insects have been reported. Under laboratory and greenhouse conditions, this study demonstrates the transmission of GVA from grapes to alternative hosts by the vine mealybug (Planococcus ficus). Results of ELISA, end-point one-step RT-PCR, and real-time RT-PCR, and in some cases electron microscopy and genome sequencing, confirmed successful transmission to three new plant species commonly found in Croatian vineyards: velvetleaf (Abutilon theophrasti), redroot pigweed (Amaranthus retroflexus), and field poppy (Papaver rhoeas), along with Chenopodium murale and the previously known host Nicotiana benthamiana, with variable infection rates. Depending on the host species, symptoms in the form of leaf reddening, yellow spots, reduced growth of lateral shoots, systemic vein clearing, foliar deformation and rugosity, and dwarfism were observed in GVA-infected plants, whereas no symptoms were observed in infected plants of A. theophrasti. Reverse transmission from these new hosts to grapevines by Pl. ficus was not successful. These results confirm four new GVA host species and open new research venues.

Chemosensory detection of glucosinolates as token stimuli for specialist insects on brassicaceous plants: discovery and impact.

In this paper, we take a historical perspective by going back to Verschaffelt's landmark study published in 1910, in which he found that glucosinolates were used as token stimuli by larvae of Pieris butterflies, specialist feeders on plants in the family Brassicaceae. This classic discovery provided key evidence for Fraenkel(Science 129:1466-1470, 1959) to elaborate on the function of secondary plant substances and for Ehrlich and Raven(Evolution 18:586-608, 1964) to put forward the hypothesis of insect-plant coevolution. The discovery by Schoonhoven (Kon Nederl Akad Wetensch Amsterdam Proc Ser C70:556-568, 1967) of taste neurons highly sensitive to glucosinolates in Pieris brassicae was an important milestone in elucidating the chemosensory basis of host-plant specialization. The molecular basis of glucosinolate sensitivity was elucidated recently (Yang et al., PLoS Genet 17, 2021) paving the way to unravel the evolution of gustatory receptors tuned to glucosinolates that are crucial for host-plant selection of Pieris butterflies. We propose a hypothetical model for the evolution of labeled-line neurons tuned to token stimuli.

Update of the Xylella spp. host plant database - systematic literature search up to 30 June 2023.

This scientific report provides an update of the Xylella spp. host plant database, aiming to provide information and scientific support to risk assessors, risk managers and researchers dealing with Xylella spp. Upon a mandate of the European Commission, EFSA created and regularly updates a database of host plant species of Xylella spp. The current mandate covers the period 2021-2026. This report is related to the ninth version of the database published in Zenodo in the EFSA Knowledge Junction community, covering literature published from 1 January 2023 up to 30 June 2023, and recent Europhyt outbreak notifications. Informative data have been extracted from 47 selected publications. Seven new host plants were identified and added to the database. These plant species were naturally infected by X. fastidiosa subsp. multiplex in France, Spain and the United States. No additional data were retrieved for X. taiwanensis, and no additional multilocus sequence tipes (STs) were identified worldwide. New information on the tolerant/resistant response of plant species to X. fastidiosa infection were added to the database. The Xylella spp. host plant species were listed in different categories based on the number and type of detection methods applied for each finding. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method (between sequencing and pure culture isolation (category A), reaches now 439 plant species, 200 genera and 69 families. Such numbers rise to 696 plant species, 307 genera and 88 families if considered regardless of the detection methods applied (category E).

A revision of the genus Ima Tindale (Mantodea: Nanomantidae: Fulciniinae) with the description of a new genus.

Ima fusca is one of a number of unusual and infrequently collected Australian mantises about which relatively little is known. Long considered a single species, morphological studies instead revealed the presence of a second cryptic species. We here describe this species as Ima corymbia sp. nov. and redescribe both Ima and Ima fusca in detail. Additionally, we describe a unique, robust species allied to Ima that was discovered with the aid of citizen science, Inimia nat gen. et sp. nov. In light of this discovery, we provide keys to both the Australian Fulciniini genera and to the species of Ima. Finally, we provide detailed behavioural and ecological records for all three species, including the peculiar host plant specificity of Ima spp. We document and discuss this specificity in depth and suggest several possible reasons for its occurrence.

Arthropod associates of Kenyan buffelgrass (Cenchrus ciliaris): a field survey for biological control candidates of a globally important invasive grass

Invasive species are the second largest contributor to biodiversity loss and drivers of ecosystem change. Buffelgrass is a C4, perennial grass native to Africa and Asia that was widely introduced across tropical and subtropical rangelands as livestock forage. Buffelgrass reduces native biodiversity and ecosystem stability in its introduced range when it escapes livestock pastures. Understanding the ecology of insects associated with buffelgrass in its native range may provide an understanding of invasion processes and biological control opportunities where buffelgrass has become an invasive challenge. Here, we present the results of a six-year survey of herbivorous arthropods of a native buffelgrass population from Kenya. Buffelgrass was examined for externally and internally feeding insects of vegetative and reproductive tissues. We also categorised buffelgrass detritivores and parasitoids that may use buffelgrass herbivores as hosts. The samples were photographed and Sanger sequenced to identify them to the lowest possible taxonomic ranking. We collected information on sample abundances, phenologies, tissues consumed, and putative diet breadths. We identified 25 morphospecies representing seven orders and 16 families. The putative host plant specialisation was as high as 67% for Diptera. Phenological variation in herbivore presence correlated with seasonal rainfall and provided a guide for when to conduct follow-up biological control agent searches. The most abundant herbivore was a gall midge (Diptera: Cecidomyiidae) that inhabits buffelgrass culms. Additional research should focus on bringing this species into containment where host choice trials can be conducted to determine if it is truly monophagous and assess its impact on buffelgrass growth.

Host Records of Lipolexis oregmae Gahan (Hymenoptera: Braconidae: Aphidiinae) with Food Plants in India (A Review Article)

The present review article deals the association of Lipolexis oregmae Gahan with their aphid host and their food plants for the possible use in biological control programme. Aphids are small sap sucking plant bugs and most important groups of phytophagous insect because of their polymorphism, host alternative heterocious behaviour and reproductive habits, they cause serious problems on agricultural and horticultural plants even at low densities so their management is necessary. L.oregmae Gahan is very important aphid parasitoids and widely distributed throughout the Asia and considered as an important parasitoids for the biological control programme. It has been successfully introduced in Florida and other areas. It is recorded on 19 aphid species (Aphis (Toxoptera) aurantii, Aphis (Toxoptera) citricidus, Aphis (Toxoptera) odinae, Aphis craccivora, Aphis fabae, Aphis gossypii, Aphis nasturtii, Aphis nerii, Aphis ruborum longisetosus, Aphis solanella, Aphis spiraecola, Greenidae formosana, Liosomaphis himalayensis, Myzus avenae, Myzus (Nectarosiphon) persicae, Rhopalosiphum maidis, Rhopalosiphum nymphaeae, Sitobion avenae, Tuberolachnus salignu) in India on several specific host plants. Its maximum parasitization was recorded on Aphis gossypii infesting (23 host plants), followed by Aphis craccivora (19 host plants), Aphis nasturtii (16 host plants), Aphis spiraecola (13 host plants) and Myzus persicae (9 host plants).

Larval Host Plants of the Butterflies under Papilionidae Family of the Western Ghats, India

Butterflies are flying jewels of nature. They are very diverse and has a great role the ecosystem maintenance. Butterflies are widely used as model insects in various studies related to evolution, ethology, insect - plant interactions and distribution (Settele &amp; Kühn, 2009; Rayalu et al,, 2013). Butterflies are among the most studied group of insects in relation to the selection of larval food plants and egg laying patterns and behavior. In relation to the larval food plant selection, considerable amount of database is available on the butterflies and their behavior. These studies have been carried out in almost all geographic regions of the world. (Wilkund, 1984; Kelly &amp; Debinski, 1998; Settele et al., 2009; Curtis et al., 2015; Nitin et al., 2018; Robinson et al., 2001; Rayalu et al., 2013, Hill et al., 2018). Butterflies are one of the most interesting and fascinating insect groups. Butterflies widely appreciated for their aesthetic value are important as ecological indicators [1]. One fifth of the world’s total butterflies are available in India. The butterflies are selective in their choice of flowers and plants they visit. Butterflies and their caterpillars are dependent on specific host plants for foliage, nectar and pollen as their food. Selection of food plants for the immature stages by the adult females is a well-known fact in butterflies and other group of insects. Thus, butterfly diversity indirectly reflects overall plant diversity, especially that of herbs and shrubs, in the given area

Co-occurring tree species drive arbuscular mycorrhizal fungi diversity in tropical forest.

It is still uncertain whether environment or host plant species is more important in determining AMF diversity; although, plant roots are usually associated with abundant AMF species in different environments. This study explored the effect of plant species and environmental factors on AMF diversity based on three co-occurring tree species (Glochidion coccineum, Schefflera octophylla, and Schima superba) on six elevations of Mt. Jianfengling. A total of 185 OTUs (operational taxonomic units) of AMF were found in the three co-occurring dominant tree species. Of which 109 unique OTUs were identified in the three co-occurring plant species, which accounted for the total number of 58.92%. Forty-five OTUs were shared by the three co-occurring tree species, accounting for a total number of 24.32%. The plant species of Schefflera octophylla was identified as having the highest AMF diversity with the largest number of OTUs of 143. The fungi in the genus of Glomus were the dominant AMF species in the three co-occurring tree species. AMF communities and diversity are quite different, either within different plant species at the same elevation or within the same plant species at different elevations. However, the altitude had no significant effect on the ACE index. Therefore, the results suggest that plant species have a more important effect on AMF diversity and community composition.

Zymograms as a Tool to Detect PPIs in Host plants of Antheraea Assamensis

Antheraea assamensis (vernacular: ‘muga’) larvae is commercially reared on two tree species of the Lauraceae family, Persea bombycina and Litsea monopetala for its golden yellow, lustrous cocoon silk. Biochemical and molecular studies suggested that the midgut digestive enzymes and their transcripts in larvae feeding on P. bombycina differ from those found in larvae feeding on L. monopetala indicating that host plant 'choice' affects the digestive physiology of this insect. Ingestion of plant proteinase inhibitors is known to influence expression of digestive enzymes. Using reverse zymography technique trypsin and chymotrypsin inhibitors were detected in herbivore-induced leaves of L. monopetala and P. bombycina that could inhibit midgut proteinases of A. assamensis. Such interactions may affect proteolytic digestion in larvae reared on different host plant species. This work may have significance in quality of silk produced by muga silkworm, ultimately benefiting the silkworm rearers/industry.

Identification, Sequencing, and Molecular Analysis of RNA2 of Artichoke Italian Latent Virus Isolates from Known Hosts and a New Host Plant Species.

Despite its first description in 1977 and numerous reports of its presence in various plant species in many countries, the molecular information available in GenBank for artichoke Italian latent virus (AILV) is still limited to a single complete genome sequence (RNA1 and 2) of a grapevine isolate (AILV-V) and a partial portion of the RNA2 sequence from an isolate of unknown origin and host. Here, we report the results of molecular analyses conducted on the RNA2 of some AILV isolates, sequenced for the first time in this study, together with the first-time identification of AILV in a new host plant species, namely chard (Beta vulgaris subsp. vulgaris), associated with vein clearing and mottling symptoms on leaves. The different AILV isolates sequenced were from artichoke (AILV-C), gladiolus (AILV-G), Sonchus (AILV-S), and chard (AILV-B). At the molecular level, the sequencing results of the RNA2 segments showed that AILV-C, AILV-G, AILV-S, and AILV-B had a length of 4629 nt (excluding the 3' terminal polyA tail), which is one nt shorter than that of the AILV-V reported in GenBank. A comparison of the RNA2 coding region sequences of all the isolates showed that AILV-V was the most divergent isolate, with the lowest sequence identities of 83.2% at the nucleotide level and 84.7% at the amino acid level. Putative intra-species sequence recombination sites were predicted among the AILV isolates, mainly involving the genomes of AILV-V, AILV-C, and AILV-B. This study adds insights into the variability of AILV and the occurrence of recombination that may condition plant infection.

DNA methylation differences between stick insect ecotypes.

Epigenetic mechanisms, such as DNA methylation, can influence gene regulation and affect phenotypic variation, raising the possibility that they contribute to ecological adaptation. Beginning to address this issue requires high-resolution sequencing studies of natural populations to pinpoint epigenetic regions of potential ecological and evolutionary significance. However, such studies are still relatively uncommon, especially in insects, and are mainly restricted to a few model organisms. Here, we characterize patterns of DNA methylation for natural populations of Timema cristinae adapted to two host plant species (i.e. ecotypes). By integrating results from sequencing of whole transcriptomes, genomes and methylomes, we investigate whether environmental, host and genetic differences of these stick insects are associated with methylation levels of cytosine nucleotides in the CpG context. We report an overall genome-wide methylation level for T. cristinae of ~14%, with methylation being enriched in gene bodies and impoverished in repetitive elements. Genome-wide DNA methylation variation was strongly positively correlated with genetic distance (relatedness), but also exhibited significant host-plant effects. Using methylome-environment association analysis, we pinpointed specific genomic regions that are differentially methylated between ecotypes, with these regions being enriched for genes with functions in membrane processes. The observed association between methylation variation and genetic relatedness, and with the ecologically important variable of host plant, suggests a potential role for epigenetic modification in T. cristinae adaptation. To substantiate such adaptive significance, future studies could test whether methylation can be transmitted across generations and the extent to which it responds to experimental manipulation in field and laboratory studies.