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The relationship between plants and insects is one of the greatest evolutionary stories in the history of life on earth. Their importance in global terrestrial ecosystem functioning is self evident, as both represent the most abundant life on the planet. While plant-insect interactions have received much attention and are easily manipulated in experimental investigations, there have been few broad-scale phylogenetic studies for circumscribed herbivorous groups. As a result, the evolutionary role of interspecific interactions in promoting herbivorous insect diversification, at both the global and local scales, remains unclear. Remarkably, one of the largest gaps in our evolutionary and ecological understanding includes the sap-feeding insects in the Auchenorrhyncha suborder (Hemiptera), which contain some of the largest, terrestrially dominant host-plant restricted insect groups known (e.g., Cicadas, planthoppers, and leafhoppers). The evolutionary success of Auchenorrhyncha is due, at least in part, to ancient associations with a consortium obligate bacterial endosymbionts that have persisted for over 260 million years. However, like their insect hosts, the diversity and evolutionary relationships of endosymbiont associations remain relatively unknown for most aucchenorrhynchan groups.The leafhoppers (Cicadomorpha: Cicadellidae) remain one of the largest, yet poorly understood insect families. Of the 22,000 currently described species, thousands remain to be described with an overall unknown diversity (some estimates suggest as many as 90% of tropical Cicadomorpha remain to be described). This is surprising, since they offer excellent models to understand ecological and biogeographic mechanisms of species diversification due to their strict host-plant specificity, limited dispersal, and high rates of local endemism. The cicadellid subfamily, Deltocephalinae, represents the largest leafhopper groups, yet their patterns of species diversification, host-plant use, and endosymbiont associations remain almost entirely unknown. This study used the Hawaiian Archipelago as a model system to investigate the roles of ecology, biogeography, and endosymbiont interactions in the diversification of the native Hawaiian leafhopper genus, Nesophrosyne (Cicadellidae: Deltocephalinae). The Hawaiian Islands offer a tractable natural laboratory to circumscribe and study plant-insect evolution due to their isolated, discrete and replicated nature, and high levels of endemism. Nesophrosyne represents one of the most diverse and ecologically dominant herbivore radiations on Hawai`i, but has eluded scientific attention for over 60 years. Species are obligate phloem feeders and are highly host-plant specific. Moreover, Nesophrosyne exhibits the quintessential characteristics of an adaptive radiation, including dramatic morphological adaptations to the endemic Hawaiian flora and adaptive diversification across the archipelago to fill habitat types from coastal to sub-alpine regions. The specific goals of this study were to 1) update the current taxonomic status of Nesophrosyne, 2) determine the diversity and phylogenetic relationships of species in the genus, 3) infer the roles of ecology and geology in the adaptive radiation, historical biogeography, and species diversification dynamics of Nesophrosyne, and 4) to reconstruct the global relationships of the dual obligate bacterial endosymbionts of Nesophrosyne and their rates of evolution.In the first chapter, the taxonomic history and status of Nesophrosyne was reviewed. The genus was redescribed, and the subgenus Nesoreias was synonymized with Nesophrosyne. Eight new species associated with the widespread host-plant species, Broussaisia arguta (Hydrangeaceae), were described. Results reveal morphologically cryptic diversity according to individual Hawaiian Islands and volcanoes within this group. A model usage of morphological and molecular characters was developed for future delimitation of species in Nesophrosyne. The second chapter reconstructed a comprehensive phylogeny for Nesophrosyne in order to determine the origins, species diversity, and host-plant use of the native Hawaiian leafhoppers. Results support a monophyletic Nesophrosyne, originating from the Western Pacific basin, with a sister-group relationship to the genus Orosius. Nesophrosyne species are characterized by high levels of morphologically cryptic diversity and local endemicity, comprising > 200 species. Species demonstrate four dominant patterns of host-plant specialization that shape species diversity: 1) diversification through host switching; 2) specialization on widespread hosts with allopatric speciation; 3) repeated, independent shifts to the same hosts; and, 4) absence or low abundance on some hosts, suggesting herbivore interactions may limit ecological opportunity.The third chapter inferred the roles of ecology and geology in the adaptive radiation, historical biogeography, and species diversification dynamics of Nesophrosyne. The molecular age of Nesophrosyne indicates a split from Orosius 4.5 million years ago (Ma), with a basal divergence on Hawai`i 3.2 Ma. The genus originated on Kaua`i and subsequently colonized younger islands as they formed. Ancestral host-plant reconstructions reveal that the plant families, Urticaceae and Rubiaceae, played important roles in the early diversification of Nesophrosyne. Results indicate that island geography have imposed significant barriers to continued gene flow, leading to extensive allopatric speciation and intra-island diversification. Finally, Nesophrosyne diversification dynamics show an initial burst in speciation rates, with a subsequent diversity-dependent decline, corresponding to island formation. Finally, chapter four examined the global relationships of Nesophrosyne's dual obligate, bacteriome restricted bacterial endosymbionts, `Candidatus Sulcia muelleri' and a novel β-proteobacterium in the `Ca. Nasuia' genus. A global bacterial phylogeny was reconstructed, revealing a shared origin for the β-proteobacterial lineages throughout Deltocephalinae genera, and potentially throughout Auchenorrhyncha. The bacteriome association and transovarial transmission of Nesophrosyne's endosymbionts were confirmed using Fluorescent in situ Hybridization techniques. Finally, inference of absolute molecular rates demonstrates highly elevated rates of molecular evolution - the fastest so far recorded. We propose a second species in the genus Nasuia to describe the novel β-proteobacterium in Nesophrosyne.Hawai`i has long been held as a model system to understand adaptive radiation and evolutionary biology, however my study is one of the first to test these patterns directly for a hyper-diverse endemic insect radiation, and for the suborder Auchenorrhyncha. The presented results illustrate that, in diverse herbivorous groups, multiple evolutionary processes play fundamental roles in species diversification, including associations with bacterial endosymbionts, host-plant specialization, insect-insect interactions, and the geologic formation of islands. These results develop both an understanding of how ecological and geological controls shape adaptive diversification in insects, and a general model for contextualizing species diversification in herbivorous insects.

The indirect defence compounds termed herbivore induced plant volatiles (HIPVs), which are used to attract beneficial fauna, are one of the most effective biological control tools for the aggregation of natural enemies of key pests. The aim of this study was to test the attraction of three aphid predators of the Chrysopidae, Coccinellidae and Syrphidae families using synthetic formulations of four main HIPVs [methyl salicylate (MeSa), benzaldehyde (B), linalool (L) and farnesene (F)] alone and in binary combinations (MeSa + B; MeSa + F; MeSa + L; F + B; B + L; F + L) in an apple orchard in the Bursa province of Turkey. This study was the first demonstration of the attraction of these aphid predators to single and binary combinations of synthetic HIPVs in an apple orchard. A larger number of coccinellids were captured using single treatments of both B and F than with other HIPV combinations. Furthermore, the chrysopid individuals studied were significantly attracted to traps baited with single HIPVs. In addition, the binary combination of MeSa + L significantly attracted more Syrphids than in both single treatments and control traps. Thus, some of the HIPV's tested were found to have potential value for the congregation of aphid predators in apple orchards. University of Bursa Uludag, Scientific Research Unit, Bursa, Turkey [UAP (Z) -2010/45] This study was supported by University of Bursa Uludag, Scientific Research Unit, Bursa, Turkey, Grant Project No: UAP (Z) -2010/45.

© 2019 Wong, Lutz, Natera, Wang, Ng, Grigoriev, Martin, Roessner, Anderson and Plett. Plant roots co-inhabit the soil with a diverse consortium of microbes of which a number attempt to enter symbiosis with the plant. These microbes may be pathogenic, mutualistic, or commensal. Hence, the health and survival of plants is heavily reliant on their ability to perceive different microbial lifestyles and respond appropriately. Emerging research suggests that there is a pivotal role for plant root secondary metabolites in responding to microbial colonization. However, it is largely unknown if plants are able to differentiate between microbes of different lifestyles and respond differently during the earliest stages of pre-symbiosis (i.e., prior to physical contact). In studying plant responses to a range of microbial isolates, we questioned: (1) if individual microbes of different lifestyles and species caused alterations to the plant root metabolome during pre-symbiosis, and (2) if these early metabolite responses correlate with the outcome of the symbiotic interaction in later phases of colonization. We compared the changes of the root tip metabolite profile of the model tree Eucalyptus grandis during pre-symbiosis with two isolates of a pathogenic fungus (Armillaria luteobubalina), one isolate of a pathogenic oomycete (Phytophthora cinnamomi), two isolates of an incompatible mutualistic fungus (Suillus granulatus), and six isolates of a compatible mutualistic fungus (Pisolithus microcarpus). Untargeted metabolite profiling revealed predominantly positive root metabolite responses at the pre-symbiosis stage, prior to any observable phenotypical changes of the root tips. Metabolite responses in the host tissue that were specific to each microbial species were identified. A deeper analysis of the root metabolomic profiles during pre-symbiotic contact with six strains of P. microcarpus showed a connection between these early metabolite responses in the root with later colonization success. Further investigation using isotopic tracing revealed a portion of metabolites found in root tips originated from the fungus. RNA-sequencing also showed that the plant roots undergo complementary transcriptomic reprogramming in response to the fungal stimuli. Taken together, our results demonstrate that the early metabolite responses of plant roots are partially selective toward the lifestyle of the interacting microbe, and that these responses can be crucial in determining the outcome of the interaction.

The predator-prey system Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) and Tetranychus urticae (Koch) (Acari: Tetranychidae) represents the most studied and the most known system among the Acari. Because of the agronomical importance of the two mite species, a wealth of modelling studies investigated the interactions of the two species at the individual level. However, regional or global level works on this system are lacking, which is impeding the investigation of climate change effects on biological control effectiveness. Here we compile and geo-locate worldwide occurrences for the two species considered, based on literature, collection and field survey data. The datasets presented in this document gather most of the literature records of both species for which locality data were available for geo-referencing (1,037 for T. urticae and 126 for P. persimilis). Geo-located data from collections and field surveys including host-plants are also presented for the first time (322 for T. urticae and 65 for P. persimilis). Phytoseiulus persimilis is also reported for the first time from Kenya and La Martinique., Acarologia, 59, 301-307

Every interaction between two organisms is a force driving the adaptation of one to the other and vice versa. This force of adaptation becomes more important as the number of interacting organisms and interaction levels increases. In this study we investigate the impact of withanolides, which are a group of plant secondary metabolites synthesized by Physalis plants, on the microbiota of two insect species in order to shed light on the mechanisms of insect-plant coevolution mediated by endosymbionts. We used the model system composed of the generalist lepidopteran moth Heliothis virescens and its close relative Heliothis subflexa, which is a specialist feeder of Physalis plants. We showed by means of bacterial 16S rRNA gene sequencing that H. subflexa has a more diversified gut microflora than H. virescens. Both gut bacterial communities were largely dominated by the genus Enterococcus. Withanolide supplementation to diet given to larvae had no significant effect on the diversity and richness of gut symbionts. In addition, we assessed the temporal expression levels of two antimicrobial peptides - i-type-lysozyme and attatcin-1 - under withanolide treatments on third instar larvae. We showed that the expression of attacin-1 was not affected by any of the treatments; however, i-type-lysozyme was upregulated after 24 hours.; Un des thèmes phares de la biologie de l’évolution est l’étude des interactions entre deux organismes et comment ces interactions deviennent des moteurs d’adaptation, ou plus précisément de coadaptation. Un exemple célèbre et largement étudié est celui des interactions entre les insectes et les plantes. Cette coévolution, souvent appelée « course aux armements », promeut plus souvent la spécialisation des insectes à un nombre réduit de quelques espèces de plantes phylogénétiquement proches qu’à l’expansion de la gamme d’hôte à un grand nombre de plantes (Ehrlich et Raven, 1964, Fox, 1981, Jaenike, 1990).Les plantes ont développé des mécanismes de défense pour se protéger contre les herbivores au moyen, entre autres, de composés appelés « métabolites secondaires de plantes » (MSP). Les insectes quant à eux ont évolué des moyens pour détoxifier leur nourriture, devenir tolérant voire même séquestrer les toxines végétales pour servir leurs propres intérêts (Heckel, 2014). Outre la gestion des toxines de plantes, les insectes doivent également résister aux attaques d’un grand nombre de pathogènes (Lacey et al., 2001).Cependant, comme pour la plupart des animaux, les insectes ne sont pas seuls pour y faire face. Ils sont accompagnés de microorganismes qu’ils portent dans leur intestins, et qui leur procure une grande variété de bienfaits (Frago et coll., 2012, Janson et coll., 2008, McFall-Ngai et coll., 2013). Les études montrant l'importance des microbes intestinaux sur ce sujet se sont multipliées au cours de la dernière décennie. Les symbiotes intestinaux sont connus pour dégrader les matières végétales indigestes, détoxifier l’organisme des MSP, et protéger l’hôte contre les agents pathogènes. Ils sont ainsi considérés comme une potentielle force évolutive capable de provoquer des changements de gamme hôtes chez les insectes. Dans certains cas, le microbiote intestinal de l'insecte serait même impliqué dans le développement de résistances aux insecticides (Pietri et Liang, 2018).Cette présente étude porte sur le système Heliothis subflexa et son espèce soeur Heliothis virescens. H. subflexa est un lépidoptère spécialiste des Physalis (Solanaceae) qui produisent des withanolides pour se défendre, alors que H. virescens peut se nourrir sur plus d’une dizaine de famille de plantes différentes excepté des Physalis (Brazzel, 1953; Cho et al., 2008). Les withanolides sont des lactones stéroïdiennes avec un ergonstane pour structure centrale (Misico et al., 2011). Ces molécules sont reconnues comme étant des antiappétants efficaces (Ascher et al., 1980), des antagonistes des ecdystéroïdes (Dinan et al., 1996), des immunosuppresseurs (Garcia et al., 2006) et pour présenter une activité antimicrobienne (Kurup, 1956). Ils sont répulsifs ou nocifs pour une grande quantité d'organismes. Une étude récente menée par Barthel et al. (2016) a montré dans des expériences d’alimentation que les withanolides bénéficiait à H. subflexa. Celui voyait en effet sa prise de poids relatif augmenter lorsque il en consommait. D’autre part, la consommation de withanolides avait un effet négatif sur H. virescens qui se traduisait par une perte de poids relatif en comparaison du contrôle. Les effets des withanolides portaient également sur l’immunité des deux insectes, l’activité phenoloxidase (PO) était augmentée chez H. subflexa alors qu’elle restait inchangée chez H. virescens. De plus l’apport de withanolides à leurs régimes alimentaires provoqua chez H. subflexa une augmentation non significative de l’expression de la plupart des gènes de l’immunité alors que ces mêmes gènes étaient réprimés chez H. virescens. Ces résultats ont inspiré la présente étude qui s’organise autour de deux questions : les microorganismes intestinaux d’H. subflexa interviennent-ils dans son adaptation aux Physalis ? Il y a-t-il un changement de composition de la microflore intestinale de ce dernier qui puisse expliquer la capacité de cet insecte à se nourrir de Physalis ? Et deuxièmement, cette étude s’intéresse à l’aspect temporel de la réponse immunitaire de cet insecte aux withanolides. Cette réponse est-elle rapide ou bien s’inscrit elle dans la durée ? Et quelle en est l’ampleur en terme que quantification de la surexpression des gènes de l’immunité ?Pour répondre à ces deux problématiques deux expériences de nutrition comprenant deux conditions de traitements ont été établies. Le premier traitement consistait en un extrait purifié de withanolide provenant de Physalis peruviana tandis que le second était du withaferin A, un withanolide disponible dans le commerce. Le traitement control était le méthanol, solvant dans lequel ces composés étaient dissouts. La première expérience consistait à appliquer les traitements de withanolides sur un régime alimentaire artificiel et de permettre à des larves de H. subflexa et H. virescens de s’en nourrir pour une durée de 48h. À l’issue de ce temps d’exposition les intestins des larves ont été disséqués et l’ADN génomique extrait. Les échantillons ont ensuite été envoyés à séquencer pour le gène bactérien ribosomal 16S. Les données brutes ont été traitées dans QIIME2 par le Dr. Shantanu Shukla qui a produit un tableau répertoriant le nombre de comptage obtenu par échantillon pour une séquence donnée. La seconde expérience consistait à exposer les larves à ces mêmes traitements sur des durées de une, six 12 et 24 heures, à l’issue desquelles l’ARN total a été extrait des larves entières, converti en ADN complémentaire et utilisé dans des réactions de PCR quantitatives en temps réel. Cela a permis de suivre au cours du temps l’expression relative de deux gènes de l’immunité : le peptide antimicrobien (AMP) attacine-1 et le lysozyme 1 de type i en réponse aux traitements.Les résultats de l’analyse métagénomique des intestins a montré que H. subflexa a une microflore intestinale plus diversifiée que celle de H. virescens, comprenant 70 familles bactériennes différentes contre seulement cinq chez H. virescens. Cependant le nombre total de séquences quantifiées dans les échantillons de H. subflexa variaient grandement. Certain échantillons comprenant seulement 388 ou 423 séquences lorsque tous les échantillons de H. virescens en avaient plus de 22687. Les deux communautés bactériennes intestinales étaient largement dominées par le genre bactérien Enterococcus. Ce dernier prévalait à 99,89% chez H. virescens et à 84,57% chez son espèce soeur. Ces observations ne sont pas inhabituelles pour des populations d’insectes de laboratoires. L’ajout de withanolides au régime alimentaire administré aux larves n'a pas eu d'effet significatif sur la diversité et la richesse intraspécifique de leurs symbiotes intestinaux. Seul la proportion relative a été impactée chez H. subflexa où l’ordre des Bacillales composait seulement 0,27% de la communauté totale sur le contrôle mais représentaient 4% et 31% lorsque les larves étaient exposées à l’extrait de withanolide et au withaferin A respectivement. Ces résultats suggèrent que H. subflexa n’a pas de communauté bactérienne résidente mais plutôt transitoire. Il a ensuite été montré que l'expression du gène de l'attacine-1 n'était pas affectée par les traitements alors le gène du lysozyme 1 de type i était surexprimé de manière significative après 24 heures chez les deux espèces comparé au temps zéro. Cependant, l’expression des deux gènes de l’immunité ne différait pas dans les conditions de traitement par rapport au contrôle, et ce pour tous les temps étudiés.

Nutritional symbioses play a central role in the ability of insects to thrive on unbalanced diets and in ensuring their evolutionary success. A genomic model for nutritional symbiosis comprises the hemipteran Acyrthosiphon pisum, and the gamma-3-proteobacterium, Buchnera aphidicola, with genomes encoding highly integrated metabolic pathways. A. pisum feeds exclusively on plant phloem sap, a nutritionally unbalanced diet highly variable in composition, thus raising the question of how this symbiotic system responds to nutritional stress. We addressed this by combining transcriptomic, phenotypic and life history trait analyses to determine the organismal impact of deprivation of tyrosine and phenylalanine. These two aromatic amino acids are essential for aphid development, are synthesized in a metabolic pathway for which the aphid host and the endosymbiont are interdependent, and their concentration can be highly variable in plant phloem sap. We found that this nutritional challenge does not have major phenotypic effects on the pea aphid, except for a limited weight reduction and a 2-day delay in onset of nymph laying. Transcriptomic analyses through aphid development showed a prominent response in bacteriocytes (the core symbiotic tissue which houses the symbionts), but not in gut, thus highlighting the role of bacteriocytes as major modulators of this homeostasis. This response does not involve a direct regulation of tyrosine and phenylalanine biosynthetic pathway and transporter genes. Instead, we observed an extensive transcriptional reprogramming of the bacteriocyte with a rapid down-regulation of genes encoding sugar transporters and genes required for sugar metabolism. Consistently, we observed continued overexpression of the A. pisum homolog of RRAD, a small GTPase implicated in repressing aerobic glycolysis. In addition, we found increased transcription of genes involved in proliferation, cell size control and signaling. We experimentally confirmed the significance of these gene expression changes detecting an increase in bacteriocyte number and cell size in vivo under tyrosine and phenylalanine depletion. Our results support a central role of bacteriocytes in the aphid response to amino acid deprivation: their transcriptional and cellular responses fine-tune host physiology providing the host insect with an effective way to cope with the challenges posed by the variability in composition of phloem sap. ispartof: FRONTIERS IN PHYSIOLOGY vol:9 issue:OCT ispartof: location:Switzerland status: published

Brassicogethes salvan (Audisio et al. Insect Systematics and Evolution, 34, 121) is certainly among the most important and unexpected recent discoveries in the European beetle fauna. The species was initially described from a couple of unidentified specimens collected in 1912 on the Maritime Alps (NW Italy). Despite a long series of attempts to recollect the species at the type locality (Rovina Lake, Mount Argentera Massif, Cuneo Province, Piedmont, NW Italy) and several neighbouring areas of the SW Alps between 2002 and 2016, no specimens of this species were found. We re-discovered B. salvan in a small high valley of the Regional Natural Park of the Maritime Alps, a few dozen kilometers from the type locality. The previously unknown larval host-plant as Descurainia tanacetifolia (L.) Rchb., Brassicaceae was determined. Some unusual life history traits were also observed. In an effort to yield a suitable taxonomic placement for this species, we present a partial preliminary molecular phylogeny for this species and related taxa. A discussion regarding some issues about its actual and potential geographic distribution in southern France and northwestern Italy is also provided. We propose an EN (Endangered) classification for this species following the IUCN criteria, and discuss aspects of its rather problematic conservation biology.

As sexual selection is a coevolutionary process between males and females, various morphological and behavioral traits have evolved in each sex. In the tetranychid mites Tetranychus urticae Koch and T. kanzawai Kishida (Acari: Tetranychidae), males can mate repeatedly, whereas females normally accept only the first copulation for fertilization. Since early times, it had been reported that males engage in precopulatory mate guarding and combat against conspecifics for females to enhance their reproductive success. On the other hand, it was believed that females do not have opportunities to choose their mates. In the last 10 or so years, however, several new findings related to mating behavior were reported. Some of the findings reinforce our established knowledge, whereas some of them explode it. Here, I review the mating behavior of T. urticae and T. kanzawai by incorporating recent findings and then propose a new direction for future research.

Attack by multiple herbivores often leads to modification of induced plant defenses compared to single herbivory, yet little is known about the effects on induced indirect plant defense. Here, we investigated the effect of sequential induction of plant defense by Mamestra brassicae caterpillar oral secretion and an infestation by Tetranychus urticae spider mites on the expression of indirect plant defense in Lima bean plants. The effect on indirect defense was assessed using behavior assays with the specialist predatory mite Phytoseiulus persimilis in an olfactometer, headspace analysis of 11 major herbivore-induced plant volatiles (HIPVs) including (E)-β-ocimene, and transcript levels of the corresponding gene Phaseolus lunatus (E)-β-ocimene synthase (PlOS). Predatory mites were found to distinguish between plants induced by spider mites and caterpillar oral secretion but not between plants with single spider mite infestation and plants induced by caterpillar oral secretion prior to spider mite infestation. Indeed, the volatile blends emitted by plants induced by spider mites only and the sequential induction treatment of caterpillar oral secretion followed by spider mite infestation, were similar. Our results suggest that plant indirect defense is not affected by previous treatment with oral secretion of M. brassicae caterpillars.

Herbivore-induced plant volatiles are often involved in direct and indirect plant defence against herbivores. Linalool is a common floral scent and found to be released from leaves by many plants after herbivore attack. In this study, a linalool/nerolidol synthase, FaNES1, was overexpressed in the plastids of chrysanthemum plants (Chrysanthemum morifolium). The volatiles of FaNES1 chrysanthemum leaves were strongly dominated by linalool, but they also emitted small amount of the C11-homoterpene, (3E)-4,8-dimethyl-1,3,7-nonatriene, a derivative of nerolidol. Four nonvolatile linalool glycosides in methanolic extracts were found to be significantly increased in the leaves of FaNES1 plants compared to wild-type plants. They were putatively identified by LC-MS-MS as two linalool-malonyl-hexoses, a linalool-pentose-hexose and a glycoside of hydroxy-linalool. A leaf-disc dual-choice assay with western flower thrips (WFT, Frankliniella occidentalis) showed, initially during the first 15 min of WFT release, that FaNES1 plants were significantly preferred. This gradually reversed into significant preference for the control, however, at 20-28 h after WFT release. The initial preference was shown to be based on the linalool odour of FaNES1 plants by olfactory dual-choice assays using paper discs emitting pure linalool at similar rates as leaf discs. The reversal of preference into deterrence could be explained by the initial nonvolatile composition of the FaNES1 plants, as methanolic extracts were less preferred by WFT. Considering the common occurrence of linalool and its glycosides in plant tissues, it suggests that plants may balance attractive fragrance with 'poor taste' using the same precursor compound.

BACKGROUND: Most insect-resistant transgenic crops employ toxins to control pests. A novel approach is to enhance the effectiveness of natural enemies by genetic engineering of the biosynthesis of volatile organic compounds (VOCs). Before the commercialisation of such transgenic plants can be pursued, detailed fundamental studies of their effects on herbivores and their natural enemies are necessary. The linalool/nerolidol synthase gene FaNES1 was constitutively expressed from strawberry in three Arabidopsis thaliana accessions, and the behaviour of the aphid Brevicoryne brassicae L., the parasitoid Diaeretiella rapae McIntosh and the predator Episyrphus balteatus de Geer was studied. RESULTS: Transgenic FaNES1-expressing plants emitted (E)-nerolidol and larger amounts of (E)-DMNT and linalool. Brevicoryne brassicae was repelled by the transgenic lines of two of the accessions, whereas its performance was not affected. Diaeretiella rapae preferred aphid-infested transgenic plants over aphid-infested wild-type plants for two of the accessions. In contrast, female E. balteatus predators did not differentiate between aphid-infested transgenic or wild-type plants. CONCLUSION: The results indicate that the genetic engineering of plants to modify their emission of VOCs holds considerable promise for facilitating biological control of herbivores. Validation for crop plants is a necessary next step to assess the usefulness of modified volatile emission in integrated pest management.

The effects of plant competition for light on the emission of plant volatile organic compounds (VOCs) were studied by investigating how different light qualities that occur in dense vegetation affect the emission of constitutive and methyl-jasmonate-induced VOCs. Arabidopsis thaliana Columbia (Col-0) plants and Pieris brassicae caterpillars were used as a biological system to study the effects of light quality manipulations on VOC emissions and attraction of herbivores. VOCs were analysed using gas chromatography-mass spectrometry and the effects of light quality, notably the red : far red light ratio (R : FR), on expression of genes associated with VOC production were studied using reverse transcriptase-quantitative PCR. The emissions of both constitutive and methyl-jasmonate-induced green leaf volatiles and terpenoids were partially suppressed under low R : FR and severe shading conditions. Accordingly, the VOC-based preference of neonates of the specialist lepidopteran herbivore P. brassicae was significantly affected by the R : FR ratio. We conclude that VOC-mediated interactions among plants and between plants and organisms at higher trophic levels probably depend on light alterations caused by nearby vegetation. Studies on plant-plant and plant-insect interactions through VOCs should take into account the light quality within dense stands when extrapolating to natural and agricultural field conditions.

Summary 1. In their natural environment, plants are faced with a multitude of attackers, of which insect herbivores and plant pathogens are an important component. In response to these attacks, plants release volatile organic compounds (VOCs), which play an important role in the communication between plants and the associated community members, such as other herbivores, phytopathogens and the natural enemies of herbivores. 2. While numerous studies have focused on either plant–pathogen or plant–insect interactions, less is known when these two sets of interactions co-occur. Depending on the mode of attack of the pathogen (necrotroph vs. biotroph) or herbivore (chewing vs. piercing-sucking) they will activate different defence pathways in the plant in which the phytohormones salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) play key roles. As these pathways can crosstalk, a pathogen infection can interfere in a plant’s defence response to herbivory, and vice versa. 3. Infestation of a plant with organisms inducing SA signalling prior to – or simultaneously with – attack by organisms that induce the JA pathway often suppresses JA signalling. However, the impact of this signalling pathway crosstalk on VOC induction is not clear cut, as there is high variability in the effects on volatile emissions, ranging from suppression to enhanced emission. The effects of the modified volatile blends on the foraging success of carnivorous natural enemies of herbivorous insects have started to be investigated. Foraging success of natural enemies generally withstands this modification of the host-induced VOC blend, but the presence or absence of key compounds is an important determinant of the response of certain carnivores. 4. Further studies incorporating plant–insect and plant–pathogen interactions at different levels of biological integration will provide valuable insight in how plants integrate signals from different suites of attacking organisms into an adaptive defence response.

The importance of trans-generational effects in shaping an individuals' phenotype and fitness, and consequently even impacting population dynamics is increasingly apparent. Most of the research on trans-generational effects still focuses on plants, mammals, and birds. In the past few years, however, increasing number of studies, especially on maternal effects, have highlighted their importance also in many insect systems. Lepidoptera, specifically butterflies, have been used as model systems for studying the role of phenotypic plasticity within generations. As ectotherms, they are highly sensitive to environmental variation, and indeed many butterflies show adaptive phenotypic plasticity in response to environmental conditions. Here, we synthesize what is known about trans-generational effects in Lepidoptera, compile evidence for different environmental cues that are important drivers of trans-generational effects, and point out which offspring traits are mainly impacted. Finally, we emphasize directions for future research that are needed for better understanding of the adaptive nature of trans-generational effects in Lepidoptera in particular, but potentially also in other organisms.

A central issue in the evolutionary ecology of species interactions is coevolution, which involves the reciprocal selection between individuals of interacting species. Understanding the importance of coevolution in shaping species interactions requires the consideration of spatial variation in their strength. This is exactly what the, recently developed, geographic mosaic theory of coevolution addresses. Another major development in the study of population ecology is the introduction of the population genomics approach in this field of research. This approach addresses spatial processes through molecular methods. It is of particular interest that population genomics is especially applicable to natural populations of non-model species. We describe how population genomics can be used in the context of the geographic mosaic of coevolution, specifically to identify coevolutionary hot-spots, and to attribute genetic variation found at specific loci to processes of selection versus trait remixing. The proposed integration of the population genomics approach with the conceptual framework of the geographic mosaic of coevolution is illustrated with a few selected, particularly demonstrative, examples from the realm of insect--plant interactions.

Invasive species represent one of the most important threats to biodiversity worldwide, with consequences for ecosystem functioning and the delivery of important ecological services to society. Several hypotheses have been generated to explain the success of exotic plants in their new ranges, with escape from their old natural enemies, such as pathogens and herbivores (the ‘enemy release hypothesis’) and novel defensive chemistry (the ‘novel weapons hypothesis’) receiving considerable attention. Thus far, virtually all studies of exotic plants and insects have been conducted in a strictly bi-trophic framework involving plants and herbivores. On the other hand, it has been argued that a better understanding of the forces regulating community structure and function should include natural enemies of the herbivores. Furthermore, indirect interactions between organisms in the plant roots (below-ground) and shoots (above-ground) are known to strongly effect the behaviour and performance of consumers in the opposite ‘compartment’. Here, we discuss a range of physiological, evolutionary and ecological aspects of plant–herbivore-natural enemy interactions involving exotic plants. Further, interactions between soil and above-ground organisms are explored with respect to studies with exotic plants. We argue that it is important to link population and community ecology to individual-level variation in the physiology and behaviour of insects across several trophic levels in studies with invasive plants. Future research with invaders should also aim to integrate physically separated compartments (e.g. plant roots and shoots). This will facilitate a more complete understanding of the factors underlying the success (or failure) of exotic plants to spread and become dominant in their new ranges. Moreover, these data will also help to unravel the relative importance of top-down and bottom-up processes in regulating communities in which exotic plants have become established. Lastly, we discuss consequences for conservation.

Behavioral and electrophysiological responses of larvae of the polyphagous moth species Helicoverpa armigera to two plant-derived allelochemicals were studied, both in larvae that had been reared on a diet devoid of these compounds and in larvae previously exposed to these compounds. In dual-choice cotton leaf disk and pepper fruit disk arena assays, caterpillars reared on a normal artificial diet were strongly deterred by strychnine and strophanthin- K. However, caterpillars reared on an artificial diet containing strychnine were insensitive to strychnine and strophanthin-K. Similarly, caterpillars reared on an artificial diet containing strophanthin-K were also desensitized to both deterrent chemicals. Electrophysiological tests revealed that the deterrent-sensitive neurons in taste sensilla on the maxillae of caterpillars reared on each deterrent- containing diet displayed reduced sensitivity to the two chemicals compared with the caterpillars reared on normal diets. We conclude that the experience-dependent behavioral plasticity was partly based on the reduced sensitivity of taste receptor neurons and that the desensitization of taste receptor neurons contributed to the crosshabituation to the two chemicals.

Summary 1Plant species employ several direct and indirect defence strategies to protect themselves against insect herbivores. Most studies, however, have focused on shoot-induced responses. Much less is known about interactions between below- and above-ground herbivores and how these may affect their respective parasitoids. 2Here, we quantify the impact of below-ground induced responses vs. that of above-ground induced responses in a feral Brassica on the performance of Pieris brassicae and its endoparasitoid Cotesia glomerata. Jasmonic acid (JA) was applied to induce the plants above- or below-ground. The glucosinolate, sugar and amino acid levels of the leaves were analysed. 3Pieris brassicae larvae grew significantly slower on shoot JA-induced (SJA) plants than on root JA-induced (RJA) and control plants, which were treated with acidic water. On RJA and control plants they showed similar developmental trajectories. Pupal masses, survival till eclosion and egg load, however, were similar on all plants. 4The development of C. glomerata larvae on SJA plants was significantly longer than that on RJA and control plants. In contrast, the parasitoid's pupal stage lasted longer in hosts feeding on control plants. The total developmental times eventually were similar in all groups. However, the masses of male and female C. glomerata adults that developed hosts on control and RJA plants were significantly larger than those from hosts on SJA plants. JA application increased total glucosinolate contents and decreased the sugars and total amino acids levels independent of whether JA was applied. However, the trajectories of herbivore-induced glucosinolate levels differed between RJA and SJA plants. 5These results show that the differential effects of above- and below-ground-induced responses on herbivores also affect higher trophic levels in a nonlinear fashion via differential changes in host plant quality. In particular, the indirect effects that below-ground herbivores have on the performance of above-ground parasitoids may exceed the direct effects of plant chemistry on herbivore performance. Consequently, above-ground and below-ground interactions mediated by induced plant responses have the potential to mediate insect community structure and function in complex ways.

Plants respond to insect herbivory with the production of volatiles that attract carnivorous enemies of the herbivores, a phenomenon called indirect defence or 'plants crying for help'. Plants are under selection to maximize Darwinian fitness, and this can be done by making the right 'decisions' (i.e. by responding to environmental stress in ways that maximize seed production). Plant decisions related to the response to herbivory in terms of the emission of herbivore-induced volatiles include 'to respond or not to respond', 'how fast to respond', 'how to respond' and 'when to stop responding'. In this review, the state-of-the-art of the research field is presented in the context of these decisions that plants face. New questions and directions for future research are identified. To understand the consequences of plant responses in a community context, it is important to expand research from individual interactions to multispecies interactions in a community context. To achieve this, detailed information on underlying mechanisms is essential and first steps on this road have been made. This selective review addresses the ecology of herbivore-induced plant volatiles (HIPVs) by integrating information on mechanisms and ecological functions. New questions are identified as well as challenges for extending current information to community ecology.