Below‐ground nematode herbivory of resistant soybean cultivars impairs the performances of an above‐ground caterpillar and its parasitoid

1. Interactions between below‐ and above‐ground organisms have attracted interest in recent years, but less is known about the effect of root‐feeding nematodes on above‐ground trophic interactions between herbivores and their natural enemies. 2. This study examined whether the presence of the soybean cyst root nematode Heterodera glycines influences the performance of the above‐ground leaf‐chewing tobacco cutworm Spodoptera litura on soybeans, Glycine max, and whether this in turn affects the success of its parasitoid, Meteorus pulchricornis. Using three soybean cultivars that varied in the level of constitutive resistance to the tobacco cutworm, the study determined whether feeding by the nematode altered the developmental and reproductive performances of the caterpillar and its parasitoid. 3. Root feeding by the nematode slowed tobacco cutworm larval development time and reduced adult body weight. Root feeding by the nematode also had a negative effect on the caterpillar's parasitoid, by prolonging development time, decreasing adult body size and reducing fecundity. These effects increased in a linear trend and varied in magnitude depending on levels of soybean constitutive resistance. 4. These findings demonstrate that root feeding by the nematode can prime soybean plants with negative impacts on their herbivore and its parasitoid, and that the impact may vary in magnitude depending on levels of soybean constitutive defence. The results emphasise the need to integrate soybean constitutive and root nematode‐induced defences for a better understanding of below‐ and above‐ground organism interactions, and to allow insights to be gained into the improvement of soybean integrated pest management programmes.     

Quantification of root water uptake in soil using X‐ray computed tomography and image‐based modelling

Spatially averaged models of root–soil interactions are often used to calculate plant water uptake. Using a combination of X‐ray computed tomography (CT) and image‐based modelling, we tested the accuracy of this spatial averaging by directly calculating plant water uptake for young wheat plants in two soil types. The root system was imaged using X‐ray CT at 2, 4, 6, 8 and 12 d after transplanting. The roots were segmented using semi‐automated root tracking for speed and reproducibility. The segmented geometries were converted to a mesh suitable for the numerical solution of Richards' equation. Richards' equation was parameterized using existing pore scale studies of soil hydraulic properties in the rhizosphere of wheat plants. Image‐based modelling allows the spatial distribution of water around the root to be visualized and the fluxes into the root to be calculated. By comparing the results obtained through image‐based modelling to spatially averaged models, the impact of root architecture and geometry in water uptake was quantified. We observed that the spatially averaged models performed well in comparison to the image‐based models with <2% difference in uptake. However, the spatial averaging loses important information regarding the spatial distribution of water near the root system.     

Influence of presence and spatial arrangement of belowground insects on host‐plant selection of aboveground insects: a field study

Abstract 1. Several studies have shown that above‐ and belowground insects can interact by influencing each others growth, development, and survival when they feed on the same host‐plant. In natural systems, however, insects can make choices on which plants to oviposit and feed. A field experiment was carried out to determine if root‐feeding insects can influence feeding and oviposition preferences and decisions of naturally colonising foliar‐feeding insects. 2. Using the wild cruciferous plant Brassica nigra and larvae of the cabbage root fly Delia radicum as the belowground root‐feeding insect, naturally colonising populations of foliar‐feeding insects were monitored over the course of a summer season. 3. Groups of root‐infested and root‐uninfested B. nigra plants were placed in a meadow during June, July, and August of 2006 for periods of 3 days. The root‐infested and the root‐uninfested plants were either dispersed evenly or placed in clusters. Once daily, all leaves of each plant were carefully inspected and insects were removed and collected for identification. 4. The flea beetles Phyllotreta spp. and the aphid Brevicoryne brassicae were significantly more abundant on root‐uninfested (control) than on root‐infested plants. However, for B. brassicae this was only apparent when the plants were placed in clusters. Host‐plant selection by the generalist aphid M. persicae and oviposition preference by the specialist butterfly P. rapae, however, were not significantly influenced by root herbivory. 5. The results of this study show that the presence of root‐feeding insects can affect feeding and oviposition preferences of foliar‐feeding insects, even under natural conditions where many other interactions occur simultaneously. The results suggest that root‐feeding insects play a role in the structuring of aboveground communities of insects, but these effects depend on the insect species as well as on the spatial distribution of the root‐feeding insects.     

Root damage to apple plants by cockchafer larvae induces a change in volatile signals below‐ and above‐ground

Volatile organic compounds (VOCs) mediate communication between plants and insects. Plants under insect herbivore attack release VOCs either at the site of attack or systemically, indicating within‐plant communication. Some of these VOCs, which may be induced only upon herbivore attack, recruit parasitoids and predatory insects to feed on the attacking insects. Moreover, some plants are able to ‘eavesdrop’ on herbivore‐induced plant volatiles (HIPVs) to prime themselves against impending attack; such eavesdropping exemplifies plant–plant communication. In apple orchards, the beetle Melolontha melolontha L. (Coleoptera: Scarabaeidae) is an important insect pest whose larvae live and feed on roots for about 4 years. In this study, we investigated whether the feeding activity of M. melolontha larvae (1) alters the volatile profile of apple roots, (2) induces the release of HIPVs systemically in the leaves, and (3) whether infested plants communicate to neighbouring non‐infested conspecifics through HIPVs. To answer these questions, we collected constitutive VOCs from intact M9 roots as well as M. melolontha larvae‐damaged roots using a newly designed ‘rhizobox’, to collect root‐released volatiles in situ, without damaging the plant root system. We also collected VOCs from the leaf‐bearing shoots of M9 whose roots were under attack by M. melolontha larvae and from shoots of neighbouring non‐infested conspecifics. Gas chromatography‐mass spectrometry analysis showed that feeding activity of M. melolontha larvae induces the release of specific HIPVs; for instance, camphor was found in the roots only after larvae caused root damage. Melolontha melolontha also induced the systemic release of methyl salicylate and (E,E)‐α‐farnesene from the leaf‐bearing shoots. Methyl salicylate and (E,E)‐α‐farnesene were also released by the shoots of non‐infested neighbouring conspecifics. These phenomena indicate the induction of specific VOCs below‐ and above‐ground upon M. melolontha larvae feeding on apple roots as well as plant–plant communication in apple plants.     

Interaction between Sitona lepidus and red clover lines selected for formononetin content

Adult clover root weevil Sitona lepidus show a feeding preference for white clover Trifolium repens over red clover Trifolium pratense. The effects on S. lepidus of three red clover T. pratense lines, selected for high, medium, or low levels of the isoflavone formononetin in foliage, were compared in three experiments using white clover as a control. In a no‐choice slant board experiment, weevil larval weights were greater for larvae feeding on white clover roots than those feeding on roots of the red clovers. The effect of larval root herbivory on plant growth was similar for all four clovers. Following root herbivory, a large increase in root and shoot formononetin levels was observed in the high‐formononetin selection of red clover but little change in the low‐formononetin red clover. In a no‐choice experiment with sexually mature female adult weevils feeding on foliage of the four clovers, all the red clovers had increased weevil mortality. Female weevils eating the high‐formononetin red clover laid fewer eggs than weevils eating white clover. The red clover diet caused a large accumulation of abdominal fat and/or oil in the weevils, whereas weevils feeding on white clover did not accumulate fat/oil. When sexually immature adult weevils were given a choice of foliage from all four clovers, white clover was eaten preferentially, and the low‐formononetin red clover was preferred to the high‐formononetin red clover. The results suggest that formononetin and associated metabolites in red clover may act as chemical defences against adult S. lepidus and that distribution in forage legumes can be manipulated by plant breeding to improve root health.     

Quantifying the impact of above‐ and belowground higher trophic levels on plant and herbivore performance by modeling1

Growing empirical evidence suggests that aboveground and belowground multitrophic communities interact. However, investigations that comprehensively explore the impacts of above‐ and belowground third and higher trophic level organisms on plant and herbivore performance are thus far lacking. We tested the hypotheses that above‐ and belowground higher trophic level organisms as well as decomposers affect plant and herbivore performance and that these effects cross the soil–surface boundary. We used a well‐validated simulation model that is individual‐based for aboveground trophic levels such as shoot herbivores, parasitoids, and hyperparasitoids while considering belowground herbivores and their antagonists at the population level. We simulated greenhouse experiments by removing trophic levels and decomposers from the simulations in a factorial design. Decomposers and above‐ and belowground third trophic levels affected plant and herbivore mortality, root biomass, and to a lesser extent shoot biomass. We also tested the effect of gradual modifications of the interactions between different trophic level organisms with a sensitivity analysis. Shoot and root biomass were highly sensitive to the impact of the fourth trophic level. We found effects that cross the soil surface, such as aboveground herbivores and parasitoids affecting root biomass and belowground herbivores influencing aboveground herbivore mortality. We conclude that higher trophic level organisms and decomposers can strongly influence plant and herbivore performance. We propose that our modelling framework can be used in future applications to quantitatively explore the possible outcomes of complex above‐ and belowground multitrophic interactions under a range of environmental conditions and species compositions.     

Differential recovery of above‐ and below‐ground rich fen vegetation following fertilization

Abstract. For seven years we studied the recovery of vegetation in a Belgian P limited rich fen (Caricion davallianae), which had been fertilized with nitrogen (200 g.m^?2) and phosphorus (50 g.m^?2) in 1992. The vegetation in this fen has low above‐ground biomass production (< 100 g m^?2) due to the strong P limitation. Above‐ground biomass was harvested from 1992 to 1998 and P and N concentrations measured. In 1998, below‐ground biomass was also harvested. The response to fertilization differed markedly between below‐ and above‐ground compartments. Above‐ground, P was the single most important factor that continued to stimulate growth 7 yr after fertilization. Below‐ground, N tended to decrease live root biomass and increase dead root biomass and seemed to have a toxic effect on the roots. In the combined NP treatment the stimulating effect of P (an increase of live root biomass) was countered by N. The 1998 soil analysis showed no difference in soil P in the plots. Thus, Fe hydroxides are not capable of retaining P in competition with fen vegetation uptake. However, higher capture of P in root Fe coatings from N plots may partially explain this negative N effect. The results suggest that N root toxicity will be amplified in strongly P limited habitats but that its persistence will be less influenced by P availability. This mechanism may be a competitive advantage for N₂ fixing species that grow in strongly P limited wetlands.     

Use of herbivore‐induced plant volatiles as search cues by Tiphia vernalis and Tiphia popilliavora to locate their below‐ground scarabaeid hosts

Japanese beetle, Popillia japonica Newman, and oriental beetle, Anomala orientalis (Waterhouse) (both Coleoptera: Scarabaeidae) are considered invasive species and have been reported as key pests of urban landscapes in the Northeastern USA. Tiphia vernalis Rohwer and Tiphia popilliavora Rohwer (Hymenoptera: Tiphiidae) were introduced as biocontrol agents against these beetles. These parasitic wasps burrow into the soil and search for grubs. When a host is found, the wasp attaches an egg in a location that is specific for the wasp species. It is unknown if these wasps can detect patches of concealed hosts from a distance above ground and what role, if any, herbivore‐induced plant volatiles play in their host location. This study evaluated the responses of female T. vernalis and T. popilliavora to grub‐infested and healthy plants in Y‐tube olfactometer bioassays. Also the effect of root herbivory on the composition of turfgrass (Poaceae) volatile profiles was investigated by collecting volatiles from healthy and grub‐infested grasses. Tiphia wasps were highly attracted to volatiles emitted by grub‐infested tall fescue (Festuca arundinacea Schreb.) and Kentucky bluegrass (Poa pratensis L.) over healthy grasses. In contrast, wasps did not exhibit a significant preference for grub‐infested perennial ryegrass (Lolium perenne L.) as compared with the control plants. The terpene levels emitted by grub‐infested Kentucky bluegrass and tall fescue were greater than that of control plants. Low levels of terpenes were observed for both test and control perennial ryegrass. The elevated levels of terpenes emitted by grub‐infested Kentucky bluegrass and tall fescue coincided with the attractiveness to the tiphiid wasps. Here, we provide evidence that plant exposure to root‐feeding insects P. japonica and A. orientalis resulted in an increase in terpenoid levels in turfgrasses, which strongly attracts their above‐ground parasitoids.     

Fine‐tuning of defences and counter‐defences in a specialised plant–herbivore system

1. The plant–herbivore arms race has been postulated to be a major driver for generating biological and biochemical diversity on Earth. Herbivore feeding is reduced by the production of chemical and physical barriers, but increases plant resistance against subsequent attack. Accordingly, specialisation is predicted to be an outcome of herbivores being able to circumvent plant‐induced defences. 2. Using a specialised plant–herbivore system, in which adult chrysomelid beetles (Chrysochus auratus) feed on leaves and larvae feed on roots of dogbane (Apocynum spp.), this study investigated whether root latex and cardenolides are effective against the soil‐dwelling larvae, and whether such defences could be circumvented by the herbivore. 3. Across two Apocynum species, C. auratus larvae were not affected by latex production or cardenolide amounts and diversity. By contrast, cardenolide apolarity was detrimental to larval growth. Yet larval feeding decreased average root cardenolide apolarity in A. cannabinum and larvae performed better on those plants. Finally, above‐ground induction rendered the plants more toxic by increasing root cardenolide apolarity and maintaining it, even during subsequent larval herbivory. 4. Therefore, the intimate relationship and interaction between Chrysochus and Apocynum are maintained by a delicate balance of herbivore manipulation and plant chemical induction.     

Factors influencing above‐ground and soil seed bank vegetation diversity at different scales in a quasi‐Mediterranean ecosystem

Questions

Are factors influencing plant diversity in a fire‐prone Mediterranean ecosystem of southeast Australia scale‐dependent?

Location

Heathy woodland, Otways region, Victoria, southeast Australia

Methods

We measured patterns of above‐ground and soil seed bank vegetation diversity and associated them with climatic, biotic, edaphic, topographic, spatial and disturbance factors at multiple scales (macro to micro) using linear mixed effect and generalized dissimilarity modelling.

Results

At the macro‐scale, we found species richness above‐ground best described by climatic factors and in the soil seed bank by disturbance factors. At the micro‐scale we found species richness best described above‐ground and in the soil seed bank by disturbance factors, in particular time‐since‐last‐fire. We found variance in macro‐scale β‐diversity (species turnover) best explained above‐ground by climatic and disturbance factors and in the soil seed bank by climatic and biotic factors.

Conclusions

Regional climatic gradients interact with edaphic factors and fire disturbance history at small spatial scales to influence species richness and turnover in the studied ecosystem. Current fire management regimes need to incorporate key climatic–disturbance–diversity interactions to maintain floristic diversity in the studied system.

     

Roles of dominant understory Sasa bamboo in carbon and nitrogen dynamics following canopy tree removal in a cool‐temperate forest in northern Japan

To clarify the role of dense understory vegetation in the stand structure, and in carbon (C) and nitrogen (N) dynamics of forest ecosystems with various conditions of overstory trees, we: (i) quantified the above‐ and below‐ground biomasses of understory dwarf bamboo (Sasa senanensis) at the old canopy‐gap area and the closed‐canopy area and compared the stand‐level biomasses of S. senanensis with that of overstory trees; (ii) determined the N leaching, soil respiration rates, fine‐root dynamics, plant area index (PAI) of S. senanensis, and soil temperature and moisture at the tree‐cut patches (cut) and the intact closed‐canopy patches (control). The biomass of S. senanensis in the canopy‐gap area was twice that at the closed‐canopy area. It equated to 12% of total biomass above ground but 41% below ground in the stand. The concentrations of NO₃^? and NH₄⁺ in the soil solution and soil respiration rates did not significantly change between cut and control plots, indicating that gap creation did not affect the C or N dynamics in the soil. Root‐length density and PAI of S. senanensis were significantly greater at the cut plots, suggesting the promotion of S. senanensis growth following tree cutting. The levels of soil temperature and soil moisture were not changed following tree cutting. These results show that S. senanensis is a key component species in this cool‐temperate forest ecosystem and plays significant roles in mitigating the loss of N and C from the soil following tree cutting by increasing its leaf and root biomass and stabilizing the soil environment.     

Plant diversity and identity effects on predatory nematodes and their prey

There is considerable evidence that both plant diversity and plant identity can influence the level of predation and predator abundance aboveground. However, how the level of predation in the soil and the abundance of predatory soil fauna are related to plant diversity and identity remains largely unknown. In a biodiversity field experiment, we examined the effects of plant diversity and identity on the infectivity of entomopathogenic nematodes (EPNs, Heterorhabditis and Steinernema spp.), which prey on soil arthropods, and abundance of carnivorous non‐EPNs, which are predators of other nematode groups. To obtain a comprehensive view of the potential prey/food availability, we also quantified the abundance of soil insects and nonpredatory nematodes and the root biomass in the experimental plots. We used structural equation modeling (SEM) to investigate possible pathways by which plant diversity and identity may affect EPN infectivity and the abundance of carnivorous non‐EPNs. Heterorhabditis spp. infectivity and the abundance of carnivorous non‐EPNs were not directly related to plant diversity or the proportion of legumes, grasses and forbs in the plant community. However, Steinernema spp. infectivity was higher in monocultures of Festuca rubra and Trifolium pratense than in monocultures of the other six plant species. SEM revealed that legumes positively affected Steinernema infectivity, whereas plant diversity indirectly affected the infectivity of Heterorhabditis EPNs via effects on the abundance of soil insects. The abundance of prey (soil insects and root‐feeding, bacterivorous, and fungivorous nematodes) increased with higher plant diversity. The abundance of prey nematodes was also positively affected by legumes. These plant community effects could not be explained by changes in root biomass. Our results show that plant diversity and identity effects on belowground biota (particularly soil nematode community) can differ between organisms that belong to the same feeding guild and that generalizations about plant diversity effects on soil organisms should be made with great caution.     

Field evidence for indirect interactions between foliar‐feeding insect and root‐feeding nematode communities on Nicotiana tabacum

Abstract 1. As herbivory often elicits systemic changes in plant traits, indirect interactions via induced plant responses may be a pervasive feature structuring herbivore communities. Although the importance of this phenomenon has been emphasised for herbivorous insects, it is unknown if and how induced responses contribute to the organisation of other major phytoparasitic taxa. 2. Survey and experimental field studies were used to investigate the role of plants in linking the dynamics of foliar‐feeding insects and root‐feeding nematodes on tobacco, Nicotiana tabacum. 3. Plant‐mediated interactions between insects and nematodes could largely be differentiated by insect feeding guild, with positive insect–nematode interactions predominating with leaf‐chewing insects (caterpillars) and negative interactions occurring with sap‐feeding insects (aphids). For example, insect defoliation was positively correlated with the abundance of root‐feeding nematodes, but aphids and nematodes were negatively correlated. Experimental field manipulations of foliar insect and nematode root herbivory also tended to support this outcome. 4. Overall, these results suggest that plants indirectly link the dynamics of divergent consumer taxa in spatially distinct ecosystems. This lends support to the growing perception that plants play a critical role in propagating indirect effects among a diverse assemblage of consumers.     

Intraspecific plant–soil feedback and intraspecific overyielding in Arabidopsis thaliana

Understanding the mechanisms of community coexistence and ecosystem functioning may help to counteract the current biodiversity loss and its potentially harmful consequences. In recent years, plant–soil feedback that can, for example, be caused by below‐ground microorganisms has been suggested to play a role in maintaining plant coexistence and to be a potential driver of the positive relationship between plant diversity and ecosystem functioning. Most of the studies addressing these topics have focused on the species level. However, in addition to interspecific interactions, intraspecific interactions might be important for the structure of natural communities. Here, we examine intraspecific coexistence and intraspecific diversity effects using 10 natural accessions of the model species Arabidopsis thaliana (L.) Heynh. We assessed morphological intraspecific diversity by measuring several above‐ and below‐ground traits. We performed a plant–soil feedback experiment that was based on these trait differences between the accessions in order to determine whether A. thaliana experiences feedback at intraspecific level as a result of trait differences. We also experimentally tested the diversity–productivity relationship at intraspecific level. We found strong differences in above‐ and below‐ground traits between the A. thaliana accessions. Overall, plant–soil feedback occurred at intraspecific level. However, accessions differed in the direction and strength of this feedback: Some accessions grew better on their own soils, some on soils from other accessions. Furthermore, we found positive diversity effects within A. thaliana: Accession mixtures produced a higher total above‐ground biomass than accession monocultures. Differences between accessions in their feedback response could not be explained by morphological traits. Therefore, we suggest that they might have been caused by accession‐specific accumulated soil communities, by root exudates, or by accession‐specific resource use based on genetic differences that are not expressed in morphological traits. Synthesis. Our results provide some of the first evidence for intraspecific plant–soil feedback and intraspecific overyielding. These findings may have wider implications for the maintenance of variation within species and the importance of this variation for ecosystem functioning. Our results highlight the need for an increased focus on intraspecific processes in plant diversity research to fully understand the mechanisms of coexistence and ecosystem functioning.     

Above‐ and belowground insect herbivores mediate the impact of nitrogen eutrophication on the soil food web in a grassland ecosystem

Insect herbivores are important drivers of ecosystem processes in grasslands, and can mediate the grassland's response to environmental change. For example, recent evidence shows that above‐ and belowground herbivory, individually and in combination, can modify how a plant community responds to nitrogen (N) eutrophication, an important driver of global change. However, knowledge about how such effects extend to the associated soil food web is lacking. In a mesocosm experiment, we investigated how communities of soil nematodes – an abundant and functionally important group of soil organisms – responded to above‐ and belowground insect herbivory at contrasting N levels. We found that the strongest influence of above‐ and belowground herbivory on the nematode community appeared at elevated N. The abundance of root‐feeding nematodes increased when either above‐ or belowground insect herbivores were present at elevated N, but when applied together the two herbivore types cancelled out one another's effect. Additionally, at elevated N aboveground herbivory increased the abundance of fungal‐feeders relative to bacterial‐feeders, which indicates changes in decomposition pathways induced by N and herbivory. Belowground herbivory increased the abundance of omnivorous nematodes. The shifts in both the herbivorous and detrital parts of the soil food web demonstrate that above‐ and belowground herbivory does not only mediate the response of the plant community to N eutrophication, but in extension also the soil food web sustained by the plant community. We conclude that feedbacks between effects of above‐ and belowground herbivory mediate the response of the grassland ecosystem to N eutrophication.     

Plant species control and soil faunal involvement in the processes of above‐ and below‐ground litter decomposition

Among the factors determining litter decomposition rates, the role of soil fauna as decomposers still remains unclear, especially for how they are involved in decomposing below‐ground root litter compared to their relatively‐known contributions to decomposing above‐ground leaf litter. We conducted a litterbag experiment using two sizes of meshes and pursued the leaf and root decomposition of six major tree species in a Japanese temperate forest over 411‐days to test the interactive effects of soil mesofauna and litter quality addressed based on two features (litter types and species) on the process. Moreover, given a possible correlation between litter traits of the leaves and roots, we examined whether soil mesofauna alters the relationship between leaf and root decomposition across species. We found that the effects of plant species identity was stronger than that of soil mesofauna for determining the litter mass loss rate and the microbial respiration rate in both above‐ground and below‐ground decomposition. In addition, we found a significant positive correlation between leaf and root litter decomposition processes, regardless of the involvement soil mesofauna. On the other hand, the presence of soil mesofauna increased microbial respiration rates in the early stage of leaf decomposition; however, soil mesofauna did not affect root microbial respiration rates during the experiment. Such differential involvement of mesofauna in the leaf and root litter decomposition may drive the general patterns of faster and slower decomposition of plant leaves and roots in the soil, respectively.     

Nematodes surfing the waves: long‐distance dispersal of soil‐borne microfauna via sea swept rhizomes

Dispersal mechanisms of soil‐borne microfauna have hitherto received little attention. Understanding dispersal mechanisms of these species is important to unravel their basic life history traits, biogeography, exchange of individuals between populations, and local adaptation. Soil‐borne nematodes and root‐feeding nematodes in particular occupy a key position in soil‐food webs and can be determinants for plant growth and vegetation structure and succession. However, their dispersal abilities have been scarcely addressed, predominantly focusing on species of agricultural importance. Still, root‐feeding nematodes are usually considered as being extremely limited and bound to the rhizosphere of plants. We investigated a mechanism for long distance dispersal of root‐feeding nematodes associated to two widespread coastal dune grasses. The nematodes are known to be crucial for the functioning of these grasses. We experimentally tested the hypothesis that root‐feeding nematodes are able to move across long distances inside rhizome fragments that are dispersed by seawater. We also tested the survival capacities of the host plants in seawater. Our study demonstrates that root‐feeding nematodes and plants are able to survive immersion in seawater, providing a mechanism for long distance dispersal of root feeding nematodes together with their host plant. Drifting rhizome fragments enable the exchange of plant material and animals between dune systems. These results provide new insights to understand the ecology of dune vegetation, the interaction with soil‐borne organisms and more importantly, re‐set the scale of spatial dynamics of a group of organisms considered extremely constrained in its dispersal capacities.     

Plant‐mediated interactions among above‐ground and below‐ground life stages of a root‐feeding weevil

1. Interactions among herbivores mediated by plant responses to herbivore injury may have large impacts on herbivore population densities. Responses may persist for weeks after injury and may affect not only the initial (inducing) herbivore, but also herbivores that are spatially or temporally separated from the initial attacker. 2. In many plant–insect interactions, multiple life stages of the insect may be associated with the same plant, and these various stages may interact indirectly with one another via induced responses. The rice water weevil (RWW), Lissorhoptrus oryzophilus, a serious global pest of rice, is one such insect. A series of experiments were performed with root‐feeding larvae and leaf‐feeding adults of the RWW using three conventional rice varieties. 3. The first objective of this study was to test whether RWW adult feeding on rice leaves resulted in altered oviposition by subsequent adults. The hypothesis for the first objective was that RWW adult feeding would decrease plant suitability, resulting in reduced oviposition by subsequent adults. 4. The second objective was to test whether injury by RWW larvae to rice roots resulted in altered oviposition by subsequent adults. The hypothesis for the second objective was that below‐ground RWW larval feeding would decrease plant suitability of rice to above‐ground RWW adults, resulting in decreased oviposition. 5. Results provided inconsistent support for the first hypothesis, indicating that responses differed among combinations of variety and injury level. Conversely, consistent support for the second hypothesis was found, indicating that larval feeding on roots decreased suitability of rice plants for oviposition.