Plant Herbivore Research Articles

Nonsensical choices? Fall armyworm moths choose seemingly best or worst hosts for their larvae, but neonate larvae make their own choices.

Selecting optimal host plants is critical for herbivorous insects, such as fall armyworm (Spodoptera frugiperda), an important maize pest in the Americas and Africa. Fall armyworm larvae are presumed to have limited mobility, hence female moths are presumed to be largely responsible for selecting hosts. We addressed host selection by fall armyworm moths and neonate and older (3rd-instar) larvae, as mediated by resistance and herbivory in maize plants. Thus, we compared discrimination among three maize cultivars with varying degrees of resistance to fall armyworm, and between plants subjected or not to two types of herbivory. The cultivars were: (i) susceptible, and deficient in jasmonic acid (JA) production and green leaf volatiles (GLV) emissions (inbred line B73-lox10); (ii) modestly resistant (B73), and; (iii) highly resistant (Mp708). The herbivory types were: (i) ongoing (= fall armyworm larvae present), and; (ii) future (= fall armyworm eggs present). In choice tests, moths laid more eggs on the highly resistant cultivar, and least on the susceptible cultivar, though on those cultivars larvae performed poorest and best, respectively. In the context of herbivory, moths laid more eggs: (i) on plants subject to versus free of future herbivory, regardless of whether plants were deficient or not in JA and GLV production; (ii) on plants subject versus free of ongoing herbivory, and; (iii) on plants not deficient in compared to deficient in JA and GLV production. Neonate larvae dispersed aerially from host plants (i.e. ballooned), and most larvae colonized the modestly resistant cultivar, and fewest the highly resistant cultivar, suggesting quasi-directional, directed aerial descent. Finally, dispersing older larvae did not discriminate among the three maize cultivars, nor between maize plants and (plastic) model maize plants, suggesting random, visually-oriented dispersal. Our results were used to assemble a model of host selection by fall armyworm moths and larvae, including recommendations for future research.

Influence of induced plant volatile and refuge in tritrophic model

Plant-induced volatile plays a significant role in plant–herbivore–carnivore interaction. Attraction rate of volatiles influences the immigration rate of carnivores, and hence, predation pressure on herbivores increases. Herbivores take refuge mechanism to protect themselves from carnivore attacks. Based on such biological phenomena, we have formulated a tritrophic model of plant–herbivore–carnivore along with herbivore refuge. In this article, we have considered two types of herbivore refuge (1) constant proportion refuge and (2) constant number of refuge. We have presented only numerical simulation for constant refuge. The model includes Holling type II functional responses for herbivores and carnivores. Positivity and boundedness of solution of the system, existence of interior equilibrium and its local stability have been shown. Global stability of positive equilibrium has been analyzed by applying higher-dimension Bendixson criteria through second additive compound matrix. Coexistence of all populations for long time has been studied. Here two parameters, attraction factor of plants volatile to carnivore and herbivore refuge, have been considered as sensitive parameters. Hopf bifurcation has occurred with respect to both of them. The stability of limit cycles during Hopf bifurcation has been studied by computing Lyapunov coefficient. Numerical simulations have been performed to justify our obtained results.

Chemical Ecology and Sociality in Aphids: Opportunities and Directions.

Aphids have long been recognized as good phytochemists. They are small sap-feeding plant herbivores with complex life cycles that can involve cyclical parthenogenesis and seasonal host plant alternation, and most are plant specialists. Aphids have distinctive traits for identifying and exploiting their host plants, including the expression of polyphenisms, a form of discrete phenotypic plasticity characteristic of insects, but taken to extreme in aphids. In a relatively small number of species, a social polyphenism occurs, involving sub-adult "soldiers" that are behaviorally or morphologically specialized to defend their nestmates from predators. Soldiers are sterile in many species, constituting a form of eusociality and reproductive division of labor that bears striking resemblances with other social insects. Despite a wealth of knowledge about the chemical ecology of non-social aphids and their phytophagous lifestyles, the molecular and chemoecological mechanisms involved in social polyphenisms in aphids are poorly understood. We provide a brief primer on aspects of aphid life cycles and chemical ecology for the non-specialists, and an overview of the social biology of aphids, with special attention to chemoecological perspectives. We discuss some of our own efforts to characterize how host plant chemistry may shape social traits in aphids. As good phytochemists, social aphids provide a bridge between the study of insect social evolution sociality, and the chemical ecology of plant-insect interactions. Aphids provide many promising opportunities for the study of sociality in insects, and to understand both the convergent and novel traits that characterize complex sociality on plants.

A meta-analysis of the evolution of increased competitive ability hypothesis: genetic-based trait variation and herbivory resistance trade-offs

Non-native organisms are an abundant component of almost all global ecosystems. A prominent framework to explain the success of non-native plants is the evolution of increased competitive ability (EICA) hypothesis. EICA predicts that plants escape from co-evolved herbivores after introduction into a non-native habitat. Assuming limited resources, a relaxation in selection pressures for resistance traits against the co-evolved specialist herbivores allows plants to allocate increased resources to traits related to fitness and/or competitive ability. Despite the prominence of the EICA hypothesis in the literature, empirical evidence has been mixed. We conducted a meta-analysis on 30 studies that focused on genetic-based trait variation and the trade-off between resistance traits and fitness to assess support for the EICA hypothesis. We found general support for EICA across studies. Performance of herbivores was higher on non-native plant populations than on native populations of the same species. Fitness trait values were higher in non-native populations, relative to native, and we found evidence for trade-offs between herbivore performance and plant fitness traits. Support for EICA was strongest when we focused on direct measurements of herbivore performance, and weakest when we assessed resistance traits, highlighting the complex and often unknown relationship between resistance traits and particular herbivores in many plant–herbivore systems.

HPLC-MS detection of pyrrolizidine alkaloids and their N-oxides in herbarium specimens dating back to the 1850s.

Premise of the StudyUnderstanding the phylogenetic distribution of defensive plant secondary metabolites is essential to the macroevolutionary study of chemically mediated plant–animal interactions. The chemical ecology of pyrrolizidine alkaloids (PAs) has been extensively studied in a number of plant–herbivore systems, including Apocynaceae (the milkweed and dogbane family) and Danainae (the milkweed and clearwing butterflies). A systematic survey is necessary to establish a detailed understanding of their occurrence across Apocynaceae. A survey of this species‐rich, mainly tropical and subtropical family will rely heavily on small tissue samples removed from herbarium specimens, some of which will be very old and/or preserved with alcohols or mercuric chloride.MethodsWe optimized PA extraction methods from small leaf fragments of recently collected silica‐dried leaves of the PA‐positive Echites umbellatus, varying crushing and extraction time. We then applied our optimized method to leaf fragments from 70–167‐year‐old herbarium specimens of E. umbellatus. To simulate the effect of alcohol treatment on PA detectability in herbarium specimens, we incubated freshly collected leaves of the PA‐positive Parsonsia alboflavescens in three different alcohols before drying and compared PA recovery to freshly dried controls. PAs were quantified using high‐performance liquid chromatography–mass spectrometry analysis. X‐ray fluorescence was used to identify mercury‐containing specimens.ResultsFifteen seconds of leaf crushing followed by 24 h of extraction were optimal for PA free‐base and N‐oxide recovery. This method yielded ~50‐fold greater PA recovery than prior methods. Half of the herbarium specimens (13 of 23), including the oldest, tested positive for PAs; leaf age did not correlate with success in PA extraction. Treatment of fresh leaves with alcohol before drying did not diminish PA recovery; mercury was observed in both PA‐positive and PA‐negative specimens.Conclusions PAs can be reliably detected in small tissue samples from herbarium specimens up to 167 years old, including specimens that had been treated with alcohol or mercury salts. The variability of PA presence among herbarium specimens of E. umbellatus indicates that multiple specimens will need to be tested before a particular species is determined to lack PAs.

Influence of repeated fertilization on forage production for native mammalian herbivores in young lodgepole pine forests

Abstract Stand thinning and fertilization are silvicultural practices designed to enhance wood and biomass production. Applications of nitrogen-based fertilizers make nutrients potentially available to all trees, plants, and wildlife in a given forest ecosystem, and therefore may affect productivity of forage plants for native mammalian herbivores. Species associated with areas of forest fertilization in temperate and boreal zones of North America include mule deer (Odocoileus hemionus), elk (Cervus elaphus), moose (Alces alces), and woodland caribou (Rangifer tarandus), snowshoe hare (Lepus americanus), and several species of voles. Impacts of fertilization on forest plant species may have important consequences for the nutrition, cover, and consequent survival of these herbivores, particularly in winter. This study tested the hypothesis (H1) that large-scale repeated fertilization, up to 20 years after the onset of treatments, would enhance the biomass production of forage plants, particularly grass, forb, shrub and tree species for native mammalian herbivores. A secondary hypothesis (H2) predicted that mosses and terrestrial lichens would decline as part of the ground vegetation in fertilized stands. Study areas were located in lodgepole pine (Pinus contorta var. latifolia) stands near Summerland, Kelowna, and Williams Lake in south-central British Columbia, Canada. Each study area had eight replicate stands: four unfertilized, and four fertilized five times at 2-year intervals. Mean biomass of total grasses responded dramatically starting in the first year after fertilization. Total forbs and herbs also followed this pattern, although not to a significant degree until after the second and third applications of fertilizer. All of the dominant grasses and forbs serve as summer forage for mule deer, moose, elk, and woodland caribou. Fireweed (Epilobium angustifolium), a preferred forage for mule deer, increased in fertilized stands. Grasses and dominant herbs in fertilized stands provide excellent forage and cover habitat for snowshoe hares and Microtus voles. Mean biomass of total shrubs was not affected by fertilization. However, saskatoon berry (Amelanchier alnifolia), prickly rose (Rosa acicularis), and red raspberry (Rubus idaeus) increased significantly in biomass in fertilized stands. Willow (Salix spp.) also increased in biomass, but was variable across treatment stands. Snowshoe hares respond favourably to enhanced shrub growth for food and cover in fertilized stands. All of these shrubs are readily eaten by deer, moose, and elk, and their structural attributes provide security and thermal cover. Mean biomass of understory Douglas-fir (Pseudotsuga menziesii) responded positively to fertilization, but subalpine fir (Abies lasiocarpa) and the three deciduous tree species did not. Dwarf shrubs such as kinnikinnick (Arctostaphylos uva-ursi), twinflower (Linnaea borealis), and dwarf blueberry (Vaccinium caespitosum) declined in fertilized stands. Thus, H1 was partially supported for some species. Increasing cover of grasses and nitrophilous herbs, and canopy cover from rapidly growing crop trees, in fertilized stands may have contributed to the decline of some dwarf shrubs. Mean crown volume index of total mosses and terrestrial lichens declined significantly in fertilized stands, thereby supporting H2. Mean biomass of total grasses (increase), R. acicularis (increase), and V. caespitosum (decline) were significantly affected after one application of fertilizer. Repeated applications of fertilizer may enhance biomass of some additional forage forbs and shrubs, but reduce biomass of some dwarf shrubs, mosses, and lichens.

Effect of Plant Sex (dioecism) on the Performance ofApocnemidophorus pipitzi(Coleoptera: Curculionidae), A Stem Boring Weevil of Brazilian Peppertree, Schinus Terebinthifolia

Brazilian peppertree, Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae), is an ornamental dioecious shrub introduced from South America that has become one of the major invasive weeds in Florida. Anecdotal evidence from the literature suggests that crushed leaves from female plants produce a more pungent aroma, indicating these plants may be better defended chemically than their male counterparts. To test this hypothesis, we compared the performance (adult feeding and survival) of the South American stem boring weevil Apocnemidophorus piptzi (Faust) (Coleoptera: Curculionidae) by caging insects on foliage collected from both male and female Brazilian peppertree plants. Results showed that weevils consumed significantly less leaf tissue from female plants compared to male plants. Furthermore, the LT50 (average time required to cause 50% mortality of the weevils) was significantly shorter when weevils fed exclusively on female leaf tissue. Our findings confirmed male-biased plant herbivory on Brazilian peppertree by one of its folivorous natural enemies.

Understanding plant–arthropod interactions in multitrophic communities to improve conservation biological control: useful traits and metrics

The role of biodiversity in the delivery of ecosystem services is increasingly being studied by trait-based functional approaches. Here, we review and discuss the contribution of a trait-based approach to understanding plant–arthropod interactions and improving conservation biological control. The stable biological control of multispecies herbivore communities requires functional diversity and a redundancy of natural enemies, including specialists and generalists, with minimal antagonistic interactions. The management of arthropod communities through plant community requires the plant community to perform several functions, including the provision of diversified trophic resources and appropriate physical habitats. Many studies have investigated the ability of plants to provide these functions, but many of the results obtained were limited to single species. The description of communities in terms of traits underlying trophic and non-trophic interactions between plants and animals would make it possible to extrapolate findings to other species. Studies on plant–herbivore and plant–pollinator interactions have identified several traits as important for trophic resource provision, in terms of resource quantity, accessibility, quality and temporal availability. By contrast, traits relating to physical habitat provision and microclimate modification have been little explored. Several metrics describing the functional composition and diversity of communities have been proposed, to extend the trait-based approach to plant community level, but the extent to which multitrophic communities are affected by plant traits remains largely unexplored. The next step will be to identify the combinations of these plant community metrics best explaining their impact on arthropod communities and disentangling the roles of plant functional composition and diversity.

Identificación de un gen codificante de polifenol oxidasa (PPO) en Theobroma cacao L. (cacao) de Ecuador

En Ecuador, las plantaciones de cacao presentan bajos promedios de producción debido a la diversidad de patógenos, especialmente a la infección por Moniliophthora roreri (monilia). Se cree que existe una relación entre el ataque del hongo y el aumento de los niveles de expresión de genes codificantes de polifenol oxidasas (PPOs) como mecanismo de defensa ante patógenos y herbívoros en diferentes plantas. Para la identificación de genes que codifican para PPOs, se seleccionaron hojas de cacao Nacional, provenientes de plantas resistentes y susceptibles a monilia, ubicadas en la Finca Experimental La Represa, propiedad de la Universidad Técnica Estatal de Quevedo. Se afinó un protocolo de extracción de ARN total de alta calidad para hojas de cacao recalcitrantes. Después de su retrotranscripción a ADNc, se realizaron ensayos de amplificación por PCR con diferentes primers, diseñados a partir de secuencias conservadas de PPOs. Los productos de amplificación permitieron la identificación de un gen de 961 pb, similar a un gen que codifica para la PPO predictiva de Theobroma cacao depositada en NCBI (XP_017978715.1) La identificación de este gen, es fundamental para evaluar a futuro los niveles de expresión y cuantificación en diferentes estados de desarrollo del fruto. Dicha cuantificación permitirá proponer herramientas de control para monilia y construir las bases para el mejoramiento genético del cacao Nacional.

Community structure of grassland ground-dwelling arthropods along increasing soil salinities.

Ground-dwelling arthropod communities are influenced by numerous biotic and abiotic factors. Little is known, however, about the relative importance of vegetation structure and abiotic environmental factors on the patterns of ground-dwelling arthropod community across a wide range of soil salinities. Here, a field survey was conducted to assess the driving forces controlling ground-dwelling arthropod community in the salinized grasslands in the Hexi Corridor, Gansu Province, China. The data were analyzed by variance partitioning with canonical correspondence analysis (CCA). We found that vegetation structure and edaphic factors were at least of similar importance to the pattern of the whole ground-dwelling arthropod community. However, when all collected ground-dwelling arthropods were categorized into three trophic guilds (predators, herbivores, and decomposers), as these groups use different food sources, their populations were controlled by different driving forces. Predators and decomposers were mainly determined by biotic factors such as vegetation cover and aboveground plant biomass and herbivores by plant density and vegetation cover. Abiotic factors were also major determinants for the variation occurring in these guilds, with predators strongly affected by soil electrical conductivity (EC) and the content of fine particles (silt + clay, CS), herbivores by soil N:P, EC, and CS, and decomposers by soil EC and organic matter content (SOM). Since plant cover, density, and aboveground biomass can indicate resource availability, which are mainly constrained by soil N:P, EC, CS, and SOM, we consider that the ground-dwelling arthropod community in the salinized grasslands was mainly influenced by resource availability.

Novel use of aliphatic n-methyl ketones as a fumigant and alternative to methyl bromide for insect control.

Fumigants like phosphine, methyl bromide and sulfuryl fluoride are highly effective for the control of structural, storage and agricultural arthropod pests. Unfortunately, many of these synthetic compounds are highly toxic to people, many pests have developed resistance to these compounds and methyl bromide, the 'gold standard' for fumigants, was de-registered because of its contribution to depletion of the stratospheric ozone layer. Alternative fumigant chemistry is needed. Several plant species produce n-aliphatic methyl ketones to prevent plant herbivory. To examine the use of methyl ketones as a fumigant, structure-mortality studies were conducted using the red imported fire ant, Solenopsis invicta Buren, as a model. A new easy-to-use, inexpensive and disposable bioassay system was developed for this study. The LC50 values for heptanone, octanone, nonanone and undecanone were 4.27, 5.11, 5.26 and 8.21 µg/cm3 of ambient air, respectively. Although heptanone, octanone and nonanone were more effective than undecanone, subsequent research was conducted with 2-undecanone because this compound already has US Environmental Protection Agency (EPA) registration as a biopesticide. In dose-response field studies, 12.4 mL of undecanone injected into mounds was the lowest application rate that produced no ant activity in the mound with no re-establishment of ants. Reagent grade undecanone was more cost-effective than methyl bromide for fire ants, adult German cockroaches and tobacco budworm eggs, but slightly more expensive for adult flour beetles. The naturally occurring methyl ketone undecanone has the potential to be an alternative to current fumigants for a variety of pest applications. © 2017 Society of Chemical Industry.

Induction and relaxation of extrafloral nectaries in response to simulated herbivory in young Mallotus japonicus plants.

The disadvantage of induced defenses compared with constitutive defenses is the time during which a plant is vulnerable to herbivory before activation. There is obvious importance in determining the costs and benefits of induced defenses. Some plants produce extrafloral nectaries (EFNs), which attract ants that protect against herbivores, and induce EFNs and extrafloral nectar in response to leaf damage. To understand induction of indirect defense by ants, we investigated the induction and relaxation of extrafloral nectar secretion and EFN formation after artificial leaf damage in young Mallotus japonicus. Plants were grown under control or leaf damage conditions a greenhouse or in the field. Following artificial leaf damage, we assessed secretion of extrafloral nectar and the number of ant workers on plants. We measured the number of EFNs on each of seven leaves produced after leaf damage. Extrafloral nectar secretion was induced within 1day following leaf damage, resulting in the attraction of numerous ant workers, and the extrafloral nectar secretion decreased to initial levels after 7 days. The number of EFNs was largest on the first leaf and smallest on the sixth leaf produced after leaf damage, but the total number of EFNs did not differ between treatments. Thus, M. japonicus rapidly induces extrafloral nectar secretion after leaf damage, followed by relaxation. Furthermore, following induction of EFNs on newly produced leaves, it may decrease the cost of induction by reducing the number of EFNs on leaves produced later.

Plant–herbivore–parasitoid interactions in an experimental freshwater tritrophic system: higher trophic levels modify competitive interactions between invasive macrophytes

Natural enemies are known to modify competitive hierarchies among terrestrial plants. Here we examine whether the same applies to freshwater systems. Lagarosiphon major (Hydrocharitaceae) is a submerged aquatic macrophyte, indigenous to South Africa. Outside its native range, it outcompetes with indigenous submerged species and degrades aquatic habitats. Hydrellia lagarosiphon (Diptera: Ephydridae) is the most abundant and ubiquitous herbivore associated with L. major in South Africa and is a potential biological control agent elsewhere. Chaenusa anervata (Hymenoptera: Braconidae: Alysiinae) is its main parasitoid. We generated an experimental system involving one, two or three trophic levels to monitor variation in the competitive ability of L. major relative to that of Myriophyllum spicatum (Haloragaceae), a second submerged macrophyte that can also be invasive. Using inverse linear models to monitor competition, we found that herbivory by H. lagarosiphon greatly reduced the competitive ability of L. major. Addition of the wasp at typical field densities halved the impact of herbivory and re-established the competitive advantage of L. major. Our results demonstrate how multitrophic interactions modify relative competitive abilities among aquatic plants, emphasize the significance of higher tropic levels in these systems and illustrate how parasitoids can reduce the effectiveness of insects released as biocontrol agents.

Belowground Plant-Herbivore Interactions Vary among Climate-Driven Range-Expanding Plant Species with Different Degrees of Novel Chemistry.

An increasing number of studies report plant range expansions to higher latitudes and altitudes in response to global warming. However, consequences for interactions with other species in the novel ranges are poorly understood. Here, we examine how range-expanding plant species interact with root-feeding nematodes from the new range. Root-feeding nematodes are ubiquitous belowground herbivores that may impact the structure and composition of natural vegetation. Because of their ecological novelty, we hypothesized that range-expanding plant species will be less suitable hosts for root-feeding nematodes than native congeneric plant species. In greenhouse and lab trials we compared nematode preference and performance of two root-feeding nematode species between range-expanding plant species and their congeneric natives. In order to understand differences in nematode preferences, we compared root volatile profiles of all range-expanders and congeneric natives. Nematode preferences and performances differed substantially among the pairs of range-expanders and natives. The range-expander that had the most unique volatile profile compared to its related native was unattractive and a poor host for nematodes. Other range-expanding plant species that differed less in root chemistry from native congeners, also differed less in nematode attraction and performance. We conclude that the three climate-driven range-expanding plant species studied varied considerably in their chemical novelty compared to their congeneric natives, and therefore affected native root-feeding nematodes in species-specific ways. Our data suggest that through variation in chemical novelty, range-expanding plant species may vary in their impacts on belowground herbivores in the new range.

Induction of Systemic Resistance against Insect Herbivores in Plants by Beneficial Soil Microbes.

Soil microorganisms with growth-promoting activities in plants, including rhizobacteria and rhizofungi, can improve plant health in a variety of different ways. These beneficial microbes may confer broad-spectrum resistance to insect herbivores. Here, we provide evidence that beneficial microbes modulate plant defenses against insect herbivores. Beneficial soil microorganisms can regulate hormone signaling including the jasmonic acid, ethylene and salicylic acid pathways, thereby leading to gene expression, biosynthesis of secondary metabolites, plant defensive proteins and different enzymes and volatile compounds, that may induce defenses against leaf-chewing as well as phloem-feeding insects. In this review, we discuss how beneficial microbes trigger induced systemic resistance against insects by promoting plant growth and highlight changes in plant molecular mechanisms and biochemical profiles.

Impacts of plant diversity on arthropod communities and plant–herbivore network architecture

AbstractAt the local scale, insect herbivore diversity is often limited by plant diversity, but little is known about how the network structure of plant and herbivore interactions changes across local plant diversity gradients. Ascertaining plant–herbivore interaction structure at the ecological community level is important for predicting responses of herbivores to plant species loss. We sampled arthropods and plants across three years, beginning in the fourth year of an experimental prairie restoration containing three treatment levels of sown plant diversity. Plots initially planted with higher plant diversity had higher arthropod species richness. Sown diversity treatments strongly affected plant–herbivore interaction structure: The increased sown diversity treatment decreased plant–herbivore connectance, increased average herbivore diet generalism, and increased herbivore robustness to plant species loss. Treatments diverged over time with the last year of sampling showing the greatest difference between treatments in plant and arthropod species richness, and plant–herbivore network structural properties. Network structural properties of the high sown diversity treatment were the least variable temporally. However, divergence of plant and arthropod between diversity treatments was not found in traditional ordinations of community taxonomic composition. While previous comparisons of plant–herbivore interaction networks across ecological gradients treated network size (biodiversity) as a confounding factor, we demonstrate that plant diversity can directly shape network structure, and higher plant diversity maintains less temporally variable ecological networks of herbivores and their host plants.

Plant-Herbivore and Plant-Pollinator Interactions of the Developing Perennial Oilseed Crop, Silphium integrifolium.

Sampling in Kansas and North Dakota documented the plant-herbivore and plant-pollinator interactions of the developing perennial oilseed crop, Silphium integrifolium Michx. The larva of the tortricid moth, Eucosma giganteana (Riley), was the most damaging floret- and seed-feeding pest in Kansas, with infested heads producing ≈85% (2015) or ≈45% (2016) fewer seeds than apparently undamaged heads. Necrosis of apical meristems caused stunting and delayed bloom in Kansas; though the source of the necrosis is not known, observations of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois; Hemiptera: Miridae), in S. integrifolium terminals suggest a possible cause. In North Dakota, E. giganteana larvae were not found, but pupae of Neotephritis finalis (Loew; Diptera: Tephritidae), a minor pest of cultivated sunflower, were common in the heads of S. integrifolium. Bees appeared highly attracted to S. integrifolium, and in all but one observation, bees were seen actively collecting pollen. The most common bees included large apids (Apis mellifera L., Svastra obliqua [Say], Melissodes spp.) and small-bodied halictids (Lasioglossum [Dialictus] spp.). Controlled pollination experiments demonstrated that S. integrifolium is pollinator dependent, due to both mechanical barriers (imperfect florets and protogyny) and genetic self-incompatibility. Subsequent greenhouse tests and AFLP confirmation of putative self-progeny show that a low (<1%) level of self-pollination is possible. If genetic self-incompatibility is eventually reduced through breeding, mechanical barriers would maintain a reliance on bees to move pollen between male and female florets. Collectively, observations on S. integrifolium show that both herbivore and pollinator management are important to maximize seed production.

Plant species, mycorrhiza, and aphid age influence the performance and behaviour of a generalist

1. Life‐history traits of herbivores are shaped by the combination of various extrinsic and intrinsic variables. However, studies investigating the impact of both variables on insect behavioural phenotypes are rare, and research including the modulation of host plant quality by arbuscular mycorrhiza (AM) (extrinsic variable) and the herbivore developmental stage (intrinsic variable) on aphid behaviour is lacking.2. To study the influences of extrinsic and intrinsic variables on aphid performance and behaviour, individuals of the generalist aphid pest Myzus persicae (Sulzer) were reared on Plantago lanceolata and Poa annua plants that were either non‐mycorrhized (NM) or mycorrhized (AM). Aphid performance was monitored over 2 weeks. Behavioural traits of nymphs were recorded twice during development after removing individuals from their feeding sites and placing them in an unknown environment (‘open field’), causing disturbance. Plant quality was determined by measuring the water content and leaf mass per area (LMA).3. Differences in body mass of nymphs at day 6 dependent on plant species and treatment were compensated by the individuals within 4 days. Behavioural traits, considered as activity and exploration, were affected by the interaction between extrinsic and intrinsic variables (activity and exploration) and changed over ontogeny (activity). Independent of AM, a lower water content and LMA were recorded in P. annua leaves.4. Overall, this study demonstrates that extrinsic and intrinsic variables need to be considered in combination and behavioural traits should be studied repeatedly during insect ontogeny to understand the complexity of microbe‐modulated plant–herbivore interactions.

Silencing OsSLR1 enhances the resistance of rice to the brown planthopper Nilaparvata lugens.

DELLA proteins, negative regulators of the gibberellin (GA) pathway, play important roles in plant growth, development and pathogen resistance by regulating multiple phytohormone signals. Yet, whether and how they regulate plant herbivore resistance remain unknown. We found that the expression of the rice DELLA gene OsSLR1 was down-regulated by an infestation of female adults of the brown planthopper (BPH) Nilaparvata lugens. On one hand, OsSLR1 positively regulated BPH-induced levels of two mitogen-activated protein kinase and four WRKY transcripts, and of jasmonic acid, ethylene and H2 O2 . On the other hand, silencing OsSLR1 enhanced constitutive levels of defence-related compounds, phenolic acids, lignin and cellulose, as well as the resistance of rice to BPH in the laboratory and in the field. The increased resistance in rice with silencing of OsSLR1 is probably due to impaired JA and ethylene pathways, and, at least in part, to the increased lignin level and mechanical hardness of rice leaf sheaths. Our findings illustrate that OsSLR1, acting as an early negative regulator, plays an important role in regulating the resistance of rice to BPH by activating appropriate defence-related signalling pathways and compounds. Moreover, our data also provide new insights into relationships between plant growth and defence.

The confounding effects of logging on tree seedling growth and herbivory in Central Amazon

AbstractLight availability is an important modulator of seedling growth and plant–herbivore dynamics. Logging increases light levels in forests, potentially altering herbivore–plant interactions that drive seedling establishment. We conducted a transplant experiment to evaluate how logging and herbivory affect seedling growth and survival in three shade‐tolerant tree species, at paired canopy gap and understory sites in logged forest and an adjacent unlogged area in central Amazonia (Brazil). Seedlings were either left exposed to naturally occurring insect herbivores or protected from insects by a fine netting structure. We measured the herbivore damage and growth rate of seedlings after 18 mo. In general, logged areas received more light than unlogged sites. Growth and herbivory rates were positively influenced by light, and herbivory was also influenced positively by logging. In gaps, increased growth mitigated foliar damage. Logging resulted in a loss of foliar tissue due to increased herbivory. Herbivory rates were higher in the understory of logged sites than in that of unlogged understory sites, but growth was similar in these areas. Thus, the understory of logged areas provided the least favorable sites for shade‐tolerant tree regeneration, due to higher herbivory rates. The effect of logging on biotic interactions can extend beyond the gaps it creates into untouched understory sites. To our knowledge, this is the first time such a pattern has been observed, highlighting the importance of evaluating the impact of logging on biotic interactions.