Plant-mediated Interactions Research Articles

Chemical Mechanism of Exogenous Jasmonic Acid-Induced Resistance in Rose Against Spodoptera exigua (Lepidoptera: Noctuidae)1

Abstract Jasmonic acid (JA) plays an important role in the indirect plant-mediated interactions between rose powdery mildew (Podosphaera pannosa [Wallr.: Fr.] de Bary) and Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) on their shared host Rosa chinensis Jacquin. Bioassays showed that the total number of eggs laid by S. exigua on rose twigs decreased significantly after the twigs were treated with exogenous JA. Gas chromatography coupled with mass spectrometry (GC-MS) showed that the volatile organic chemicals (VOCs) from roses, including alkanes, terpenes, aldehydes, ketones, alcohols, and esters, were significantly changed following treatment with JA. Based on gas chromatography-electroantennographic detection (GC-EAD) and GC-MS analysis, the electrophysiological responses of S. exigua moths could be elicited by 8 compounds from the JA-induced roses, including 3-carene, 1-dodecanol, methyl stearate, 1-tetradecanol, hexadecane, eucalyptol, β-myrcene, and 1-iodododecane. Among these chemicals, the first 6 exhibited significant repellent activity to ovipositional behaviors of the gravid moths, while the latter 2 were attractive. The inhibition index of methyl stearate at a concentration of 15 mg/ml reached 65.12%. On the other hand, the quantity of the first 6 chemicals increased significantly and the latter two decreased due to the JA induction. These results reveal a new mechanism for resistance in rose plants against S. exigua. After JA induction, the rose plants appear to up-regulate the biosynthesis of the chemicals with repellent activities against S. exigua and, in the meantime, down-regulate the attractant chemicals.

The jasmonate pathway and water loss in rice leaves induced by a stem-borer inhibit leaf-feeder growth.

Plant-mediated interactions between herbivores play an important role in regulating the composition of herbivore community. The fall armyworm (FAW), Spodoptera frugiperda, which has become one of the most serious pests on corn in China since it invaded in 2018, has been found feeding rice in the field. However, how FAW interacts with native rice insect pests remains largely unknown. Here, we investigated the interaction between FAW and a resident herbivore, striped stem borer (SSB, Chilo suppressalis) on rice. The infestation of rice leaf sheaths (LSs) by SSB larvae systemically enhanced the level of jasmonic acid (JA), abscisic acid (ABA), and trypsin proteinase inhibitors (TPIs), reduced relative water content (RWC) in leaf blades (LBs), and suppressed the growth of FAW larvae. In contrast, because FAW larvae infested LBs and did not affect defence responses in LSs, they did not influence the performance of SSB larvae. Using different mutants, together with bioassays and chemical analysis, we revealed that SSB-induced suppression of FAW larvae growth depended on both the SSB-activated JA pathway and RWC in LBs, whereas the ABA pathway activated by SSB larvae promoted the growth of FAW larvae by impeding water loss. These results provide new insights into mechanisms underlying plant-mediated interactions between herbivores.

Salinity stress alters plant-mediated interactions between above- and below-ground herbivores

Below-ground herbivory impacts plant development and often induces systemic responses in plants that affect the performance and feeding behavior of above-ground herbivores. Meanwhile, pest-damaged root tissue can enhance a plant's susceptibility to abiotic stress such as salinity. Yet, the extent to which herbivore-induced plant defenses are modulated by such abiotic stress has rarely been studied. In this study, we examine whether root feeding by larvae of the turnip moth, Agrotis segetum (Lepidoptera: Noctuidae) affects the performance of the above-ground, sap-feeding aphid Aphis gossypii (Hemiptera: Aphididae) on cotton, and assess whether those interactions are modulated by salinity stress. In the absence of salinity stress, A. segetum root feeding does not affect A. gossypii development. On the other hand, under intense salinity stress (i.e., 600 mM NaCl), A. segetum root feeding decreases aphid development time by 16.1 % and enhances fecundity by 72.0 %. Transcriptome, metabolome and bioassay trials showed that root feeding and salinity stress jointly trigger the biosynthesis of amino acids in cotton leaves. Specifically, increased titers of valine in leaf tissue relate to an enhanced performance of A. gossypii. Taken together, salinity stress alters the interaction between above- and below-ground feeders by changing amino acid accumulation. Our findings advance our understanding of how plants cope with concurrent biotic and abiotic stressors, and may help tailor plant protection strategies to varying production contexts.

Functional characterization of fatty acyl-coenzyme A reductase, RcFAR1, specially expressed by Rosa chinensis consequent to infection by rose powdery mildew, Podosphaera pannosa

Rose (Rosa chinensis), as the most popular cut flowers in the world, is perennially attacked by rose powdery mildew (Podosphaera pannosa) and beet armyworm (Spodoptera exigua). The indirect plant-mediated interactions between these two pests always exist in the ternary system consisting of these three organisms, but little is known about the molecular mechanisms for such interactions. In this paper, we investigated the function of an insect-resistance-related gene in rose, RcFAR1, encoding a fatty acyl coenzyme A reductase. The gene was expressed in the roses when the plants were infected by P. pannosa, and as a consequence, the resistance of the roses against S. exigua was significantly induced. The results from heterologous expression of RcFAR1 in Saccharomyces cerevisiae showed that RcFAR1 primarily accumulated primary alcohols, including C12:0, C16:0, and C18:0 by using GC-MS analyses. Overexpression in Arabidopsis thaliana resulted in 4.0-, 3.6-, 8.2-, and 3.1-fold increases in the contents of fatty alcohols in T1 generation plants of A. thaliana for C12:0, C14:0, C16:0, and C18:0, respectively, suggesting that RcFAR1 catalyzes the biosynthesis of primary alcohols of C12:0, C14:0, C16:0, and C18:0 in the plants. Transient expression in the tobacco showed that RcFAR1 localized to the cytoplasm or the cell membrane. Our study has elucidated the molecular mechanism for the synthesis of dodecanol, tetradecanol, hexadecanol and other primary alcohols in P. pannosa-infected roses, and thus revealed one of the important molecular regulatory mechanisms by which the resistances of the roses against S. exigua are induced by the infection of the roses by P. pannosa.

Girdling behavior of the longhorn beetle modulates the host plant to enhance larval performance

BackgroundPreingestive behavioral modulations of herbivorous insects on the host plant are abundant over insect taxa. Those behaviors are suspected to have functions such as deactivation of host plant defenses, nutrient accumulation, or modulating plant-mediated herbivore interactions. To understand the functional consequence of behavioral modulation of insect herbivore, we studied the girdling behavior of Phytoecia rufiventris Gautier (Lamiinae; Cerambycidae) on its host plant Erigeron annuus L. (Asteraceae) that is performed before endophytic oviposition in the stem.ResultsThe girdling behavior significantly increased the larval performance in both field monitoring and lab experiment. The upper part of the girdled stem exhibited lack of jasmonic acid induction upon larval attack, lowered protease inhibitor activity, and accumulated sugars and amino acids in compared to non-girdled stem. The girdling behavior had no effect on the larval performance of a non-girdling longhorn beetle Agapanthia amurensis, which also feeds on the stem of E. annuus during larval phase. However, the girdling behavior decreased the preference of A. amurensis females for oviposition, which enabled P. rufiventris larvae to avoid competition with A. amurensis larvae.ConclusionsIn conclusion, the girdling behavior modulates plant physiology and morphology to provide a modulated food source for larva and hide it from the competitor. Our study implies that the insect behavior modulations can have multiple functions, providing insights into adaptation of insect behavior in context of plant-herbivore interaction.

Volatile-mediated oviposition preference for healthy over root-infested plants by the European corn borer.

The selection of oviposition sites by female moths is crucial in shaping their progeny performance and survival, and consequently in determining insect fitness. Selecting suitable plants that promote the performance of the progeny is referred to as the Preference-Performance hypothesis (or 'mother-knows-best'). While root infestation generally reduces the performance of leaf herbivores, little is known about its impact on female oviposition. We investigated whether maize root infestation by the Western corn rootworm (WCR) affects the oviposition preference and larval performance of the European corn borer (ECB). ECB females used leaf volatiles to select healthy plants over WCR-infested plants. Undecane, a compound absent from the volatile bouquet of healthy plants, was the sole compound to be upregulated upon root infestation and acted as a repellent for first oviposition. ECB larvae yet performed better on plants infested below-ground than on healthy plants, suggesting an example of 'bad motherhood'. The increased ECB performance on WCR-infested plants was mirrored by an increased leaf consumption, and no changes in the plant primary or secondary metabolism were detected. Understanding plant-mediated interactions between above- and below-ground herbivores may help to predict oviposition decisions, and ultimately, to manage pest outbreaks in the field.

Indirect plant-mediated interactions between heterospecific parasitoids that develop in different caterpillar species.

Parasitoids induce physiological changes in their herbivorous hosts that affect how plants respond to herbivory. The signature of parasitoids on induced plant responses to feeding by parasitized herbivores indirectly impacts insect communities interacting with the plant. The effect may extend to parasitoids and cause indirect interaction between parasitoids that develop inside different herbivore hosts sharing the food plant. However, this type of interactions among parasitoid larvae has received very little attention. In this study, we investigated sequential and simultaneous plant-mediated interactions among two host-parasitoid systems feeding on Brassica oleracea plants: Mamestra brassicae parasitized by Microplitis mediator and Pieris rapae parasitized by Cotesia rubecula. We measured the mortality, development time, and weight of unparasitized herbivores and performance of parasitoids that had developed inside the two herbivore species when sharing the food plant either simultaneously or sequentially. Plant induction by parasitized or unparasitized hosts had no significant effect on the performance of the two herbivore host species. In contrast, the two parasitoid species had asymmetrical indirect plant-mediated effects on each other's performance. Cotesia rubecula weight was 15% higher on plants induced by M. mediator-parasitized hosts, compared to control plants. In addition, M. mediator development time was reduced by 30% on plants induced by conspecific but not heterospecific parasitoids, compared to plants induced by its unparasitized host. Contrary to sequential feeding, parasitoids had no effect on each other's performance when feeding simultaneously. These results reveal that indirect plant-mediated interactions among parasitoid larvae could involve any parasitoid species whose hosts share a food plant.

Saliva-Mediated Contrasting Effects of Two Citrus Aphid Species on Asian Citrus Psyllid Feeding Behavior and Plant Jasmonic Acid Pathway.

While herbivorous insect saliva plays a crucial role in the interaction between plants and insects, its role in the inter-specific interactions between herbivorous insects has received little attention. Pre-infestation of citrus plants with Aphis spiraecola Patch and Aphis (Toxoptera) citricidus (Kirkaldy) exhibited positive and negative effects on the performance (feeding and reproduction) of Diaphorina citri Kuwayama. We explored the role of saliva in this plant-mediated interaction by infiltrating fresh and boiled aphid saliva into plants and detecting D. citri feeding behavior and citrus plant defense response. Leaf infiltration of A. spiraecola saliva disrupted the subsequent feeding of D. citri, indicated by prolonged extracellular stylet pathway duration and decreased phloem sap ingestion duration. By contrast, infiltration of A. citricidus saliva decreased the duration of the extracellular stylet pathway and phloem sap ingestion of D. citri. Furthermore, gene expression analysis showed that several salicylic acid (SA)- and jasmonic acid (JA)-pathway-related genes were activated by A. spiraecola saliva infiltration. However, two SA-pathway-related genes were activated and three JA-pathway-related genes were suppressed following A. citricidus saliva infiltration. Treatment with boiled saliva did not similarly impact D. citri feeding behavior or plant defense response. This study suggests that salivary components (those that can be inactivated by heating) from two citrus aphid species differently affect plant defenses and that they were responsible for the contrasting plant-mediated effects of two citrus aphids on the feeding behavior of D. citri. This study indicates a novel three-way citrus aphid-plant-citrus psyllid interaction.

Variation in the Outcome of Plant-Mediated Pathogen Interactions in Potato: Effects of Initial Infections on Conspecific vs. Heterospecific Subsequent Infections

Plants are often attacked sequentially by multiple enemies. Pathogen sequential co-infections can lead to indirect interactions mediated by plant induced responses whose outcome is contingent on differences in the magnitude and type of plant induced defences elicited by different species or guilds. To date, however, most studies have tested unidirectional effects of one pathogen on another, not discerning between conspecific vs. heterospecific infections, and often not measuring plant induced responses underlying such outcomes. To address this, we conducted a greenhouse experiment testing for the impact of initial infection by two leaf pathogens (Alternaria solani and Phytophthora infestans) on subsequent infection by each of these pathogens on potato (Solanum tuberosum) plants, and also measured induced plant defences (phenolic compounds) to inform on interaction outcomes. We found contrasting results depending on the identity of the initially infecting pathogen. Specifically, initial infection by A. solani drove induced resistance (lower necrosis) by subsequently infecting A. solani (conspecific induced resistance) but had no effect on subsequent infection by P. infestans. In contrast, initial infection by P. infestans drove induced resistance to subsequent infection by both conspecifics and A. solani. Patterns of plant induced defences correlated with (and potentially explained) induced resistance to conspecific but not heterospecific (e.g., in the case of P. infestans) subsequent infection. Overall, these results further our understanding of plant-mediated pathogen interactions by showing that plant-mediated interactions between pathogen species can be asymmetrical and in some cases not reciprocal, that pathogen species can vary in the importance of conspecific vs. heterospecific effects, and shed mechanistic insight into the role of plant induced responses driving such interactions.

Two-way plant-mediated interactions between a plant parasitic nematode and a foliar herbivore arthropod

Interactions between belowground and aboveground heterotrophic communities with no direct physical contact can be connected by the plant as a mediator. Plants respond to the attack of herbivores by producing a suite of defensive compounds that can affect the choice and performance of other herbivores. The aim of this study was to determine the impact of one herbivore's activity on the acceptability of that plant to another species of herbivore. Two herbivores were tested; root-knot nematode, Meloidogyne incognita (RKN), a belowground plant-parasitic nematode, and the two-spotted spider mite, Tetranychus urticae (TSSM), an aboveground folivore. We conducted herbivore preference and performance tests on Lima bean (LB) (Phaseolus lunatus cv. Henderson) as an optimal host for TSSM, and tomato (Solanum lycopersicum cv. Rutgers) which is a sub-optimal host for TSSM but optimal host for RKN. We used two-choice glass olfactometers to measure the response of RKN to plants that were exposed to TSSM versus a clean LB plant. RKN infected the clean plants at a significantly greater rate than the TSSM exposed plants. TSSM preference was measured, using leaf discs and two-choice olfactometers containing a RKN infected plant versus a clean plant at different days post-inoculation (DPI) of the RKN. TSSM preferred the clean plants to those with 25-day old RKN infections on LB, but preferred RKN infected tomato plants at 1 DPI. We also tested the effect of the inoculation (1 DPI) of the entomopathogenic nematode (EPN) Steinernema carpocapsae on tomato plants and TSSM preferred the EPN inoculated plants. We carried out a non-choice performance test for TSSM on both LB and tomato on plants inoculated with RKN versus clean plants and observed no effect of RKN exposure on TSSM performance. This research shows that plants can mediate interactions between below and aboveground herbivores that share the same plant.

A rapidly spreading deleterious aphid endosymbiont that uses horizontal as well as vertical transmission

Endosymbiotic bacteria that live inside the cells of insects are typically only transmitted maternally and can spread by increasing host fitness and/or modifying reproduction in sexual hosts. Transinfections of Wolbachia endosymbionts are now being used to introduce useful phenotypes into sexual host populations, but there has been limited progress on applications using other endosymbionts and in asexual populations. Here, we develop a unique pathway to application in aphids by transferring the endosymbiont Rickettsiella viridis to the major crop pest Myzus persicae. Rickettsiella infection greatly reduced aphid fecundity, decreased heat tolerance, and modified aphid body color, from light to dark green. Despite inducing host fitness costs, Rickettsiella spread rapidly through caged aphid populations via plant-mediated horizontal transmission. The phenotypic effects of Rickettsiella were sensitive to temperature, with spread only occurring at 19°C and not 25°C. Body color modification was also lost at high temperatures despite Rickettsiella maintaining a high density. Rickettsiella shows the potential to spread through natural M. persicae populations by horizontal transmission and subsequent vertical transmission. Establishment of Rickettsiella in natural populations could reduce crop damage by modifying population age structure, reducing population growth and providing context-dependent effects on host fitness. Our results highlight the importance of plant-mediated horizontal transmission and interactions with temperature as drivers of endosymbiont spread in asexual insect populations.

Plant jasmonic acid mediated contrasting effects of two citrus aphid species on Diaphorina citri Kuwayama.

Herbivores may influence each other directly and through plant mediated inter-specific interactions. The Asian citrus psyllid (Diaphorina citri Kuwayama) and citrus aphids are key pests that can co-exist on citrus, but their plant-mediated interaction between them is unknown. Here we investigated plant-mediated effect of two citrus aphid species, the polyphagous Aphis spiraecola Patch and the oligophagous Aphis (Toxoptera) citricidus (Kirkaldy) on the feeding behavior and reproduction of Diaphorina citri, and explored the underlying mechanisms. In comparison with those on aphid free plants, Diaphorina citri had decreased reproduction and reduced phloem feeding on Aphis spiraecola pre-infested plants, while the reproduction and feeding efficiency were increased on Aphis citricidus pre-infested plants. Jasmonic acid (JA) dependent defense was significantly activated by Diaphorina citri feeding on Aphis spiraecola pre-infested plants, but was suppressed by Diaphorina citri feeding on Aphis citricidus pre-infested plants compared with that on aphid free plant. By contrast, only one tested marker gene in salicylic acid (SA) signaling was activated by Diaphorina citri feeding on Aphis spiraecola pre-infested plants. Furthermore, exogenous application of methyl jasmonate, but not SA, conferred resistance against Diaphorina citri in our citrus trials. Our results indicate that pre-infestation by two citrus aphid species differentially altered Diaphorina citri induced citrus JA dependent defense, which resulted in different effect on subsequent Diaphorina citri performance. © 2022 Society of Chemical Industry.

Competitive Plant-Mediated and Intraguild Predation Interactions of the Invasive Spodoptera frugiperda and Resident Stemborers Busseola fusca and Chilo partellus in Maize Cropping Systems in Kenya.

Simple SummaryInvasion of fall armyworm led to co-inhabitation with resident stemborers in maize cropping systems in Kenya. As a result, exploitative and interference intraguild interactions occur between these lepidopteran pests. However, mechanistic insights into these interactions are poorly understood. These interspecific interactions may impact population dynamics and niche displacement of these pests in maize crops. Fall armyworm dominates resident stemborers in maize crops where they co-exist. This is due to plant-mediated and predation competitive advantages exhibited by fall armyworm over stemborers. Understanding such interactions provides crucial information for designing pest management strategies for these lepidopteran pests.Following its recent invasion of African countries, fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae), now co-exists with resident stemborers such as Busseola fusca (Lepidoptera: Noctuidae) and Chilo partellus (Lepidoptera: Crambidae) causing severe damage to maize crops. Due to niche overlap, interspecific interactions occur among the three species, but the mechanisms and degree remain unclear. In this study, we assessed plant-mediated intraspecific and interspecific interactions, predation in laboratory and semi-field settings, and larval field occurrence of S. frugiperda and the two stemborer species. Larval feeding assays to evaluate competitive plant-mediated interactions demonstrated that initial S. frugiperda feeding negatively affected subsequent stemborer larval feeding and survival, suggesting induction of herbivore-induced mechanisms by S. frugiperda, which deters establishment and survival of competing species. Predation assays showed that, at different developmental larval stages, second–sixth instars of S. frugiperda preyed on larvae of both B. fusca and C. partellus. Predation rates of S. frugiperda on stemborers was significantly higher than cannibalism of S. frugiperda and its conspecifics (p < 0.001). Cannibalism of S. frugiperda in the presence of stemborers was significantly lower than in the presence of conspecifics (p = 0.04). Field surveys showed a significantly higher number of S. frugiperda larvae than stemborers across three altitudinally different agroecological zones (p < 0.001). In conclusion, this study showed that the invasive S. frugiperda exhibited a clear competitive advantage over resident stemborers within maize cropping systems in Kenya. Our findings reveal some of the possible mechanisms employed by S. frugiperda to outcompete resident stemborers and provide crucial information for developing pest management strategies for these lepidopteran pests.

Investigating the potential for plant-mediated interactions between two biological control agents for Brazilian peppertree

ABSTRACT Invasive species cause damage to ecosystems by altering and dominating native habitats. Classical biological control can be a safe and effective way to control invasive species, especially in areas where chemical and mechanical control are not recommended, because of potential damage to non-target species, difficulty to access sites, and the costs associated with the treatment of large areas. Schinus terebinthifolia, Brazilian peppertree (BP) was introduced into Florida as an ornamental plant in the 1890s and is considered an aggressive invasive species in Florida. Pseudophilothrips ichini was the first biological control agent of BP released in Florida in 2019 and three Calophya spp., are under study as potential biological control agents. Feeding by Calophya can either elicit a hypersensitive response (HR) from BP that kills immatures at the feeding point or susceptibility with complete development and adult emergence. Pseudophilothrips ichini feeding does not elicit such response. To determine if previously elicited HR to the feeding of Calophya lutea affected P. ichini or its impact on, we measured the change in plant growth and the number of adults after one generation of P. ichini on susceptible and hypersensitive BP. After one generation of thrips feeding, plant height was the only factor that differed between plants that were hypersensitive and susceptible to Calophya lutea exposure, with hypersensitive plants being significantly shorter than susceptible plants. Our results suggest that even when HR is elicited by prior feeding of Calophya lutea, it will not affect P. ichini feeding and reproduction and should enhance control of BP.

Leaf-chewing herbivores affect preference and performance of a specialist root herbivore

Plants interact with a diversity of phytophagous insects above- and belowground. By inducing plant defence, one insect herbivore species can antagonize or facilitate other herbivore species feeding on the same plant, even when they are separated in space and time. Through systemic plant-mediated interactions, leaf-chewing herbivores may affect the preference and performance of root-feeding herbivores. We studied how six different leaf-chewing herbivore species of Brassica oleracea plants affected oviposition preference and larval performance of the root-feeding specialist Delia radicum. We expected that female D. radicum flies would oviposit where larval performance was highest, in accordance with the preference–performance hypothesis. We also assessed how the different leaf-chewing herbivore species affected defence-related gene expression in leaves and primary roots of B. oleracea, both before and after infestation with the root herbivore. Our results show that leaf-chewing herbivores can negatively affect the performance of root-feeding D. radicum larvae, although the effects were relatively weak. Surprisingly, we found that adult D. radicum females show a strong preference to oviposit on plants infested with a leaf-chewing herbivore. Defence-related genes in primary roots of B. oleracea plants were affected by the leaf-chewing herbivores, but these changes were largely overridden upon local induction by D. radicum. Infestation by leaf herbivores makes plants more attractive for oviposition by D. radicum females, while decreasing larval performance. Therefore, our findings challenge the preference–performance hypothesis in situations where other herbivore species are present.

Leafminer attack accelerates the development of soil-dwelling conspecific pupae via plant-mediated changes in belowground volatiles.

Summary Herbivore population dynamics are strongly influenced by the interactions established through their shared host. Such plant‐mediated interactions can occur between different herbivore species and different life developmental stages of the same herbivore. However, whether these interactions occur between leaf‐feeding herbivores and their soil‐dwelling pupae is unknown.We studied whether tomato (Solanum lycopersicum) leaf herbivory by the American serpentine leafminer Liriomyza trifolii affects the performance of conspecific pupae exposed to the soil headspace of the plant. To gain mechanistic insights, we performed insect bioassays with the jasmonate‐deficient tomato mutant def‐1 and its wild‐type, along with phytohormones, gene expression and root volatiles analyses.Belowground volatiles accelerated leafminer metamorphosis when wild‐type plants were attacked aboveground by conspecifics. The opposite pattern was observed for def‐1 plants, in which aboveground herbivory slowed metamorphosis. Leafminer attack induced jasmonate and abscisic acid accumulation and modulated volatile production in tomato roots in a def‐1‐dependent manner.Our results demonstrate that aboveground herbivory triggers changes in root defence signalling and expression, which can directly or indirectly via changes in soil or microbial volatiles, alter pupal development time. This finding expands the repertoire of plant–herbivore interactions to herbivory‐induced modulation of metamorphosis, with potential consequences for plant and herbivore community dynamics.

Impact of parasitoid-associated polydnaviruses on plant-mediated herbivore interactions.

Insect herbivores interact via plant-mediated interactions in which one herbivore species induces changes in plant quality that affects the performance of a second phytophagous insect that shares the food plant. These interactions are often asymmetric due to specificity in induced plant responses to herbivore attack, amount of plant damage, elicitors in herbivore saliva and plant organ damaged by herbivores. Parasitoids and their symbiotic polydnaviruses alter herbivore physiology and behaviour and may influence how plants respond to parasitized herbivores. We argue that these phenomena affect plant-mediated interactions between herbivores. We identify that the extended phenotype of parasitoid polydnaviruses is an important knowledge gap in interaction networks of insect communities.

Host-mediated, cross-generational intraspecific competition in a herbivore species

Conspecific insect herbivores co-occurring on the same host plant interact both directly through interference competition and indirectly through exploitative competition, plant-mediated interactions and enemy-mediated interactions. However, the situation is less clear when the interactions between conspecific insect herbivores are separated in time within the same growing season, as it is the case for multivoltine species. We hypothesized that early season herbivory would result in reduced egg laying and reduced performance of the next generation of herbivores on previously attacked plants. We tested this hypothesis in a choice experiment with box tree moth females (Cydalima perspectalis Walker, Lepidoptera: Crambidae). These females were exposed to box trees (Buxus sempervirens L., Buxaceae) that were either undamaged or attacked by conspecific larvae earlier in the season. We then compared the performance of the next generation larvae on previously damaged vs undamaged plants. Previous herbivory had no effect on oviposition behaviour, but the weight of next generation larvae was significantly lower in previously damaged plants. There was a negative correlation between the number of egg clutches laid on plants by the first generation and the performance of the next generation larvae. Overall, our findings reveal that early season herbivory reduces the performance of conspecific individuals on the same host plant later in the growing season, and that this time-lagged intraspecific competition results from a mismatch between the oviposition preference of females and the performance of its offspring.

Plant-mediated rhizospheric interactions in rice and water spinach intercropping enhance Si uptake by rice

Plant-mediated rhizospheric interactions in rice and water spinach intercropping enhance Si uptake by rice

A spotlight on the phytobiome: Plant-mediated interactions in an illuminated world

Artificial light at night (ALAN) is a growing phenomenon threatening the world's natural ecosystems. ALAN has received a lot of attention in relation to many different taxa. However, comparatively little is known about how ALAN affects plant growth, fitness and physiology, and how this alters interactions in the phytobiome food web. There is a lot of evidence for involvement of light cycles and light quality in plant growth and physiological processes, including seasonal timing and defense regulation. Surprisingly, however, only very few studies have investigated how ALAN, typically light of low density and occurring at night, affects plant-mediated interactions. A handful of studies describe bottom-up and top-down effects in plant-aphid-parasitoid systems, pollinator responses and effects on ground-dwelling nocturnal organisms. How herbivores of other feeding guilds are impacted is not clear. Importantly, very little is known about how ALAN may impact mutualistic and antagonistic associations with the plant microbiome, above- and belowground. In this Invited View, I synthesize what is known about effects of ALAN on plants and plant-mediated interactions. I identify several key knowledge gaps that exist in the literature and discuss areas that need future attention.