Biological control is not easily available to all farmers, particularly those with limited technical or financial resources. Yet, traditional communities have long managed insect pests using locally adapted, nature-based methods. Many of these practices, rooted in indigenous knowledge, are environmentally sustainable, culturally appropriate, and resilient to local conditions. This knowledge has played an important role in shaping what is now known as Integrated Pest Management (IPM). This review synthesizes evidence on traditional biocontrol strategies, including natural compounds from plants, emphasizing the mechanisms of plant-mediated defenses, associational resistance, plant-soil feedback, and the conservation of natural enemies and pollinators to support integrated pest and pollinator management. By integrating centuries of empirical knowledge with contemporary ecological insights, these strategies demonstrate effective pest suppression, promote agroecosystem resilience, and support sustainable productivity. Understanding the ecological interactions in agricultural systems and biological mechanisms underlying traditional strategies highlights the potential of combining time-tested practices with modern science to develop context-specific, nature-based solutions for sustainable agriculture and IPM.

Trade-offs between induced plant defenses and competitive growth are regarded as being universal. This seems particularly true for often-studied early succession annuals, where exposure to competition often suppresses defense expression. However, whether such trade-offs are universal across plant life histories remains unclear, especially considering recent work demonstrating that the trade-off can be artificially uncoupled. We test the hypothesis that Solidago altissima, a perennial herbaceous plant, naturally uncouples this trade-off by adjusting its investment in chemical defenses when exposed to competitive cues, allowing for persistence in high-competition environments despite herbivore pressure. Using a factorial glasshouse experiment, we manipulated competition cues (far-red light and conspecific neighbors) and insect herbivory to assess impacts on growth, resistance, and secondary metabolite production. S. altissima maintained or even enhanced herbivore-induced resistance in the presence of competition cues. Bioassays revealed reduced herbivore performance on previously damaged plants, particularly when they were exposed to neighbors. Metabolomic profiling showed herbivory-induced production of several secondary metabolite classes. Most notably, we found competition-enhanced production of hydroxycinnamic acids, dominated by 3-O-(E)-feruloylquinic acid, associated with resistance. Our findings challenge the generality of the growth-defense trade-off and highlight the importance of ecological context and life-history strategy in shaping plastic responses.

Methyl salicylate (MeSA) is an herbivore-induced plant volatile (HIPV) known to attract natural enemies of herbivores; however, its effectiveness as a semiochemical across diverse cropping systems and broad geographic regions remains unclear. In this 2-year field study, we sampled natural enemies using MeSA-baited and unbaited (control) yellow sticky traps across multiple cropping systems in the Mid-Atlantic and Northeastern United States (New York, Pennsylvania, Virginia and New Jersey), including three annual crops (corn, potatoes, and soybean) and four perennial crops (apples, blueberries, cranberries and grapes). Sticky traps were deployed for 4 weeks during the preharvest period, with deployment timing adjusted to the phenology of each crop. For each trap, we recorded both the number of natural enemies and their community composition, including abundance and diversity (Shannon index). We found that hoverflies (Diptera: Syrphidae) were specifically attracted to MeSA in perennial cropping systems. Although natural enemy communities were overall more diverse in annual crops, MeSA tended to increase Shannon diversity in perennial systems. Collectively, these results suggest that HIPVs such as MeSA may be useful for enhancing hoverfly attraction in less-disturbed perennial cropping systems.

Functional intercropping aims to beneficially associate two or more plant species or varieties, simultaneously increasing plant diversity and the provisioning of ecosystem services. Although the benefits of diversified cropping systems are widespread and well documented, the underlying mechanisms of increased pest resistance and the relative contributions of different modes of plant defense remain unclear. Plant chemistry can mediate resistance to herbivores through toxic or antidigestive modes of action (direct defenses) or by providing host finding cues that recruit natural enemies that predate on herbivore populations (indirect defenses). Both direct and indirect defense can be elevated in response to previous herbivore damage leading to induced resistance. Here we address the question of how intercropping with four companion plants (alfalfa, bean, Desmodium, and red clover) affects the constitutive and induced expression of plant direct/indirect defenses and resulting herbivore resistance. We found that defensive plant secondary metabolite production of focal maize plants varies with both, previous herbivore damage (induction treatment) and the presence of an intercrop species. Intercropping - specifically with Desmodium - alters the expression of plant chemical defenses and increases plant resistance in 1) no-choice bioassays by reducing larval performance and 2) the incidence of damaged leaves at the field-scale experiment. Thereby some intercrop species do not only directly affect maize plant secondary metabolism but also alter how defensive metabolites are expressed in response to herbivory (intercrop-mediated induced responses). In contrast to direct resistance, the expression of indirect resistance did not vary with intercropping or herbivory suggesting that under realistic field conditions, direct defenses are more reliable as pest control mechanisms than chemical information-mediated indirect defenses. However, within-plant spatial separation of predation pressure suggests a role of vegetation structure in the efficiency of biocontrol. We present evidence that ‘intercrop-mediated induced responses’ is an integrated ecological mechanism determining the outcome of associational resistance (or susceptibility) and conclude that intercrop-mediated alterations of constitutive and herbivory-induced secondary metabolite production mediate increased associational resistance in diversified maize systems.

Diversified agricultural systems such as intercropping and cover cropping provide a wide range of emergent properties that can positively impact agricultural performance metrics. Both cropping systems by leveraging distinct ecological processes such as associational resistance and plant-soil feedbacks can facilitate soil health while increasing pest resistance and crop productivity. However, the extent to which the cropping system in general and the companion plant species in particular induce changes to plant metabolism as a mechanism mediating plant resistance remains understudied and limits a wider application of companion cropping technologies. To close this gap, we use microcosm experiments that simulate intercropping and cover cropping practices by manipulating plant neighbourhood and soil conditioning to investigate how three different companion legume species change plant secondary metabolite profiles and the resulting effects on herbivore resistance of maize plants. By utilizing a conventional maize variety (genetically modified; bt-transformed), we further test the potential for such ecosystem services to persist under industrialized agricultural systems. The non-volatile secondary metabolite profiles of maize leaves and roots differed across intercropping and cover cropping systems, while volatile organic compound emissions remained largely unchanged. Defence-related compounds such as benzoxazinoids were generally upregulated under intercropping, while the companion plant identity further shaped the maize defence profile with bean intercropping specifically upregulating benzoxazinoid compounds. Resistance bioassays with the generalist herbivore Spodoptera frugiperda revealed that intercropping significantly reduces leaf damage relative to cover cropping. Among the intercrops, beans increase larval mortality while alfalfa decreases larval mortality on maize plants. Synthesis and applications. We demonstrate that intercropping and cover cropping can shape the overall secondary metabolite profiles of maize and mediate herbivore resistance. These findings underscore that crop diversification strategies can specifically modulate the expression of chemical defences linked to herbivore resistance. In practical terms, this means that diversified cropping systems can be optimized to enhance constitutive levels of pest resistance, potentially reducing the reliance on insecticides, increasing sustainability and supporting yield. The fact that positive resistance effects persist even when using pest-resistant GM crops suggests companion cropping practices as a valid tool to increase the sustainable management of insect pests.

Plants can respond to herbivore attack by inducing resistance traits that affect subsequent herbivore performance and behaviour. Here, we investigate how such induced responses in Solidago altissima L. (tall goldenrod) function to spread herbivore damage more evenly across plant populations, thereby reducing the amount of herbivory for each individual plant. In field and laboratory experiments with Trirhabda virgata J. L. LeConte (1865) beetle larvae, we demonstrate that herbivory induces strong resistance in S. altissima, resulting in reduced larval growth and behavioural avoidance of previously damaged plants. Volatile organic compounds (VOCs) emitted from damaged plants serve as olfactory cues for larval decision-making, suggesting a form of chemical aposematism informing the beetles' movement through the plant population. Beetle larvae use these cues to move away from damaged plants and preferentially colonize undamaged neighbours, particularly when plants are connected by overlapping foliage. Isolated plants, by contrast, experience significantly more damage due to reduced larval emigration. With seasonal surveys, we found a shift from clumped to a more even herbivore distribution, driven by plant-induced resistance and VOC signalling. These results support a 'risk-spreading' function of inducible resistance, contingent on herbivore mobility and plant connectivity, and offer an alternative ecological framework for the evolution of inducible plant defence traits beyond traditional cost-saving hypotheses. This research underscores the role of plant chemical signalling and spatial structure in shaping herbivore-plant interactions and community dynamics.Read the free for this article on the Journal blog.

The black soldier fly frass fertilizer (BSFFF) has gained global attention as a multipurpose input for soil fertilization and pest and disease management. However, there are limited studies that have examined its effects on insect pest resistance and the underlying mechanisms. We investigated the impact of amending soil with BSFFF on maize growth, defense gene expression and resistance to a polyphagous insect herbivore, Spodoptera frugiperda (Lepidoptera: Noctuidae) through larval feeding assay. Maize growth was evaluated by measuring plant height, chlorophyll concentration, and biomass accumulation in soils amended with BSFFF, synthetic fertilizers (Di-ammonium phosphate and Calcium ammonium nitrate) and unfertilized soils at various growth stages. Larval feeding assays were conducted using leaf discs from maize plants grown in different amended soils. The expression level of three maize defense genes: pathogenesis related protein 5 (pr-5), maize proteinase inhibitors (mpi), and lipoxygenase 3 (lox-3) were analyzed using quantitative polymerase chain reaction (qPCR) while yield was assessed through a field trial over two cropping seasons. Maize plants grown in BSFFF amended soils showed 30% more growth, higher chlorophyll, 0.93-2.86 t ha- 1 higher yield, and 48% better nitrogen use efficiency than from those in synthetic or unfertilized soils. Moreover, S. frugiperda larvae consumed significantly less leaf tissue from maize plants grown in BSFFF amended soils than synthetically fertilized and non-fertilized soils. Maize defense genes pr-5, mpi, and lox-3 were highly expressed both constitutively and inductively in maize planted in BSFFF amended soils compared to those grown in synthetically fertilized and non-fertilized soils. We observed a significant negative correlation between mpi gene expression and larval feeding, suggesting its role in maize resistance. Our results show that soil amendment with BSFFF strengthens plant defense systems and positively impacts plant growth and yield, contributing to increased agricultural productivity and sustainability.

This Editorial introduces the Virtual Issue ‘Herbivore‐derived elicitors of plant responses’ that includes the following papers: Louis et al . (2013), Acevedo et al . (2018), Danner et al . (2018), Kessler (2018), Moreira et al . (2018), Iida et al . (2019), Harris & Pitzschke (2020), Orlovskis & Reymond (2020), Raffa et al . (2020), Fernández de Bobadilla et al . (2021), Griese et al . (2021), Yamasaki et al . (2021), Chen et al . (2023, 2025), Zeng et al . (2023), Grandi et al . (2024), Sorg et al . (2025). Access the Virtual Issue at www.newphytologist.com/virtualissues .

The current study investigated the impact of biochar on root exudate chemistry and characterized exudate molecule abundance as a function of biochar application rates. In exudates trickled over biochar, organic oxygen-rich compounds were the most common molecules stemming from biochar, comprising 67 % of the abundance of biochar-derived compounds. Eighty percent of these compounds stemming from biochar were hydrophilic. On the other hand, biochar-retained molecules were mostly lipophilic (87 %) and consisted mainly of lipid-related compounds (52 %). In addition, root-exuded molecules with ≥ 20 aliphatic-carbon atoms were retained by biochar (representing 44 % of all retained molecules) but were not released from biochar. These findings indicate that biochar can increase the hydrophilic:lipophilic balance of root exudates. In soil, this change could influence the spatial heterogeneity of dissolved organic matter and the role of root exudates in modulating plant-plant and plant-microbe interactions.

Seemingly small ecological changes can have large, ramifying effects that defy expectations. Such are keystone effects in ecosystems. Phloem-feeding insect herbivores can act as keystone species by altering community structure and species interactions via plant-mediated or ant-mediated mechanisms. Plant responses triggered by phloem feeders can disrupt tri-trophic interactions induced by leaf-chewing herbivores, while ants that tend phloem feeders can deter or prey on other arthropods. Here, we investigate how phloem-feeding herbivores change caterpillar-parasitoid interactions on Quercus alba (white oak) trees in natural forests. We factorially manipulated the presence of phloem-feeding insects as well as ant access on Q. alba branches over multiple years and sites and measured parasitism rates of co-occurring caterpillars. While 19.3% of caterpillars were parasitized when phloem feeders were removed, the presence of phloem feeders completely suppressed parasitism of caterpillars (0%). This stark pattern was consistent across the diverse community of phloem feeders and caterpillars. Our manipulation of ant access had no effect on parasitism of caterpillars, implicating a plant-mediated mechanism. We further assessed the mechanistic hypothesis that phloem feeders suppress plant emission of caterpillar-induced volatile compounds, which could disrupt host-location behavior by parasitoids of caterpillars. Phloem feeders indeed reduced concentrations of four volatile compounds, consistent with the putative plant volatile-mediated mechanism. Given the important role of parasitoids in controlling herbivore populations, this keystone effect of phloem feeders offers novel insight into community dynamics in forests and potentially other terrestrial ecosystems.

Crop cultivation practices and soil legacies are intrinsically linked and are hypothesized to influence direct and indirect plant defences against phytophagous insects. In this study, we tested how soils conditioned by push-pull (maize (Zea mays)- Desmodium spp.- Brachiaria spp. intercrop) or maize monoculture (non-push-pull) affect maize phytochemistry and subsequent resistance to fall armyworm (Spodoptera frugiperda Smith, Lepidoptera: Noctuidae). We hypothesised that conditioning soil with push-pull positively impacted maize growth, metabolism, and subsequent direct and indirect resistance to an invasive herbivore pest. Maize was grown in soils collected from push-pull and maize monoculture fields. We compared maize growth, herbivore larval feeding, production of defense secondary metabolites on maize grown in soils conditioned by push-pull and non-push-pull cropping. As a proxy for indirect defence effects, we also measured behavioural responses of egg-larval parasitoid Chelonus bifoveolatus Szpligeti (Hymenoptera: Braconidae) to maize volatiles from plants planted in soils conditioned by each cropping system. Maize plants grown in soil conditioned by push-pull had a higher biomass accumulation and plant height. Higher quantities and more diverse volatile and non-volatiles metabolites were observed in maize grown in push-pull soil in comparison to those grown in maize monoculture soil. Behavioural assays showed that S. frugiperda neonate fed more on leaf tissue from maize plants planted in soil conditioned by maize monoculture than those planted in push-pull conditioned soil. Parasitoid wasps were more attracted to volatiles from maize planted in push-pull conditioned soils than those planted in non-push-pull soils. Our results indicate that conditioning soil with polyculture push-pull enhances maize growth, alters phytochemistry and subsequent direct and indirect resistance to S. frugiperda.

Intercropping is drawing increasing attention as a strategy to increase crop yields and manage pest pressure, however the mechanisms of associational resistance in diversified cropping systems remain controversial. We conducted a controlled experiment to assess the impact of co-planting with silverleaf Desmodium (Desmodium uncinatum) on maize secondary metabolism and resistance to herbivory by the spotted stemborer (Chilo partellus). Maize plants were grown either in the same pot with a Desmodium plant or adjacent to it in a separate pot. Our findings indicate that co-planting with Desmodium influences maize secondary metabolism and herbivore resistance through both above and below-ground mechanisms. Maize growing in the same pot with a Desmodium neighbor was less attractive for oviposition by spotted stemborer adults. However, maize exposed only to above-ground Desmodium cues generally showed increased susceptibility to spotted stemborer herbivory (through both increased oviposition and larval consumption). VOC emissions and tissue secondary metabolite titers were also altered in maize plants exposed to Desmodium cues, with stronger effects being observed when maize and Desmodium shared the same pot. Specifically, benzoxazinoids were strongly suppressed in maize roots by direct contact with a Desmodium neighbor while headspace emissions of short-chain aldehydes and alkylbenzenes were increased. These results imply that direct root contact or soil-borne cues play an important role in mediating associational effects on plant resistance in this system.

Plant induced responses to environmental stressors are increasingly studied in a behavioral ecology context. This is particularly true for plant induced responses to herbivory that mediate direct and indirect defenses, and tolerance. These seemingly adaptive alterations of plant defense phenotypes in the context of other environmental conditions have led to the discussion of such responses as intelligent behavior. Here we consider the concept of plant intelligence and some of its predictions for chemical information transfer in plant interaction with other organisms. Within this framework, the flow, perception, integration, and storage of environmental information are considered tunable dials that allow plants to respond adaptively to attacking herbivores while integrating past experiences and environmental cues that are predictive of future conditions. The predictive value of environmental information and the costs of acting on false information are important drivers of the evolution of plant responses to herbivory. We identify integrative priming of defense responses as a mechanism that allows plants to mitigate potential costs associated with acting on false information. The priming mechanisms provide short- and long-term memory that facilitates the integration of environmental cues without imposing significant costs. Finally, we discuss the ecological and evolutionary prediction of the plant intelligence hypothesis.

Plants defend themselves from herbivory by either reducing damage (resistance) or minimizing its negative fitness effects with compensatory growth (tolerance). Herbivore pressure can fluctuate from year to year in an early secondary successional community, which can create temporal variation in selection for defence traits. We manipulated insect herbivory and successional age of the community as agents of natural selection in replicated common gardens with the perennial herb Solidago altissima. In these genotypic selection experiments, herbivory consistently selected for better defended plants in both successional communities. Herbivore suppression increased plant survival and the probability of flowering only in mid-succession. Despite these substantial differences in the effects of herbivory between early and mid-succession, the selection on defence traits did not change. Succession affected selection only on aboveground biomass, with positive selection in early but not mid-succession, suggesting an important role of competition in the selective environment. These results demonstrate that changes in the community that affect key life-history traits in an individual species can occur over very short timescales in a dynamic secondary successional environment. The resulting community context-driven variation in natural selection may be an important, yet overlooked, contributor to adaptive mosaics across populations.

Volatile organic compounds (VOCs) in general and herbivory-induced plant volatiles (HIPVs) in particular are increasingly understood as major mediators of information transfer between plant tissues. Recent findings have moved the field of plant communication closer to a detailed understanding of how plants emit and perceive VOCs and seem to converge on a model that juxtaposes perception and emission mechanisms. These new mechanistic insights help to explain how plants can integrate different types of information and how environmental noise can affect the transmission of information. At the same time, ever-new functions of VOC-mediated plant-plant interactions are being revealed. Chemical information transfer between plants is now known to fundamentally affect plant organismal interactions and, additionally, population, community, and ecosystem dynamics. One of the most exciting new developments places plant-plant interactions along a behavioral continuum with an eavesdropping strategy at one end and mutually beneficial information-sharing among plants within a population at the other. Most importantly and based on recent findings as well as theoretical models, plant populations can be predicted to evolve different communication strategies depending on their interaction environment. We use recent studies from ecological model systems to illustrate this context dependency of plant communication. Moreover, we review recent key findings about the mechanisms and functions of HIPV-mediated information transfer and suggest conceptual links, such as to information theory and behavioral game theory, as valuable tools for a deeper understanding of how plant-plant communication affects ecological and evolutionary dynamics.

Farmers looking to maximize ecosystem services often use diversification practices on their fields to increase abundance and diversity of insect natural enemies. These practices affect functional traits of natural enemies such as body size that can play an important role in their effectiveness as biological control agents. However, landscape features out of the control of farmers might also affect functional traits of natural enemies and their herbivores, including land use surrounding farms. There have been few studies elucidating how landscape complexity and local diversity interact to affect functional traits, and ultimately ecosystem services such as predation on herbivore pests. We examined combined effects of landscape complexity and a local management practice (push‐pull) on lady beetle size, and its consequences for egg predation of lepidopteran pests in Kenyan smallholder maize farms. Cheilomenes sulphurea (Olivier) (Coleoptera: Coccinellidae), a potential predator of the invasive fall armyworm, Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae), was collected in push‐pull and control fields along a landscape gradient. We measured beetle size and conducted feeding assays with fall armyworm eggs. We found that female beetles had larger bodies in landscapes with greater complexity. Predation rates not only increased as a response to beetle size but also in response to landscape complexity, suggesting it is not just size that determines predation. Surprisingly, we did not find any effect of the local management practice or its interaction on functional traits or predation rates. Our study suggests that landscape complexity could benefit pest control through two mechanisms: (1) increase in predator body size, leading to higher predation rates; and (2) changes in predator behavior as a function of landscape characteristics – increasing egg predation. Further studies on these mechanisms would allow deeper understanding of landscape simplification's effect on ecosystem services, as mediated by morphological and behavioral traits, and help us harness these traits to increase biological control.

Light quality and chemicals in a plant's environment can provide crucial information about the presence and nature of antagonists, such as competitors and herbivores. Here, we evaluate the roles of three sources of information-shifts in the red:far red (R:FR) ratio of light reflected off of potentially competing neighbors, induced metabolic changes to damage by insect herbivores, and induced changes to volatile organic compounds emitted from herbivore-damaged neighboring plants-to affect metabolic responses in the tall goldenrod, Solidago altissima. We address the hypothesis that plants integrate the information available about competitors and herbivory to optimize metabolic responses to interacting stressors by exposing plants to the different types of environmental information in isolation and combination. We found strong interactions between the exposure to decreased R:FR light ratios and damage on the induction of secondary metabolites (volatile and non-volatile) in plants. Similarly, the perception of VOCs emitted from neighboring plants was altered by the simultaneous exposure to spectral cues from neighbors. These results suggest that plants integrate spectral and chemical environmental cues to change the production and perception of volatile and non-volatile compounds and highlight the role of plant context-dependent metabolic responses in mediating population and community dynamics.

Stickiness of vegetative tissues has evolved multiple times in different plant families but is rare and understudied in flowers. While stickiness in general is thought to function primarily as a defense against herbivores, it may compromise mutualistic interactions (such as those with pollinators) in reproductive tissues. Here, we test the hypothesis that stickiness on flower petals of the High-Andean plant, Bejaria resinosa (Ericaceae), functions as a defense against florivores. We address ecological consequences and discuss potential trade-offs associated with a repellant trait expressed in flowers that mediate mutualistic interactions. In surveys and manipulative experiments, we assess florivory and resulting fitness effects on plants with sticky and non-sticky flowers in different native populations of B. resinosa in Colombia . In addition, we analyze the volatile and non-volatile components in sticky and non-sticky flower morphs to understand the chemical information context within which stickiness is expressed. We demonstrate that fruit set is strongly affected by floral stickiness but also varies with population. While identifying floral stickiness as a major defensive function, our data also suggest that the context-dependency of chemical defense functionality likely arises from differential availability of primary pollinators and potential trade-offs between chemical defense with different modes of action.