Shared Host Plant Research Articles

Herbivore-induced volatiles reduce the susceptibility of neighboring tomato plants to transmission of a whitefly-borne begomovirus.

Plant viruses exist in a broader ecological community, with key components include non-vector herbivores that can impact vector abundance, behavior, and virus transmission within shared host plants. However, little is known about the effects of non-vector herbivores infestation on the virus transmission by vector insects on the neighboring plants through inter-plant airborne chemicals. In this study, we investigated how volatiles emitted from tomato plants infested with the two-spotted spider mite (Tetranychus urticae) affect the infection of Tomato yellow leaf curl virus (TYLCV) transmitted by the whitefly (Bemisia tabaci) in the neighboring plants. Exposure of neighboring tomato plants to volatiles released from T. urticae-infested tomato plants reduced subsequent herbivory as well as TYLCV transmission and infection, and JA signaling pathway was essential for generation of the inter-plant defense signals. We also demonstrated that (E)-β-Ocimene and MeSA were two volatiles induced by T. urticae that synergistically attenuated TYLCV transmission and infection in tomato. Thus, our findings suggest that plant-plant communication via volatiles likely represents a widespread defensive mechanism that substantially contributes to plant fitness. Understanding such phenomena may help us to predict the occurrence and epidemic of multiple herbivores and viruses in the agroecosystem, ultimately to manage pest and virus outbreaks.

Microbe‐induced plant resistance alters aphid inter‐genotypic competition leading to rapid evolution with consequences for plant growth and aphid abundance

Plants and insect herbivores are two of the most diverse multicellular groups in the world, and both are strongly influenced by interactions with the belowground soil microbiome. Effects of reciprocal rapid evolution on ecological interactions between herbivores and plants have been repeatedly demonstrated, but it is unknown if (and how) the soil microbiome could mediate these eco‐evolutionary processes on a shared host plant. We tested the role of a plant‐beneficial soil bacterium Acidovorax radicis in altering eco‐evolutionary interactions between different aphid genotypes (Sitobion avenae, genotypes Sickte and Fescue) feeding on barley Hordeum vulgare. We measured fecundity, longevity and population growth of two aphid genotypes reared separately or together (population mixture) on three different barley varieties that were inoculated with or without A. radicis. Results showed that across all plant varieties A. radicis increased plant growth and suppressed aphid populations via reduced longevity and fecundity. The strength of effect was dependent on aphid genotype and barley variety, while the direction of effect was altered by aphid population mixture. Using Lotka–Volterra modelling, we demonstrated that while A. radicis inoculation decreased growth rates for both aphid genotypes it increased the competitiveness of one genotype against the other. In general, in the presence of A. radicis, the Fescue aphid genotype became more inhibitory of Sickte aphids, while Sickte aphids facilitated the growth of Fescue aphids. Our work demonstrates that plant rhizosphere microbiomes exert community‐level influences by mediating eco‐evolutionary interactions between herbivores and host plants. By altering competitive interaction outcomes among aphids and thus impacting processes such as rapid evolution, soil microbes contribute to the short‐ and long‐term structure and functioning of terrestrial habitats.

Why fitness impacts of different herbivores may combine nonadditively, and why it matters to the ecology and evolution of plant-herbivore communities

Background and aims – The manner by which the effects of multiple antagonists combine is a fundamental issue in ecology. This issue has been especially important in plant-herbivore evolutionary ecology—particularly predicting whether the combined fitness impacts of multiple herbivores on a shared host plant can be inferred by simply adding the individual impacts that each herbivore has when feeding alone. Despite accumulating empirical data, relatively little theoretical progress has been made in explaining why impacts of herbivore damage often combine nonadditively, as well as predicting the conditions that lead to a greater-than-additive (synergistic) or to a less-than-additive (subadditive) pattern. Material and methods – Based on considerations of limiting resources and source-sink relationships, I proposed and tested two hypotheses: 1) The fitness impacts of two species of herbivores that affect the same resource (i.e. feed on the same tissue in a similar fashion) will combine in a synergistic pattern (if that resource is not limiting reproduction when plants do not experience herbivory), and 2) The fitness impacts of two herbivores that affect different resources (i.e. feed on different tissues) will combine in a subadditive pattern. I performed a field experiment in which horsenettle (Solanum carolinense) was exposed to a factorial combination of four levels of leaf herbivory and five levels of simulated floral herbivory. Key results – The results were consistent with both hypotheses: 1) The combined fitness impact of flower damage that was simulated as being caused by two florivorous species feeding on the same plants was greater than the sum of the same total amount of damage when the two species were simulated as feeding individually; and 2) The combined fitness impact of the leaf and floral damage was less than the sum of the same total amount of damage when the two species fed individually. Conclusions – The main ecoevolutionary implication of these results is that subadditive impacts of leaf- and flower-feeding herbivores could weaken selection for resistance in horsenettle (or any plant species that hosts multiple herbivores), and thus subadditive impacts may contribute to the maintenance of diverse herbivore communities sharing a species of host plant.

Undercover operation: Belowground insect herbivory modifies systemic plant defense and repels aboveground foraging insect herbivores

Plants attacked by insects may induce defenses locally in attacked plant tissues and/or systemically in non-attacked tissues, such as aboveground herbivory affecting belowground roots or belowground herbivory modifying aboveground tissues (i.e., cross-compartment systemic defense). Through induced systemic plant defenses, above-and belowground insect herbivores indirectly interact when feeding on a shared host plant. However, determining the systemic effects of herbivory on cross-compartment plant tissues and cascading consequences for herbivore communities remains underexplored. The goal of this study was to determine how belowground striped cucumber beetle (Acalymma vittatum) larval herbivory alters aboveground zucchini squash (Cucurbita pepo subsp. pepo) defenses and interactions with herbivores, including adult cucumber beetles and squash bugs (Anasa tristis). To explore this question, field and laboratory experiments were conducted to compare responses of aboveground herbivores to belowground larvae-damaged plants and non-damaged control plants. We also characterized changes in defensive chemicals and nutritional content of aboveground plant structures following belowground herbivory. We discovered belowground herbivory enhanced aboveground plant resistance and deterred aboveground foraging herbivores. We also found that larvae-damaged plants emitted higher amounts of a key volatile compound, (E)-β-ocimene, compared to non-damaged controls. Further investigation suggests that other mechanisms, such as plant nutrient content, may additionally contribute to aboveground herbivore foraging decisions. Collectively, our findings underscore connections between above-and belowground herbivore communities as mediated through induced systemic defenses of a shared host plant. Specifically, these findings indicate that belowground larval herbivory systemically enhances plant defenses and deters a suite of aboveground herbivores, suggesting larvae may manipulate aboveground plant defenses for their own benefit, while plants may benefit from enhanced systemic defenses against multi-herbivore attack.

Plant silicon defences reduce the performance of a chewing insect herbivore which benefits a contemporaneous sap‐feeding insect

Abstract Plant‐mediated interactions between phytophagous insects are ubiquitous. Silicon (Si) accumulation can defend plants against chewing insect herbivores, although sap‐feeders are comparatively less affected. It remains unknown how Si impacts interspecific interactions between chewing and sap‐feeding insect herbivores when sharing a host plant. We grew the model grass Brachypodium distachyon with (+Si) or without (−Si) Si and assessed the impacts of Si supplementation on the contemporaneous performance and interguild interactions between a chewing (Helicoverpa armigera) and a sap‐feeding (Rhopalosiphum padi) insect herbivore. We further performed dual‐choice tests to assess insect preferences for +Si or −Si plants with or without prior insect attack. Si reduced the relative growth rate (RGR) of both separately and contemporaneously fed caterpillars (H. armigera). Conversely, aphid abundance was higher on +Si plants compared to −Si plants. Caterpillar RGR and aphid abundance were negatively correlated on shared host plants. Furthermore, decreased caterpillar RGR on +Si plants benefitted aphid colonisation, indicating the plant‐mediated effects of Si on interspecific competition between the two insects. Attack by caterpillars induced leaf Si accumulation, regardless of aphid presence. In dual‐choice tests, caterpillars preferred aphid‐attacked −Si plants to aphid‐attacked +Si plants, whereas aphids preferred caterpillar‐attacked +Si plants to caterpillar‐attacked −Si plants. Our results provide the first evidence for plant‐mediated effects of Si on interspecific competition between two insect herbivores. We suggest that the dissimilar effects of Si against different feeding guilds of herbivores may promote asymmetry in interspecific competition when sharing host plants, potentially impacting insect abundance and distribution.

The Inhibitory Effect of Powdery Mildew-Induced Volatiles from Rose on Host Selection Behavior of Beet Armyworm Moths (Lepidoptera: Noctuidae)

Abstract Plant-mediated indirect interactions (PMIIs) between phytopathogenic fungi and herbivorous insects on shared host plants occur in nature. Knowledge of PMIIs is critical in plant molecular breeding and integrated pest management. We studied the response and chemical mechanism of beet armyworm, Spodoptera exigua (Hübner), adults to rose plants, Rosa chinensis Jacquin, infected with rose powdery mildew, Podosphaera pannosa (Wallr.: Fr.) de Bary. Using gas chromatography-electroantennographic detection (GC-EAD) coupled with electroantennogram (EAG), we found that beet armyworm antennae responded to 8, 11, and 3 volatile organic compounds (VOCs) from noninfected roses, mildew-infected roses, and mildew alone, respectively. The EAG analyses showed 11 chemicals (e.g., limonene [1], 2-ethyl-1-hexanol [2], linalool [3], nonanal [4], (E)-β-caryophyllene [5], 1-dodecanol [7], nhexadecane [9], 1-hexadecanol [11], methyl palmitate [12], 1-octadecanol [14], and n-butyl hexadecanoate [15]) elicited electrophysiological responses of beet armyworm antennae with significant dose-response relationships (P < 0.05). The EAG responses to the three chemicals (3, 11, and 15) were greater than that to the reference chemical [i.e., (E)-2-hexenal] at 0.5, 5.0, and 50.0 mg/ml. Olfactory and ovipositional behavior assays indicated that three chemicals (2, 3, and 5) significantly attracted beet armyworm females and four chemicals (7, 11, 14, and 15) strongly repelled females. Chemicals 2, 3, and 5 from healthy roses appear to be responsible for the attraction of beet armyworm moths to healthy roses, whereas chemicals 7, 11, 14, and 15 from mildew-infected roses play key roles in inhibiting attraction of moths. VOCs from mildew alone did not attract or repel beet armyworm moths.

Bacterial Endosymbionts of Bactericera maculipennis and Three Mitochondrial Haplotypes of B. cockerelli (Hemiptera: Psylloidea: Triozidae)

Insects harbor bacterial endosymbionts that provide their hosts with nutritional benefit or with protection against natural enemies, plant defenses, insecticides, or abiotic stresses. We used directed sequencing of 16S rDNA to identify and compare endosymbionts of Bactericera maculipennis (Crawford) and the western, central, and northwestern haplotypes of B. cockerelli (Šulc) (Hemiptera: Psylloidea: Triozidae). Both species are native to North America, are known to harbor the plant pathogen 'Candidatus Liberibacter solanacearum' and develop on shared host plants within the Convolvulaceae. The Old-World species Heterotrioza chenopodii (Reuter) (Psylloidea: Triozidae), now found in North America, was included as an outgroup. 16S sequencing confirmed that both Bactericera species harbor 'Candidatus Liberibacter solanacearum' and revealed that both species harbor unique strains of Wolbachia and Sodalis. However, the presence of Wolbachia and Sodalis varied among haplotypes of B. cockerelli. The central and western haplotypes harbored the same strains of Wolbachia, which was confirmed by Sanger sequencing of the wsp and ftsZ genes. Wolbachia was also detected in very low abundance from the northwestern haplotype by high-throughput sequencing of 16S but was not detected from this haplotype by PCR screening. The northwestern and central haplotypes also harbored Sodalis, which was not detected in the western haplotype. Heterotrioza chenopodii harbored an entirely different community of potential endosymbionts compared with the Bactericera spp. that included Rickettsia and an unidentified bacterium in the Enterobacteriaceae. Results of this study provide a foundation for further research on the interactions between psyllids and their bacterial endosymbionts.

Symptomatology, (Co)occurrence and Differential Diagnostic PCR Identification of 'Ca. Phytoplasma solani' and 'Ca. Phytoplasma convolvuli' in Field Bindweed.

Field bindweed (Convolvulus arvensis) is one of the major natural plant hosts and reservoirs of ‘Candidatus Phytoplasma solani’ (‘Ca. P. solani’), the causal agent of plant diseases in diverse agricultural crops, including Bois noir (BN) disease of grapevine. Phylogenetically, the most closely related phytoplasma to ‘Ca. P. solani’, the ‘Ca. P. convolvuli’, induces disease in field bindweed that is known by its symptoms as bindweed yellows (BY). The occurrence, coinfection and symptoms association of the two phytoplasmas in shared host plants were the subject of this study. Specific primers for the amplification of the elongation factor Tu gene (tuf) were developed for the identification of ‘Ca. P. convolvuli’ (by conventional nested PCR), as well as primers for simultaneous detection of ‘Ca. P. solani’ and ‘Ca. P. convolvuli’ by duplex SYBR Green real-time PCR. Among symptomatic bindweed plants, 25 and 41% were infected with a single phytoplasma species, ‘Ca. P. solani’ and ‘Ca. P. convolvuli’, respectively, while 34% were infected with both phytoplasmas. None of the non-symptomatic control plants carried phytoplasma, while non-symptomatic plants from our previous epidemiological studies in BN-affected vineyards were confirmed to be infected solely with ‘Ca. P. solani’. Stamp gene typing revealed Rqg50 and Rqg31 ‘Ca. P. solani’ genotypes in plants coinfected with ‘Ca. P. convolvuli’, while three diverse genotypes (Rqg50, GGY and Rpm35) were identified in a single locality with symptomatic bindweeds infected solely with ‘Ca. P. solani’. Variations in symptoms and their association with each of the phytoplasmas are described and documented. The symptom of bushy appearance could be single out as specific for ‘Ca. P. convolvuli’ infection, while occurrence of ‘Ca. P. solani’ could not be unequivocally associated with specific alterations in infected bindweeds. The results are discussed in the context of the epidemiological and ecological complexity of ‘Ca. P. solani’-induced diseases and the relationship between the two phytoplasma relatives in shared host plant.

Begomovirus-Associated Betasatellite Virulence Factor βC1 Attenuates Tobacco Defense to Whiteflies via Interacting With Plant SKP1.

Plant-mediated interactions between plant viruses and their vectors are important determinants of the population dynamics of both types of organisms in the field. The whitefly Bemisia tabaci can establish mutualism with begomoviruses via their shared host plants. This mutualism is achieved by the interaction between virulence factors and their host proteins. While the virulence factor βC1 encoded by tomato yellow leaf curl China betasatellite (TYLCCNB), a subviral agent associated to the begomovirus tomato yellow leaf curl China virus (TYLCCNV), may interact with plant protein MYC2, thereby establishing the indirect mutualism between TYLCCNV and whitefly, whether other mechanisms are involved remains unknown. Here, we found the in vitro and in vivo interactions between βC1 and tobacco protein S-phase kinase associated protein 1 (NtSKP1). Silencing the expression of NtSKP1 enhanced the survival rate and fecundity of whiteflies on tobacco plants. NtSKP1 could activate the transcription of genes in jasmonic acid (JA) pathways by impairing the stabilization of JAZ1 protein. Moreover, βC1-NtSKP1 interaction could interfere JAZ1 degradation and attenuate the plant JA defense responses. These results revealed a novel mechanism underlying the better performance of whiteflies on TYLCCNV/TYLCCNB-infected plants.

A systematic review of the direct and indirect effects of herbivory on plant reproduction mediated by pollination.

BackgroundPlant reproduction is influenced by the net outcome of plant–herbivore and plant–pollinator interactions. While both herbivore impacts and pollinator impacts on plant reproduction have been widely studied, few studies examine them in concert.MethodologyHere, we review the contemporary literature that examines the net outcomes of herbivory and pollination on plant reproduction and the impacts of herbivores on pollination through damage to shared host plants using systematic review tools. The direct or indirect effects of herbivores on floral tissue and reported mechanisms were compiled including the taxonomic breadth of herbivores, plants and pollinators.ResultsA total of 4,304 studies were examined producing 59 relevant studies for synthesis that reported both pollinator and herbivore measures. A total of 49% of studies examined the impact of direct damage to floral tissue through partial florivory while 36% of studies also examined the impact of vegetative damage on pollination through folivory, root herbivory, and stem damage. Only three studies examined the effects of both direct and indirect damage to pollination outcomes within the same study.ConclusionsIt is not unreasonable to assume that plants often sustain simultaneous forms of damage to different tissues and that the net effects can be assessed through differences in reproductive output. Further research that controls for other relative drivers of reproductive output but examines more than one pathway of damage simultaneously will inform our understanding of the mechanistic relevance of herbivore impacts on pollination and also highlight interactions between herbivores and pollinators through plants. It is clear that herbivory can impact plant fitness through pollination; however, the relative importance of direct and indirect damage to floral tissue on plant reproduction is still largely unknown.

A non‐vector herbivore indirectly increases the transmission of a vector‐borne virus by reducing plant chemical defences

Abstract Vectors and viruses exist in communities consisting of many interacting species. Although the cascading effects of predators or parasitoids on disease spread via direct effects on vectors have been investigated, little is known about the effects of other free‐living species in communities on the transmission of vector‐borne viruses via indirect (host‐plant mediated) effects on vectors. In the present study, we used a food web consisting of tomato plants Solanum lycopersicum, two tomato herbivores (the vector whitefly, Bemisia tabaci, and the non‐vector two‐spotted spider mite, Tetranychus urticae) and a whitefly‐vectored plant virus (Tomato yellow leaf curl virus, TYLCV) to study how T. urticae may affect TYLCV transmission by B. tabaci via host‐plant mediated effects on B. tabaci. We found that T. urticae infestation promoted B. tabaci feeding, thereby increasing TYLCV transmission to tomato plants. These increases were associated with T. urticae‐induced reductions in two flavonoids (rutin and quercetin trisaccharide) of tomato plants. Elevation of rutin and quercetin trisaccharide levels in T. urticae‐infested plants via exogenous stem applications reduced B. tabaci feeding and TYLCV transmission. Therefore, suppression of these flavonoids by T. urticae infestation was the most likely explanation for the observed changes in B. tabaci feeding behaviour and TYLCV transmission. Our results show that by reducing flavonoids in tomato plants, a non‐vector herbivore can indirectly increase the transmission of a vector‐borne plant virus. These findings indicate that species that are far removed from the direct vector–virus interactions can indirectly affect vector‐borne virus transmission by altering the chemical defences of the shared host plant. A free Plain Language Summary can be found within the Supporting Information of this article.

Facilitation between invasive herbivores: hemlock woolly adelgid increases gypsy moth preference for and performance on eastern hemlock

1. Interactions between invertebrate herbivores with different feeding modes are common on long‐lived woody plants. In cases where one herbivore facilitates the success of another, the consequences for their shared host plant may be severe. Eastern hemlock (Tsuga canadensis), a canopy‐dominant conifer native to the eastern U.S., is currently threatened with extirpation by the invasive stylet‐feeding hemlock woolly adelgid (Adelges tsugae). The effect of adelgid on invasive hemlock‐feeding folivores remains unknown.2. This study evaluated the impact of feeding by hemlock woolly adelgid on gypsy moth (Lymantria dispar) larval preference for, and performance on, eastern hemlock. To assess preference, 245 field‐grown hemlocks were surveyed for gypsy moth herbivory damage and laboratory paired‐choice bioassays were conducted. To assess performance, gypsy moth larvae were reared to pupation on adelgid‐infested or uninfested hemlock foliage, and pupal weight, proportional weight gain, and larval period were analysed.3. Adelgid‐infested hemlocks experienced more gypsy moth herbivory than did uninfested control trees, and laboratory tests confirmed that gypsy moth larvae preferentially feed on adelgid‐infested hemlock foliage. Gypsy moth larvae reared to pupation on adelgid‐infested foliage gained more weight than larvae reared on uninfested control foliage.4. These results suggest that the synergistic effect of adelgid and gypsy moth poses an additional threat to eastern hemlock that may increase extirpation risk and ecological impact throughout most of its range.

Heritable Epichlo\xeb symbiosis shapes fungal but not bacterial communities of plant leaves

Keystone microbial species have driven eco-evolutionary processes since the origin of life. However, due to our inability to detect the majority of microbiota, members of diverse microbial communities of fungi, bacteria and viruses have largely been ignored as keystone species in past literature. Here we tested whether heritable Epichloë species of pooidae grasses modulate microbiota of their shared host plant.

Responses to Host Plant Volatiles and Identification of Odorant Binding Protein and Chemosensory Protein Genes in Bradysia odoriphaga

The chive maggot Bradysia odoriphaga Yang et Zhang (Diptera: Sciaridae) is a devastating agricultural pest that feeds on liliaceous vegetables and edible mushrooms. The shared host plant volatiles and chemosensory genes of B. odoriphaga may together play crucial roles for insects to identify their host. However, the responses of B. odoriphaga to host volatiles remain unclear. Electroantennography (EAG) and behavioral bioassays were performed on 12 volatiles shared in Allium and Pleurotus. Hexanal evoked in both male and female adults extremely significant EAG responses. In behavioral assays, 3rd-instar larvae and female adults can be significantly repelled by methyl propyl disulfide, 1-octen-3-ol, or hexanal at the concentration of 100 mg/mL. Third-instar larvae and female adults were significantly attracted by limonene with a concentration of 10 and 100 mg/mL, respectively. In addition, 57 chemosensory genes, including 51 odorant binding proteins (OBPs) and 6 chemosensory proteins (CSPs), were identified...

Aphids can acquire the nitrogen delivered to plants by arbuscular mycorrhizal fungi

Abstract Above‐ and below‐ground organisms can interact by altering the quality of shared host plants. Arbuscular mycorrhizal fungi (AMF) influence plant nutrient uptake, including nitrogen (N) acquisition. Under low N and phosphorus conditions, AMF delivery of N from organic sources not immediately available to the plant can have large impacts on plant N status, a limiting nutrient in the aphid diet. This study investigated the effect of AMF colonisation upon aphid number and determined the consequences of AMF directly accessing an organic nutrient patch that the plant cannot. We hypothesised that AMF colonisation of plants will increase plant and aphid N status, plant performance and aphid number, but only when the AMF had direct access to the added organic patch. Barley plants hosting the grain aphid Sitobion avenae were colonised by the AMF, Funneliformis mosseae, or no AMF. A two‐compartment microcosm was used to separate the plant roots from a 15N‐labelled organic patch in a second compartment. AMF‐colonised plants, but without access to the second compartment, were used to examine the effect of AMF colonisation on aphid number. In a separate treatment, and to determine whether AMF access to a plant inaccessible N source modified the effect of AMF colonisation on aphid number, AMF hyphae were permitted access to the second compartment containing an organic patch. As a control for AMF accessing a larger substrate volume, AMF were allowed access to a second compartment without an organic patch. When the AMF accessed the organic patch, more N from the patch was delivered to the plant resulting in a higher grain N concentration although plant growth was depressed. More N from the patch was also delivered to the aphids, but the N status of the aphid remained unchanged. Regardless of the level of access to the organic patch, AMF colonisation did not affect aphid number. Our data show that by accessing N sources not readily available to plants, AMF can indirectly deliver N to above‐ground organisms, a finding which has major implications for N‐transfer between higher trophic levels. A plain language summary is available for this article.

Pine defenses against the pitch canker disease are modulated by a native insect newly associated with the invasive fungus

Tomicus piniperda (Coleptera, Curculionidae) is a native insect in Europe and now potential enabler of the invasive fungal pathogen of pines, Fusarium circinatum. The co-occurence of T. piniperda and F. circunatum could increase disease incidence via (1) insect wounding when they bore galleries into shoots of healthy trees, and (2) by acting as vectors that introduce fungal propagules directly. The extent of damage by F. circinatum is likely to be influenced by tree defenses, which can depend upon pine species, environmental conditions, and responses to other biotic and abiotic challenges. Indirect interactions among plant enemies can arise when the attack by one enemy alters the shared host plant in a way that affects a second enemy. We tested for indirect interactions between T. piniperda and F. circinatum mediated by plant defenses. Our study employed 100 potted, identically treated, seedlings of Pinus pinaster and P. radiata. Plants were randomly allocated to one of five different treatments: inoculation with T. piniperda alone, inoculation with F. circinatum alone, inoculation with T. piniperda and F. circinatum together, a mock treatment with sterilized water, and true controls. We assessed plant mortality, and measured plant height and diameter, crown size, resin flow after T. piniperda attack, the size of lesions from fungal infection, and phloem chemistry (terpenes and nitrogen). There were conspicuous differences between pine species in their defensive responses to inoculations: P. pinaster showed increases in numerous terpenes following attack by T. piniperda but was unresponsive to F. circinatum, while P. radiata increased terpene concentrations with exposure to either F. circinatum or T. piniperda. In P. radiata, fungal growth within the plant (as reflected by lesion size) was reduced by coincident insect attack. This suggests that plant defensive responses against the insect also functioned as deterrents to a fungal enemy. Thus the combination of T. piniperda and F. circinatum should not be as dangerous to pine stands as if the insect disabled defences against the fungus. Nonetheless, the insect can only increase fungal introductions by increasing wounds and moving propagules. There is a need for field studies of damage from F. circinatum in different pine species with low vs. high abundance of T. piniperda. Better understanding of pine defenses against F. circinatum, and genetic variation in defense responses, would contribute to the development of safe, effective, and sustainable tactics for managing damage from F. circinatum to pine forests in Spain and elsewhere.

Omnivore-herbivore interactions: thrips and whiteflies compete via the shared host plant

Phytophagy is a common feature among pure herbivorous insects and omnivores that utilise both plant and prey as food resources; nevertheless, experimental evidence for factors affecting their interactions is restricted to intraguild predation and predator-mediated competition. We herein focused on plant-mediated effects that could result from plant defence activation or quality alteration and compared the performance of an omnivore, the western flower thrips Frankliniella occidentalis, and a pure herbivore, the greenhouse whitefly Trialeurodes vaporariorum, on cucumber plants previously infested with either species. Furthermore, we recorded their behavioural responses when given a choice among infested and clean plants. Whiteflies laid less eggs on plants previously exposed to thrips but more on whitefly-infested plants. Thrips survival was negatively affected on whitefly-infested than on thrips-infested or clean plants. Notably, whiteflies developed significantly faster on plants infested with conspecifics. In accordance, whiteflies avoided thrips-infested plants and preferred whitefly-infested over clean plants. Thrips showed no preference for either infested or clean plants. Our study is a first report on the role of plant-mediated effects in shaping omnivore-herbivore interactions. Considering the factors driving such interactions we will likely better understand the ecology of the more complex relationships among plants and pest organisms.

Aboveground herbivory induced jasmonates disproportionately reduce plant reproductive potential by facilitating root nematode infestation.

Different plant feeders, including insects and parasitic nematodes, can influence each other by triggering systemic changes in their shared host plants. In most cases, however, the underlying mechanisms are unclear, and the consequences for plant fitness are not well understood. We studied the interaction between leaf feeding Manduca sexta caterpillars and root parasitic nematodes in Nicotiana attenuata. Simulated M.sexta attack increased the abundance of root parasitic nematodes in the field and facilitated Meloidogyne incognita reproduction in the glasshouse. Intact jasmonate biosynthesis was found to be required for both effects. Flower counts revealed that the jasmonate-dependent facilitation of nematode infestation following simulated leaf attack reduces the plant's reproductive potential to a greater degree than would be expected from the additive effects of the individual stresses. This work reveals that jasmonates mediate the interaction between a leaf herbivore and root parasitic nematodes and illustrates how plant-mediated interactions can alter plant's reproductive potential. The selection pressure resulting from the demonstrated fitness effects is likely to influence the evolution of plant defense traits in nature.

Geographical co-occurrence of butterfly species: the importance of niche filtering by host plant species.

The relevance of interspecific resource competition in the context of community assembly by herbivorous insects is a well-known topic in ecology. Most previous studies focused on local species assemblies that shared host plants. Few studies evaluated species pairs within a single taxon when investigating the effects of host plant sharing at the regional scale. Herein, we explore the effect of plant sharing on the geographical co-occurrence patterns of 232 butterflies distributed across the Japanese archipelago; we use two spatial scales (10×10 and 1×1km grids) to this end. We considered that we might encounter one of two predictable patterns in terms of the relationship between co-occurrence and host sharing among butterflies. On the one hand, host sharing might promote distributional exclusivity attributable to interspecific resource competition. On the other hand, sharing of host plants may promote co-occurrence attributable to filtering by resource niche. At both grid scales, we found significant negative correlations between host use similarity and distributional exclusivity. Our results support the hypothesis that the butterfly co-occurrence pattern across the Japanese archipelago is better explained by filtering via resource niche rather than interspecific resource competition.

The multidimensional behavioural hypervolumes of two interacting species predict their space use and survival

Individual animals differ consistently in their behaviour, thus impacting a wide variety of ecological outcomes. Recent advances in animal personality research have established the ecological importance of the multidimensional behavioural volume occupied by individuals and by multispecies communities. Here, we examine the degree to which the multidimensional behavioural volume of a group predicts the outcome of both intra- and interspecific interactions. In particular, we test the hypothesis that a population of conspecifics will experience low intraspecific competition when the population occupies a large volume in behavioural space. We further hypothesize that populations of interacting species will exhibit greater interspecific competition when one or both species occupy large volumes in behavioural space. We evaluate these hypotheses by studying groups of katydids (Scudderia nymphs) and froghoppers (Philaenus spumarius), which compete for food and space on their shared host plant, Solidago canadensis. We found that individuals in single-species groups of katydids positioned themselves closer to one another, suggesting reduced competition, when groups occupied a large behavioural volume. When both species were placed together, we found that the survival of froghoppers was greatest when both froghoppers and katydids occupied a small volume in behavioural space, particularly at high froghopper densities. These results suggest that groups that occupy large behavioural volumes can have low intraspecific competition but high interspecific competition. Thus, behavioural hypervolumes appear to have ecological consequences at both the level of the population and the community and may help to predict the intensity of competition both within and across species.