Host-associated Differentiation Research Articles

Unveiling Cryptic Species Diversity and Genetic Variation of Lasiodiplodia (Botryosphaeriaceae, Botryosphaeriales) Infecting Fruit Crops in Taiwan.

The genus Lasiodiplodia, a member of the family Botryosphaeriaceae, is an important fungal disease genus in agriculture. However, the Lasiodiplodia species survey and genetic diversity in Taiwan remain unclear. This study aimed to investigate the Lasiodiplodia species associated with various fruit species to explore the cryptic Lasiodiplodia species diversity, validate species delimitation, and unveil cryptic genetic diversity. Overall, six Lasiodiplodia species were identified, with several new records of infection identified. Additionally, phylogenetic analyses indicated that the relations of all isolates of L. theobromae might be paraphyletic. They were grouped with L. brasiliense based on Automatic Barcode Gap Discovery (ABGD), Automatic Partitioning (ASAP) and structure-based clustering analyses. These analyses did not provide conclusive evidence for L. brasiliensis as a stable species. It may be necessary to gather more information to clarify the species delineation. The multiple new records of Lasiodiplodia species with high genetic diversity and differentiation revealed that the diversity of Lasiodiplodia in Taiwan was underestimated in the past. We found that L. theobromae has the highest number of haplotypes but the lowest number of haplotype and nucleotide diversities, indicating a recent population expansion. This was supported by the significant negative Tajima's D and Fu and Li's D* tests. The high genetic diversity, low gene flow, and host-associated differentiation of Lasiodiplodia species indicate that they might harbour powerful evolutionary potential in Taiwan. This study provided critical insights into genetic variation, host-associated differentiation, and demography of Lasiodiplodia species, which would be helpful for disease management of related pathogens.

Multiple mechanisms contribute to isolation-by-environment in the redheaded pine sawfly, Neodiprion lecontei.

Isolation by environment (IBE) is a population genomic pattern that arises when ecological barriers reduce gene flow between populations. Although current evidence suggests IBE is common in nature, few studies have evaluated the underlying mechanisms that generate IBE patterns. In this study, we evaluate five proposed mechanisms of IBE (natural selection against immigrants, sexual selection against immigrants, selection against hybrids, biased dispersal, environment-based phenological differences) that may give rise to host-associated differentiation within a sympatric population of the redheaded pine sawfly, Neodiprion lecontei, a species for which IBE has previously been detected. We first characterize the three pine species used by N. lecontei at the site, finding morphological and chemical differences among the hosts that could generate divergent selection on sawfly host-use traits. Next, using morphometrics and ddRAD sequencing, we detect modest phenotypic and genetic differentiation among sawflies originating from different pines that is consistent with recent, in situ divergence. Finally, via a series of laboratory assays - including assessments of larval performance on different hosts, adult mate and host preferences, hybrid fitness, and adult eclosion timing - we find evidence that multiple mechanisms contribute to IBE in N. lecontei. Overall, our results suggest IBE can emerge quickly, possibly due to multiple mechanisms acting in concert to reduce migration between different environments.

Prey-associated genetic differentiation in two species of silver fly (Diptera: Chamaemyiidae), Leucotaraxis argenticollis and L. piniperda

Abstract Sympatric host-associated genetic differentiation is a prominent pattern that could lead to speciation. In insects, there are numerous examples of host-associated differentiation among herbivores that prefer different plants, and parasitoids that prefer different hosts, but few examples for specialist predators. We developed new microsatellite loci for two species of silver fly, Leucotaraxis argenticollis (Zetterstedt) and L. piniperda (Malloch) (Diptera: Chamaemyiidae), being evaluated as biological control agents for the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), in eastern North America where it is a nonnative pest. We obtained DNA from specimens of both fly species feeding on native A. tsugae in western North America, as well as on other western and eastern adelgid species. We performed population genetic analyses using the new loci and DNA barcode sequences. Our results confirmed east–west allopatric divergence and uncovered nested genetic differentiation associated with different adelgid prey species and their host plants in western North America for both species of silver flies. For both species, there is also evidence for a longer history of diversification in the west, with ancestral specialization of feeding on pine adelgids, which was retained after range expansion to the east. More recently, divergence to feeding on new adelgid prey species occurred in the west. Our findings are consistent with the hypothesis that host-alternating life cycles in Adelgidae may provide temporary escape from specialist predators. We discuss the implications for biological control efficacy and potential for lineage hybridization as western flies are released in the east to control A. tsugae.

Host association, environment, and geography underlie genomic differentiation in a major forest pest.

Diverse geographic, environmental, and ecological factors affect gene flow and adaptive genomic variation within species. With recent advances in landscape ecological modelling and high-throughput DNA sequencing, it is now possible to effectively quantify and partition their relative contributions. Here, we use landscape genomics to identify determinants of genomic differentiation in the forest tent caterpillar, Malacosoma disstria, a widespread and irruptive pest of numerous deciduous tree species in North America. We collected larvae from multiple populations across Eastern Canada, where the species experiences a diversity of environmental gradients and feeds on a number of different host tree species, including trembling aspen (Populus tremuloides), sugar maple (Acer saccharum), red oak (Quercus rubra), and white birch (Betula papyrifera). Using a combination of reciprocal causal modelling (RCM) and distance-based redundancy analyses (dbRDA), we show that differentiation of thousands of genome-wide single nucleotide polymorphisms (SNPs) among individuals is best explained by a combination of isolation by distance, isolation by environment (spatial variation in summer temperatures and length of the growing season), and differences in host association. Configuration of suitable habitat inferred from ecological niche models was not significantly related to genomic differentiation, suggesting that M.disstria dispersal is agnostic with respect to habitat quality. Although population structure was not discretely related to host association, our modelling framework provides the first molecular evidence of host-associated differentiation in M.disstria, congruent with previous documentation of reduced growth and survival of larvae moved between natal host species. We conclude that ecologically mediated selection is contributing to variation within M.disstria, and that divergent adaptation related to both environmental conditions and host association should be considered in ongoing research and management of this important forest pest.

Improving Natural Enemy Selection in Biological Control through Greater Attention to Chemical Ecology and Host-Associated Differentiation of Target Arthropod Pests.

Simple SummarySome species of insect herbivores can feed on a wide variety of plant species. Over evolutionary time, insect herbivores can associate preferentially with different host-plant species, which frequently leads to genetic divergence between populations of an herbivore species. This phenomenon, referred to as host-associated differentiation (HAD), not only affects insect herbivores, but can also impact their associated natural enemies, particularly predatory or parasitic insects, which are responsible for biological control in agroecosystems. Although the mechanisms underlying HAD in populations of herbivores and associated natural enemies remain underexplored, we argue that the chemical communication between plants, herbivores, and natural enemies likely plays a major role. Chemical cues emitted by plants and insect herbivores influence natural enemy foraging behavior, and divergent chemical cues can lead to natural enemy HAD, ultimately shaping biological control. In this synthesis paper, we explore how the chemical ecology of HAD could influence classical, conservation, and augmentative biological control, and propose research agendas to further biological control efficacy through natural enemy selection.Host-associated differentiation (HAD) refers to cases in which genetically distinct populations of a species (e.g., herbivores or natural enemies) preferentially reproduce or feed on different host species. In agroecosystems, HAD often results in unique strains or biotypes of pest species, each attacking different species of crops. However, HAD is not restricted to pest populations, and may cascade to the third trophic level, affecting host selection by natural enemies, and ultimately leading to HAD within natural enemy species. Natural enemy HAD may affect the outcomes of biological control efforts, whether classical, conservation, or augmentative. Here, we explore the potential effects of pest and natural enemy HAD on biological control in agroecosystems, with emphases on current knowledge gaps and implications of HAD for selection of biological control agents. Additionally, given the importance of semiochemicals in mediating interactions between trophic levels, we emphasize the role of chemical ecology in interactions between pests and natural enemies, and suggest areas of consideration for biological control. Overall, we aim to jump-start a conversation concerning the relevance of HAD in biological control by reviewing currently available information on natural enemy HAD, identifying challenges to incorporating HAD considerations into biological control efforts, and proposing future research directions on natural enemy selection and HAD.

Predicting the occurrence of host‐associated differentiation in parasitic arthropods: a quantitative literature review

AbstractParasite populations associated with different host species can encounter a variety of isolating reproductive barriers, leading to each population independently accumulating genome‐wide genetic differences due to their host associations. This phenomenon is called host‐associated differentiation (HAD) and has been proposed as an indicator of early diversification among parasitic arthropods. Although many parasite–host case study systems have been tested for the genetic signature of HAD (e.g., FST≥0.15 between sympatric, host‐associated populations in the absence of allopatry), it is unknown which isolating reproductive barriers best predict the general occurrence of HAD. HAD development has been attributed to biological and ecological factors that either directly generate reproductive isolation between parasites living on different hosts, such as ‘immigrant inviability’ (i.e., lower fitness of immigrants in non‐native environments), or that promote the accumulation of host‐specific genetic adaptations, such as the gallmaking feeding mode. In fact, some of these factors are shared across multiple case studies, suggesting that the occurrence of HAD is generalizable and can be predicted based on the incidence of significant biological and ecological factors. By means of a discriminant function analysis (DFA), this research assessed 108 arthropod parasite–host case studies for ecological and biological factors significantly correlated with the occurrence of HAD and whether these factors could be used to distinguish the presence of HAD from its absence. The DFA demonstrated that case studies that developed HAD could be distinguished from case studies that did not develop HAD. The results of the DFA were corroborated by a ‘non‐iterative partial least squares’ (NIPALS) discriminant model and a nominal logistic regression. Case studies with HAD could be robustly separated from case studies without HAD based on the incidence of these predictive factors: immigrant inviability, gallmaking, endophagy, recent range invasions of either hosts or parasites, differential host phenology, and differential parasite morphology. These results were used in an infinite random forest analysis to generate a hierarchy of conditional probabilities that separated HAD presence from absence. The results provide researchers with a tool for reliably predicting which untested parasite–host system would likely develop HAD. Immigrant inviability, gallmaking, and their combination were strongly correlated with the presence of HAD, which indicated parasite–host systems with these traits were highly likely to develop HAD. Contrary to expectation, endophagous feeding was negatively correlated with HAD presence, which indicated phytophagous endophagous feeders (excepting gallmakers) were highly unlikely to develop HAD. Furthermore, parasitoids were shown to be just as likely to develop HAD as not. Unfortunately, potentially significant predictive factors (e.g., allochrony) were excluded from analysis because too few case studies have been specifically tested for these factors. Furthermore, this analysis was biased by the lack of ‘negative’ publication results and the overrepresentation of research laboratories that primarily study HAD. Future research should accumulate novel HAD case studies that specifically test for allochrony, differential microbial associations, and morphological differentiation.

Genomic evidence for host‐associated differentiation in an animal parasite, Dermacentor variabilis, the American dog tick

AbstractThe process responsible for the formation of genetically distinct populations associated with different host species is known as host‐associated differentiation (HAD). Many insect parasites of plants have been shown to exhibit HAD but there have been fewer studies of HAD in parasites of vertebrate animals. Previous to this study, HAD has been documented in at least three species of ticks. The American dog tick, Dermacentor variabilis (Say) (Acari: Ixodidae) was chosen as the focal species for this study due to its importance as the vector of tularemia and Rocky Mountain spotted fever. Previous population genetic studies of this tick found the existence of various haplotypes but the tick’s host origins were unknown. In this study, ticks were collected from 15 vertebrate host species to test for HAD using single nuclear polymorphisms (SNPs). In total, 136 individual D. variabilis ticks were sequenced using ddRADseq. Genomic evidence was found to point to D. variabilis exhibiting HAD on eight different hosts. A STRUCTURE analysis showed that the highest posterior probability was obtained with a population size of eight and these populations correlated with host species. Pairwise FST values were as high as 0.622 and indicated a range of genetic distinction between host groups. In addition, ticks collected from the vegetation appeared as one homogenous distinct genotype suggesting the existence of nidicolous (nest dwelling) and non‐nidicolous genotypes. The identification of host race formation occurring in this animal parasite has implications for the understanding of D. variabilis pathogen transmission and targeted control efforts because genetically distinct populations can differ in traits relevant to these applications.

Host‐associated differentiation of target pests should be assessed before using gene drive as a pest control tool − an opinion

AbstractAdvances in gene editing have made feasible the potential use of gene drive for pest control. Ecological risk assessments will certainly be required before this technology can be released into open fields. In this article, I argue for the importance to include host‐associated differentiation (HAD) as part of ecological risk assessment models due to its potential to modulate gene drive spread and risk. Depending on the context, HAD may hamper or facilitate pest control efforts using gene drives. Overlooking HAD may impair pest suppression goals and inflate estimations of effective population sizes, whereas its inclusion within gene drive deployment strategies, as a form of ecological containment, may facilitate gene drive implementation under specific scenarios. Because HAD varies geographically and among closely related species, it will need to be assessed on a case‐by‐case basis. Failure to incorporate HAD within ecological risk assessment models may undermine pest control goals and diminish the accuracy of estimated ecological risks associated with gene drive releases.

Differences in Microbiota Between Two Multilocus Lineages of the Sugarcane Aphid (Melanaphis sacchari) in the Continental United States

Abstract The sugarcane aphid (SCA), Melanaphis Sacchari (Zehntner) (Hemiptera: Aphididae), has been considered an invasive pest of sugarcane in the continental United States since 1977. Then, in 2013, SCA abruptly became a serious pest of U.S. sorghum and is now a sorghum pest in 22 states across the continental United States. Changes in insect-associated microbial community composition are known to influence host-plant range in aphids. In this study, we assessed whether changes in microbiota composition may explain the SCA outbreak in U.S. sorghum. We characterized the SCA bacterial microbiota on sugarcane and grain sorghum in four U.S. states, using a metabarcoding approach. In addition, we used taxon-specific polymerase chain reaction (PCR) primers to screen for bacteria commonly reported in aphid species. As anticipated, all SCA harbored the primary aphid endosymbiont Buchnera aphidicola, an obligate mutualistic bacterial symbiont. Interestingly, none of the secondary symbionts, facultative bacteria typically associated with aphids (e.g., Arsenophonus, Hamiltonella, Regiella) were present in either the metabarcoding data or PCR screens (with the exception of Rickettsiella and Serratia, which were detected by metabarcoding at low abundances <1%). However, our metabarcoding detected bacteria not previously identified in aphids (Arcobacter, Bifidobacterium, Citrobacter). Lastly, we found microbial host-associated differentiation in aphids that seems to correspond to genetically distinct aphid lineages that prefer to feed on grain sorghum (MLL-F) versus sugarcane (MLL-D).

Analysis of Genetic Variation Among Cowpea Aphid (Hemiptera: Aphididae) Populations Evidenced from Mitochondrial and Nuclear DNA Sequences

AbstractAphis craccivora Koch (Hemiptera: Aphididae) or cowpea aphid is a polyphagous insect pest that feeds on a variety of leguminous plants. We determined the contribution of host-associated genetic differentiation on population structure using the sequence data generated from analysis of mitochondrial cytochrome b oxidase (Cytb) and nuclear elongation factor-1 alpha (EF1-alpha) of A. craccivora collected from cultivated yardlong bean [Vigna unguiculata (L.) Walp. ssp. sesquipedalis (L.) H. Ohashi.] (Fabales: Fabaceae) and winged bean [Psophocarpus tetragonolobus (L.) D.C.] (Fabales: Fabaceae). Phylogenetic and haplotype network analyses revealed no evidence of strong host plant or geographical clustering in both the mitochondrial and nuclear gene dataset. A moderate, low-magnitude genetic distance (FST) between host plants and geographical localities was found in this study. An analysis of molecular variance (AMOVA) revealed that host plant and geography do not influence the structure of genetic variation in A. craccivora populations. Genetic variation between host plants at a location and host plants among locations demonstrated no consistent result for population subdivision of A. craccivora. These results suggest that geographical location and host plants do not significantly influence the genetic structure of A. craccivora, and this might be due to their high reproductive (parthenogenesis) ability and high migration (airborne) between host plants and regions of the country.

Is there a host-associated molecular and morphological differentiation between sympatrically occurring individuals of the invasive leaf miner Cameraria ohridella?

The leaf-miner moth Cameraria ohridella, a pest in Central Europe, causes severe damage to trees. Host-associated differentiation (HAD) for this species has been suggested previously based on the occurrence of a specific mitochondrial haplotype. We assessed genetic diversity and population structure for sympatrically occurring individuals collected in association with two host species, Ohio buckeye (Aesculus glabra) and horse chestnut (Ae. hippocastanum), using six microsatellite loci (SSR) and mtDNA sequences that encode parts of cytochrome oxidase I and II. To infer population structure and assign individuals to clusters, we employed Bayesian clustering. We further characterized the relationships between genetic distance and geographical distance (IBD) in analyzed samples. Although our results derived from the SSR loci analyses demonstrating that there was no population substructuring caused by the hosts, we found evidence of differences in wing size, which might be attributed to the quality of food resources available to larvae. The population structure with K = 2 cannot be interpreted as the result of IBD; rather, it reflects a population differentiation due to demographic or genetic processes (e.g., an origin of invaders). Although genetic diversity was relatively high (He> 0.5), the population had a deficiency of heterozygotes (FIS > 0), which was most likely due to nonrandom mating and, possibly, a Wahlund effect. A star-like haplotype network and negative Tajima’s D support the genetic effect of bottleneck followed by population expansion. Based on presumably neutral markers, we conclude that C. ohridella appeared to be a good model for studying evolution toward a generalist invasive species, rather than HAD.

Are Eurosta solidaginis on Solidago rugosa a divergent host-associated race?

The ball-gall fly Eurosta solidaginis is considered a classic example of host-race formation in herbivorous insects, with host-associated races evolving at least twice, including the well-known pair on Solidago altissima and S. gigantea. Yet E. solidaginis has been occasionally observed galling other Solidago species. Here, we explore the origins of E. solidaginis on Solidago rugosa. We hypothesize that flies associated with S. rugosa are derived from the S. altissima host-race, and ask whether S. rugosa-associated flies have initiated host-race formation. We compared genetic variation among seventeen E. solidaginis populations collected from S. rugosa, S. altissima, and S. gigantea, in an adjacent COI/COII region of the mitochondrial genome. Across the study area, E. solidaginis flies from S. rugosa were as diverged from S. altissima-flies as they were from S. gigantea-flies (pairwise ΦPT 0.075 and 0.78 respectively) but S. altissima and S. gigantea-flies appeared considerably less diverged (0.002). This pattern was driven by the majority of flies, regardless of host-plant, sharing the same haplotype across the study area. However, we detected several site/region-specific haplotypes, not shared among host species. At the local site scale we were able to distinguish S. gigantea-associated fly haplotypes from either S. altissima or S. rugosa haplotypes, but the majority of S. altissima and S. rugosa-flies shared the same haplotype locally. These patterns of haplotype diversity support existing evidence of host-associated divergence in S. altissima- and S. gigantea-associated flies, and suggest that S. rugosa flies are either the same host-race as, or are recently derived from, S. altissima flies. Successful development on S. rugosa and the use of S. rugosa in the absence of use on sympatric S. altissima suggests that E. solidaginis either has a single oligophagous race using both S. altissima and S. rugosa or is in the earliest stages of host-associated differentiation.

Population genetic structure of Zeugodacus tau species complex in Thailand

AbstractThe tephritid fruit fly Zeugodacus tau is a serious agriculture pest, especially of cucurbits in Thailand, where it is classified as a complex species of nine siblings (Z. tau A, B, C, D, E, F, G, I and J). Based on single‐strand conformation polymorphism (SSCP) analysis, 33 distinct mitochondrial cytochrome c oxidase subunit I (mtCOI) haplotypes were found in three sibling species, Z. tau A, C and J, in Thailand. Genetic structure analysis of the population revealed relatively large genetic differences among these sibling species, reflecting a tendency toward speciation. The maximum likelihood tree and median‐joining network reconstructed from the mtCOI sequences of 33 haplotypes supported the separation of these three sibling species within the Z. tau complex. The three‐level hierarchical analysis of molecular variance based on geographical regions and the Mantel test for isolation‐by‐distance showed significant genetic structuring of the Z. tau complex in Thailand. However, the genetic differentiation among geographical groups was rather low, which may be reasonably explained by natural and human mediated dispersal, as well as host associated differentiation. The SSCP analysis on the population genetic structure of Z. tau species complex in the present study should benefit pest management.

Using host-associated differentiation to track source population and dispersal distance among insect vectors of plant pathogens.

Small, mobile insects are notoriously challenging to track across landscapes and manage in agricultural fields. However, genetic differentiation among insect populations and host plants acquired through host‐associated differentiation could be exploited to infer movement within crop systems and damage potential. Although many insects exhibit host‐associated differentiation, management strategies for insect vectors of plant pathogens assume a homogenous population. Nevertheless, phenotypic changes derived from host‐associated differentiation could manifest in altered behavior or physiology affecting the likelihood of vector–pathogen–plant interactions, or the subsequent efficiency of pathogen transmission. We used SNPs to assess genotypic structure and host‐associated differentiation in the cowpea aphid, Aphis craccivora Koch (Hemiptera: Aphididae). To do so, we sampled A. craccivora across the Midwestern United States. from two host plants, alfalfa (Medicago sativa) and black locust (Robinia pseudoacacia)—putative source populations for winged migrants. Simultaneously, we sampled winged A. craccivora landing in pumpkin fields where they transmit viruses. Structure analyses supported host‐associated differentiation by identifying two major genotypic groups: an alfalfa group containing a single multilocus genotype and a locust group containing all others. Winged locust‐group aphids landed at a much greater magnitude within focal fields during year 2 than year 1, while those in the alfalfa group remained fairly consistent. Spatial autocorrelation analyses indicated locust‐group aphid movement was characterized by small‐scale dispersal during year 2, likely originating from populations within 10 km. We also detected strong temporal differences in colonization from the two host plants. Early in the summer, most winged aphids (79.4%) derived from the locust group, whereas late in the summer more (58.3%) were from the alfalfa group. Because early crop growth stages are more susceptible to damage from aphid‐vectored viruses, these data implicate locust as the more important source and illustrate how host‐associated differentiation can be used to track dispersal and inform management of heterogeneous pest populations.

Is there host-associated differentiation in marine herbivorous amphipods?

Is there host-associated differentiation in marine herbivorous amphipods?

Genetic Structure of Liriomyza trifolii (Diptera: Agromyzidae) Associated With Host Plants From Southeastern Mexico.

Host-associated differentiation (HAD) has played a major role in insect diversification at both macroevolutionary and microevolutionary scales. This evolutionary process has been reported in insects associated with wild and domesticated plant species. In particular, domesticated species harbor large genetic and phenotypic diversity associated with traits of human interest, including variation in nutrition, phenology, fruit, and leaf shape. This diversity may alter selection regimes affecting insect evolution and host specialization. The genus Liriomyza includes highly polyphagous species that are characterized for living and feeding inside plant leaves. Ecological and genetic data suggest the presence of cryptic species within this genus. Moreover, there is evidence of HAD in a group of populations of Liriomyza trifolii (Burgess) associated with Capsicum annum L. (Solanaceae). In this work, we explored HAD in L. trifolii populations from southeastern Mexico, and inquire into differentiation specific to peppers based on cytochrome oxidase I. We also evaluated the relationship between the genetic structure of leafminers and the different types of C. annuum. Our main results did not support previous findings of specialization of L. trifolli on C. annuum. Nevertheless, we found a divergent group of haplotypes associated to Allium cepa (Aspargales: Amaryllidaceae) in sympatric condition to Physalis philadelphica Lam. (Solanales: Solanaceae) and C. annum, suggesting the presence of HAD, as well as significant genetic differentiation of L. trifolii associated to peppers from Oaxaca and Yucatán.

Habitat or temporal isolation: Unraveling herbivore-parasitoid speciation patterns using double digest RADseq.

Ecological speciation is often observed in phytophagous insects and their parasitoids due to divergent selection caused by host‐associated or temporal differences. Most previous studies have utilized limited genetic markers or distantly related species to look for reproductive barriers of speciation. In our study, we focus on closely related species of Lygus bugs and two sister species of Peristenus parasitoid wasps. Using mitochondrial DNA COI and genomewide SNPs generated using ddRADseq, we tested for potential effects of host‐associated differentiation (HAD) or temporal isolation in this system. While three species of Lygus are clearly delineated with both COI and SNPs, no evidence of HAD or temporal differentiation was detected. Two Peristenus sister species were supported by both sets of markers and separated temporally, with P. mellipes emerging early in June and attacking the first generation of Lygus, while P. howardi emerging later in August and attacking the second generation of their hosts. This is one of the few studies to examine closely related hosts and parasitoids to examine drivers of diversification. Given the results of this study, the Lygus‐Peristenus system demonstrates temporal isolation as a potential barrier to reproductive isolation for parasitoids, which could indicate higher parasitoid diversity in regions of multivoltine hosts. This study also demonstrates that incorporating systematics improves studies of parasitoid speciation, particularly by obtaining accurate host records through rearing, carefully delimiting cryptic species and examining population‐level differences with genomic‐scale data among closely related taxa.

Cryptic diversity within grass-associated Abacarus species complex (Acariformes: Eriophyidae), with the description of a new species, Abacarus plumiger n. sp.

Accurate estimation of species richness is often complex as genetic divergence is not always accompanied by appreciable morphological differentiation. In consequence, cryptic lineages or species evolve. Cryptic speciation is common especially in taxa characterized by small and simplified bodies, what makes their proper identification challenging. The cereal rust mite, Abacarus hystrix, was regarded for a long time as a species associated with a wide range of grass hosts, whereas wide host ranges are rather rare in eriophyoid mites. Therefore, the generalist status of A. hystrix was questioned. In this paper we demonstrate that the diversity within Abacarus species associated with grasses is more complex than it was previously thought. The 78 Abacarus mtDNA COI sequences used in this study formed 10 highly supported clades (bootstrap value 99%) and four more distinct genetic lineages were represented by unique sequences. The genetic distances between them ranged from 6.6 to 26.5%. Moreover, morphological study and genetic approach based on the combination of the Poisson Tree Processes model for species delimitation (PTP) and a Bayesian implementation of PTP (bPTP), and Neighbour Joining analyses led to delimitation of a new species within the Abacarus complex: Abacarus plumiger, specialized on smooth brome (Bromus inermis). Furthermore, our analyses demonstrated a pattern of host-associated differentiation within the complex. Overall, our study indicates that cryptic speciation occurs in the grass-associated Abacarus genus, and suggests the need for more extensive sampling using integrative methods.

Instar- and host-associated differentiation of bacterial communities in the Mediterranean fruit fly Ceratitis capitata.

Microorganisms are acknowledged for their role in shaping insects’ evolution, life history and ecology. Previous studies have shown that microbial communities harbored within insects vary through ontogenetic development and among insects feeding on different host-plant species. In this study, we characterized the bacterial microbiota of the highly polyphagous Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae), at different instars and when feeding on different host-plant species. Our results show that the bacterial microbiota hosted within the Mediterranean fruit fly differs among instars and host-plant species. Most of the bacteria harbored by the Mediterranean fruit fly belong to the phylum Proteobacteria, including genera of Alphaproteobacteria such as Acetobacter and Gluconobacter; Betaprotobacteria such as Burkholderia and Gammaproteobacteria such as Pseudomonas.

Partitioning of herbivore hosts across time and food plants promotes diversification in the Megastigmus dorsalis oak gall parasitoid complex.

Communities of insect herbivores and their natural enemies are rich and ecologically crucial components of terrestrial biodiversity. Understanding the processes that promote their origin and maintenance is thus of considerable interest. One major proposed mechanism is ecological speciation through host‐associated differentiation (HAD), the divergence of a polyphagous species first into ecological host races and eventually into more specialized daughter species. The rich chalcid parasitoid communities attacking cynipid oak gall wasp hosts are structured by multiple host traits, including food plant taxon, host gall phenology, and gall structure. Here, we ask whether the same traits structure genetic diversity within supposedly generalist parasitoid morphospecies. We use mitochondrial DNA sequences and microsatellite genotypes to quantify HAD for Megastigmus (Bootanomyia) dorsalis, a complex of two apparently generalist cryptic parasitoid species attacking oak galls. Ancient Balkan refugial populations showed phenological separation between the cryptic species, one primarily attacking spring galls, and the other mainly attacking autumn galls. The spring species also contained host races specializing on galls developing on different host‐plant lineages (sections Cerris vs. Quercus) within the oak genus Quercus. These results indicate more significant host‐associated structuring within oak gall parasitoid communities than previously thought and support ecological theory predicting the evolution of specialist lineages within generalist parasitoids. In contrast, UK populations of the autumn cryptic species associated with both native and recently invading oak gall wasps showed no evidence of population differentiation, implying rapid recruitment of native parasitoid populations onto invading hosts, and hence potential for natural biological control. This is of significance given recent rapid range expansion of the economically damaging chestnut gall wasp, Dryocosmus kuriphilus, in Europe.