Histories of host shifts and cospeciation among free‐living parasitoids of Rhagoletis flies

Host shifts by specialist insects can lead to reproductive isolation between insect populations that use different hosts, promoting diversification. When both a phytophagous insect and its ancestrally associated parasitoid shift to the same novel host plant, they may cospeciate. However, because adult parasitoids are free living, they can also colonize novel host insects and diversify independent of their ancestral host insect. Although shifts of parasitoids to new insect hosts have been documented in ecological time, the long‐term importance of such shifts to parasitoid diversity has not been evaluated. We used a genus of flies with a history of speciation via host shifting (Rhagoletis [Diptera: Tephritidae]) and three associated hymenopteran parasitoid genera (Diachasma, Coptera and Utetes) to examine cophylogenetic relationships between parasitoids and their host insects. We inferred phylogenies of Rhagoletis, Diachasma, Coptera and Utetes and used distance‐based cophylogenetic methods (ParaFit and PACo) to assess congruence between fly and parasitoid trees. We used an event‐based method with a free‐living parasitoid cost model to reconstruct cophylogenetic histories of each parasitoid genus and Rhagoletis. We found that the current species diversity and host–parasitoid associations between the Rhagoletis flies and parasitoids are the primary result of ancient cospeciation events. Parasitoid shifts to ancestrally unrelated hosts primarily occur near the branch tips, suggesting that host shifts contribute to recent parasitoid species diversity but that these lineages may not persist over longer time periods. Our analyses also stress the importance of biologically informed cost models when investigating the coevolutionary histories of hosts and free‐living parasitoids.     

Herbivore species identity rather than diversity of the non‐host community determines foraging behaviour of the parasitoid wasp Cotesia glomerata

Extensive research has been conducted to reveal how species diversity affects ecosystem functions and services. Yet, consequences of diversity loss for ecosystems as a whole as well as for single community members are still difficult to predict. Arthropod communities typically are species‐rich, and their species interactions, such as those between herbivores and their predators or parasitoids, may be particularly sensitive to changes in community composition. Parasitoids forage for herbivorous hosts by using herbivore‐induced plant volatiles (indirect cues) and cues produced by their host (direct cues). However, in addition to hosts, non‐suitable herbivores are present in a parasitoid's environment which may complicate the foraging process for the parasitoid. Therefore, ecosystem changes in the diversity of herbivores may affect the foraging efficiency of parasitoids. The effect of herbivore diversity may be mediated by either species numbers per se, by specific species traits, or by both. To investigate how diversity and identity of non‐host herbivores influence the behaviour of parasitoids, we created environments with different levels of non‐host diversity. On individual plants in these environments, we complemented host herbivores with 1–4 non‐host herbivore species. We subsequently studied the behaviour of the gregarious endoparasitoid Cotesia glomerata L. (Hymenoptera: Braconidae) while foraging for its gregarious host Pieris brassicae L. (Lepidoptera: Pieridae). Neither non‐host species diversity nor non‐host identity influenced the preference of the parasitoid for herbivore‐infested plants. However, after landing on the plant, non‐host species identity did affect parasitoid behaviour, whereas non‐host diversity did not. One of the non‐host species, Trichoplusia ni Hübner (Lepidoptera: Noctuidae), reduced the time the parasitoid spent on the plant as well as the number of hosts it parasitized. We conclude that non‐host herbivore species identity has a larger influence on C. glomerata foraging behaviour than non‐host species diversity. Our study shows the importance of species identity over species diversity in a multitrophic interaction of plants, herbivores, and parasitoids.     

Spatiotemporal dynamics of the bacterial microbiota on lacustrine Cladophora glomerata (Chlorophyta)

The branched periphytic green alga Cladophora glomerata, often abundant in nearshore waters of lakes and rivers worldwide, plays important ecosystem roles, some mediated by epibiotic microbiota that benefit from host‐provided surface, organic C, and O₂. Previous microscopy and high‐throughput sequencing studies have indicated surprising epibiont taxonomic and functional diversity, but have not included adequate consideration of sample replication or the potential for spatial and temporal variation. Here, we report the results of 16S rRNA amplicon‐based phylum‐to‐genus taxonomic analysis of Cladophora‐associated bacterial epibiota sampled in replicate from three microsites and at six times during the open‐water season of 2014, from the same lake locale (Picnic Point, Lake Mendota, Dane Co., WI, USA) explored by high‐throughput sequencing studies in two previous years. Statistical methods were used to test null hypotheses that the bacterial community: (i) is homogeneous across microsites tested, and (ii) does not change over the course of a growth season or among successive years. Results indicated a dynamic microbial community that is more strongly influenced by sampling day during the growth season than by microsite variation. A surprising diversity of bacterial genera known to be associated with the key function of methane‐oxidation (methanotrophy), including relatively high‐abundance of Crenothrix, Methylomonas, Methylovulum, and Methylocaldum–showed intraseasonal and interannual variability possibly related to temperature differences, and microsite preferences possibly related to variation in methane abundance. By contrast, a core assemblage of bacterial genera seems to persist over a growth season and from year to year, possibly transmitted by a persistent attached host resting stage.     

Growth,development, and behaviour of the parasitised and unparasitised larvae of a shelter‐building moth and consequences for the resulting koinobiont parasitoid

Most attention to size‐time trade‐offs of insects has focused on herbivore risk, with considerably less attention paid to parasitoids. Here, we focus on parasitoid risk, comparing the fates of unparasitised herbivore hosts and parasitised hosts that protect the parasitoids. Success of a koinobiont parasitoid (host grows after parasitisation) depends on maintaining a delicate balance with its host, thereby ensuring its own survival while the host grows. To evaluate growth rate–mortality rate relationships of host and parasitoid, we compared several aspects of the growth, phenology, and behaviour of unparasitised fern moth [Herpetogramma theseusalis (Walker) (Lepidoptera: Crambidae)] larvae and larvae parasitised by Alabagrus texanus (Cresson) (Hymenoptera: Braconidae), a solitary koinobiont (one parasitoid per host) wasp. Host larvae feed and construct shelters on sensitive fern, Onoclea sensibilis L. (Dryopteridaceae). Alabagrus texanus parasitise early‐instar moths in late summer, which overwinter in their host, emerging in mid‐summer to pupate and eclose. During the autumn following hatching and the immediately following spring, parasitised and unparasitised moth larvae did not differ in size, took similar time to choose between satisfactory and unsatisfactory foods, and built similar shelters. Prior to any other changes noted, more parasitised than unparasitised larvae also died when severely starved. Parasitised larvae subsequently grew less and pupated later than unparasitised ones (small size, slow growth), but consumed similar amounts of food. Although the numerically dominant parasitoid of fern moths, we concluded that A. texanus do not efficiently exploit their hosts.     

Strong dispersal in a parasitoid wasp overwhelms habitat fragmentation and host population dynamics

The population dynamics of a parasite depend on species traits, host dynamics and the environment. Those dynamics are reflected in the genetic structure of the population. Habitat fragmentation has a greater impact on parasites than on their hosts because resource distribution is increasingly fragmented for species at higher trophic levels. This could lead to either more or less genetic structure than the host, depending on the relative dispersal rates of species. We examined the spatial genetic structure of the parasitoid wasp Hyposoter horticola, and how it was influenced by dispersal, host population dynamics and habitat fragmentation. The host, the Glanville fritillary butterfly, lives as a metapopulation in a fragmented landscape in the Åland Islands, Finland. We collected wasps throughout the 50 by 70 km archipelago and determined the genetic diversity, spatial population structure and genetic differentiation using 14 neutral DNA microsatellite loci. We compared the genetic structure of the wasp with that of the host butterfly using published genetic data collected over the shared landscape. Using maternity assignment, we also identified full‐siblings among the sampled parasitoids to estimate the dispersal range of individual females. We found that because the parasitoid is dispersive, it has low genetic structure, is not very sensitive to habitat fragmentation and has less spatial genetic structure than its butterfly host. The wasp is sensitive to regional rather than local host dynamics, and there is a geographic mosaic landscape for antagonistic co‐evolution of host resistance and parasite virulence.     

A molecular tool to identify Anastatus parasitoids of the brown marmorated stink bug

Globally, Anastatus species (Hymenoptera: Eupelmidae) are associated with the invasive agricultural pest Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). In Europe, the polyphagous Anastatus bifasciatus (Geoffroy) is the most prevalent native egg parasitoid on H. halys eggs and is currently being tested as a candidate for augmentative biological control. Anastatus bifasciatus frequently displays behavior without oviposition, and induces additional host mortality through oviposition damage and host feeding that is not measured with offspring emergence. This exacerbates accurate assessment of parasitism and host impact, which is crucial for efficacy evaluation as well as for pre‐ and post‐release risk assessment. To address this, a general Anastatus primer set amplifying a 318‐bp fragment within the barcoding region of the cytochrome oxidase I (COI) gene was developed. When challenged with DNA of three Anastatus species —A. bifasciatus, Anastatus japonicus Ashmead, and Anastatus sp.—, five scelionid parasitoid species that might be encountered in the same host environments and 11 pentatomid host species, only Anastatus DNA was successfully amplified. When applied to eggs of the target host, H. halys, and an exemplary non‐target host, Dendrolimus pini L. (Lepidoptera: Lasiocampidae), subjected to host feeding, no Anastatus amplicons were produced. Eggs of the two host species containing A. bifasciatus parasitoid stages, from 1‐h‐old eggs to pupae, and emerged eggs yielded Anastatus fragments. Confirmation of parasitoid presence with dissections and subsequent PCRs with the developed primer pair resulted in 95% success for 1‐h‐old parasitoid eggs. For both host species, field‐exposed sentinel emerged eggs stored dry for 6 months, 100% of the specimens produced Anastatus amplicons. This DNA‐based screening method can be used in combination with conventional methods to better interpret host‐parasitoid and parasitoid‐parasitoid interactions. It will help address ecological questions related to an environmentally friendly approach for the control of H. halys in invaded areas.     

Strong specificity in the interaction between parasitoids and symbiont‐protected hosts

Coevolution between hosts and parasites may promote the maintenance of genetic variation in both antagonists by negative frequency‐dependence if the host–parasite interaction is genotype‐specific. Here we tested for specificity in the interaction between parasitoids (Lysiphlebus fabarum) and aphid hosts (Aphis fabae) that are protected by a heritable defensive endosymbiont, the γ‐proteobacterium Hamiltonella defensa. Previous studies reported a lack of genotype specificity between unprotected aphids and parasitoids, but suggested that symbiont‐conferred resistance might exhibit a higher degree of specificity. Indeed, in addition to ample variation in host resistance as well as parasitoid infectivity, we found a strong aphid clone‐by‐parasitoid line interaction on the rates of successful parasitism. This genotype specificity appears to be mediated by H. defensa, highlighting the important role that endosymbionts can play in host–parasite coevolution.     

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.     

Food web associations and effect of trophic resources and environmental factors on parasitoids expanding their host range into non‐native hosts

Trophic interactions and environmental conditions determine the structure of food webs and the host expansion of parasitoids into novel insect hosts. In this study, we investigate plant–insect–parasitoid food web interactions, specifically the effect of trophic resources and environmental factors on the presence of the parasitoids expanding their host range after the invasion of Chrysodeixis chalcites (Esper) (Lepidoptera: Noctuidae). We also consider potential candidates for biological control of this non‐native pest. A survey of larval stages of Plusiinae (Lepidoptera: Noctuidae) and their larval parasitoids was conducted in field and vegetable greenhouse crops in 2009 and 2010 in various locations of Essex and Chatham‐Kent counties in Ontario, Canada. Twenty‐one plant–host insect–host parasitoid associations were observed among Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), C. chalcites, and larval parasitoids in three trophic levels of interaction. Chrysodeixis chalcites, an old‐world species that had just arrived in the region, was the most common in our samples. The larval parasitoids Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae), Cotesia vanessae (Reinhard), Cotesia sp., Microplitis alaskensis (Ashmead), and Meteorus rubens (Nees) (all Hymenoptera: Braconidae) expanded their host range into C. chalcites changing the structure of the food web. Copidosoma floridanum (Ashmead) (Hymenoptera: Encyrtidae) was the most common parasitoid of T. ni that was not found in the invasive species. Plant species, host abundance, and agro‐ecosystem were the most common predictors for the presence of the parasitoids expanding their host range into C. chalcites. Our results indicate that C. sonorensis, C. vanessae, and C. floridanum should be evaluated for their potential use in biological control of C. chalcites and T. ni.     

Patterns of temporal and enemy niche use by a community of leaf cone moths (Caloptilia) coexisting on maples (Acer) as revealed by metabarcoding

The diversity of herbivorous insects is often considered a function of host plant diversity. However, recent research has uncovered many examples of closely related herbivores using the same host plant(s), suggesting that partitioning of host plants is not the only mechanism generating diversity. Herbivores sharing hosts may utilize different parts of the same plant, but such resource partitioning is often not apparent; hence, the factors that allow closely related herbivores to coexist are still largely undetermined. We examined whether partitioning of phenology or natural enemies may explain the coexistence of leaf cone moths (Caloptilia; Gracillariidae) associated with maples (Acer; Sapindaceae). Larval activity of 10 sympatric Caloptilia species found on nine maple species was monitored every 2–3 weeks for a total of 13 sampling events, and an exhaustive search for internal parasitoid wasps was conducted using high‐throughput sequencing. Blocking primers were used to facilitate the detection of wasp larvae inside moth tissue. We found considerable phenological overlap among Caloptilia species, with two clear peaks in July and September–October. Coexisting Caloptilia species also had largely overlapping parasitoid communities; a total of 13 chalcid and ichneumon wasp species attacked Caloptilia in a nonspecific fashion at an overall parasitism rate of 46.4%. Although coexistence may be facilitated by factors not accounted for in this study, it appears that niche partitioning is not necessary for closely related herbivores to stably coexist on shared hosts. Co‐occurrence without resource partitioning may provide an additional axis along which herbivorous insects attain increased species richness.     

Abundance of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) and its parasitoids on vegetables and cassava plants in Burkina Faso (West Africa)

The whitefly Bemisia tabaci is a pest of many agricultural and ornamental crops worldwide and particularly in Africa. It is a complex of cryptic species, which is extremely polyphagous with hundreds of host plants identified around the world. Previous surveys in western Africa indicated the presence of two biotypes of the invasive MED species (MED‐Q1 and MED‐Q3) living in sympatry with the African species SSA and ASL. This situation constitutes one of the rare cases of local coexistence of various genetic entities within the B. tabaci complex. In order to study the dynamics of the distribution and abundance of genetic entities within this community and to identify potential factors that could contribute to coexistence, we sampled B. tabaci populations in Burkina Faso in 2015 and 2016 on various plants, and also their parasitoids. All four genetic entities were still recorded, indicating no exclusion of local species by the MED species. While B. tabaci individuals were found on 55 plant species belonging to eighteen (18) families showing the high polyphagy of this pest, some species/biotypes exhibited higher specificity. Two parasitoid species (Eretmocerus mundus and Encarsia vandrieschei) were also recorded with E. mundus being predominant in most localities and on most plants. Our data indicated that whitefly abundance, diversity, and rate of parasitism varied according to areas, plants, and years, but that parasitism rate was globally highly correlated with whitefly abundance suggesting density dependence. Our results also suggest dynamic variation in the local diversity of B. tabaci species/biotypes from 1 year to the other, specifically with MED‐Q1 and ASL species. This work provides relevant information on the nature of plant–B. tabaci‐parasitoid interactions in West Africa and identifies that coexistence might be stabilized by niche differentiation for some genetic entities. However, MED‐Q1 and ASL show extensive niche overlap, which could ultimately lead to competitive exclusion.     

Nonhost diversity and density reduce the strength of parasitoid–host interactions

The presence of nonprey or nonhosts is known to reduce the strength of consumer– resource interactions by increasing the consumer's effort needed to find its resource. These interference effects can have a stabilizing effect on consumer–resource dynamics, but have also been invoked to explain parasitoid extinctions. To understand how nonhosts affect parasitoids, we manipulated the density and diversity of nonhost aphids using experimental host–parasitoid communities and tested how this affects parasitation efficiency of two aphid parasitoid species. To further study the behavioral response of parasitoids to nonhosts, we tested for changes in parasitoid time allocation in relation to their host‐finding strategies. The proportion of successful attacks (attack rate) in both parasitoid species was reduced by the presence of nonhosts. The parasitoid Aphidius megourae was strongly affected by increasing nonhost diversity with the attack rate dropping from 0.39 without nonhosts to 0.05 with high diversity of nonhosts, while Lysiphlebus fabarum responded less strongly, but in a more pronounced way to an increase in nonhost density. Our experiments further showed that increasing nonhost diversity caused host searching and attacking activity levels to fall in A. megourae, but not in L. fabarum, and that A. megourae changed its behavior after a period of time in the presence of nonhosts by increasing its time spent resting. This study shows that nonhost density and diversity in the environment are crucial determinants for the strength of consumer–resource interactions. Their impact upon a consumer's efficiency strongly depends on its host/prey finding strategy as demonstrated by the different responses for the two parasitoid species. We discuss that these trait‐mediated indirect interactions between host and nonhost species are important for community stability, acting either stabilizing or destabilizing depending on the level of nonhost density or diversity present.     

Next‐generation DNA barcoding: using next‐generation sequencing to enhance and accelerate DNA barcode capture from single specimens

DNA barcoding is an efficient method to identify specimens and to detect undescribed/cryptic species. Sanger sequencing of individual specimens is the standard approach in generating large‐scale DNA barcode libraries and identifying unknowns. However, the Sanger sequencing technology is, in some respects, inferior to next‐generation sequencers, which are capable of producing millions of sequence reads simultaneously. Additionally, direct Sanger sequencing of DNA barcode amplicons, as practiced in most DNA barcoding procedures, is hampered by the need for relatively high‐target amplicon yield, coamplification of nuclear mitochondrial pseudogenes, confusion with sequences from intracellular endosymbiotic bacteria (e.g. Wolbachia) and instances of intraindividual variability (i.e. heteroplasmy). Any of these situations can lead to failed Sanger sequencing attempts or ambiguity of the generated DNA barcodes. Here, we demonstrate the potential application of next‐generation sequencing platforms for parallel acquisition of DNA barcode sequences from hundreds of specimens simultaneously. To facilitate retrieval of sequences obtained from individual specimens, we tag individual specimens during PCR amplification using unique 10‐mer oligonucleotides attached to DNA barcoding PCR primers. We employ 454 pyrosequencing to recover full‐length DNA barcodes of 190 specimens using 12.5% capacity of a 454 sequencing run (i.e. two lanes of a 16 lane run). We obtained an average of 143 sequence reads for each individual specimen. The sequences produced are full‐length DNA barcodes for all but one of the included specimens. In a subset of samples, we also detected Wolbachia, nontarget species, and heteroplasmic sequences. Next‐generation sequencing is of great value because of its protocol simplicity, greatly reduced cost per barcode read, faster throughout and added information content.     

Fast Technology Analysis Enables Identification of Species and Genotypes of Latent Microsporidia Infections in Healthy Native Cameroonians

Several enteric microsporidia species have been detected in humans and other vertebrates and their identifications at the genotype level are currently being elucidated. As advanced methods, reagents, and disposal kits for detecting and identifying pathogens become commercially available, it is important to test them in settings other than in laboratories with “state‐of‐the‐art” equipment and well‐trained staff members. In the present study, we sought to detect microsporidia DNA preserved and extracted from FTA (fast technology analysis) cards spotted with human fecal suspensions obtained from Cameroonian volunteers living in the capital city of Yaoundé to preclude the need for employing spore‐concentrating protocols. Further, we tested whether amplicon nucleotide sequencing approaches could be used on small aliquots taken from the cards to elucidate the diversity of microsporidia species and strains infecting native residents. Of 196 samples analyzed, 12 (6.1%) were positive for microsporidia DNA; Enterocytozoon bieneusi (Type IV and KIN‐1), Encephalitozoon cuniculi, and Encephalitozoon intestinalis were identified. These data demonstrate the utility of the FTA cards in identifying genotypes of microsporidia DNA in human fecal samples that may be applied to field testing for prevalence studies.     

Concordance of bacterial communities of two tick species and blood of their shared rodent host

High‐throughput sequencing is revealing that most macro‐organisms house diverse microbial communities. Of particular interest are disease vectors whose microbiome could potentially affect pathogen transmission and vector competence. We investigated bacterial community composition and diversity of the ticks Dermacentor variabilis (n = 68) and Ixodes scapularis (n = 15) and blood of their shared rodent host, Peromyscus leucopus (n = 45) to quantify bacterial diversity and concordance. The 16S rRNA gene was amplified from genomic DNA from field‐collected tick and rodent blood samples, and 454 pyrosequencing was used to elucidate their bacterial communities. After quality control, over 300 000 sequences were obtained and classified into 118 operational taxonomic units (OTUs, clustered at 97% similarity). Analysis of rarefied communities revealed that the most abundant OTUs were tick species‐specific endosymbionts, Francisella and Rickettsia, and the commonly flea‐associated bacterium Bartonella in rodent blood. An Arsenophonus and additional Francisella endosymbiont were also present in D. variabilis samples. Rickettsia was found in both tick species but not in rodent blood, suggesting that it is not transmitted during feeding. Bartonella was present in larvae and nymphs of both tick species, even those scored as unengorged. Relatively, few OTUs (e.g. Bartonella, Lactobacillus) were found in all sample types. Overall, bacterial communities from each sample type were significantly different and highly structured, independent of their dominant OTUs. Our results point to complex microbial assemblages inhabiting ticks and host blood including infectious agents, tick‐specific endosymbionts and environmental bacteria that could potentially affect arthropod‐vectored disease dynamics.     

Parasite‐mediated selection in a natural metapopulation of Daphnia magna

Parasite‐mediated selection varying across time and space in metapopulations is expected to result in host local adaptation and the maintenance of genetic diversity in disease‐related traits. However, nonadaptive processes like migration and extinction‐(re)colonization dynamics might interfere with adaptive evolution. Understanding how adaptive and nonadaptive processes interact to shape genetic variability in life‐history and disease‐related traits can provide important insights into their evolution in subdivided populations. Here we investigate signatures of spatially fluctuating, parasite‐mediated selection in a natural metapopulation of Daphnia magna. Host genotypes from infected and uninfected populations were genotyped at microsatellite markers, and phenotyped for life‐history and disease traits in common garden experiments. Combining phenotypic and genotypic data a Q_ST–F_ST‐like analysis was conducted to test for signatures of parasite mediated selection. We observed high variation within and among populations for phenotypic traits, but neither an indication of host local adaptation nor a cost of resistance. Infected populations have a higher gene diversity (Hs) than uninfected populations and Hs is strongly positively correlated with fitness. These results suggest a strong parasite effect on reducing population level inbreeding. We discuss how stochastic processes related to frequent extinction‐(re)colonization dynamics as well as host and parasite migration impede the evolution of resistance in the infected populations. We suggest that the genetic and phenotypic patterns of variation are a product of dynamic changes in the host gene pool caused by the interaction of colonization bottlenecks, inbreeding, immigration, hybrid vigor, rare host genotype advantage and parasitism. Our study highlights the effect of the parasite in ameliorating the negative fitness consequences caused by the high drift load in this metapopulation.     

Herbivore egg deposition induces tea leaves to arrest the egg‐larval parasitoid Ascogaster reticulata

Plants are able to activate direct and indirect defences against egg deposition by herbivorous insects. A known indirect defence is the production of synomones to help egg‐ and egg‐larval parasitoids to locate their hosts. The wasp Ascogaster reticulata Watanabe (Hymenoptera: Braconidae) is a solitary egg‐larval parasitoid of the moth Adoxophyes honmai Yasuda (Lepidoptera: Tortricidae), which lays eggs and feeds as caterpillars on the leaves of the tea plant Camellia sinensis (L.) Kuntze (Theaceae). Here, we studied whether or not oviposition by A. honmai induces tea plants to produce synomones that help the parasitoid to locate its host. An olfactometer bioassay suggested that synomones produced by the infested plants did not attract the parasitoid over a short range. However, a contact bioassay showed that tea leaves were induced to arrest the parasitoid 24 h after egg deposition and remained induced until the host‐egg masses were no more attractive to the parasitoids. Wing scales and deposits of adult moths and the contents of the egg masses did not induce the tea leaves to arrest the parasitoid, but the contents of the female moth's reproductive system did. Synomone induction was systemic: uninfested leaves in the vicinity of egg‐laden leaves also arrested the parasitoid.     

Plant host and soil origin influence fungal and bacterial assemblages in the roots of woody plants

Microbial communities in plant roots provide critical links between above‐ and belowground processes in terrestrial ecosystems. Variation in root communities has been attributed to plant host effects and microbial host preferences, as well as to factors pertaining to soil conditions, microbial biogeography and the presence of viable microbial propagules. To address hypotheses regarding the influence of plant host and soil biogeography on root fungal and bacterial communities, we designed a trap‐plant bioassay experiment. Replicate Populus, Quercus and Pinus plants were grown in three soils originating from alternate field sites. Fungal and bacterial community profiles in the root of each replicate were assessed through multiplex 454 amplicon sequencing of four loci (i.e., 16S, SSU, ITS, LSU rDNA). Soil origin had a larger effect on fungal community composition than did host species, but the opposite was true for bacterial communities. Populus hosted the highest diversity of rhizospheric fungi and bacteria. Root communities on Quercus and Pinus were more similar to each other than to Populus. Overall, fungal root symbionts appear to be more constrained by dispersal and biogeography than by host availability.     

Tracking the elusive history of diversification in plant–herbivorous insect–parasitoid food webs: insights from figs and fig wasps

The food webs consisting of plants, herbivorous insects and their insect parasitoids are a major component of terrestrial biodiversity. They play a central role in the functioning of all terrestrial ecosystems, and the number of species involved is mind‐blowing (Nyman et al. 2015 ). Nevertheless, our understanding of the evolutionary and ecological determinants of their diversity is still in its infancy. In this issue of Molecular Ecology, Sutton et al. ( 2016 ) open a window into the comparative analysis of spatial genetic structuring in a set of comparable multitrophic models, involving highly species‐specific interactions: figs and fig wasps. This is the first study to compare genetic structure using population genetics tools in a fig‐pollinating wasp (Pleistodontes imperialis sp1) and its main parasitoid (Sycoscapter sp.A). The fig‐pollinating wasp has a discontinuous spatial distribution that correlates with genetic differentiation, while the parasitoid bridges the discontinuity by parasitizing other pollinator species on the same host fig tree and presents basically no spatial genetic structure. The full implications of these results for our general understanding of plant–herbivorous insect–insect parasitoids diversification become apparent when envisioned within the framework of recent advances in fig and fig wasp biology.     

First record of the bacterial endosymbiont Wolbachia for phytophagous hoverflies from genus Merodon (Diptera: Syrphidae)

Wolbachia is a widespread bacterial endosymbiont among arthropod species. It influences the reproduction of the host species and also mitochondrial DNA diversity. Until now there were only a few studies that detected Wolbachia infections in hoverflies (Diptera: Syrphidae), and this is the first broader study with the aim of examining the incidence of Wolbachia in the hoverfly genus Merodon. The obtained results indicate an infection rate of 96% and the presence of both Wolbachia supergroup A and B, which are characteristic for most of the infected arthropod species. Additionally, the presence of multiple Wolbachia strains in the Merodon aureus group species was detected and the mitochondrial DNA COI‐based relationships of the group are discussed in the light of infection. Finally, we discuss plant‐mediated horizontal transmission of Wolbachia strains among the studied hoverfly species.