Combined transcriptome and metabolome analysis identifies triterpenoid-induced defense responses in Myzus persicae Sülzer-infested peach.

The defense response of peach (Prunus persica) to insect attack involves changes in gene expression and metabolites. Piercing/sucking insects such as green peach aphid cause direct damage by obtaining phloem nutrients and indirect damage by spreading plant viruses. To investigate the response of peach trees to aphids, the leaf transcriptome and metabolome of two genotypes with different sensitivities to green peach aphid (GPA, Myzus persicae) were studied. The transcriptome analysis of infected peach leaves showed two different response patterns. The gene expression of aphid-susceptible peach plants infected by aphids was more similar to that of the control plants, while the gene expression of aphid-resistant peach plants infected by aphids showed strongly induced changes in gene expression compared with the response in the control plants. Furthermore, gene transcripts in defense-related pathways, including plant-pathogen interaction, MAPK signaling, and several metabolic pathways, were more strongly enriched upon aphid infestation. Untargeted secondary metabolite profiling confirmed that aphid treatment induced larger changes in aphid-resistant peaches than in aphid-susceptible peaches. Consistent with transcriptomic alterations, nine triterpenoids showed extremely significant GPA-induced accumulation in aphid-resistant peaches, whereas triterpenoid abundance remained predominantly unchanged or undetected in aphid- susceptible peaches. Furthermore, some types of transcription factors (including WRKYs, ERFs, NACs, etc.) were more strongly induced upon GPA infestation in aphid-resistant peaches but not in aphid-susceptible peaches. Aphid feeding-dependent transcriptome and metabolite profiles provide the foundation for understanding the molecular mechanisms underlying the response of peach to aphid infestation. These results suggested that accumulation of specialized triterpenoids and the corresponding pathway transcripts may play a key role in peach GPA resistance.

A highly accumulated secretory protein from cotton bollworm interacts with basic helix-loop-helix transcription factors to dampen plant defense.

Caterpillar oral secretion (OS) contains active molecules that modulate plant defense signaling. We isolated an effector-like protein (Highly Accumulated Secretory Protein 1, HAS1) from cotton bollworm (Helicoverpa armigera) that is the most highly accumulated secretory protein of the nondigestive components in OS and belongs to venom R-like protein. Elimination of HAS1 by plant-mediated RNA interference reduced the suppression of OS on the defense response in plants. Plants expressing HAS1 are more susceptible to insect herbivory accompanied by the reduced expressions of multiple defense genes. HAS1 binds to the basic helix-loop-helix (bHLH) transcription factors, including GoPGF involved in pigmented gland formation and defense compounds biosynthesis in cotton and MYC3/MYC4 the main regulators in jasmonate (JA) signaling in Arabidopsis. The binding activity is required for HAS1 to inhibit the activation of bHLHs on plant defense gene expressions. Together with our previous study that another venom R-like protein HARP1 in cotton bollworm OS blocks JA signaling by interacting with JASMONATE-ZIM-domain repressors, we conclude that the venom R-like proteins in OS interfere with plant defense in a dual suppression manner. Considering the venom proteins in parasitic wasp assault the immune system of its host animal, our investigation reveals their conserved function in carnivorous and herbivorous insects.

Water availability and plant-herbivore interactions.

Water is essential to plant growth and drives plant evolution and interactions with other organisms such as herbivores. However, water availability fluctuates, and these fluctuations are intensified by climate change. How plant water availability influences plant-herbivore interactions in the future is an important question in basic and applied ecology. Here we summarize and synthesize the recent discoveries on the impact of water availability on plant antiherbivore defense ecology and the underlying physiological processes. Water deficit tends to enhance plant resistance and escape traits (i.e. early phenology) against herbivory but negatively affects other defense strategies, including indirect defense and tolerance. However, exceptions are sometimes observed in specific plant-herbivore species pairs. We discuss the effect of water availability on species interactions associated with plants and herbivores from individual to community levels and how these interactions drive plant evolution. Although water stress and many other abiotic stresses are predicted to increase in intensity and frequency due to climate change, we identify a significant lack of study on the interactive impact of additional abiotic stressors on water-plant-herbivore interactions. This review summarizes critical knowledge gaps and informs possible future research directions in water-plant-herbivore interactions.

Characterizing serotonin biosynthesis in Setaria viridis leaves and its effect on aphids.

KEY MESSAGE: A combined transcriptomic and metabolic analysis of Setaria viridis leaves responding to aphid infestation was used to identify genes related to serotonin biosynthesis. Setaria viridis (green foxtail), a short life-cycle C4 plant in the Poaceae family, is the wild ancestor of Setaria italica (foxtail millet), a resilient crop that provides good yields in dry and marginal land. Although S. viridis has been studied extensively in the last decade, the molecular mechanisms of insect resistance in this species remain under-investigated. To address this issue, we performed a metabolic analysis of S. viridis and discovered that these plants accumulate the tryptophan-derived compounds tryptamine and serotonin. To elucidate the defensive functions of serotonin, Rhophalosiphum padi (bird cherry-oat aphids) were exposed to this compound, either by exogenous application to the plant medium or with artificial diet bioassays. In both cases, exposure to serotonin increased aphid mortality. To identify genes that are involved in serotonin biosynthesis, we conducted a transcriptome analysis and identified several predicted S. viridis tryptophan decarboxylase (TDC) and tryptamine 5-hydroxylase (T5H) genes. Two candidate genes were ectopically expressed in Nicotiana tabacum, where SvTDC1 (Sevir.6G066200) had tryptophan decarboxylase activity, and SvT5H1 (Sevir.8G219600) had tryptamine hydroxylase activity. Moreover, the function of the SvTDC1 gene was validated using virus-induced gene silencing in S. italica, which caused a reduction in serotonin levels. This study provides the first evidence of serotonin biosynthesis in Setaria leaves. The biosynthesis of serotonin may play an important role in defense responses and could prove to be useful for developing more pest-tolerant Setaria italica cultivars.

Evidence for tissue-specific defence-offence interactions between milkweed and its community of specialized herbivores.

Coevolution between plants and herbivores often involves escalation of defence-offence strategies, but attack by multiple herbivores may obscure the match of plant defence to any one attacker. As herbivores often specialize on distinct plant parts, we hypothesized that defence-offence interactions in coevolved systems may become physiologically and evolutionarily compartmentalized between plant tissues. We report that roots, leaves, flower buds and seeds of the tropical milkweed (Asclepias curassavica) show increasing concentrations of cardenolide toxins acropetally, with latex showing the highest concentration. In vitro assays of the physiological target of cardenolides, the Na+ /K+ -ATPase (hereafter "sodium pump"), of three specialized milkweed herbivores (root-feeding Tetraopes tetrophthalmus, leaf-feeding Danaus plexippus, and seed-feeding Oncopeltus fasciatus) show that they are proportionally tolerant to the cardenolide concentrations of the tissues they eat. Indeed, molecular substitutions in the insects' sodium pumps predicted their tolerance to toxins from their target tissues. Nonetheless, the relative inhibition of the sodium pumps of these specialists by the concentration versus composition (inhibition controlled for concentration, what we term "potency") of cardenolides from their target versus nontarget plant tissues revealed different degrees of insect adaptation to tissue-specific toxins. In addition, a trade-off between toxin concentration and potency emerged across plant tissues, potentially reflecting coevolutionary history or plant physiological constraints. Our findings suggest that tissue-specific coevolutionary dynamics may be proceeding between the plant and its specialized community of herbivores. This novel finding may be common in nature, contributing to ways in which coevolution proceeds in multispecies communities.

Silencing the alarm: an insect salivary enzyme closes plant stomata and inhibits volatile release.

Herbivore-induced plant volatiles (HIPVs) are widely recognized as an ecologically important defensive response of plants against herbivory. Although the induction of this 'cry for help' has been well documented, only a few studies have investigated the inhibition of HIPVs by herbivores and little is known about whether herbivores have evolved mechanisms to inhibit the release of HIPVs. To examine the role of herbivore effectors in modulating HIPVs and stomatal dynamics, we conducted series of experiments combining pharmacological, surgical, genetic (CRISPR-Cas9) and chemical (GC-MS analysis) approaches. We show that the salivary enzyme, glucose oxidase (GOX), secreted by the caterpillar Helicoverpa zea on leaves, causes stomatal closure in tomato (Solanum lycopersicum) within 5 min, and in both tomato and soybean (Glycine max) for at least 48 h. GOX also inhibits the emission of several HIPVs during feeding by H. zea, including (Z)-3-hexenol, (Z)-jasmone and (Z)-3-hexenyl acetate, which are important airborne signals in plant defenses. Our findings highlight a potential adaptive strategy where an insect herbivore inhibits plant airborne defenses during feeding by exploiting the association between stomatal dynamics and HIPV emission.

Anti-herbivore silicon defences in a model grass are greatest under Miocene levels of atmospheric CO2.

Silicon (Si) has an important role in mitigating diverse biotic and abiotic stresses in plants, mainly via the silicification of plant tissues. Environmental changes such as atmospheric CO2 concentrations may affect grass Si concentrations which, in turn, can alter herbivore performance. We recently demonstrated that pre-industrial atmospheric CO2 increased Si accumulation in Brachypodium distachyon grass, yet the patterns of Si deposition in leaves and whether this affects insect herbivore performance remains unknown. Moreover, it is unclear whether CO2 -driven changes in Si accumulation are linked to changes in gas exchange (e.g. transpiration rates). We therefore investigated how pre-industrial (reduced; rCO2 , 200 ppm), ambient (aCO2 , 410 ppm) and elevated (eCO2 , 640 ppm) CO2 concentrations, in combination with Si-treatment (Si+ or Si-), affected Si accumulation in B. distachyon and its subsequent effect on the performance of the global insect pest, Helicoverpa armigera. rCO2 increased Si concentrations by 29% and 36% compared to aCO2 and eCO2 respectively. These changes were not related to observed changes in gas exchange under different CO2 regimes, however. The increased Si accumulation under rCO2 decreased herbivore relative growth rate (RGR) by 120% relative to eCO2, whereas rCO2 caused herbivore RGR to decrease by 26% compared to eCO2 . Si supplementation also increased the density of macrohairs, silica and prickle cells, which was associated with reduced herbivore performance. There was a negative correlation among macrohair density, silica cell density, prickle cell density and herbivore RGR under rCO2 suggesting that these changes in leaf surface morphology were linked to reduced performance under this CO2 regime. To our knowledge, this is the first study to demonstrate that increased Si accumulation under pre-industrial CO2 reduces insect herbivore performance. Contrastingly, we found reduced Si accumulation under higher CO2 , which suggests that some grasses may become more susceptible to insect herbivores under projected climate change scenarios.

Inconsistent annual compensation for floral herbivory by an iterocarpic thistle.

PREMISE: Plants experiencing steep reproductive losses from herbivores should favor strategies promoting tolerance or resistance to that herbivory. However, the degree to which such strategies succeed in improving plant fitness under natural conditions needs further evaluation, especially for iterocarpic species. We tested whether reproductive effort by the iterocarpic Cirsium undulatum Spreng. (Wavyleaf thistle) provided within-season tolerance for floral herbivory through response to apical damage. METHODS: We imposed apical damage and manipulated floral herbivory on later-flowering, non-apical flowerheads for two seasons. We asked: (1) is there evidence of compensatory potential to tolerate apical flowerhead damage? If so, (2) does the amount of herbivore pressure on non-apical flowerheads influence the magnitude of any compensatory response; and (3) is the response to apical damage sufficient to increase plant seed production under ambient floral herbivory over the flowering season? RESULTS: Plants showed compensatory potential for apical head loss; apical damage increased seed contributions from later, lower positioned flowerheads. Further, the intensity of subsequent herbivore pressure influenced compensation outcomes. Equitable seed production under both levels of ambient herbivory occurred only in the year in which plants were larger and insect pressure was lower. Finally, the response to apical damage was sufficient to compensate for apical seed loss, but it did not consistently increase overall annual seed production under ambient floral herbivory. CONCLUSIONS: Although this iterocarpic species can compensate for apical damage, tolerance for floral herbivory varied between years.

Changes in arthropod community but not plant quality benefit a specialist herbivore on plants under reduced water availability.

Plants growing under reduced water availability can affect insect herbivores differently, in some instances benefitting them. However, the forces mediating these positive impacts remain mostly unclear. To identify how water availability impacts plant quality and multi-trophic interactions, we conducted manipulative field studies with two populations of the specialist herbivore Pieris rapae, and its host plant, Rorippa indica. We found that P. rapae larvae experienced higher survival on R. indica growing under low water availability compared with plants grown under high water availability. Higher survival of eggs and larvae was related to the reduced abundance of other herbivores and natural enemies. Water availability had differential impacts on other members of the herbivore community by altering plant quality. Low water availability decreased the quality of R. indica to most herbivores, as indicated by reduced abundance in the field and decreased relative growth rate in laboratory feeding assays. In contrast, P. rapae larval performance was not affected by sympatric R. indica grown under different water availability. These results indicate that local P. rapae populations possess physiological adaptations to overcome fluctuations in host quality. Our findings illustrate that reduced water availability is beneficial to a specialist herbivore but detrimental to most other herbivores. Our work highlights the complex effects of the arthropod communities associated with plants in determining the impacts of water availability on insect herbivores.

Diel activity patterns and arrestment behaviour in host associations of green mirids (Creontiades dilutus).

Many plant bugs (Miridae) are generalist herbivores that feed on multiple host species. The reasons these bugs move across hosts and the behavioural mechanisms responsible for their retention at specific hosts remain elusive. Green mirids (Creontiades dilutus) are endemic to Australia. These insects are important pests of cotton (Gossypium hirsutum) and even in low numbers can cause substantial damage to crops. These bugs are also present in relatively much higher numbers on pigeon pea (Cajanus cajan) planted alongside cotton fields, and evidence shows they move across these crops in both directions. Observations of these highly mobile insects in the field are challenging, but indirect evidence suggests that they may be nocturnal. This study evaluated: (1) the diel (24 h) period in which C. dilutus adults were most active, (2) whether they respond to plant volatiles immediately prior to landing on host substrates, and (3) if their presence on a host is in response to attraction or arrestment cues. The results suggest that C. dilutus bugs are typically most active early in the evenings, after remaining motionless during the day (unless disturbed). Their movement (at night) was arrested by hosts prior to touching plant tissues. There was no evidence to suggest that these bugs are attracted by volatiles beyond 2 cm. These outcomes demonstrate that insect behaviours need to be investigated within their typical activity periods, and that arrestment cues possibly play a central role in the host finding process of generalist C. dilutus and probably, therefore, other mirid species.

Transcriptomic analyses reveal a systemic defense role of the uninfested adjacent leaf in tea plant (Camellia sinensis) attacked by tea geometrids (Ectropis obliqua).

To get a more detailed understanding of the interaction between tea plant (Camellia sinensis) and tea geometrids (Ectropis obliqua), transcriptomic profile in undamaged adjacent leaf (TGL) of tea geometrids fed local leaves (LL) was investigated for the first time. Here, approximately 245 million clean reads contained 39.39 Gb of sequence data were obtained from TGL. Further analysis revealed that systemic response was induced in TGL after tea geometrids feeding on LL, although the defense response was weaker than that in LL. The differentially expressed genes (DEGs) identification analysis showed little overlap of DEGs between TGL and LL. Comparative transcriptome analysis suggested that JA signal regulated resistant pathway was induced in LL; whereas primary metabolism pathway was activated in TGL in response to tea geometrids feeding. This study reveals a novel resistance mechanism of TGL to tea geometrids feeding.

The Laccase Gene Family Mediate Multi-Perspective Trade-Offs during Tea Plant (Camellia sinensis) Development and Defense Processes.

Laccase (LAC) plays important roles in different plant development and defense processes. In this study, we identified laccase genes (CsLACs) in Camellia sinensis cv 'Longjing43' cultivars, which were classified into six subclades. The expression patterns of CsLACs displayed significant spatiotemporal variations across different tissues and developmental stages. Most members in subclades II, IV and subclade I exhibited contrasting expression patterns during leaf development, consistent with a trade-off model for preferential expression in the early and late developmental stages. The extensive transcriptional changes of CsLACs under different phytohormone and herbivore treatment were observed and compared, with the expression of most genes in subclades I, II and III being downregulated but genes in subclades IV, V and VI being upregulated, suggesting a growth and defense trade-off model between these subclades. Taken together, our research reveal that CsLACs mediate multi-perspective trade-offs during tea plant development and defense processes and are involved in herbivore resistance in tea plants. More in-depth research of CsLACs upstream regulation and downstream targets mediating herbivore defense should be conducted in the future.

Endosymbionts facilitate rapid evolution in a polyphagous herbivore.

Maternally transmitted bacterial symbionts can be important mediators of the interactions between insect herbivores and their foodplants. These symbionts are often facultative (present in some host individuals but not others) and can have large effects on their host's phenotype, thus giving rise to heritable variation upon which selection can act. In the cowpea aphid (Aphis craccivora), it has been established that the facultative endosymbiont Arsenophonus improves aphid performance on black locust trees (Robinia pseudoacacia) but not on fava (Vicia faba). Here, we tested whether this fitness differential translated into contemporaneous evolution of aphid populations associated with the different plants. In a laboratory study lasting 16 weeks, we found that the frequency of Arsenophonus-infected individuals significantly increased over time for aphid populations on black locust but declined for aphid populations on fava. By the end of the experiment, Arsenophonus infection was >3× more common on black locust than fava, which is comparable to previously described infection frequencies in natural field populations. Our results clearly demonstrate that aphid populations with mixed facultative symbiont infection status can rapidly evolve in response to the selective environments imposed by different host plants. This selection differential may be a sufficient explanation for the global association between Arsenophonus-infected cowpea aphids and black locust trees, without invoking additional assortative mechanisms. Because the aphid and plant originate from different parts of the world, we further hypothesize that Arsenophonus infection may have acted as a preadaptation that has promoted functional specialization of infected aphids on a novel host plant.

Leaf vibrations produced by chewing provide a consistent acoustic target for plant recognition of herbivores.

Plant defenses that respond to the threat of herbivory require accurate sensing of the presence of herbivores. Herbivory cues include mechanical damage, elicitors from insect saliva or eggs, and airborne volatiles emitted by wounded plants. Plants can also respond to the leaf vibrations produced by chewing herbivores. However, previous studies of the influence of feeding vibrations on plant defenses have been limited to single species pairs. In this study we test the hypothesis that chewing vibrations differ among herbivore species, both in their acoustic features and in their potential effect on plant defense responses. We first compare the acoustic traits of larval feeding vibrations in ten species from six families of Lepidoptera and one family of Hymenoptera. We then test responses of Arabidopsis thaliana plants to variation among feeding vibrations of different individuals of one species, and to feeding vibrations of two species, including a pierid butterfly and a noctuid moth. All feeding vibrations consisted of repetitive pulses of vibration associated with leaf tissue removal, although chewing rates varied between species and between large and small individuals within species. The frequency spectra of the vibrations generated by leaf feeding were similar across all ten species. Induced increases in anthocyanins in A. thaliana did not differ when plants were played vibrations from different individuals, or vibrations of two species of herbivores with different chewing rates, when amplitude was held constant. These results suggest that feeding vibrations provide a consistent set of cues for plant recognition of herbivores.

Meta-analysis of the role of entomopathogenic and unspecialized fungal endophytes as plant bodyguards.

Herbaceous plants harbour species-rich communities of asymptomatic endophytic fungi. Although some of these endophytes are entomopathogenic, many are not, and remarkably little is known about how the presence of these fungi in plant tissues affects phytophagous insects. Here we show through a meta-analysis that both entomopathogenic and nonentomopathogenic endophytes have a negative effect on insect herbivores. Growth and performance of polyphagous and sucking insects are reduced by nonentomopathogenic endophytes, but monophages are unaffected, likely because the latter are better adapted to secondary metabolites produced or induced by the fungi. Furthermore, studies using excised leaves report weaker effects than those with intact plants, likely caused by chemical changes being masked by leaf excision. Most surprisingly, endophyte infection of seeds produces the greatest effect on insect herbivores in subsequent mature plants, even though the usual mode of fungal transmission is infection of leaves by airborne spores. We conclude that these ubiquitous hidden fungi may be important bodyguards of plants. However, in order to fully understand their roles in plant protection, we must be aware that minor differences in experimental design can lead to contradictory results.

Phytochemical variation in treetops: causes and consequences for tree-insect herbivore interactions.

The interaction of plants and their herbivorous opponents has shaped the evolution of an intricate network of defences and counter-defences for millions of years. The result is an astounding diversity of phytochemicals and plant strategies to fight and survive. Trees are specifically challenged to resist the plethora of abiotic and biotic stresses due to their dimension and longevity. Here, we review the recent literature on the consequences of phytochemical variation in trees on insect-tree-herbivore interactions. We discuss the importance of genotypic and phenotypic variation in tree defence against insects and suggest some molecular mechanisms that might bring about phytochemical diversity in crowns of individual trees.

Rapid defense responses in maize leaves induced by Spodoptera exigua caterpillar feeding.

Insects such as the beet armyworm (Spodoptera exigua) cause extensive damage to maize (Zea mays). Maize plants respond by triggering defense signaling, changes in gene expression, and biosynthesis of specialized metabolites. Leaves of maize inbred line B73, which has an available genome sequence, were infested with S. exigua for 1 to 24 h, followed by comparisons of the transcript and metabolite profiles with those of uninfested controls. The most extensive gene expression responses occurred rapidly, within 4-6 h after caterpillar infestation. However, both gene expression and metabolite profiles were altered within 1 h and continued to change during the entire 24 h experiment. The defensive functions of three caterpillar-induced genes were examined using available Dissociation transposon insertions in maize inbred line W22. Whereas mutations in the benzoxazinoid biosynthesis pathway (Bx1 and Bx2) significantly improved caterpillar growth, the knockout of a 13-lipoxygenase (Lox8) involved in jasmonic acid biosynthesis did not. Interestingly, 9-lipoxygenases, which lead to the production of maize death acids, were more strongly induced by caterpillar feeding than 13-lipoxygenases, suggesting an as yet unknown function in maize defense against herbivory. Together, these results provide a comprehensive view of the dynamic transcriptomic and metabolomic responses of maize leaves to caterpillar feeding.

Impacts of silicon-based grass defences across trophic levels under both current and future atmospheric CO2 scenarios.

Silicon (Si) has important functional roles in plants, including resistance against herbivores. Environmental change, such as increasing atmospheric concentrations of CO2, may alter allocation to Si defences in grasses, potentially changing the feeding behaviour and performance of herbivores, which may in turn impact on higher trophic groups. Using Si-treated and untreated grasses (Phalaris aquatica) maintained under ambient (400 ppm) and elevated (640 and 800 ppm) CO2 concentrations, we show that Si reduced feeding by crickets (Acheta domesticus), resulting in smaller body mass. This, in turn, reduced predatory behaviour by praying mantids (Tenodera sinensis), which consequently performed worse. Despite elevated CO2 decreasing Si concentrations in P. aquatica, this reduction was not large enough to affect the feeding behaviour of crickets or their predator. Our results suggest that Si-based defences in plants have adverse impacts on both primary and secondary trophic taxa, and these are not likely to decline under future climate change scenarios.

Oxidizable Phenolic Concentrations Do Not Affect Development and Survival of Paropsis Atomaria Larvae Eating Eucalyptus Foliage.

Insect folivores can cause extensive damage to plants. However, different plant species, and even individuals within species, can differ in their susceptibility to insect attack. Polyphenols that readily oxidize have recently gained attention as potential defenses against insect folivores. We tested the hypothesis that variation in oxidizable phenolic concentrations in Eucalyptus foliage influences feeding and survival of Paropsis atomaria (Eucalyptus leaf beetle) larvae. First we demonstrated that oxidizable phenolic concentrations vary both within and between Eucalyptus species, ranging from 0 to 61 mg.g-1 DM (0 to 81% of total phenolics), in 175 samples representing 13 Eucalyptus species. Foliage from six individuals from each of ten species of Eucalyptus were then offered to batches of newly hatched P. atomaria larvae, and feeding, instar progression and mortality of the first and second instar larvae were recorded. Although feeding and survival parameters differed dramatically between individual plants, they were not influenced by the oxidizable phenolic concentration of leaves, suggesting that P. atomaria larvae may have effective mechanisms to deal with oxidizable phenolics. Larvae feeding on plants with higher nitrogen (N) concentrations had higher survival rates and reached third instar earlier, but N concentrations did not explain most of the variation in feeding and survival. The cause of variation in eucalypt herbivory by P. atomaria larvae is therefore still unknown, although oxidizable phenolics could potentially defend eucalypt foliage against other insect herbivores.

Landscape effects of a non-native grass facilitate source populations of a native generalist bug, Stenotus rubrovittatus, in a heterogeneous agricultural landscape.

Non-native plant species can provide native generalist insects, including pests, with novel food and habitats. It is hypothesized that local and landscape-level abundances of non-native plants can affect the population size of generalist insects, although generalists are assumed to be less sensitive to habitat connectivity than specialists. In a heterogeneous landscape in Japan, the relationship between the density of a native pest of rice (Stenotus rubrovittatus (Matsumura) (Heteroptera: Miridae)) and the abundance of Italian ryegrass (Lolium multiflorum Lam. (Poales: Poaceae)), a non-native meadow grass known to facilitate S. rubrovittatus, was analyzed. Statistical analyses of data on bug density, vegetation, and the spatial distribution of fallow fields and meadows dominated by Italian ryegrass, obtained by field surveys, demonstrated that local and landscape-level abundances of Italian ryegrass (the unmowed meadow areas within a few hundred meters of a sampling plot) positively affected bug density before its immigration into rice fields. Our findings suggest that a generalist herbivorous insect that prefers non-native plants responds to spatial availability and connectivity of plant species patches at the metapopulation level. Fragmentation by selective mowing that decreases the total area of source populations and increases the isolation among them would be an effective and environmentally-friendly pest management method.