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Podisus maculiventris (spined soldier bug) is a generalist predator studied for its biocontrol potential. This species has a large dorsal abdominal gland (DAG) that releases pheromones that can also be important semiochemicals for other organisms. Despite our growing understanding of gland development, the conditions that elicit releases are largely unknown. To determine if male age or gland development affects the chemical composition and release behavior, we dissected adult male bugs and profiled the chemical composition of the male DAG 1, 7, and 14 d post-eclosion. To determine if gland development is related to sexual maturity, we counted the number of sperm present in the seminal vesicles at the same time points. Finally, we measured the diurnal release patterns of different aged males and in various male-female combinations. We observed that newly eclosed adults have under-developed glands and male seminal vesicles contained few sperm. One week post-eclosion the DAG contained previously reported pheromone compounds and males contained many sperm. Mirroring the trend in reproductive maturation and gland development, the number of pheromone releases increased with age and the majority of releases followed a scotophase pattern unaffected by sexual composition. These findings link male age to 1) dorsal abdominal gland development 2) release behavior and 3) sexual maturity, which will help our understanding of when these olfactory cues are present for other organisms, like prey, to perceive.

Natural variation in light has historically correlated with seasonality, providing an honest cue to organisms with seasonal life history cycles. However, with the onset of widespread light at night (LAN), the reliability of light as a cue has decreased in polluted areas, making its timing or intensity potentially clash with temperature trends. These clashing cues may influence biological systems on multiple levels. Yet, a few studies have connected behavioral underpinnings and larger community-level processes, resulting in a knowledge gap bridging individual-, population-, and community-level responses to mismatched cues. We experimentally investigated impacts of cool temperature and LAN on a lady beetle-aphid-fava system to test how light and temperature influenced aphid population growth and their underlying behavioral drivers. We used Coccinella septempunctata and Coleomegilla maculata beetles to understand the interaction of the environment and predation on pea aphid (Acyrthosiphon pisum) population growth. Aphids and their predators reacted differently to variation in light and temperature, influencing the strength of aphid-driven and predator-driven dynamics in the different conditions. We observed evidence of aphid-driven dynamics in the cool, light conditions where aphids excel and exhibited strong anti-predator behavior. In contrast, we found stronger predator-driven dynamics in warm conditions where lady beetle predatory success was higher. Overall, we found that LAN has context-dependent effects on insect communities due to the varied responses each player has to its environment.

1. Maternal provisioning can reduce offspring vulnerability to predators by promoting offspring growth and eliciting of antipredator behaviours. Mothers perceiving predation risk may improve offspring survival if producing larger, higher‐quality offspring. However, empirical evidence suggests that offspring quality is often reduced, probably reflecting predator‐induced physiological costs, or a selfish maternal strategy aimed at producing more offspring by sacrificing their quality. While perception and impact of predators can vary across the prey's life stage, a majority of studies have focused on understanding how reproductive allocation decisions are influenced by the risk of predation during adulthood. 2. In this study, Leptinotarsa decemlineata beetles were used to examine if the risk of predation during the larval stage: (i) impacts the mother's physiological condition, including body mass and metabolic rate; and (ii) alters maternal allocation of reproductive resources to offspring quantity versus quality. 3. Results revealed that L. decemlineata mothers responded to perceived predation risk by producing clutches with fewer but larger eggs, thus increasing offspring provisioning. Surprisingly, while females that had faced predation risk as larva emerged with a similar body mass to control females, they exhibited lower metabolic rates. 4. Although predation risk in L. decemlineata larvae is known to impair their ability to acquire and maintain energy resources, adult females appeared to ameliorate such costs by improving their metabolic efficiency and by allocating more of their limited reproductive resources to produce fewer but better‐quality offspring.

Prey commonly use volatile chemicals released from predators to infer the level of danger and can enact phenotypic changes to increase their chance of survival. Because some predators emit volatiles that are also used in plant defense signaling, there is the potential for plants to also respond to predator cues. In the Colorado potato beetle, Leptinotarsa decemlineata, predator spined soldier bug, Podisus maculiventris, potato, Solanum tuberosum, system, the beetle responds to the predator aggregation semiochemical, which is comprised of predator-specific compounds and compounds that are known to be used by plants as green leaf volatile signals to induce their own defenses. Given this shared sensory cue in the system we asked the question; is the effect of the predator semiochemical on prey driven by the full predator semiochemical, or are there bioactive compounds in the blend that are also shared with the plants that are responsible for the prey behavioral changes? By fractionating the semiochemical into three treatments (full blend, shared cues, and predator only) and dispensing it in a replicated potato field with free-ranging herbivores, we found that the cues shared with the plant reduced herbivore feeding by 37 percent and the full blend by 41 percent compared to the control or predator specific fraction. Potato plants also responded to the shared cues by growing larger over the season and initiating flowering earlier, indicating that prey responses to the semiochemical could be direct or mediated by the plant’s response to the semiochemical. These findings highlight the potential utility of using shared cues for management purposes. Rather than using a semiochemical treatment that has a single target audience (i.e., the pest), we showed that a cue shared across multiple trophic levels decreased plant damage and increased growth, while eliciting anti-predation behavior in the prey.

Despite the ubiquity of parental effects and their potential impact on evolutionary dynamics, their contribution to the evolution of ecologically relevant adaptations remains poorly understood. Using quantitative genetics, here we demonstrate that parental effects contribute substantially to the evolutionary potential of larval antipredator responses in a leaf beetle (Leptinotarsa decemlineata). Previous research showed that larger L. decemlineata larvae elicit stronger antipredator responses, and mothers perceiving predators improved offspring responses by increasing intraclutch cannibalism –an extreme form of offspring provisioning. We now report substantial additive genetic variation underlying maternal ability to induce intraclutch cannibalism, indicating the potential of this adaptive maternal effect to evolve by natural selection. We also show that paternal size, a heritable trait, impacted larval responses to predation risk, but that larval responses themselves had little additive genetic variation. Together, these results demonstrate how larval responses to predation risk can evolve via two types of parental effects, both of which provide indirect sources of genetic variation for offspring traits.

Entomopathogenic nematodes (EPNs) have potential as an alternate means of controlling soil-dwelling pests in settings such as school athletic fields, where use of chemical pesticides is often restricted or prohibited. Athletic fields are also unique among turfgrass systems, as their distinct pattern of foot traffic can result in compaction and other soil properties varying across different areas of the field, potentially causing variability in EPN performance even within a single field, as many abiotic and biotic soil properties are known to influence EPN efficacy. We tested the efficacy of the EPNs Steinernema feltiae and Heterorhabditis bacteriophora against third-instar grubs of the Japanese beetle Popillia japonica in high-traffic and low-traffic areas of two soccer fields in New York State, one grown atop loam soil and the other atop loamy sand. Efficacy was low in the loam soil but modest for both species in the loamy sand, though the only significant increase over controls occurred in S. feltiae-inoculated plots within low traffic areas in 2016. Non-metric multidimensional scaling revealed positive associations between efficacy of both EPN species and soil sand content, suggesting that sandy soils are most optimal for curative applications against turfgrass pests. Soil biotic factors, such as microarthropod abundance, were not found to have an effect on EPNs. These results will aid turfgrass managers by improving knowledge of the conditions required for effective use of EPNs.

1. Although many vector-borne pathogens are transmitted by an array of vector species, most studies do not account for the potential effects of species interactions. 2. By manipulating conspecific and heterospecific vector density in small experimental mesocosms, this study disentangled the impact of vector density and community composition on vector movement and plant virus transmission in the potato virus Y system. 3. The following predictions were tested: (i) increasing aphid density will increase aphid movement and virus transmission; (ii) adding low-efficiency vectors and thereby decreasing the average transmission efficiency of the vector assemblage will decrease virus transmission; and (iii) aphid movement and the average vector transmission efficiency will mediate the effect of aphid density and community composition on virus transmission. 4. It was found that initial density positively affected aphid movement, but had no effect on virus transmission, and that conspecific density was more important than heterospecific density. Conversely, community composition affected both aphid movement and virus transmission. These effects were driven by species identity, rather than species richness per se. 5. The results of this study emphasise the importance of accounting for vector behaviour, and analysing it within the context of the wider vector assemblage.

Summary Landscape composition affects local arthropod biodiversity, including herbivorous insects and their predators, yet to date landscape effects on insect-vectored plant diseases have received little attention. Here, we examine how landscape composition affects the prevalence of a viral pathogen in host plants, and the role the arthropod vector assemblage plays in mediating landscape effects. We measured the effect of landscape composition (measured as percentage of cropland and unmanaged land) on the plant virus Potato virus Y (PVY), its aphid vectors, and their coccinellid predators during the 2012 and 2013 field seasons at 19 to 21 farms. In both years, we found a positive relationship between final virus prevalence and percentage of cropland within 500, 1000, and 1500 m surrounding study sites. Percentage of cropland also had a significant negative effect on aphid species richness, and the aphid community composition in turn affected PVY prevalence. By contrast, landscape composition had no measurable effect on coccinellid abundance or species richness in this study. Synthesis and applications. Our work demonstrates that landscape composition plays an important role in vector-borne pathogen spread, and that pathogen spread appears to be mediated by the effects of the landscape on the insect vector community. The small spatial scale (≤1500 m) of the effects seen in our study indicates that on-farm management practices have the potential to reduce virus prevalence on small-scale farms. Farmers may be able to reduce Potato virus Y prevalence by on-farm diversification, by isolating potato fields from other agricultural crops, and by not using saved potato seed. This article is protected by copyright. All rights reserved.

Agricultural intensification impacts local arthropod communities. The temporal and spatial variation of agricultural environments can have a significant impact on insect pest populations, yet little work has been done to date on the effect of intra-annual variation (within season) or spatiotemporal effects on arthropod functional community composition. The aim of this research was to evaluate the effects of intra-annual variation and landscape composition on the aphid community. To that end, we investigated the following research question: How do intra-annual variation and landscape composition affect aphid abun- dance, species richness, and functional community composition? In this study, we quantified landscape com- position as percent cropland, intra-annual variation as sampling week measured throughout the growing season, and aphid functional community composition as crop virus transmission—or vectoring—ability. We collected data in two agricultural regions: a diversified agricultural region in New York State (NY) and an agriculturally intense potato-growing region in Wisconsin (WI). We found that the interactive effect of land- scape composition and intra-annual variation significantly affected aphid abundance and species richness in both study regions, and functional community composition in NY. These results indicate that spatiotempo- ral shifts in agroecosystems have significant implications for aphid functional community composition.

Lethal predators and pathogens can reduce the size of pest populations and help regulate crop-damaging herbivores. Additionally, predators like the spined soldier bug (Podisus maculiventris) can elicit non-consumptive effects in herbivores such as the Colorado potato beetle (Leptinotarsa decemlineata), causing changes in prey behavior, physiology and life history. While it is known that lethal predators and pathogens interact, there is little known about the interaction of predator-induced non-consumptive effects and pathogens on their shared hosts. Using the spined soldier bug, which is known to elicit non-consumptive effects on potato beetles (e.g. reduced feeding), we studied the interaction of predator-induced non-consumptive effects and the fungal pathogen Beauveria bassiana on the survival of Colorado potato beetle larvae. In laboratory microcosms we found a 16–50% increase in survival of fungus-treated beetles held with non-lethal male stink bugs. We also studied the predator-fungus interaction on jasmonic acid-treated plants to assess whether elevated levels of host plant defenses made larvae more susceptible to fungal infection. Beetles’ susceptibility to fungal infection did not change when provided jasmonic-acid treated foliage as food. Finally, we determined that two volatile compounds (E-2-hexenal and alpha-terpineol), produced as part of the bugs’ aggregation pheromone, reduced conidial germination, resulting in higher levels of beetle survival. Our findings suggest that stink bug odors protect prey against fungal pathogens.

The risk of consumption is a pervasive aspect of ecology and recent work has focused on synthesis of consumer-resource interactions (e.g., enemy-victim ecology). Despite this, theories pertaining to the timing and magnitude of defenses in animals and plants have largely developed independently. However, both animals and plants share the common dilemma of uncertainty of attack, can gather information from the environment to predict future attacks and alter their defensive investment accordingly. Here, we present a novel, unifying framework based on the way an organism's ability to defend itself during an attack can shape their pre-attack investment in defense. This framework provides a useful perspective on the nature of information use and variation in defensive investment across the sequence of attack-related events, both within and among species. It predicts that organisms with greater proportional fitness loss if attacked will gather and respond to risk information earlier in the attack sequence, while those that have lower proportional fitness loss may wait until attack is underway. This framework offers a common platform to compare and discuss consumer effects and provides novel insights into the way risk information can propagate through populations, communities, and ecosystems.

Insect herbivores express tremendous ontogenetic variation in traits related to growth and maturation, but also as an evolutionary consequence of ecological interactions with plants and predators. These selective pressures can either reinforce or restrict expression of particular ontogenetic strategies, allowing herbivores to simultaneously cope with plant resistance and risk of predation through ontogenetic change. For example, whereas an increase in defense-sabotaging behavior, aposematism and sequestration along herbivore ontogeny seems to be reinforced by both bottom-up and top-down forces, some ontogenetic trends in anti-predator behavior can be limited by plant resistance. Communication among plants, herbivores and their natural enemies is also influenced by insect ontogenies. The study of ontogenetic strategies of herbivores requires the assessment of the genetic variation, heritability and adaptive value across herbivore development, considering the variation in plant quality and predation risk.

Herbivore-induced plant defences regulated by the phytohormones jasmonic acid (JA) and salicylic acid (SA) are predicted to influence herbivore population dynamics, in part because they can operate in a density-dependent manner. While there is ample evidence that herbivore-induced plant responses affect individual performance and growth of herbivores, whether they scale-up to regulate herbivore population dynamics is still unclear. We evaluated the consequences of variation in plant defences and herbivore density on herbivore development, reproduction and density-dependent population growth. We investigated potential mechanisms affecting the strength of herbivore density-dependent processes by manipulating jasmonate expression, quantifying plant defensive traits (phytohormones JA and SA and serine proteinase inhibitors) and adding aphids (Macrosiphum euphorbiae) at different densities to plants to simulate different initial population density and herbivore load. We manipulated jasmonate defences by using genetically modified lines of tomato plants (Solanum lycopersicum) with elevated or suppressed jasmonate-dependent defences. Jasmonate-insensitive plants cannot induce the defences regulated by the JA pathway, while jasmonate-overexpressing plants constitutively express jasmonate-dependent defences. We found that jasmonate defences provided resistance against aphids and influenced density-dependent processes. Jasmonate-overexpressing plants reduced aphid reproduction, prolonged developmental time, dampened aphid populations across all aphid densities and caused density-independent aphid population growth. Jasmonate-overexpressing plants showed high JA-dependent constitutive levels of resistance and were unable to activate the SA pathway in response to aphid feeding. In contrast, jasmonate-insensitive plants increased aphid reproduction, shortened developmental time, reduced population growth only at high initial densities and promoted strong negative density-dependent population growth. Aphid feeding on jasmonate-insensitive plants did not induce jasmonate-dependent defences, but induced the SA pathway in a density-dependent manner, which resulted in negative density-dependent aphid population growth. Aphid feeding on jasmonate-insensitive and jasmonate-overexpressing plants differentially activated the salicylate pathway, revealing a negative crosstalk between the defensive phytohormones JA and SA. By muting or enhancing jasmonate-mediated responses and quantifying SA phytohormone induction, we demonstrated that plant defences are a key factor driving not only the performance, but also the density dependence processes and population growth of herbivores.

A growing number of studies have manipulated intraspecific plant diversity and found dramatic changes in the densities of associated insect herbivores and their predators. While these studies have been essential for quantifying the net ecological consequences of intraspecific plant diversity, they have been less effective at uncovering the ways in which plant diversity alters trophic interactions within arthropod communities. We manipulated intraspecific plant diversity and predation risk in the field in a factorial design to reveal how a mixture of plant genotypes changes the response of an herbivorous beetle (Leptinotarsa decemlineata) to a common stink bug predator (Podisus maculiventris). We repeated the manipulations twice across the ontogeny of the beetle to examine how the effects of diversity on the predator-prey interaction differ between larval and adult stages. We found that intraspecific plant diversity, mixtures of susceptible and resistant varieties of potato (Solanum tuberosum), reduced larval survival by 20% and adult oviposition by 34%, which surprisingly put survival and oviposition lower in the mixed-genotype plots than in the resistant monocultures. Moreover, we found that predation risk reduced larval survival 25% and 11% in resistant and susceptible monocultures, respectively, but had no effect in the mixture. This result indicated that our genotypic mixing treatment interacted nonadditively with predation risk such that plant diversity altered the predator-prey interaction by changing the responses of the beetles to their stink bug predators. In addition, even though predation risk reduced larval survival, it increased adult overwintering survival by 9%, independently of plant treatment, suggesting that these interactions change through ontogeny. A key implication of our study is that plant diversity influences arthropod communities not only by changing resource quality, as past studies have suggested, but also by changing interactions between species within the arthropod community.

In the study of insect-vectored plant viruses, colonizing vector species remain the focus. However, non-colonizing vector species, those that do not settle and reproduce on the viral plant host, are often the most abundant in the field and may be the largest contributors to disease spread. While non-colonists may have a substantial effect on disease prevalence, the factors influencing their movement and transmission on non-host plants have been little studied. Here we evaluated how a common biological control agent (Hippodamia convergens), host and non-host plant abundance, and plant spatial distribution impact the movement and density of a wingless non-colonizing vector [Rhopalosiphum padi (L.)] and transmission of potato virus Y (PVY) in potatoes in experimental arenas. The results of this work illustrate the importance of plant species function (host or non-host) and distribution to vector behavior and disease spread. Predation, host plant abundance, and plant spatial distribution interactively affected viral prevalence within infected arenas. Increasing the number of vector non-host plants increased the distance and frequency of aphid movement, and the effect was influenced by plant spatial distribution, the arrangement of plant species in the experimental arena. Increasing the number of vector host plants increased the density of aphids. Although the interaction of the plant and predator treatments affected the proportion of potato plants infected in arenas where infection occurred, and host abundance and spatial distribution impacted vector movement and viral prevalence, aphid movement did not appear to mediate the effect of plant and predator treatments on PVY prevalence. This work demonstrates that both wingless non-colonizing vector behavior and transmission are aggregated responses to multiple environmental drivers.

Many omnivorous insects are important biological control agents, and their success is influenced by both plant resistance and prey availability. The potential impact of these two factors is complicated by the fact that they may not be independent: Resistant plants also often support fewer herbivorous prey. We studied how lifetime development, growth, fecundity and preference of the omnivorous stink bug, Podisus maculiventris, was affected by jasmonate-induced plant defenses and amount of prey available. P. maculiventris survival was 70 % lower on high-resistance (jasmonate-overexpressing) plants compared to low-resistance (jasmonate-insensitive) plants. However, surviving P. maculiventris grew and achieved equal fecundity on low- and high-resistance plants. When given a choice, P. maculiventris preferred low-resistance plants, but did not differentiate between caterpillar prey reared on high- or low-resistance plants. Low prey availability impacted distinct aspects of P. maculiventris performance: Development time was lengthened, and nymphal and adult mass were reduced, but survival was not impacted. We did not detect any interactive effects between plant resistance and prey availability for any measure of P. maculiventris. Thus, we found remarkably compartmentalized impacts of plant resistance and prey availability for this omnivorous insect.

Predator–prey interactions primarily focus on prey life-stages that are consumed. However, animals in less vulnerable life-stages might also be influenced by the presence of a predator, making our understanding of predation-related impacts across all life-stages of prey essential. It has been previously demonstrated that Podisus maculiventris is a voracious predator of eggs and larvae of Leptinotarsa decemlineata, and that larvae will alter their behavior to avoid predation. However, the adult beetles are not readily consumed by P. maculiventris, raising the question of whether they will respond to predators to protect themselves or their offspring. Here, we examine the effect of predation risk by P. maculiventris, on three adult behaviors of L. decemlineata; colonization, oviposition, and feeding, and the resulting impact on host plant damage. In an open-field test, there was no difference in natural beetle colonization between plots with predation risk and control treatments. However, subsequent host plant damage by adult beetles was 63.9% less in predation risk treatments. Over the lifetime of adult beetles in field mesocosms, per capita feeding was 23% less in the predation risk treatment. Beetle oviposition was 37% less in the presence of predators in a short-term, greenhouse assay, and marginally reduced in longer term field mesocosms. Our results indicate that predation risk can drive relatively invulnerable adult herbivores to adjust behaviors that affect themselves (feeding) and their offspring (oviposition). Thus, the full impact of predator presence must be considered across the prey life cycle.

A consequence of plant diversity is that it can allow or force herbivores to consume multiple plant species, which studies indicate can have major effects on herbivore fitness. An underappreciated but potentially important factor modulating the consequences of multi-species diets is the extent to which herbivores can choose their diets versus being forced to consume specific host-plant sequences. We examined how host-selection behavior alters the effects of multi-species diets using the Colorado potato beetle (Leptinotarsa decemlineata) and diets of potato plants (Solanum tuberosum), tomato plants (S. lycopersicum), or both. When we gave beetles simultaneous access to both plants, allowing them to choose their diets, their final mass was within 0.1% of the average mass across both monocultures and 43.6% lower than mass on potato, the superior host in monoculture. This result indicates these beetles do not benefit from a mixed diet, and that the presence of tomato, an inferior but suitable host, makes it difficult to use potato. In contrast, when we forced beetles to switch between host species, their final mass was 37.8% less than the average of beetles fed constant diets of either host species and within 3.5% of the mass on tomato even though they also fed on potato. This indicates preventing host-selection behavior magnified the negative effects of this multi-species diet. Our results imply that ecological contexts that constrain host-selection or force host-switches, such as communities with competition or predation, will lead plant species diversity to reduce the performance of insect herbivores.

The success of sustainable crop production depends on our ability to select or create varieties that can allocate resources to both growth and defence. However, breeding efforts have emphasized increases in yields but have partially neglected defence traits against pests. Estimating the costs of multiple defences against tuber herbivores and the tradeoffs among them, as well as understanding the relationship between yield and multiple defences is still unknown but relevant to both basic and applied ecology. Using twenty commercial potato varieties available in Colombia and the tuber herbivore Tecia solanivora, we tested whether high yielding varieties show a reduction in three types of defence: constitutive and induced resistance, as well as tolerance. Specifically, we determined (1) the costs in terms of yield of all three defences, (2) the possible tradeoffs among them, and (3) if oviposition preference was related to the expression of these defences. We detected no costs in terms of yield of constitutive and induced resistance to tuber damage. We did, however, find evidence of costs of being able to tolerate tuber herbivory. While we found no tradeoffs among any of the estimated defences, there was a positive correlation between aboveground compensatory growth and tolerance in terms of tuber production, suggesting that after damage there are no shifts in the allocation of resources from aboveground to belowground biomass. Finally, we found that females laid more eggs on those varieties with the lowest level of constitutive resistance. In conclusion our findings suggest that in potatoes, breeding for higher yields has not caused any reduction in constitutive or induced resistance to tuber damage. This is not the case for tolerance where those varieties with higher yields are also less likely to tolerate tuber damage. Given the high incidence of tuber pests in Colombia, selecting for higher tolerance could allow for high productivity in the presence of herbivores. Finding mechanisms to decouple the tolerance response from yield should be a new priority in potato breeding in Colombia to guarantee a higher yield in both the presence and absence of herbivores.

Theory on condition-dependent risk-taking indicates that when prey are in poor condition, their anti-predator responses should be weak. However, variation in responses resulting from differences in condition is generally considered an incidental by-product of organisms living in a heterogeneous environment. Using Leptinotarsa decemlineata beetles and stinkbug (Podisus maculiventris) predators, we hypothesised that in response to predation risk, parents improve larval nutritional condition and expression of anti-predator responses by promoting intraclutch cannibalism. We showed that mothers experiencing predation risk increase production of unviable trophic eggs, which assures provisioning of an egg meal to the newly hatched offspring. Next, we experimentally demonstrated that egg cannibalism reduces L. decemlineata vulnerability to predation by improving larval nutritional condition and expression of anti-predator responses. Intraclutch cannibalism in herbivorous insects might be a ubiquitous strategy, aimed to overcome the dual challenge of feeding on protein-limited diets while living under constant predation threat.

Because predation risk typically alters how prey forage for food, interactions between predation risk and food availability are commonly found. Less is known about how host plant quality and predation risk interact to affect prey behaviour and physiology. Using the caterpillar, Manduca sexta, and its predator, Podisus maculiventris, the effects of predation risk and host plant quality on caterpillar feeding, growth, assimilation efficiency, and resting metabolic rate were tested. Overall, caterpillars on low-resistance tomato plants (jasmonate-insensitive) gained 14% more mass than caterpillars on high-resistance plants (wild-type tomato). On low-resistance plants, the presence of predators caused caterpillars to eat 32% less, but they gained the same mass as unthreatened caterpillars (i.e. a 19% increase in assimilation efficiency). In addition, caterpillars showed a 17% increase in resting metabolic rate in the presence of predators. On high-resistance plants, predation risk caused a decrease in feeding, but did not alter assimilation efficiency or resting metabolic rate. The reduction in physiological responses to predation risk on high- versus low-resistance plants demonstrates a tradeoff between the ability to respond to predation risk and the ability to grow, especially on well-defended plants.

Early-season herbivory can cause plants to induce resistance to subsequent herbivores, and this ubiquitous plant defense strategy has been shown to be adaptive when subsequent vegetative-feeding herbivores impact plant fitness. However, a growing number of studies show that leaf herbivory can also induce defenses in plant reproductive tissues, which may deter mutualists such as pollinators and seed dispersers, or antagonists such as florivores and seed predators. Due to their direct interaction with plant reproductive tissues, deterrence of these mutualists or antagonists may have large negative or positive effects on plant fitness. Despite numerous predictions, we know little regarding the fitness consequences of leaf-to-reproductive tissue induction in nature. Here, using observations of natural populations and manipulative field experiments, we show that leaf herbivory by the invasive Japanese beetle (Popillia japonica) induces an accumulation of jasmonic acid and complex phenolics in reproductive tiss...

The cost of inbreeding (inbreeding depression, ID) is an important variable in the maintenance of reproductive variation. Ecological interactions such as herbivory could modulate this cost, provided that defence traits harbour deleterious mutations and herbivores are responsible for differences in fitness. In the field, we manipulated the presence of herbivores on experimentally inbred and outcrossed plants of Solanum carolinense (horsenettle) for three years. Damage was greater on inbred plants, and ID for growth and fitness was significantly greater under herbivory. Inbreeding reduced phenolic expression both qualitatively (phytochemical diversity) and quantitatively, indicating deleterious load at loci related to the biosynthesis of defence compounds. Our results indicate that inbreeding effects on plant-herbivore interactions are mediated by changes to functional plant metabolites, suggesting that variation in inbreeding could be a predictor of defence trait variation. The magnitude of herbivore-mediated, ecological ID indicates that herbivores could maintain outcrossing mating systems in nature.

Worldwide, many crops rely on insect pollination. Insufficient pollination can reduce fruit and seed set by directly reducing pollen deposition, and can also affect offspring quality, such as growth rate and resistance to herbivores, by limiting outcrossing opportunities. Both effects are important in fruit agroecosystems where fruit size and the quality of seeds for re-planting are dependent on sufficient pollination. We experimentally manipulated pollination of the cape gooseberry, Physalis peruviana L. (Solanaceae), to test the effects of honey and bumble bee pollination compared to manual outcrossing and autonomous self-pollination on fruit and offspring characteristics. Compared to manual and self-pollination, bee pollination increased fruit size, seed set and germination rates, supporting the hypothesis that sufficient pollination increases plant fitness. Interestingly, plant growth rate and herbivore resistance were significantly and marginally greater in manually outcrossed plants compared to self-pollinated offspring, suggesting that inbreeding reduces offspring quality. Herbivore resistance and plant growth did not differ between one honeybee visit and self-pollination suggesting that multiple pollinator visits are needed to prevent inbreeding events. Our data suggest that the quantity and quality of pollen deposited by bee visitation can significantly alter ecologically and economically relevant traits in this agroecosystem. Zusammenfassung Verschiedene Nutzpflanzen weltweit brauchen Insektenbestaubung, um hohe Ertrage zu erzielen. Ungenugende Bestaubung kann, vermittelt durch eine geringe Pollenablage, die Grosse von Fruchten und Samen reduzieren oder die Qualitat der Nachkommen durch Inzuchtdepression beeinflussen. Beide Effekte sind wichtig in Obst-Agrarokosystemen, wo Fruchtgrose und die Qualitat der Samen fur die Wiederbepflanzung eine grosse Rolle spielen und von ausreichender Bestaubung abhangig sind. Wir haben experimentell die Bestaubung von Physalis-Pflanzen (Physalis peruviana) manipuliert, um die Auswirkungen von Honigbienen- und Hummel-Bestaubung im Vergleich zu manueller Fremdbestaubung und Selbstbestaubung auf Frucht- und Nachkommeneigenschaften zu testen. ImVergleich zur manuellen und Selbstbestaubung, erhohte Bienenbestaubung sowohl Samenansatz und Fruchtgrose, als auch die Keimungsrate. Unsere Ergebnisse unterstutzen die Hypothese, dass Insektenbestaubung die Fitness der Pflanze erhoht und auch von Interesse fur die Produzenten von Physalis sein sollte. Beachtlich war, dass Nachkommen von manuell fremdbestaubten Fruchten eine marginal hohere Resistenz gegen Herbivorie aufwiesen

Aphids increase production of winged individuals as a generalized response to multiple threats, including predators, competitors, and poor host plant quality. While wing formation in response to these individual threats is well documented, few investigations have evaluated whether combined threats lead to additive or non-additive outcomes. We tested the interactive effects of predation risk and plant quality on population growth and wing induction in the potato aphid, Macrosiphum euphorbiae. Plant quality was varied using phytohormonal manipulations of tomato (Solanum lycopersicum) to elevate or suppress the jasmonate and salicylate defense pathways. Predation risk was altered by exposing aphids to lethal or risk (unable to feed) individuals of the convergent lady beetle, Hippodamia convergens. Phytohormonal treatments resulted in >4-fold variation in aphid population growth and thus strongly affected plant quality; however, the percentage of winged individuals was no different across plant types. Predators similarly reduced aphid abundance, but also elicited a ~3-fold increase in wing formation, an effect that was similar in magnitude when comparing lethal with risk predators. The overall impact of plants and predators on aphids was largely additive, an outcome that was unexpected given the likelihood for interactions between these two factors and our prior results with other herbivores in this system. We discuss this discrepancy in the context of phenotypic plasticity, non-lethal predator effects, and the ecological challenges faced by wing dimorphic insects.

Omnivorous plant-feeding predators have been predicted to both increase and decrease prey consumption on resistant host-plants because of behavioral shifts in food preferences and direct ingestion of phytotoxins, respectively. To help resolve this debate, we reviewed the published literature on plant defense-heteropteran interactions using both vote-counting and meta-analytical approaches. The Heteroptera are ideal for this analysis because as a group they are broadly omnivorous, critical in the biocontrol of crop pests, and frequently come in contact with plants varying in quality. We identified 37 studies that matched our search criteria, involving at least 16 species of Heteroptera. Overall, plant resistance lowered the abundance of heteropterans in the field, but had virtually no impact on their performance when reared in the lab (aside from a significant, albeit minor, increase in development time). Prey consumption was strongly affected by plant resistance; however, the outcome was extremely variable with near equal evidence for increasing (22 cases) vs. decreasing (21 cases) predation on resistant host-plants. Thus, prey consumption is far more variable across plant-types differing in quality when compared with either abundance or performance. Heteropteran family and developmental stage (adult vs. nymph) were poor predictors of the outcome for prey suppression. Our results indicate that the feeding ecology of omnivorous heteropterans is highly contingent on plant defense expression, more so than other ecologically-relevant traits, but the factors mediating behavioral shifts in prey consumption remain elusive.

Plant resistance and predation have strong independent and interacting eff ects on herbivore survival, behavior, and patterns of herbivory. Historically, research has emphasized variation in the consumption of herbivores by enemies. Recent work, however, demonstrates that predators also elicit important changes in the traits of their prey, but we do not know how this is infl uenced by plant quality. In this study, we quantify how the consumptive and non-consumptive eff ects of predators vary along a gradient of plant resistance using tomato plants (Solanum lycopersicum), tobacco hornworms (Manduca sexta), and predaceous stinkbugs (Podisus maculiventris). We manipulated resource quality using three tomato lines that vary in the expression of the jasmonate pathway, a phytohormonal pathway that is central in mediating resistance to insects. Resistant plants had higher levels of defensive proteins and glandular trichomes than low resistance plants. Th e consumptive and non-consumptive eff ects of predators were quantifi ed on the three tomato lines by comparing the impact of ‘lethal’ predators that both kill and scare prey with ‘risk’ predators whose mouthparts were surgically impaired to prevent killing. Across several fi eld experiments, the total cascading eff ect of predators on plant damage was 80.4% lower on jasmonate-overexpressing (highly resistant) plants compared to that on wild-type or jasmonate-insensitive (low resistance) plants. Th is dramatic attenuation of predator eff ects was due to a 66% reduction in consumption on high resistance plants, and also because of a 65% decline in non-consumptive eff ects. Numerous studies in natural and agricultural habitats have documented that predator eff ects tend to be weaker on well-defended plants; our results provide novel mechanistic insight into this pattern by demonstrating that plant resistance substantially weakens both the consumptive and non-consumptive impacts of predators.

Management of green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), in bell pepper, Capsicum annuum L., was explored through a combination of plant growth-promoting rhizobacteria (PGPR) and endemic biological control in New York in 2006 and 2007. We hypothesized that by using PGPR-treated peppers 1) M. persicae infestations would be reduced via induced resistance, 2) natural enemies would be lured to plants through the elicitation of volatile organic compounds, and 3) yield amount and quality would be improved. Pepper seed was planted in soil containing the PGPR formulation BioYield or untreated soil. Plants were transplanted to field plots and then treated with an insecticide regimen designed to remove or conserve populations of natural enemies. Apterous aphids and natural enemies were counted weekly on plants and pepper fruit were harvested, graded and weighed three times. PGPR did not directly or indirectly reduce aphid densities in either year. In 2006, there were more natural enemies in PGPR-treated plots than untreated ones, but this was probably a density-dependent response to aphid densities rather than a response of natural enemies to volatiles from PGPR-treated plants. For the first harvest date in 2006, yield of all fruit grades, especially the premium Fancy Grade, was 1.7-2.3 times greater in PGPR-treated plots than in untreated plots. However, no differences in yield were observed for the other two harvest dates or overall yield in 2006; no differences in yield among treatments were detected in 2007. Our results suggest that PGPR will not significantly impact M. persicae infestations or natural enemy populations but could enhance yield and quality of pepper fruit in some years.

The non-consumptive (or trait-mediated) effects of predators on prey are known to contribute substantially to the negative impact of insect predators on herbivorous insects. Our goal now is to understand what factors alter the relative importance of the consumptive (or density-mediated) and non-consumptive components of the total predator impact. This is important both for understanding the effects of predators in natural systems as well as for successfully manipulating predators for biological control in agriculture. In this study, we tested whether herbivore ontogeny influenced the contribution of consumptive and non-consumptive effects of a predator on herbivore survivorship and plant damage by the herbivores. We addressed these questions using the native plant Solanum ptychanthum Dunal (Solanaceae), the predator Podisus maculiventris Say (Heteroptera: Pentatomidae), and first-, third-, and fourth-instar Manduca sexta L. (Lepidoptera: Sphingidae). In field cage experiments, we found that first- and third-instar M. sexta were more vulnerable to predators compared to fourth instars. In the presence of predators, M. sexta caterpillars spent less time on feeding compared to caterpillars in the absence of predators. The amount of damage the plants received was reduced in the presence of the predator and the consumptive and non-consumptive components contributed approximately equally to this reduction. Thus, the non-consumptive component of the predator is important for all of the herbivore stages vulnerable to predation in our study. We conclude with a discussion of possible implications of considering non-consumptive effects of predators in biological control of agricultural pests.

1. Herbivory can induce resistance in a plant and the induced phenotype may be disfavoured by subsequent herbivores. Yet, as the distance between plants in a population increases, limited mobility may make a herbivore more likely to feed and oviposit on host plants in its immediate surroundings. 2. The present study tested whether a herbivore’s preference and distribution across plants with different induced phenotypes was influenced by the spatial distribution of plants. A fragmented population of Solanum dulcamara plants was created. This consisted of discrete, spatially separated patches with different histories of damage, either herbivory from adult flea beetles (Psylliodes affinis), tortoise beetles (Plagiometriona clavata), or mechanical damage. Each patch was separated by 7 m and consisted of 12 plants that were spaced 30 cm apart. Then a fixed number of adult tortoise beetles were introduced to each patch, and movement and oviposition within and between spatially separate homogeneous patches (receiving one type of damage) were compared with movement and oviposition within heterogeneous patches (containing all three types of damage) over the growing season. 3. Flea beetle and tortoise beetle herbivory consistently induced different phytochemical responses in S. dulcamara (polyphenol oxidase and peroxidase), and adult tortoise beetles avoided oviposition on the flea beetle induced plants within heterogeneous patches. However, between homogeneous patches, plant phenotype did not influence oviposition. Colonisation by naturally occurring flea beetle adults followed a similar pattern. 4. These results suggest that the heterogeneity of plant phenotypes can influence herbivore choice and distribution at small but not large spatial scales.

Plants in nature are attacked sequentially by herbivores, and theory predicts that herbivore-specific responses allow plants to tailor their defenses. We present a novel field test of this hypothesis, and find that specific responses of Solanum dulcamara lead to season-long consequences for two naturally colonizing herbivores, irrespective of the second herbivore to attack plants. This result indicates that responses induced by the initial herbivore made plants less responsive to subsequent attack. We show that initial herbivory by flea beetles and tortoise beetles induce distinct plant chemical responses. Initial herbivory by flea beetles lowered the occurrence of conspecifics and tortoise beetles relative to controls. Conversely, initial herbivory by tortoise beetles did not influence future herbivory. Remarkably, the experimentally imposed second herbivore to feed on plants did not modify consequences (induced resistance or lack thereof) of the first attacker. Induction of plant chemical responses was consistent with these ecological effects; i.e. the second herbivore did not modify the plant's initial induced response. Thus, canalization of the plant resistance phenotype may constrain defensive responses in a rapidly changing environment.

Variability in plant chemistry has long been believed to suppress populations of insect herbivores by constraining herbivore resource selection behavior in ways that make herbivores more vulnerable to predation. The focus on behavior, however, overlooks the pervasive physiological effects of plant variability on herbivores. Here we propose the plant variability-gut acclimation hypothesis, which posits that plant chemical variability constrains herbivore anti-predator defenses by frequently requiring herbivores to acclimate their guts to changing plant defenses and nutrients. Gut acclimation, including changes to morphology and detoxification enzymes, requires time and nutrients, and we argue these costs will constrain how and when herbivores can mount anti-predator defenses. A consequence of this hypothesis is stronger top-down control of herbivores in heterogeneous plant populations.

Chemical ecology is a mechanistic approach to understanding the causes and consequences of species interactions, distribution, abundance, and diversity. The promise of chemical ecology stems from its potential to provide causal mechanisms that further our understanding of ecological interactions and allow us to more effectively manipulate managed systems. Founded on the notion that all organisms use endogenous hormones and chemical compounds that mediate interactions, chemical ecology has flourished over the past 50 years since its origin. In this essay we highlight the breadth of chemical ecology, from its historical focus on pheromonal communication, plant-insect interactions, and coevolution to frontier themes including community and ecosystem effects of chemically mediated species interactions. Emerging approaches including the -omics, phylogenetic ecology, the form and function of microbiomes, and network analysis, as well as emerging challenges (e.g., sustainable agriculture and public health) are guiding current growth of this field. Nonetheless, the directions and approaches we advocate for the future are grounded in classic ecological theories and hypotheses that continue to motivate our broader discipline.

Predators can affect herbivores both through direct consumption (density-mediated interactions) and by changing behavioural, physiological or morphological attributes of the prey (trait-mediated interactions). These effects on the herbivore can in turn affect the plant through density- and trait-mediated indirect interactions (DMIIs and TMIIs). While the effects of DMIIs and TMIIs imposed by predators has been shown to influence plant density and plant communities, we know little about the effects on plant quality. In addition, the DMII and TMII components of the predator may influence each other so that the total effect of the predator on the plant is not simply the sum of the DMII and TMII. We examined DMIIs and TMIIs between a stinkbug predator and a caterpillar, and show how these interactions affect plant quality, as measured by damage, resistance to herbivores, and a defence chemical, peroxidase. We used novel methods to estimate the independent and non-additive contribution of DMIIs and TMIIs to the plant phenotype. Both predator-induced DMIIs and TMIIs caused decreases in the amount of caterpillar herbivory on plants; a strong non-additive effect between the two resulted from redundancy in their effects. TMIIs initiated by the predator were primarily responsible for a decrease in induced plant resistance. However, DMIIs predominated for reducing the production of peroxidase. These data demonstrate how DMIIs and TMIIs initiated by predators cascade through tri-trophic interactions to affect plant damage and induced resistance.

Interspecific competition between phytophagous insects can occur when plant responses induced by an early-season herbivore alter host quality for later colonizers. Recent evidence for specificity in the elicitation of induced plant responses by different attackers suggests that dynamics of host use in the field may be more complex than previously anticipated, because host suitability for colonizing herbivores may depend on which herbivore species has initially damaged a plant. In each of two years, we manipulated the first herbivore to attack Solanum dulcamara plants in an experimental population using several different arthropod species and subsequently monitored colonization by natural herbivores over the course of the growing season. We additionally performed weekly herbivore counts in wild S. dulcamara populations following natural variation in herbivore arrival. Plant-mediated interactions occurred primarily between two leaf-feeding beetles, Psylliodes affinis and Plagiometriona clavata. In both manipulative and observational experiments, P. clavata oviposition was reduced on plants initially damaged by P. affinis (or a third leaf-feeding beetle, Lema trilinea) relative to plants that were initially undamaged. Lowered P. clavata occurrence continued through subsequent life-history stages, resulting in decreased emergence of second-generation P. clavata adults on these plants. The occurrence of P. affinis was also lowered on plants damaged by conspecifics in both manipulative and observational experiments. Resistance against P. affinis also followed applications of jasmonic acid, an elicitor of plant defensive responses. Conversely, early-season damage by P. clavata did not influence plant quality for either later conspecifics or P. affinis. Initial herbivory by the spittlebug Aphrophora saratogensis or generalist taildropper slugs (Prophysaon sp.) likewise had no influence on P. clavata and P. affinis colonization, whereas L. trilinea damage did not affect later arriving P. affinis. Hence, only a subset of early-season damagers influenced herbivore occurrence on S. dulcamara. Preference tests examining P. affinis feeding and P. clavata oviposition confirmed that specificity in elicitation of induced plant responses produced the divergent herbivore occurrence patterns observed in the field. Overall, the existence of plant-mediated competitive asymmetry between herbivore species on S. dulcamara highlights the dynamic nature of plant resistance and its potential role in organizing herbivore communities.

Plants respond to herbivore damage by inducing defences that can affect the abundance of herbivores and predators. These tritrophic interactions may be influenced by heterogeneity in plant neighbourhood. 2. In the present study, the effects of induced responses on the abundance of herbivores (flea beetles and aphids), omnivores (pirate bugs and thrips), and predators (lady beetles and spiders) on individual plants and their neighbours between and within patches composed of three tomato plants was investigated. 3. Herbivore damage was manipulated to create homogeneous patches where either all or none of the plants had defences induced by herbivore damage, and heterogeneous patches where only one of the plants was induced. 4. Arthropod abundance on plants at different scales was compared by testing between patch effects (patch level), for neighbourhood effects at the plant pheno- type level (neighbourhood level), and between near and far plants (within patch position). 5. At the patch level, plants in homogeneously induced patches contained fewer flea beetles and pirate bugs, but more lady beetles, compared with homogeneously non-induced patches. There was no effect of patch type on the abundance of aphids, thrips, and spiders on plants. 6. At the neighbourhood level, induced plants in heterogeneous patches contained more flea beetles and pirate bugs compared with induced plants in homogeneous patches, indicating that the abundance of some herbivores and omnivores on induced plants varied depending on the phenotype of the other plants within the patch. Within patch position, there was no evidence that the abundance of herbivores or predators on non-induced plants was affected by proximity to an induced plant. 7. Therefore, variation in plant neighbourhood generated by induced plant responses affected the abundance of three arthropods from three feeding guilds.

Plants defend themselves against attack from insects and pathogens with various resistance strategies. The jasmonate and salicylate signaling pathways are two induced responses that protect plants against these attackers. Knowledge of the range of organisms that are affected by each response is important for understanding how plants coordinate their defenses against multiple attackers and the generality of effect of different resistance mechanisms. The jasmonate response is known to protect plants against a wide range of insect herbivores; in this study, we examined the role of the jasmonate response in susceptibility to eight pathogens with diverse lifestyles in the laboratory and field. Recent biochemical models suggest that the lifestyle of the pathogen (necrotroph versus biotroph) should predict whether the jasmonate response will be involved in resistance. We tested this by examining the susceptibility of wild-type (cv Castlemart with no known genes for resistance to the pathogens used) and jasmonate-deficient mutant tomato (Lycopersicon esculentum) plants (def1) and by employing rescue treatments of the mutant. Plant susceptibility to five of the eight pathogens we examined was reduced by the jasmonate response, including two bacteria (Pseudomonas syringae and Xanthomonas campestris), two fungi (Verticillium dahliae and Fusarium oxysporum f. sp. lycopersici), and an oomycete (Phytophthora infestans). Susceptibility to three fungi was unaffected (Cladosporium fulvum, Oidium neolycopersici, and Septoria lycopersici). Our results indicate that the jasmonate response reduces damage by a wide range of pathogens from different lifestyles, a result that contrasts with the emerging picture of diseases on Arabidopsis. Thus, the generality of jasmonate-based resistance of tomato challenges the view that ecologically distinct plant parasites are resisted via different mechanisms.

One goal of phytohormonal ecology is to study the interactions between biotic and abiotic stress at hierarchical levels of biological organization. From an ecological perspective, exposure to one stress may alter the plant's probability of being exposed to another stress. From a mechanistic perspective, hormonal and biochemical signaling in- teractions between responses to each stress may influence the severity or ability to adaptively respond to the subsequent stress. In this article, we consider the relationship between plant water and salt stress and attack by pathogens and herbivores. Empirical data suggest that water stress and the probability of attack by pathogens and herbivores are correlated between habitats. Biochemical interactions between plant responses to water and salt stress and insect and pathogen attack are also interrelated. Initial biochemical models indicated that abscisic acid (ABA), an important hormone in responses to water and salt stress, had a synergistic positive role with jasmonate-induced defenses against herbivores and an an- tagonistic role with salicylate-based resistance to some pathogens. Based on this back- ground, we developed predictions about how water and salt stress would alter plant resis- tance to insects and pathogens and tested the predictions using tomato plants as a model system. We used polyphenol oxidase activity as a marker of the jasmonate response and pathogenesis-related protein P4 as a marker of the salicylate response. First, we examined levels of chemical defense in wild-type and ABA-deficient plants and the ability of these plants to resist insect and pathogen attack. In the second experiment, we exposed plants to short-term salinity stress and tested their subsequent resistance to a chewing insect Spodoptera exigua and the bacterial speck pathogen Pseudomonas syringae pv. tomato. We have two key findings. First, ABA-deficient plants had higher levels of salicylate-mediated responses and were more resistant to bacterial speck disease, consistent with the proposed role of salicylate in defense against pathogens. This suggests linkage between water avail- ability to the plant and salicylate action in pathogenesis through ABA signaling. ABA- deficient plants had reduced resistance to the insect Spodoptera exigua, suggesting a positive correlation between responses to water stress and herbivory. The lack of difference in chemical expression of the jasmonate (JA) response (polyphenol oxidase activity) between wild-type and ABA-deficient plants did not support the proposed mechanism of synergism with the jasmonate response. Second, salt stress reduced the chemical induction (e.g., pathogenesis-related protein P4) of the salicylate response, but this did not affect resistance to the pathogen. Salt stress did not alter resistance to the herbivore Trichoplusia ni, but did alter the negative signal interaction between the jasmonate and salicylate responses. Under control conditions, the jasmonate and salicylate responses are antagonistic to one another, with induction of one response reducing the inducibility of the other. Under salt stress conditions, the negative effect of salicylate on the jasmonate response was reduced. Thus, complex interactions occur between ABA, JA, and SA, hormones that are important regulators of abiotic and biotic stress responses. Phytohormonal ecology is attempting to link ecological and hormonal interactions to develop a predictive framework for how and why plants coordinate responses to the environment.

Plants employ a variety of defence mechanisms, some of which act directly by having a negative effect on herbivores and others that act indirectly by attracting natural enemies of herbivores. In this study we asked if a common jasmonate-signalling pathway links the regulation of direct and indirect defences in plants. We examined the performance of herbivores (direct defence) and the attraction of natural enemies of herbivores (indirect defence) to wild-type tomato plants and mutant plants that are deficient in the production of the signalling hormone jasmonic acid. Wild-type plants supported lower survivorship of caterpillars compared with jasmonic acid-deficient plants. Damaged wild-type plants were more attractive to predaceous mites compared with undamaged wild-type plants, whereas damaged jasmonate-deficient plants were not more attractive to predators. Damaged wild-type plants induced a greater production of volatile compounds (primarily the sesquiterpene β-caryophyllene and the monoterpenes α-pinene, β-pinene, 2-carene and β-phellandrene) compared with damaged jasmonatedeficient plants. Treating jasmonate-deficient plants with exogenous jasmonic acid restored both the direct and indirect defence capabilities, demonstrating that jasmonic acid is an essential regulatory component for the expression of direct and indirect plant defence.

Summary 1 Plant traits can act as defences against herbivores both by reducing herbivore performance directly and by increasing the effectiveness of the natural enemies of herbivores. Natural enemy performance and rate of parasitism can be affected by plant traits and/or changes in herbivore quality. 2 Jasmonic acid is responsible for the induction of many changes in plant resistance that occur following herbivore attack. This study examines the effects of jasmonate-induced defences on the abundance and performance of natural enemies, as well as the interaction between induced plant responses and parasitism in their ability to kill herbivores. 3 In a tomato field containing plants induced with jasmonic acid and control plants, the abundance of natural enemies was counted using several census techniques. Induced resistance affected the abundance of natural enemies of herbivores differently. One predator of aphids, syrphid flies, was negatively affected by the decrease in herbivore abundance on induced plants. One parasitoid of caterpillars, Hyposoter exiguae Viereck, was not affected by induced resistance in this study although it was positively affected in a previous study. Two other natural enemies, a parasitoid of aphids and ladybeetle predators, were not affected by induced resistance. 4 Induced resistance and parasitism both reduced the survivorship of herbivores. In a 2 × 2 factorial design with induced resistance crossed by parasitism, the interaction between the effects of induced resistance and parasitism on herbivore survival was tested. Two trials of this experiment were conducted; one where induced resistance affected both herbivore quantity and quality and one where induced resistance only affected herbivore quality (herbivore density was equalized). 5 Parasitoids were more effective at killing herbivores feeding on control plants than herbivores on induced plants. This difference was due to a difference in herbivore quality, not herbivore quantity. Herbivores feeding on induced plants have lower mass than herbivores on control plants and this appears to be a major factor reducing the performance of developing parasitic wasps. 6 Thus, jasmonate-induced responses influence natural enemies species in differing ways, sometimes reducing the density of herbivores and sometimes reducing the quality of herbivores for natural enemies.

The jasmonate (JA) and salicylate (SA) signaling pathways in plants provide resistance to herbivorous insects and pathogens. It is known that these pathways interact, sometimes resulting in antagonism between the pathways. We tested how the timing and concentration of elicitation of each pathway influenced the interaction between the jasmonate and salicylate pathways measured in terms of five biochemical responses and biological resistance to caterpillars and bacteria. The salicylate pathway had a stronger effect on the jasmonate pathway than did the reverse. The negative signal interaction was generated by two distinct paths in the plant. A negative interaction in the biochemical expression of the two pathways was most consistent in the simultaneous elicitation experiments compared to when the elicitors were temporally separated by two days. Herbivore bioassays with Spodoptera exigua also consistently reflected an interaction between the two pathways in the simultaneous elicitation experiments. The negative signal interaction reducing biological resistance to the herbivore was also demonstrated in some temporally separated treatment combinations where attenuation of the biochemical response was not evident. Concentration of the elicitors had an effect on the pathway interaction with consistent biochemical and biological antagonism in the high concentration experiments and inconsistent antagonism in the low concentration experiments. The bacterial pathogen, Pseudomonas syringae pv. tomato (Pst), consistently showed reduced lesion development on plants with SA responses activated and, in some experiments, on JA-elicited plants. Resistance to Pst was not reduced or enhanced in dual-elicited plants. Thus, signal interaction is most consistent when elicitors are applied at the same time or when applied at high doses. Signal interaction affected the herbivore S. exigua, but not the pathogen Pst.

Plant quality and predators are important factors affecting herbivore population growth, but how they interact to regulate herbivore populations is not well understood. We manipulated jasmonate-induced plant resistance, exposure to the natural predator community and herbivore density to test how these factors jointly and independently affect herbivore population growth. On low-resistance plants, the predator community was diverse and abundant, promoting high predator consumption rates. On high-resistance plants, the predator community was less diverse and abundant, resulting in low predator consumption rate. Plant resistance only directly regulated aphid population growth on predator-excluded plants. When predators were present, plant resistance indirectly regulated herbivore population growth by changing the impact of predators on the herbivorous prey. A possible mechanism for the interaction between plant resistance and predation is that methyl salicylate, a herbivore-induced plant volatile attractive to predators, was more strongly induced in low-resistance plants. Increased plant resistance reduced predator attractant lures, preventing predators from locating their prey. Low-resistance plants may regulate herbivore populations via predators by providing reliable information on prey availability and increasing the effectiveness of predators.

Herbivores can greatly reduce plant fitness. Error management theory (EMT) predicts the evolution of adaptive plant defensive strategies that err towards making less-costly errors so as to avoid making rare, costly errors. EMT provides a common framework for understanding observed levels of variation in plant defense among and within species.

integration of physiological responses has received less attention. This is the subject of this special issue.Prey physiological responses are important at all stages of the predator–prey interaction. They are a major part of the prey’s primary, fight or flight, response, are mechanis-tic drivers of behavioral and morphological changes, help prepare prey for future attack, and secondarily respond to changes caused by primary responses. We are beginning to understand how, in the initial steps of predator detection, sensory systems, such as visual and olfactory ones, may act synergistically to gather information regarding risk (Kats and Dill 1998; Hartman and Abrahams 2000). Following detection, the physiological status of the prey (Koivula et al. 1995; Martin and Lopez 1999), prey genotype (Den-nis et al. 2010), and personality (Sih et al. 2004) influence whether and how they respond. Physiological responses also aid in defense once the predator initiates attack. For example, tadpoles previously exposed to predator cues have adaptive morphological changes linked to elevated stress hormone levels giving them an advantage in escap-ing predation (Hossie et al. 2010), dragonfly predators select for higher arginine kinase enzyme that powers faster swimming speed and escape performance in damselfly prey (Strobbe et al. 2010), and caterpillars can increase digestive efficiency to compensate for reductions in feeding (Thaler et al. 2012). Finally, parental exposure to predation risk can influence offspring behavior, morphology, and physiol-ogy (Agrawal et al. 1999; Sheriff et al. 20092010, ; Storm and Lima 2010; Zanette et al. 2011) and these effects may lead to adaptive phenotypes dependent upon the match between the maternal and offspring environment (Sheriff and Love 2013). Given that the primary response of prey to the immediate threat of predation is the “stress response” (Sapolsky et al. 2000) and central to this is the activation of the hypothalamic–pituitary–adrenal axis, much work has