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Several studies have shown that insectivorous birds are attracted to herbivore‐damaged trees even when they cannot see or smell the actual herbivores or their feces. However, it often remained an open question whether birds are attracted by herbivore‐induced changes in leaf odor or in leaf light reflectance or by both types of changes. Our study addressed this question by investigating the response of great tits (Parus major) and blue tits (Cyanistes caeruleus) to Scots pine (Pinus sylvestris) damaged by pine sawfly larvae (Diprion pini). We released the birds individually to a study booth, where they were simultaneously offered a systemically herbivore‐induced and a noninfested control pine branch. In the first experiment, the birds could see the branches, but could not smell them, because each branch was kept inside a transparent, airtight cylinder. In the second experiment, the birds could smell the branches, but could not see them, because each branch was placed inside a nontransparent cylinder with a mesh lid. The results show that the birds were more attracted to the herbivore‐induced branch in both experiments. Hence, either type of the tested cues, the herbivore‐induced visual plant cue alone as well as the olfactory cues per se, is attractive to the birds., Both great tits and blue tits were attracted to systemically herbivore‐damaged pines when they could only see or only smell the experimental branches. This is the first ever study to show that both vision and olfaction alone are enough for attraction of insectivorous birds to herbivore‐damaged trees.

An insect’s phenotype can be influenced by the experiences of the parental generation. However, the effects of the parental symbiotic microbiome and host plant use on the offspring are unclear. We addressed this gap of knowledge by studying Pieris brassicae, a multivoltine butterfly species feeding on different brassicaceous plants across generations. We investigated how disturbance of the parental bacterial community by antibiotic treatment affects F(1) larval traits. We tested the effects depending on whether F(1) larvae are feeding on the same plant species as their parents or on a different one. The parental treatment alone had no impact on the biomass of F(1) larvae feeding on the parental plant species. However, the parental treatment had a detrimental effect on F(1) larval biomass when F(1) larvae had a different host plant than their parents. This effect was linked to higher larval prophenoloxidase activity and greater downregulation of the major allergen gene (MA), a glucosinolate detoxification gene of P. brassicae. Bacterial abundance in untreated adult parents was high, while it was very low in F(1) larvae from either parental type, and thus unlikely to directly influence larval traits. Our results suggest that transgenerational effects of the parental microbiome on the offspring’s phenotype become evident when the offspring is exposed to a transgenerational host plant shift. IMPORTANCE Resident bacterial communities are almost absent in larvae of butterflies and thus are unlikely to affect their host. In contrast, adult butterflies contain conspicuous amounts of bacteria. While the host plant and immune state of adult parental butterflies are known to affect offspring traits, it has been unclear whether also the parental microbiome imposes direct effects on the offspring. Here, we show that disturbance of the bacterial community in parental butterflies by an antibiotic treatment has a detrimental effect on those offspring larvae feeding on a different host plant than their parents. Hence, the study indicates that disturbance of an insect’s parental microbiome by an antibiotic treatment shapes how the offspring individuals can adjust themselves to a novel host plant.

Parasitic wasps which attack insects infesting processed stored food need to locate their hosts hidden inside these products. Their host search is well-known to be guided by host kairomones, perceived via olfaction or contact. Among contact kairomones, host cuticular hydrocarbons (CHCs) may provide reliable information for a parasitoid. However, the chemistry of CHC profiles of hosts living in processed stored food products is largely unknown. Here we showed that the ectoparasitoid Holepyris sylvanidis uses CHCs of its host Tribolium confusum, a worldwide stored product pest, as kairomones for host location and recognition at short range. Chemical analysis of T. confusum larval extracts by gas chromatography coupled with mass spectrometry revealed a rich blend of long-chain (C25-C30) hydrocarbons, including n-alkanes, mono-, and dimethylalkanes. We further studied whether host larvae leave sufficient CHCs on a substrate where they walk along, thus allowing parasitoids to perceive a CHC trail and follow it to their host larvae. We detected 18 CHCs on a substrate that had been exposed to host larvae. These compounds were also found in crude extracts of host larvae and made up about a fifth of the CHC amount extracted. Behavioral assays showed that trails of host CHCs were followed by the parasitoids and reduced their searching time until successful host recognition. Host CHC trails deposited on different substrates were persistent for about a day. Hence, the parasitoid H. sylvanidis exploits CHCs of T. confusum larvae for host finding by following host CHC trails and for host recognition by direct contact with host larvae.

Significance Plant defenses against herbivorous insects can target the feeding stages and the egg stage. Feeding-induced plant defenses are known to be primed by cues indicating imminent infestation, including sex pheromones. However, priming of egg-induced plant defenses has been unknown so far. Therefore, we studied whether a plant’s response to insect sex pheromones, which might indicate imminent egg depositions, primes defenses against the eggs. Indeed, exposure of pine to the sex pheromones of an herbivorous sawfly primes the tree’s defense against sawfly eggs. The priming effect results in enhanced egg mortality, enhanced accumulation of hydrogen peroxide in egg-laden needles, and differential expression of several defense-related pine genes. These findings open up exciting research perspectives in plant protection from insect infestation., Plants respond to insect infestation with defenses targeting insect eggs on their leaves and the feeding insects. Upon perceiving cues indicating imminent herbivory, such as damage-induced leaf odors emitted by neighboring plants, they are able to prime their defenses against feeding insects. Yet it remains unknown whether plants can amplify their defenses against insect eggs by responding to cues indicating imminent egg deposition. Here, we tested the hypothesis that a plant strengthens its defenses against insect eggs by responding to insect sex pheromones. Our study shows that preexposure of Pinus sylvestris to pine sawfly sex pheromones reduces the survival rate of subsequently laid sawfly eggs. Exposure to pheromones does not significantly affect the pine needle water content, but results in increased needle hydrogen peroxide concentrations and increased expression of defense-related pine genes such as SOD (superoxide dismutase), LOX (lipoxygenase), PAL (phenylalanine ammonia lyase), and PR-1 (pathogenesis related protein 1) after egg deposition. These results support our hypothesis that plant responses to sex pheromones emitted by an herbivorous insect can boost plant defensive responses to insect egg deposition, thus highlighting the ability of a plant to mobilize its defenses very early against an initial phase of insect attack, the egg deposition.

Global change has complex eco-evolutionary consequences for organisms and ecosystems, but related concepts (e.g., novel ecosystems) do not cover their full range. Here we propose an umbrella concept of “ecological novelty” comprising (1) a site-specific and (2) an organism-centered, eco-evolutionary perspective. Under this umbrella, complementary options for studying and communicating effects of global change on organisms, ecosystems, and landscapes can be included in a toolbox. This allows researchers to address ecological novelty from different perspectives, e.g., by defining it based on (a) categorical or continuous measures, (b) reference conditions related to sites or organisms, and (c) types of human activities. We suggest striving for a descriptive, non-normative usage of the term “ecological novelty” in science. Normative evaluations and decisions about conservation policies or management are important, but require additional societal processes and engagement with multiple stakeholders., BioScience, 69 (11)

Maladaptive sexual interactions among heterospecific individuals (sexual interference) can prevent the coexistence of animal species. Thus, the avoidance of sexual interference by divergence of mate recognition systems is crucial for a stable coexistence in sympatry. Mate recognition systems are thought to be under tight genetic control. However, we demonstrate that mate recognition systems of two closely related sympatric leaf beetle species show a high level of host-induced phenotypic plasticity. Mate choice in the mustard leaf beetles, Phaedon cochleariae and P. armoraciae, is mediated by cuticular hydrocarbons (CHCs). Divergent host plant use causes a divergence of CHC phenotypes, whereas similar host use leads to their convergence. Consequently, both species exhibit significant behavioral isolation when they feed on alternative host species, but mate randomly when using a common host. Thus, sexual interference between these syntopic leaf beetles is prevented by host-induced phenotypic plasticity rather than by genotypic divergence of mate recognition systems.

Elms (Ulmus spp.) have long been appreciated for their environmental tolerance, landscape and ornamental value, and the quality of their wood. Although elm trees are extremely hardy against abiotic stresses such as wind and pollution, they are susceptible to attacks of biotic stressors. Over 100 phytopathogens and invertebrate pests are associated with elms: fungi, bacteria and insects like beetles and moths, and to a lesser extent aphids, mites, viruses and nematodes. While the biology of the pathogen and insect vector of the Dutch elm disease has been intensively studied, less attention has been paid so far to the defence mechanisms of elms to other biotic stressors. This review highlights knowledge of direct and indirect elm defences against biotic stressors focusing on morphological, chemical and gene regulation aspects. First, we report how morphological defence mechanisms via barrier formation and vessel occlusion prevent colonisation and spread of wood- and bark-inhabiting fungi and bacteria. Second, we outline how secondary metabolites such as terpenoids (volatile terpenoids, mansonones and triterpenoids) and phenolics (lignans, coumarins, flavonoids) in leaves and bark are involved in constitutive and induced chemical defence mechanisms of elms. Third, we address knowledge on how the molecular regulation of elm defence is orchestrated through the interaction of a huge variety of stress- and defence-related genes. We conclude by pointing to the gaps of knowledge on the chemical and molecular mechanisms of elm defence against pest insects and diseases. An in-depth understanding of defence mechanisms of elms will support the development of sustainable integrated management of pests and diseases attacking elms.

Experience and memory of environmental stimuli that indicate future stress can prepare (prime) organismic stress responses even in species lacking a nervous system. The process through which such organisms prepare their phenotype for an improved response to future stress has been termed 'priming'. However, other terms are also used for this phenomenon, especially when considering priming in different types of organisms and when referring to different stressors. Here we propose a conceptual framework for priming of stress responses in bacteria, fungi and plants which allows comparison of priming with other terms, e.g. adaptation, acclimation, induction, acquired resistance and cross protection. We address spatial and temporal aspects of priming and highlight current knowledge about the mechanisms necessary for information storage which range from epigenetic marks to the accumulation of (dormant) signalling molecules. Furthermore, we outline possible patterns of primed stress responses. Finally, we link the ability of organisms to become primed for stress responses (their 'primability') with evolutionary ecology aspects and discuss which properties of an organism and its environment may favour the evolution of priming of stress responses.

Anthropogenic land use may shape vegetation composition and affect trophic interactions by altering concentrations of host plant metabolites. Here, we investigated the hypotheses that: (1) plant N and defensive secondary metabolite contents of the herb Plantago lanceolata are affected by land use intensity (LUI) and the surrounding vegetation composition (=plant species richness and P. lanceolata density), and that (2) changes in plant chemistry affect abundances of the herbivorous weevils Mecinus pascuorum and Mecinus labilis, as well as their larval parasitoid Mesopolobus incultus, in the field. We determined plant species richness, P. lanceolata density, and abundances of the herbivores and the parasitoid in 77 grassland plots differing in LUI index in three regions across Germany. We also measured the N and secondary metabolite [the iridoid glycosides (IGs) aucubin and catalpol] contents of P. lanceolata leaves. Mixed-model analysis revealed that: (1) concentrations of leaf IGs were positively correlated with plant species richness; leaf N content was positively correlated with the LUI index. Furthermore: (2) herbivore abundance was not related to IG concentrations, but correlated negatively with leaf N content. Parasitoid abundance correlated positively only with host abundance over the three regions. Structural equation models revealed a positive impact of IG concentrations on parasitoid abundance in one region. We conclude that changes in plant chemistry due to land use and/or vegetation composition may affect higher trophic levels and that the manifestation of these effects may depend on local biotic or abiotic features of the landscape.

Plants can respond to insect egg deposition and thus resist attack by herbivorous insects from the beginning of the attack, egg deposition. We review ecological effects of plant responses to insect eggs and differentiate between egg-induced plant defenses that directly harm the eggs and indirect defenses that involve egg parasitoids. Furthermore, we discuss the ability of plants to take insect eggs as warning signals; the eggs indicate future larval feeding damage and trigger plant changes that either directly impair larval performance or attract enemies of the larvae. We address the questions of how egg-associated cues elicit plant defenses, how the information that eggs have been laid is transmitted within a plant, and which molecular and chemical plant responses are induced by egg deposition. Finally, we highlight evolutionary aspects of the interactions between plants and insect eggs and ask how the herbivorous insect copes with egg-induced plant defenses and may avoid them by counteradaptations.

Insect olfactory orientation along odour plumes has been studied intensively with respect to pheromonal communication, whereas little knowledge is available on how plant odour plumes (POPs) affect olfactory searching by an insect for its host plants. The primary objective of this review is to examine the role of POPs in the attraction of insects. First, we consider parameters of an odour source and the environment which determine the size, shape and structure of an odour plume, and we apply that knowledge to POPs. Second, we compare characteristics of insect pheromonal plumes and POPs. We propose a 'POP concept' for the olfactory orientation of insects to plants. We suggest that: (i) an insect recognises a POP by means of plant volatile components that are encountered in concentrations higher than a threshold detection limit and that occur in a qualitative and quantitative blend indicating a resource; (ii) perception of the fine structure of a POP enables an insect to distinguish a POP from an unspecific odorous background and other interfering plumes; and (iii) an insect can follow several POPs to their sources, and may leave the track of one POP and switch to another one if this conveys a signal with higher reliability or indicates a more suitable resource. The POP concept proposed here may be a useful tool for research in olfactory-mediated plant-insect interactions.

The role of phenotypical plasticity in ecological speciation and the evolution of sexual isolation remains largely unknown. We investigated whether or not divergent host plant use in an herbivorous insect causes assortative mating by phenotypically altering traits involved in mate recognition. We found that males of the mustard leaf beetle Phaedon cochleariae preferred to mate with females that were reared on the same plant species to females provided with a different plant species, based on divergent cuticular hydrocarbon profiles that serve as contact pheromones. The cuticular hydrocarbon phenotypes of the beetles were host plant specific and changed within 2 weeks after a shift to a novel host plant species. We suggest that plant-induced phenotypic divergence in mate recognition cues may act as an early barrier to gene flow between herbivorous insect populations on alternative host species, preceding genetic divergence and thus, promoting ecological speciation.

Vegetation complexity is characterized by two major traits, i.e., plant chemical and plant structural complexity. Plant species diversity strongly determines these traits. Furthermore, plant structures affect microclimatic conditions, which in turn influence the emission and dispersion of plant volatiles (e.g., chemical complexity). Plant volatile chemical complexity may significantly affect orientation of herbivorous and carnivorous arthropods. Therefore, the way in which plant chemical and plant structural complexity act “in concert” may influence foraging and mating success of arthropods, and thus, finally, community composition. This review emphasizes an integrative view on the relationship between plant species diversity, plant structural complexity, plant volatiles (chemical complexity) and their effects on arthropods. Three new hypotheses are raised, which predict possible relations between plant volatile complexity and plant species diversity: (1) saturation-, (2) step-by-step, (3) incoherence-hypothesis. We conclude that arthropod orientation in natural environments is strongly determined by the relationship between plant volatile diversity and plant species diversity. Furthermore, we emphasize that structural complexity of the vegetation affects plant volatile diversity and thus, arthropod orientation. We review available information on how insects actually respond to complexity during olfactory and visual search and ask for both laboratory and field studies to further unravel the mechanisms of interactions between vegetation traits and their impact on arthropod orientation.

Insects live in a highly complex odorant world. Within a variety of odor blends, they need to locate potential food sources, mates, and oviposition sites to gain reproductive success. In nature, volatile cues leading to a resource are always present with numerous other volatiles—here referred to as background odor—which may affect the parasitoid's response to resource-indicating cues. Three different types of background odor are discussed in this article: (a) irrelevant background odor, (b) background odor that may mask the resource-indicating signals, and (c) background odorants that may “sharpen the view” for resource-indicating odor and enhance the response to these. Odor orientation to resources especially in herbivorous and parasitic insects are addressed.

So far, it was unknown whether immune responses of insect eggs are inducible or suppressed by parasitism. We investigated whether transcription of immune related genes in eggs of Manduca sexta changed in response to parasitism by Trichogramma evanescens . First, using DDRT-PCR, several cDNA elements known to represent immune related M. sexta genes inducible by bacterial challenge were isolated from eggs. In addition, two novel cDNAs were found: (a) immulectin-V ( IML-V ) suggested to be involved in recognition of foreign bodies, and (b) a new like-moricin protein with possible antimicrobial effects ( L-Mor ). Quantitative real time RT-PCR analyses revealed enhanced transcription in parasitized eggs compared to unparasitized ones for IML-V , prophenoloxidase ( ProPO ), prophenoloxidase activating protease I ( PAP I ), and proparalytic peptide ( ProPP ). No significant differences between parasitized and unparasitized eggs were detected for sequences encoding the antimicrobial peptides L-Mor , leureptin Leu, and attacin II Att II . Transcript levels of other antibacterial peptides were suppressed after parasitization for 3 d (cecropin 6, Cec 6 ) and 2 d (gloverin, Glov ). While nearly 100% of the Manduca eggs contained Trichogramma specimens 1 d after exposure to parasitoids, only 64% of the host eggs harbored parasitoid larvae 4 d after parasitization. Our data demonstrate that the immune system of Manduca eggs shows differentiated responses to parasitization and suggest that insect eggs can defend against parasitization.

Wolbachia are obligatory, cytoplasmatically inherited alpha-proteobacteria, which are common endosymbionts in arthropods where they may cause reproductive abnormalities. Many insects are well known to protect themselves from deleterious microorganisms by antibiotic components. In this study, we addressed the question whether Wolbachia are able to infect insects containing antimicrobial anthraquinones and anthrones, and if so, whether these genotypes of Wolbachia comprise a monophyletic cluster within one of the known supergroups. Leaf beetles of the taxon Galerucini (Galerucinae) are known to contain 1,8-dihydroxylated anthraquinones and anthrones. Also, the scale insect Dactylopius contains an anthraquinone glycoside, carminic acid. Our analyses revealed that a representative of the Galerucini, Galeruca tanaceti and Dactylopius, are indeed infected by endosymbiotic Wolbachia bacteria. Phylogenetic analysis of the wsp and ftsZ genes of these bacteria revealed that strains in G. tanaceti cluster in supergroup A, whereas those present in Dactylopius are distinctive from each other and from those of G. tanaceti. They are clustering in supergroups A and B. Wolbachia strains present in close, but anthraquinone-free relatives of G. tanaceti were shown to belong also to supergroup A. From these results, we can conclude (1) a double infection in Dactylopius, (2) that the presence of antimicrobial compounds such as anthraquinones does not necessarily protect insects from infection by Wolbachia, and (3) that genotypes of Wolbachia-infecting anthraquinone-containing insects most likely do not comprise a unique genotype. These results show that Wolbachia bacteria might be adapted to cope even with conditions usually detrimental to other bacteria and that these adaptations are widespread among Wolbachia supergroups.

Summary Chrysomelidae are a taxon with an enormous plethora of highly specialised herbivorous species. The present study provides an overview of the knowledge available so far on cues guiding chrysomelids to locate a host plant. Host location behaviour will be addressed from different trophic perspectives. Cues from undamaged host plants are distinguished from cues released from damaged ones. The role of host plant cues is considered with respect to the surrounding vegetation and to the presence of competitors. Only very little is known on how enemies searching for prey influence a chrysomelid's choice for a plant. Finally, also the impact of phytopathogens on host location in Chrysomelidae is addressed. The pheno- and genotypic plasticity of chrysomelid host location behaviour might have facilitated pioneering new host plants. For a better understanding of adaptive evolution, we conclude that future studies on host plant location by chrysomelids need to address in addition to ecological and behaviourals aspects more intensively also the molecular questions of adaptation.

1 The two most abundant cockchafer species in Europe, the forest cockchafer Melolontha hippocastani Fabr. and the European cockchafer Melolontha melolontha L., tend to form calamitous mass breedings with casual reports on sympatric and simultaneous occurrence. 2 Both species are known to use feeding-induced green leaf volatiles (GLV) as primary attractants (sexual kairomones) for mate finding. The attractiveness of GLV is enhanced by the sex pheromones 1,4-benzoquinone in M. hippocastani and toluquinone in M. melolontha. Phenol attracts males from both species. All three compounds are present in females of both species. 3 In the present study, it is confirmed that only male M. melolontha perform the typical swarming flight at dusk, as has already been shown for M. hippocastani. Furthermore, whether swarming Melolontha males were cross-attracted to heterospecific females, and whether males could discriminate olfactorily between conspecific and heterospecific females, was tested in the field. 4 Males of both species preferred females when given the choice between females and males of the other species. However, they preferred conspecific females when females from both species were offered simultaneously. 5 The results suggest that species-specific pheromone blends contribute to precopulatory reproductive isolation in sympatric populations of M. melolontha and M. hippocastani, but are not mutually exclusive or indispensable prerequisites for mate finding as in other insects.

Plants are able to "notice" insect egg deposition and to respond by activating direct and indirect defenses. An overview of these defenses and the underlying mechanisms is given from a tritrophic perspective. First, the interface between plant and eggs is addressed with respect to the mode of attachment of eggs on the plant surface. It is elucidated which plant cells might respond to components from insect eggs or the egg deposition. The scarce knowledge on the elicitors associated with the eggs or the egg-laying female is outlined. Since endosymbiotic microorganisms are often present on the eggs, and microorganisms are also abundant on the leaf surface, the role of these hidden players for eliciting oviposition-induced plant responses is considered. Furthermore, the question of which physiological and molecular processes are induced within the plant in response to egg deposition is addressed. Second, studies on the response of the herbivorous insect to oviposition-induced plant defenses are outlined. Third, the importance of oviposition-induced plant volatiles and contact cues for host and prey location of parasitoids and predators is discussed in the context of other informative chemicals used by carnivores when searching for food. Finally, physiological and ecological costs of oviposition-induced plant responses are addressed.

1. The Salicaceae have been suggested as ancestral host plants ofChrysomela species (Coleoptera: Chrysomelidae). In Chrysomela lapponica, somepopulations are specialised on salicaceous plants, but others have switched tobirch.Thisstudy aimedtoelucidatethesignificanceofnaturalenemiesaspossibleselective forces for the host plant shift of C.lapponica from willow to birch.2. Two C.lapponica populations were studied, one specialised on willow Salixborealis in Finland, and another one specialised on birch Betula pubescens in theCzech Republic. Abundances ofpredators and parasitoids on birches and willowswere recorded at both population sites. Furthermore, field and laboratory experi-ments were conducted.3.Field datadonotsupportthehypothesisthat generalistpredatorsaffected thehost shift from willow to birch inC.lapponica.4. Parasitism of C.lapponica (pre)pupae by a specialised phorid fly was signifi-cantly stronger in specimens living on willow than in birch-living ones.5. The predatory syrphid Parasyrphus nigritarsis specialised on Chrysomelinaewas only detected on willows. The syrphid preferred to orient towards substratestreatedwithdefensivelarvalsecretionorfaecesofthewillow-specialised C.lapponicaspecimens compared with the birch-specialised ones.6. The data suggest that specialised parasitoids and predators might have beendriving forces for C.lapponica to leave willows and to pioneer birches as sites witha lowered risk ofpredation and parasitism. This hypothesis is discussed withrespecttoresultsofearlierstudiesontheimpactofbottom-upeffectsbytheplant.Keywords. Chrysomela lapponica, Chrysomelidae, host shift, parasitoid, preda-tor, selection, specialisation.

This study investigated the physiologically adaptive significance of elytral coloring and other thermal adaptations to different climes of Central and Northern Europe in a leaf beetle. Adults of Chrysomela lapponica L. differ in the coloring pattern of their red and black elytra when comparing populations from Finnish Lapland (Northern Europe) and from the Czech Republic (Central Europe). While the elytra of adults of the Czech population were bright red in color with a proportion of 51% of black marks, the relative size of the black marks of the Finnish beetle’s elytra was significantly higher (68%). When exposed to light, the dark morphs from Finland increased their body temperature within a shorter time and reached higher mean body temperatures than the lighter morphs from the Czech Republic. The walking speeds of the two different morphs did not differ at temperatures of 20, 15, and 10°C. However, at 5°C, the walking speed of the melanic beetles from Finland was significantly higher. The specific metabolic rate during overwintering of the adults was significantly higher in the Finnish morph at a temperature of 5°C compared with the Czech morph. The average and maximum temperatures during overwintering in the leaf litter layer in the Czech Republic were more variable and on average higher than under the snow cover in Finland. These results on the thermoregulation in C. lapponica are discussed with special respect to melanic elytral coloring as adaptation toward lower ambient temperatures.

376.The leaf beetle species Chrysomela lapponica, which belongs to the so-called C.interrupta group, forms distinct allopatric populations either on willows (Salicaceae) orbirches (Betulaceae). It was recently suggested that, on several occasions, host plantshifts from Salicaceae to Betulaceae occurred independently within the C. interruptagroup. Our study aims to elucidate bottom-up effects of the host plants that might haveshaped the evolution of host plant specialization in the populations of C. lapponica,and thus, to shed some light on the driving forces of host shifts within the C. interruptagroup, too. We compared the oviposition behaviour and performance of two C.lapponica populations, one of which has adapted to birches and the other to willows.The studies were conducted under laboratory conditions, eliminating the impact ofnatural enemies. Experiments involving the transfer of individuals of the birch-specialized population to willows and vice versa with individuals of the willow-specialized population to birches aimed to examine the plasticity in host plant use.Females of each population almost exclusively chose their natural host plant foroviposition, when offering birch and willow in dual choice experiments. Whenspecimens of the two C. lapponica populations were reared on their natural hostplants, the birch specialists suffered higher mortality, needed a longer period ofdevelopment and produced less larval defensive secretion than the willow specialists.When the birch specialists were fed with willow, these performance parametersdecreased even more. Other parameters, such as body weight and fecundity, did notdiffer between birch and willow specialists when they were fed with their natural hostplant. While individuals of the birch-specialized population could be reared on willow,all neonate larvae from the willow-specialized population died after being transferredto birch. The significance of these bottom-up effects for the evolution of host plantspecialization in C. lapponica is discussed.J. Gross, N. E. Fatouros and M. Hilker, Institut fu¨r Biologie, Freie Universita¨t Berlin,Haderslebener Str. 9, DE-12163 Berlin, Germany (hilker@zedat.fu-berlin.de).

Phenotypic plasticity enables invididuals to change their phenotype in response to their environment. These phenotypic changes can affect many interactions between the members of a community. Plants are able to respond towards herbivore attack by defensive mechanisms directly affecting the herbivore and by so-called indirect defences that negatively affect the herbivore by maintenance or attraction of carnivores. The phenotypic changes of plants caused by induced defences may vary with the type of attackers. Different attackers can evoke different plant responses due to specific elicitors or wounding. These different plant responses may be mediated by different choreographies of gene expression. Symbiotic and pathogenic microorganisms associated with the plant or the herbivore may play an important role in the induction process. Thus, a plethora of biotic factors affect the physiological, chemical, and molecular characteristics of plants in response to attack. The adaptiveness of phenotypic plasticity in terms of induced responses depends on the balance of their physiological and ecological costs and benefits. An integrated approach is necessary considering ecological, molecular and chemical aspects to gain deeper insight into induced defence and its application in environmentally benign crop protection. Phanotypische Plastizitat befahigt Individuen, ihren Phanotyp in Reaktion auf Umweltreize zu andern. Die phanotypischen Veranderungen konnen zahlreiche Interaktionen zwischen den Mitgliedern einer Biozonose beeinflussen. Angriffe von Herbivoren konnen in Pflanzen direkte und indirekte Verteidigungsmechanismen induzieren. Wahrend die direkte Verteidigung sich unmittelbar gegen die Herbivoren richtet, wirkt die indirekte Abwehr uber die Beherbergung oder Anlockung von Carnivoren auf die Herbivoren ein. Die induzierten phanotypischen Veranderungen der Pflanze sind je nach Typ des Angreifers sehr unterschiedlich. Unterschiedliche Herbivore konnen aufgrund verschiedener Frasverhalten und aufgrund spezifischer Elicitoren jeweils ganz unterschiedliche pflanzliche Reaktionen hervorrufen. Die Vielfalt der pflanzlichen Antworten auf Herbivorenfras wird bestimmt durch unterschiedliche Muster in der Expression der an der Abwehr beteiligten Gene. Symbiontische und pathogene Mikroorganismen, die mit der Pflanze oder den Herbivoren assoziiert sind, konnen eine wichtige Rolle im Induktionsprozess spielen. Demnach beeinflusst eine Fulle biotischer Faktoren die physiologischen, chemischen und molekularen Charakteristika der frasinduzierten pflanzlichen Verteidigung. Der adaptive Wert der phanotypischen Plastizitat, die sich in der Vielfalt der induzierten Verteidigungsmechanismen spiegelt, hangt vom Gleichgewicht der physiologischen und okologischen Kosten und Nutzen der Abwehrreaktionen ab. Zum tieferen Verstandnis der induzierten pflanzlichen Abwehr gegen Herbivore sowie zur Nutzung der induzierten Abwehrreaktion im umweltvertraglichen Pflanzenschutz ist eine integrierte Herangehensweise notwendig, die sowohl okologische wie auch molekulare und chemische Aspekte berucksichtigt.

Plants are under continuous threat of being challenged by herbivorous insects and pathogenic micro-organisms. How plants respond to multiple antagonists that may co-occur has been investigated by researchers on the ecological, pharmacological, and genetic level. In this review we focus on recent studies of ecological cross-effects between phyllophagous herbivores and phytopathogenic fungi. Interactions between the two types of plant antagonists may be direct, plant-mediated or both. We present studies which describe a) potentially plant-mediated cross-effects but where direct effects cannot be excluded (‘direct/plant-mediated effects’), b) plant-mediated cross-effects that are confined to the attacked plant part (‘locally plant-mediated effects’) and c) plant-mediated cross-effects on a systemic scale (‘systemic effects’). Also, studies are addressed which attempted to directly link plant physiological changes induced by the herbivore and fungal attack with effects on the antagonists. Special attention will be given to spatial and temporal aspects of plant fungal infection and herbivore infestation. Pflanzen werden oft gleichzeitig von herbivoren Insekten und phytopathogenen Mikroorgansimen bedroht. Die Reaktion der Pflanze auf verschiedene, gleichzeitig auftretende Antagonisten wurde schon vielfach unter okologischen, chemischen und molekularen Aspekten untersucht. Diese Ubersicht konzentriert sich auf okologische Wechselwirkungen zwischen phyllophagen Herbivoren und phytopathogenen Pilzen. Wechselwirkungen zwischen diesen beiden Antagonistentypen konnen ganz direkt sein, oder durch die Pflanze vermittelt werden, oder beides. Es werden Studien berucksichtigt, die folgende Formen der Wechselwirkungen analysieren: (a) potentiell pflanzenvermittelte Effekte, wobei aber direkte Interaktionen nicht ausgeschlossen werden konnen (“direkte/pflanzenvermittelte Wechselwirkung”), (b) pflanzenvermittelte Effekte, die auf den unmittelbar angegriffenen Pflanzenteil beschrankt sind (“lokale pflanzenvermittelte Wechselwirkung”), (c) pflanzenvermittelte systemische Wechselwirkungen (“systemische Effekte”). Weiterhin werden solche Studien in den Uberblick einbezogen, die einen Zusammenhang suchen zwischen induzierten physiologischen Veranderungen der Pflanze nach Angriff durch Herbivore oder Pilze und den Auswirkungen dieser Veranderungen auf die Antagonisten. Besondere Aufmerksamkeit wird den raumlichen und zeitlichen Aspekten der Induktion von Abwehrmasnahmen durch Herbivorenfras und Pilzbefall an einer Pflanze gewidmet.

Mate finding in the European cockchafer, Melolontha melolontha, has been investigated in the field. Our data suggest that mainly males show flight activity at dusk. In a landing cage bioassay, male cockchafers preferred cages baited with females over cages baited with males. Gas chromatographic analysis of beetle extracts with electronantennographic detection revealed the presence of electrophysiologically active compounds, among them toluquinone. In funnel trap bioassays none of these compounds was attractive towards males per se. A mixture of green leaf volatiles (GLV) mimicking the bouquet of mechanically damaged leaves was highly attractive to M. melolontha males. The attractiveness of the same GLV mixture was synergistically enhanced when toluquinone was added to the lure. GLV attract males to damaged leaves. Toluquinone as a sex pheromone indicates the presence of conspecific females and synergistically enhances the attractiveness of GLV.

Summary 1. Swarming males of Melolontha hippocastani are known to locate females that stay feeding within the host trees by orienting towards damage-induced plant volatiles (green leaf volatiles) and a sex pheromone. Thus, volatiles emitted by freshly damaged leaves might indicate to a male the presence of currently feeding females. 2. The hypothesis was studied that volatiles from freshly damaged leaves are more attractive to males than volatiles from old damaged leaves. The odour bouquets of damaged leaves from three plant species that have been shown to attract male M. hippocastani in the field were analysed 10 min (fresh damage) and 1.5 h (old damage) after damaging, using coupled gas chromatography–mass spectrometry. The results showed clear differences between the bouquets: the bouquet of freshly damaged leaves of all species consisted of typical leaf aldehydes, i.e. hexanal, (Z)-3-hexenal, (Z)-2-hexenal, (E)-2-hexenal, the leaf alcohol (Z)-3-hexen-1-ol, and the corresponding acetate. One and a half hours after damage, aldehydes had almost vanished and (Z)-3-hexen-1-ol and (Z)-3-hexenyl acetate predominated; however males of M. hippocastani were equally attracted to traps baited with volatiles from old and freshly damaged leaves in field experiments. When traps were baited with synthetic volatile mixtures mimicking the bouquets of old and freshly damaged leaves, M. hippocastani males even preferred the old damage mixture. 3. Experiments addressing the role of individual green leaf volatiles revealed that only (Z)-3-hexen-1-ol was highly attractive while the other compounds tested individually were behaviourally inactive, however all tested compounds elicited comparable electrophysiological responses on male M. hippocastani antennae. 4. In analogy to the term aggregation kairomone used for feeding-induced plant volatiles that attract both sexes of an insect, the term sexual kairomone is suggested to describe the novel function of (Z)-3-hexen-1-ol in the sexual communication of M. hippocastani.

Experience and memory of environmental stimuli that indicate future stress can prepare (prime) organismic stress responses even in species lacking a nervous system. The process through which such organisms prepare their phenotype for an improved response to future stress has been termed 'priming'. However, other terms are also used for this phenomenon, especially when considering priming in different types of organisms and when referring to different stressors. Here we propose a conceptual framework for priming of stress responses in bacteria, fungi and plants which allows comparison of priming with other terms, e.g. adaptation, acclimation, induction, acquired resistance and cross protection. We address spatial and temporal aspects of priming and highlight current knowledge about the mechanisms necessary for information storage which range from epigenetic marks to the accumulation of (dormant) signalling molecules. Furthermore, we outline possible patterns of primed stress responses. Finally, we link the ability of organisms to become primed for stress responses (their 'primability') with evolutionary ecology aspects and discuss which properties of an organism and its environment may favour the evolution of priming of stress responses.

Plant diversity is known to affect success of host location by pest insects, but its effect on olfactory orientation of non-pest insect species has hardly been addressed. First, we tested in laboratory experiments the hypothesis that non-host plants, which increase odour complexity in habitats, affect the host location ability of herbivores and parasitoids. Furthermore, we recorded field data of plant diversity in addition to herbivore and parasitoid abundance at 77 grassland sites in three different regions in Germany in order to elucidate whether our laboratory results reflect the field situation. As a model system we used the herb Plantago lanceolata, the herbivorous weevil Mecinus pascuorum, and its larval parasitoid Mesopolobus incultus. The laboratory bioassays revealed that both the herbivorous weevil and its larval parasitoid can locate their host plant and host via olfactory cues even in the presence of non-host odour. In a newly established two-circle olfactometer, the weeviĺs capability to detect host plant odour was not affected by odours from non-host plants. However, addition of non-host plant odours to host plant odour enhanced the weeviĺs foraging activity. The parasitoid was attracted by a combination of host plant and host volatiles in both the absence and presence of non-host plant volatiles in a Y-tube olfactometer. In dual choice tests the parasitoid preferred the blend of host plant and host volatiles over its combination with non-host plant volatiles. In the field, no indication was found that high plant diversity disturbs host (plant) location by the weevil and its parasitoid. In contrast, plant diversity was positively correlated with weevil abundance, whereas parasitoid abundance was independent of plant diversity. Therefore, we conclude that weevils and parasitoids showed the sensory capacity to successfully cope with complex vegetation odours when searching for hosts.

Mate finding in the forest cockchafer, Melolontha hippocastani, occurs during a spectacular swarming period at dusk. The swarming flights are mainly performed by males whereas most of the females stay within the host trees and continue feeding. Males orientate towards damage-induced green leaf volatiles (GLV) allowing location of mechanically damaged foliage. In order to distinguish between unspecific leaf damage and damage caused by feeding females, male cockchafers orientate by a sex attractant. Here we show this compound to be 1,4-benzoquinone, which has been known for more than 40 years as a highly effective defence compound used by numerous arthropod species to repel enemies. 1,4-benzoquinone synergistically increased the number of males caught in GLV-baited funnel traps during the swarming period. Significantly more males landed on wire cages baited with a combination of 1,4-benzoquinone and GLV than on cages baited with only GLV. The results suggest that the sex pheromone of M. hippocastani might have evolved from a primary role as a defence compound.

The food web of Symmorphus cristatus wasps, leaf beetle larvae (Coleoptera: Chrysomelidae) and willow (Salix spp.) trees is a model system for studying the chemical ecology of plant, herbivore and predator interactions. However, little is known about the natural history and prey use of the predatory wasps. We conducted detailed observations of nesting behavior and quantified time allocation to nest building activities in Big Pine Creek in the eastern Sierra of California. Symmorphus cristatus exhibits aggressive territorial behavior over nesting and mating sites, but does not respond aggressively to kleptoparasitism by cuckoo wasps Chrysis nitidula. We also compared prey use, nest provisioning and nest architecture of wasps at Big Pine Creek and at Sebastopol, near the central California coast. Using trap-nests we identified two new prey species for S. cristatus at Sebastopol: Plagiodera californica and Chrysomela schaefferi (Coleoptera: Chrysomelidae). There were significant differences in nest ...

A bioassay was developed to examine the response of ticks towards potential repellents that may protect vertebrates against tick bites. Such tick repellents must be effective despite the unavoidable presence of various attractive host-derived stimuli. Therefore, a moving-object-bioassay (MO-bioassay) was developed that mimicks body warmth and movement of vertebrates by a rotating and heated drum. Compounds which were tested for their effects on ticks were applied onto a small elevated area of the drum. Ticks were allowed to approach the drum by walking on a glass rod which ended 1 mm away from the local elevation. Ticks could cling to this elevation that intermittently passed by, whereas the remaining drum surface was too far away from the tip of the rod to be contacted by the ticks. Without the presence of any repellents, 85.5% of 600 hungry, field-collected Ixodes ricinus nymphs moved to the heated, rotating drum within 2 min. Further experiments with unfed I. ricinus nymphs were performed to test whether one established and two potential tick repellents elicit an avoidance reaction in the ticks despite the proven attractiveness of the drum. Freshly applied DEET (N,N-diethyl-m-toluamide) at a concentration of 0.11 mg cm -2 proved active as a repellent in the MO-bioassay over a distance of a few mm as well as by direct contact. A similar repellent effect was observed with (-)-myrtenal at 1 mg cm -2 , but not at 0.1 mg cm -2 , indicating that this terpenaldehyde is a weaker repellent for l. ricinus nymphs than DEET. No repellent effect was observed with camphor (0.1 mg cm -2 ). The MO-bioassay thus is a rapid, simple and low-cost test method allowing the investigation of tick host-contact behaviour as well as the screening of candidate repellents which are either perceived as volatiles or via contact chemoreception.

Studies of multitrophic interactions show that insect faeces may act as a defensive device against predators, as kairomone source for attraction of antagonists and as a significant energy source for micro-organisms. In the present study, we investigated effects of larval faeces from leaf beetles of the subfamiliy Cassidinae towards a generalist predator, the ant Myrmica rubra. Most cassidine larvae collect their faeces together with exuviae as so-called abdominal defensive shields on two movable spines at the posterior tip. The effects of these abdominal shields towards M. rubra were studied in three cassidine species, which feed mono- or oligophagously upon tansy (Chrysanthemum vulgare): Cassida denticollis and C. sanguinosa which possess such faecal shields and, for comparison, C. stigmatica with shields made of exuviae only (=skin shield). Bioassays revealed that larvae with both faecal and skin shields were attacked by the ant M. rubra more often than larvae whose shields had been removed. This attractiveness of shields towards ants contrasts with other studies, which found that abdominal shields of chrysomelid larvae act as defensive mechanisms against generalist predators like ants. To characterize the attractive cues of the shields, we studied possible chemical and physical stimuli. Olfactometer bioassays with M. rubra and chemical analyses revealed that plant-derived volatiles from faecal shields of C. denticollis attracted the ant, whereas odour from skin shields of C. stigmatica did not. Skin shields also emitted volatiles which derived from tansy, but in much lower quantities. Exclusion of contact to surface chemicals of a faecal shield reduced the ants' aggressive behaviour, whereas a change in the moisture content of a faecal shield had no influence. Visual stimuli cannot be ruled out as enhancing the ants' reaction towards faecal shields with their attractive volatiles, and are suggested to play a major role in the ants' response towards skin shields. This novel attractive effect of the abdominal shields of cassidine larvae is discussed, especially with respect to host plant chemistry and possible functions of the shields that might outweigh the negative consequences of the attraction of the predator M. rubra.

Host-foraging behavior of the tachinid parasitoid, Drino inconspicua Meigen (Diptera: Tachinidae), was studied by laboratory bioassays to elucidate the role of physical and chemical factors for host finding and recognition. Larvae of the European spruce sawfly, Gilpinia hercyniae Hartig (Hymenoptera: Diprionidae), were used as hosts. While volatiles of spruce twigs with feeding sawfly larvae did not attract the parasitoid, movements of host larvae and of dummies of the host significantly elicited a positive response at short range. Females of D. inconspicua showed a direct walking behavior to a moving object at distances of 9-10 cm. The maximum distance at which the parasitoids were attracted by movement was 16 cm. At short range, parasitoid females preferred to contact a moving larval dummy made of filter paper rather than an unmoved dummy or an unmoved freshly killed larva of C hercyniae. The tachinid females which were reared from G. hercyniae larvae showed no preference for this host species when compared with larvae of Diprion pini L. (Hymenoptera: Diprionidae) and the unnatural host species Galleria mellonella L. (Lepidoptera: Pyralidae). Furthermore, D. inconspicua did not prefer certain instars of G. hercyniae for oviposition. The role of cuticular chemicals of C. hercyniae larvae for host acceptance was tested by offering host larvae washed with solvents of different polarities and unwashed larvae, Each tested parasitoid female readily accepted both treated and untreated larvae for oviposition. When a hexane extract of the cuticle of host larvae was applied to a dummy, ovipositing D. inconspicua did not significantly distinguish between a treated dummy and a control dummy. Whereas the parasitoid's response to dummies offered as oviposition sites did not depend on the presence of cuticular extracts of hosts, the softness of the dummies was crucial. The parasitoid females significantly preferred soft dummies (hardiness unit [HU]:0.05± 0.01 Nmm -2 ) to hard ones (HU: 207.72± 6.16 Nmm -2 ) for oviposition. Thus, physical factors like movement of the host and its softness clearly play a major role in host foraging of D. inconspicua rather than chemical signals of the host or its host plant.

Plant resistance to the feeding by herbivorous insects has recently been found to be positively or negatively influenced by prior egg deposition. Here we show how crucial it is to conduct experiments on plant responses to herbivory under conditions that simulate natural insect behaviour. We used a well- studied plant – herbivore system, Arabidopsis thaliana and the cabbage white butterfly Pieris brassicae, testing the effects of naturally laid eggs (rather than egg extracts) and allowing larvae to feed gregariously as they do naturally (rather than placing single larvae on plants). Under natural conditions, newly hatched larvae start feeding on their egg shells before they consume leaf tissue, but access to egg shells had no effect on subsequent larval performance in our experiments. However, young larvae feeding gregariously on leaves previously laden with eggs caused less feeding damage, gained less weight during the first 2 days, and suffered twice as high a mortality until pupation compared to larvae feeding on plants that had never had eggs. The concentration of the major anti-herbivore defences of A. thaliana, the glucosinolates, was not significantly increased by oviposition, but the amount of the most abundant member of this class, 4-methylsulfinylbutyl glucosinolate was 1.8-fold lower in larval-damaged leaves with prior egg deposition compared to damaged leaves that had never had eggs. There were also few significant changes in the transcript levels of glucosinolate metabolic genes, except that egg deposition suppressed the feeding-induced up-regulation of FMOGS-OX2, a gene encoding a flavin monooxygenase involved in the last step of 4-methylsulfinylbutyl glucosinolate biosynthesis. Hence, our study demonstrates that oviposition does increase A. thaliana resistance to feeding by subsequently hatching larvae, but this cannot be attributed simply to changes in glucosinolate content.

Behavioural responses of animals to volatiles in their environment are generally dependent on context. Most natural odours are mixtures of components that can each induce different behaviours when presented on their own. We have investigated how a complex of two olfactory stimuli is evaluated by Drosophila flies in a free-flying two-trap choice assay and how these stimuli are encoded in olfactory receptor neurons. We first observed that volatiles from apple cider vinegar attracted flies while carbon dioxide (CO2) was avoided, confirming their inherent positive and negative values. In contradiction with previous results obtained from walking flies in a four-field olfactometer, in the present assay the addition of CO2 to vinegar increased rather than decreased the attractiveness of vinegar. This effect was female-specific even though males and females responded similarly to CO2 and vinegar on their own. To test whether the female-specific behavioural response to the mixture correlated with a sexual dimorphism at the peripheral level we recorded from olfactory receptor neurons stimulated with vinegar, CO2 and their combination. Responses to vinegar were obtained from three neuron classes, two of them housed with the CO2-responsive neuron in ab1 sensilla. Sensitivity of these neurons to both CO2 and vinegar per se did not differ between males and females and responses from female neurons did not change when CO2 and vinegar were presented simultaneously. We also found that CO2-sensitive neurons are particularly well adapted to respond rapidly to small concentration changes irrespective of background CO2 levels. The ability to encode temporal properties of stimulations differs considerably between CO2- and vinegar- sensitive neurons. These properties may have important implications for in- flight navigation when rapid responses to fragmented odour plumes are crucial to locate odour sources. However, the flies’ sex-specific response to the CO2-vinegar combination and the context-dependent hedonics most likely originate from central rather than peripheral processing.

1. Previous laboratory bioassays indicate that exocrine glandular secretions of larvae of Gastrophysaviridula repel conspecific adults and deter them from feeding and oviposition. The present study was conducted to investigate the influence of larvae of G. viridula on conspecific adults in the field. 2. Within the G. viridula population studied, two generations were observed in a year. Occurrence of the different developmental stages overlapped temporally. 3. Some individual plants of Rumex obtusifolius, the host of the G. viridula population studied, grew so close to each other that they were considered as a plant group. When investigating the spatial distribution of larvae and adults within such plant groups, larvae were rarely found on plant groups on which adults were feeding. 4. A field experiment revealed that adults avoided plants of R. obtusifolius infested by conspecific larvae of the second and third instar. Adults still avoided these damaged plants when larvae had left them for pupation. 5. Gastrophysaviridula avoided oviposition on leaves and plants infested by conspecific larvae. Larvae of the second instar significantly deterred oviposition when present at a high density (33.3 larvae/dm2), whereas larvae of the first instar did not deter oviposition of conspecifics at either density tested. The oviposition deterring effect was also observed when just exocrine glandular secretion of larvae of the second instar was applied to the leaves in amounts equivalent to a density of 33.3 larvae/dm2. 6. Availability of food (R. obtusifolius) largely exceeded its exploitation in each group of plants examined. This may be due to either the spatial separation of adults and larvae or the low population density observed on these plant groups.

SUMMARY The ectoparasitic mite Varroa destructor and honey bee pathogenic viruses have been implicated in the recent demise of honey bee colonies. Several studies have shown that the combination of V. destructor and deformed wing virus (DWV) poses an especially serious threat to honey bee health. Mites transmitting virulent forms of DWV may cause fatal DWV infections in the developing bee, while pupae parasitised by mites not inducing or activating overt DWV infections may develop normally. Adult bees respond to brood diseases by removing affected brood. This hygienic behaviour is an essential part of the bees' immune response repertoire and is also shown towards mite-parasitised brood. However, it is still unclear whether the bees react towards the mite in the brood cell or rather towards the damage done to the brood. We hypothesised that the extent of mite-associated damage rather than the mere presence of parasitising mites triggers hygienic behaviour. Hygienic behaviour assays performed with mites differing in their potential to transmit overt DWV infections revealed that brood parasitised by ‘virulent’ mites (i.e. mites with a high potential to induce fatal DWV infections in parasitised pupae) were removed significantly more often than brood parasitised by ‘less virulent’ mites (i.e. mites with a very low potential to induce overt DWV infections) or non-parasitised brood. Chemical analyses of brood odour profiles suggested that the bees recognise severely affected brood by olfactory cues. Our results suggest that bees show selective, damage-dependent hygienic behaviour, which may be an economic way for colonies to cope with mite infestation.

Allelopathy, a phenomenon where compounds produced by one plant limit the growth of surrounding plants, is a controversially discussed factor in plant- plant interactions with great significance for plant community structure. Common mycorrhizal networks (CMNs) form belowground networks that interconnect multiple plant species; yet these networks are typically ignored in studies of allelopathy. We tested the hypothesis that CMNs facilitate transport of allelochemicals from supplier to target plants, thereby affecting allelopathic interactions. We analyzed accumulation of a model allelopathic substance, the herbicide imazamox, and two allelopathic thiophenes released from Tagetes tenuifolia roots, by diffusion through soil and CMNs. We also conducted bioassays to determine how the accumulated substances affected plant growth. All compounds accumulated to greater levels in target soils with CMNs as opposed to soils without CMNs. This increased accumulation was associated with reduced growth of target plants in soils with CMNs. Our results show that CMNs support transfer of allelochemicals from supplier to target plants and thus lead to allelochemical accumulation at levels that could not be reached by diffusion through soil alone. We conclude that CMNs expand the bioactive zones of allelochemicals in natural environments, with significant implications for interspecies chemical interactions in plant communities.

A major aim of chemical ecology is to gain deeper insight into how organismic responses to the abiotic and biotic environment are regulated by naturally produced chemicals. Chemical ecologists pursue this aim by combining chemical, molecular, and ecological expertise. While many ecological studies focus on the impact of the plethora of species on community or ecosystem functions, numerous chemoecological studies aim to elucidate the ecological relevance of a comparable bounty of natural products, their biosynthesis, transfer and metabolism as well as the organismic responses to them (Hartmann 2007). Awareness of the parallels between studies of biodiversity and chemodiversity may promote finding answers to our proximate (how) and ultimate (why) questions on the chemical mediation of organismic responses to environmental stimuli. When comparing biodiversity studies and chemoecological studies with respect to: (i) the functions of species and of natural products; (ii) the dynamics by which a community of species is established and by which a blend of chemicals is biosynthesized; and (iii) the quantification of biodiversity and chemodiversity, some informative parallels may be drawn

Precise and deep comprehension of plant responses to herbivorous arthropods requires detailed knowledge of how a plant "notices" the attack. Herbivore attack is not restricted to plant wounding by feeding, but instead different phases of attack that elicit a plant response need to be distinguished: touch, oviposition and feeding. Touch, secretions released with eggs and regurgitate delivered during feeding may act in concert as elicitors of plant defence. Here, we discuss the current knowledge of what a plant "notices" during the different phases of herbivore attack and how it responds at the molecular, physiological and ecological level. Understanding the mechanisms of plant responses to the different phases of herbivore attack will be a key challenge in unravelling the complex communication pathways between plants and herbivores.

Female parasitic wasps seek hosts for their offspring often in a dynamic environment. Foraging egg parasitoids rely on a variety of chemical cues originating from the adult host, host products, or the host plant rather than from the attacked host stage--the insect egg itself. Besides pupae, insect eggs are the most inconspicuous host stage attacked by parasitic wasps. To overcome the problem of low detectability of host eggs, egg parasitoids have evolved several strategies such as exploiting long-range kairomones of the adult hosts, for example, host aggregation and sex pheromones, plant synomones induced by egg deposition or host feeding, or short-range contact cues derived from the adult host or the host plant. Moreover, egg parasitoids have evolved the ability to use chemical espionage in combination with hitchhiking on the adult host (phoresy) to compensate their limited flight capability and to gain access to freshly laid host eggs. Here, we provide a comprehensive overview on the variety of host-foraging strategies of egg parasitoids exploiting chemical signals. Furthermore, the use of such infochemicals is discussed with respect to the wasps' dietary breadth and their ability to learn. Copyright 2008, Oxford University Press.

The Palaearctic leaf beetle Chrysomela lapponica usually feeds upon willows in the northern region of its occurrence. However, in Central Europe, some populations are known that have specialised on birch. In this study, we investigated the significance of other herbivores occurring together on the same host plants as possible exploitative competitors of C. lapponica. Two populations were studied: a population from Finland specialised on the willow Salix borealis, and a population from the Czech Republic, specialised on the birch Betula pubescens. Abundances of folivorous and suctivorous insects on both host plants were recorded at both population sites. The willow leaf beetle Phratora vitellinae was the most abundant herbivorous insect at both study sites on willow. A field study was conducted to examine the effects of P. vitellinae on the performance of C. lapponica. The presence of P. vitellinae larvae on the same twig upon which C. lapponica larvae were feeding did not affect increase of body weight in C. lapponica larvae. Thus, the high resource availability of both willows and birches suggest that interspecific competition is unlikely to be a selection factor driving the evolution of host shift in C. lapponica.

The chemical defence of pine against herbivorous insects has been intensively studied with respect to its effects on the performance and behaviour of the herbivores as well as on the natural enemies of pine herbivores. The huge variety of terpenoid pine components play a major role in mediating numerous specific food web interactions. The constitutive terpenoid pattern can be adjusted to herbivore attack by changes induced by insect feeding or oviposition activity. Recent studies on folivorous pine sawflies have highlighted the role of induced pine responses in herbivore attack and have demonstrated the importance of analysing the variability of pine defence and its finely tuned specificity with respect to the herbivore attacker in a multitrophic context.

The larval secretions of the Chrysomelinae (Coleoptera, Chrysomelidae) are generally considered to be chemical defense substances against predators and parasites. The experiments presented in this paper provide evidence that the range of activity of these larval secretions also extends to interactions between different conspecific developmental stages and between competing phytophagous species. Four chrysomeline species were tested: Gastrophysa viridula De Geer, Phaedon cochleariae (F.), Plagiodera versicolora (Laich.), and Phratora vitellinae (L.). In the latter species, we did not test the intraspecific effect of the natural larval secretion, but the activity of its purchasable main component, salicylaldehyde (synthetic larval secretion). In G. viridula, Ph. cochleariae, and Ph. vitellinae the (synthetic) larval secretions act as oviposition deterrents against conspecific females. An investigation of the persistence of the ovipositiondeterring activity of the larval secretion in G. viridula revealed that the deterrent effect is lost after 20 to 26 hours. In each of the four tested species the (synthetic) larval secretion deters feeding of conspecific adults. Since P. versicolora and Ph. vitellinae may occur on the same host plant (e.g. the willow Salix fragilis L.), the interspecific effect of the larval secretion between competing phytophagous species was examined in these two willow leaf beetles. The larval secretions of both species and salicylaldehyde, respectively, act as interspecific repellent and feeding deterrent against adults of the other species. Zusammenfassung Intra- und interspezifische Effekte der Larvensekrete einiger Chrysomeliden (Coleoptera) Die Sekrete der Larven der Chrysomelinae (Fam. Chrysomelidae) werden im allgemeinen als chemische Abwehrstoffe gegen Pradatoren und Parasiten betrachtet. Die hier dargestellten Untersuchungen zeigen, das die Wirkung der Larvensekrete nicht nur auf die Feindabwehr begrenztist. Das Wirkungsspektrum umfast daruber hinaus auch Interaktionen zwischen verschiedenen Entwicklungsstadien einer Art bzw. zwischen konkurrierenden phytophagen Arten. Folgende Chrysomelinenarten wurden untersucht: Gastrophysa viridula De Geer, Phaedon cochleariae (F.), Phratora vitellinae (L.) und Plagiodera versicolora (Laich.). Da das Larvensekret von Ph. vitellinae Salicylaldehyd als Hauptkomponente enthalt, wurde hier – wenn nicht anders erwahnt – die Wirkung von synthetischem Salicylaldehyd getestet. Bei G. viridula, Ph. cochleariae und Ph. vitellinae wirkt das Larvensekret bzw. die authentische synthetische Substanz als hochwirksames Eiablage-Deterrens auf konspezifische Weibchen. Die eiablagehemmende Wirkung des Larvensekretes von P. versicolora wurde nicht getestet. Eine Untersuchung der Wirkungsdauer der eiblagehemmenden Aktivitat des Larvensekretes von G. viridula ergab, das die Hemmwirkung nach 20 bis 26 Stunden nicht mehr nachweisbar ist. Bei alien oben genannten vier Arten hemmt das Larvensekret bzw. dessen authentische synthetische Substanz den Fras von Adulten derselben Art. Diese frashemmende Aktivitat ist bei G. viridula, Ph. cochleariae und Ph. vitellinae mindestens 18 Stunden wirksam. Das Larvensekret von P. verskolora zeigte bei 18-stundiger Versuchsdauer keine frashemmende Wirkung auf Adulte derselben Art; erst bei Reduktion der Versuchsdauer auf drei Stunden konnte hier eine signifikant frashemmende Wirkung nachgewiesen werden. P. verskolora und Ph. vitellinae konnen als Weidenblattkafer an derselben Wirtspflanze auftreten, Deshalb wurde auch die interspezifische Wirkung der Larvensekrete dieser beiden Chrysomelinenarten gepruft. Das Larvensekret von Ph. vitellinae sowie auch dessen authentische synthetische Substanz (Salicylaldehyd) wirkt auf adulte P. verskolora als Repellent und Frashemmstoff. Ebenso wirkt urngekehrt das Larvensekret von P. verskolora abschreckend und frashemmend auf adulte Ph. vitellinae.

The ancestral host plants of Chrysomela lapponica are Salicaceae rich in salicylic glycosides (SGs), which serve as precursors for larval chemical defensive secretions. Nevertheless, some populations have shifted to plants poor in SGs or even lacking these compounds. To study whether this shift is accompanied by adaptations to novel SG-poor host plants, we reared C. lapponica larvae from five geographical populations on host plants with high (Salix myrsinifolia) or low (S. caprea) SG content. Individuals from two populations (Finland and Kola region in Russia) associated in nature with SG-rich S. myrsinifolia showed higher survival and shorter developmental time on native host species than on foreign SG-poor S. caprea, thus demonstrating local adaptations to their ancestral SG-rich host plant. Individuals from a Belarus population associated in nature with SG-poor S. caprea showed higher survival on this species than on foreign SG-rich S. myrsinifolia, thus demonstrating local adaptation to the novel SG-poor host. On the other hand, individuals from two other populations associated in nature with SG-poor plants (Baikal and Ural region) performed equally well on both SG-rich S. myrsinifolia and SG-poor S. caprea in our rearing experiments, thus showing no local adaptation to a specific SG-host type, but rather a wide feeding niche including several Salicaceae species of different SG-type. Our results suggest that diet breadth of C. lapponica is a local phenomenon, and that adaptation strategies to novel host plants may differ between populations of a single leaf beetle species.