Pathogen-mediated natural and manipulated population collapse in an invasive social insect.

SignificanceInvasive social insects are among the most damaging of invasive organisms and have proved universally intractable to biological control. Despite this, populations of some invasive social insects collapse from unknown causes. We report long-term studies demonstrating that infection by a microsporidian pathogen causes populations of a globally significant invasive ant to collapse to local extinction, providing a mechanistic understanding of a pervasive phenomenon in biological invasions: the collapse of established populations from endogenous factors. We apply this knowledge and successfully eliminate two large, introduced populations of these ants. More broadly, microsporidian pathogens should be evaluated for control of other supercolonial invasive social insects. Diagnosing the cause of unanticipated population collapse in invasive organisms can lead to applied solutions.

Sublethal pesticide exposure in non-target terrestrial ecosystems: From known effects on individuals to potential consequences on trophic interactions and network functioning.

Over the last decades, the intensification of agriculture has resulted in an increasing use of pesticides, which has led to widespread contamination of non-target ecosystems in agricultural landscapes. Plants and arthropods inhabiting these systems are therefore chronically exposed to, at least, low levels of pesticides through direct pesticide drift, but also through the contamination of their nutrient sources (e.g. soil water or host/prey tissues). Pesticides (herbicides, acaricides/insecticides and fungicides) are chemical substances used to control pests, such as weeds, phytophagous arthropods and pathogenic microorganisms. These molecules are designed to disturb specific physiological mechanisms and induce mortality in targeted organisms. However, under sublethal exposure, pesticides also affect biological processes including metabolism, development, reproduction or inter-specific interactions even in organisms that do not possess the molecular target of the pesticide. Despite the broad current knowledge on sublethal effects of pesticides on organisms, their adverse effects on trophic interactions are less investigated, especially within terrestrial trophic networks. In this review, we provide an overview of the effects, both target and non-target, of sublethal exposures to pesticides on traits involved in trophic interactions between plants, phytophagous insects and their natural enemies. We also discuss how these effects may impact ecosystem functioning by analyzing studies investigating the responses of Plant-Phytophage-Natural enemy trophic networks to pesticides. Finally, we highlight the current challenges and research prospects in the understanding of the effects of pesticides on trophic interactions and networks in non-target terrestrial ecosystems.

Prediction of the potential distribution area of Spodoptera frugiperda and its parasitic wasp, Trichogramma pretiosum.

Spodoptera frugiperda is a migratory agricultural pest with fast-spreading speed, long migration distance, and wide host range, which seriously threatens the safety of economic crops. To predict the trends of S. frugiperda and its parasitoid wasp Trichogramma pretiosum in their habitats under current and future climatic conditions, based on MaxEnt model and geographic distribution data of their historical occurrence, we project the feasibility of introducing T. pretiosum to control S. frugiperda by evaluating on their potential global distribution. The results show that, under the current greenhouse gas concentration, the potential distribution area of S. frugiperda is concentrated in 50° N-30° S, with a total area of 1.74 × 106 km2 , and the potential distribution area of T. pretiosum in the whole world is 2.91 × 106 km2 . The suitable areas of T. pretiosum cover almost all the suitable areas of S. frugiperda, which indicates that T. pretiosum can be introduced to control S. frugiperda. The results of this study can provide a theoretical basis for the monitoring and early warning of S. frugiperda and the use of T. pretiosum to control S. frugiperda.

Functional response and mutual interference in the parasitoid Coptera haywardi (Oglobin) (Hymenoptera: Diapriidae) attacking Anastrepha ludens (Loew) (Diptera: Tephritidae) pupae.

Functional response and mutual interference are important attributes of natural enemies that should be analysed in species with the potential to be used as biological control agents in order to increase the predictive power of the possible benefits and/or consequences of their release in the field. Our main objective was to determine the functional response and mutual interference of Coptera haywardi (Oglobin), a pupal parasitoid of economically important fruit flies (Diptera: Tephritidae). The functional response of C. haywardi on A. ludens pupae corresponded to a type II model, with an attack rate of 0.0134 host pupa/h and a handling time of 1.843 h, which reveals a meticulous selection process of pupal hosts. The effect of mutual interference among foraging females was negatively correlated with increased parasitoid density in the experimental arena, showing a gradual decline in attack rate per individual female. The increase in the number of foraging females also had an impact on the number of oviposition scars per pupa and the number of immature parasitoids per dissected pupa, but not on the percentage of adult emergence or the sex ratio. Our results suggest that C. haywardi could act as a complementary parasitoid in the control of fruit fly pupae, since the random distribution of these pupae in the soil would decrease the possibility of aggregation and mutual interference between foraging females.

Functional response of Franklinothrips vespiformis (Thysanoptera: Aeolothripidae) to eggs and nymphs of Bemisia tabaci (Hemiptera: Aleyrodidae).

The Middle East Asia Minor 1 biotype of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is a greenhouse and field crop pest of global significance. The objective of this study was to assess the potential of the generalist predatory thrips, Franklinothrips vespiformis Crawford (Thysanoptera: Aeolothripidae), as a biological control agent for B. tabaci. This was achieved by determining the functional responses of F. vespiformis larvae and adults to the egg and nymphal stages of B. tabaci under laboratory conditions. Analyses consisted of 10 replicates of each predator and prey stage combination on bean leaf discs for a 24-h period. Following logistic regression analyses to determine the functional response type exhibited, response parameters were estimated with nonlinear least squares regression using Roger's equation. Results showed that F. vespiformis larvae and adults exhibited a Type II functional response when feeding on immature B. tabaci. The handling times (Th) of F. vespiformis larvae and adults were magnitudes higher for B. tabaci nymphs than they were for eggs, which were in part driven by the higher attack rates (a) observed on eggs. The maximum attack rate (T/Th) for B. tabaci eggs and nymphs exhibited by first-stage larvae, second-stage larvae, and adult F. vespiformis increased with increasing predator age. Results from this study suggest that F. vespiformis larvae and particularly adults are promising biological control agents for B. tabaci and are efficient predators at both low and high prey densities.

The Biology and Ecology of Parasitoid Wasps of Predatory Arthropods.

Parasitoid wasps are important components of insect food chains and have played a central role in biological control programs for over a century. Although the vast majority of parasitoids exploit insect herbivores as hosts, others parasitize predatory insects and arthropods, such as ladybird beetles, hoverflies, lacewings, ground beetles, and spiders, or are hyperparasitoids. Much of the research on the biology and ecology of parasitoids of predators has focused on ladybird beetles, whose parasitoids may interfere with the control of insect pests like aphids by reducing ladybird abundance. Alternatively, parasitoids of the invasive ladybird Harmonia axyridis may reduce its harmful impact on native ladybird populations. Different life stages of predatory insects and spiders are susceptible to parasitism to different degrees. Many parasitoids of predators exhibit intricate physiological interrelationships with their hosts, adaptively manipulating host behavior, biology, and ecology in ways that increase parasitoid survival and fitness.

Sublethal chemical stimulation of arthropod parasitoids and parasites of agricultural and environmental importance.

An increasing number of studies have reported stimulation of various organisms in the presence of environmental contaminants. This has created a need to critically evaluate sublethal stimulation and hormetic responses of arthropod parasitoids and parasites following exposure to pesticides and other contaminants. Examining this phenomenon with a focus on arthropods of agricultural and environmental importance serves as the framework for this literature review. This review shows that several pesticides, with diverse chemical structures and different modes of action, applied individually or in combination at sublethal doses, commonly stimulate an array of arthropod parasitoids and parasites. Exposure at sublethal doses can enhance responses related to physiology (e.g., respiration, total lipid content, and total protein content), behavior (e.g., locomotor activity, antennal drumming frequency, host location, and parasitization), and fitness (longevity, growth, fecundity, population net and gross reproduction). Concordantly, the parasitic potential (e.g., infestation efficacy, parasitization rate, and parasitoid/parasite emergence) can be increased, and as a result host activities inhibited. There is some evidence illustrating hormetic dose-responses, but the relevant literature commonly included a limited number and range of doses, precluding a robust differentiation between sub- and superNOAEL (no-observed-adverse-effect level) stimulation. These results reveal a potentially significant threat to ecological health, through stimulation of harmful parasitic organisms by environmental contaminants, and highlight the need to include sublethal stimulation and hormetic responses in relevant ecological pesticide risk assessments. Curiously, considering a more utilitarian view, hormesis may also assist in optimizing mass rearing of biological control agents for field use, a possibility that also remains neglected.

Cannibalistic enemy-pest model: effect of additional food and harvesting.

Biological control using natural enemies with additional food resources is one of the most adopted and ecofriendly pest control techniques. Moreover, additional food is also provided to natural enemies to divert them from cannibalism. In the present work, using the theory of dynamical system, we discuss the dynamics of a cannibalistic predator prey model in the presence of different harvesting schemes in prey (pest) population and provision of additional food to predators (natural enemies). A detailed mathematical analysis and numerical evaluations have been presented to discuss the pest free state, coexistence of species, stability, occurrence of different bifurcations (saddle-node, transcritical, Hopf, Bogdanov-Takens) and the impact of additional food and harvesting schemes on the dynamics of the system. It has been obtained that the multiple coexisting equilibria and their stability depend on the additional food (quality and quantity) and harvesting rates. Interestingly, we also observe that the pest population density decreases immediately even when small amount of harvesting is implemented. Also the eradication of pest population (stable pest free state) could be achieved via variation in the additional food and implemented harvesting schemes. The individual effects of harvesting parameters on the pest density suggest that the linear harvesting scheme is more effective to control the pest population rather than constant and nonlinear harvesting schemes. In the context of biological control programs, the present theoretical work suggests different threshold values of implemented harvesting and appropriate choices of additional food to be supplied for pest eradication.

Potential demographic impact of the insecticide mixture between thiacloprid and deltamethrin on the cotton aphid and two of its natural enemies.

The use of pesticides impairs biological control in the agroecosystems and thus compromises the effectiveness of natural enemies against populations of pest species. The concerns over pesticides should expand beyond mortality and encompass their sublethal effects and their consequences to the target insect species and natural enemies to aid in our understanding of the potential and consequential use of these compounds. The present study aimed to determine the effects of an insecticide mixture on life-history and demographic parameters of the cotton aphid Aphis gossypii Glover (Hemiptera: Aphididae) and two of its main parasitoids - Aphidius flaviventris Kurdjumov (Hymenoptera: Aphelinidae) and Aphidius colemani Viereck (Hymenoptera: Braconidae). Based on the obtained results, thiacloprid + deltamethrin in its lethal concentration dose 20% of the pest population (LC20) significantly affected the cotton aphid for two generations, increasing developmental time and demographic parameters. The LC20 manifested changes in many demographic parameters of the parasitoid A. flaviventris. This concentration also increased preadult and female longevity, total pre-ovipositional period, and mean generation time (T) of A. colemani, but no other demographic parameters were affected. Nonetheless, the insecticide mixture did not affect the parasitism rate of A. colemani. Thus, the thiacloprid + deltamethrin mixture significantly impaired the cotton aphid population and its parasitoid A. flaviventris. Therefore, the use of thiacloprid + deltamethrin is not encouraged for controlling the parasitoid A. flaviventris, but it is a relatively safe compound for A. colemani.

Aphaereta pallipes (Hymenoptera: Braconidae) and Dirhinus anthracia (Hymenoptera: Chalcididae) associated with Peckia (Euboettcheria) collusor (Diptera: Sarcophagidae) in Brazil.

Flies of the Sarcophagidae family are widely distributed in the world, occupying different habitats. Some species have a high degree of synanthropy and are therefore often found in households in the urban environment. In Brazil, there is still little information related to the natural enemies of these insects in the urban environment, where population control is strictly chemical. Therefore, larvae and pupae of Peckia (Euboettcheria) collusor (Curran and Walley) (Diptera: Sarcophagidae) species were exposed in an urbanized location, and the presence and prevalence of parasitoids in the natural control of these immature stages was evaluated. We report for the first time the species Aphaereta pallipes (Say) (Hymenoptera: Braconidae) and Dirhinus anthracia Walker (Hymenoptera: Chalcididae), associated with P. (E.) collusor, highlighting the importance of these parasitoids in natural control in the urban environment, in addition to expanding the list of hosts for both parasitoid species and the distribution of this parasitoid-host interaction for Brazil and the Neotropical region.

First record of Fusarium concentricum (Hypocreales: Hypocreaceae) isolated from the moth Polychrosis cunninhamiacola (Lepidoptera: Tortricidae) as an entomopathogenic fungus.

Fusarium concentricum Nirenberg & O' Donnell (Ascomycota: Hypocreales) is a fungal species known to infect plants, but never reported as entomopathogenic. Polychrosis cunninhamiacola Liu et Pei (Lepidoptera: Tortricidae: Olethreutinae) is a major and widespread insect pest causing economic losses to cultivated Chinese fir Cunninghamia lanceolata (Lamb.) Hook. It is routinely controlled by extensive use of chemical insecticides, which is perceived as environmentally unsustainable. During March and April of 2019-2020, muscardine cadavers of larvae and pupae of P. cunninhamiacola infected with growing fungus were collected in a fir forest in northern Guangdong Province, China. Conidia were isolated and cultured on PDA medium, from which the fungal strain was identified as F. concentricum FCPC-L01 by morphology and by sequence alignment match with Tef-1α gene. Pathogenicity bioassays at the conidial concentration 1 × 107 revealed P. cunninhamiacola adults and Danaus chrysippus (L.) (Lepidoptera: Nymphalidae) larvae are sensitive to the fungal infection, but not the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae). We believe results indicate this fungal strain might be applicable against specific target insect pests. As this is the first record of a natural infection caused by F. concentricum in insects, we propose host specificity tests should be done to evaluate its potential as a biocontrol agent.

Archetype models upscale understanding of natural pest control response to land-use change.

Control of crop pests by shifting host plant availability and natural enemy activity at landscape scales has great potential to enhance the sustainability of agriculture. However, mainstreaming natural pest control requires improved understanding of how its benefits can be realized across a variety of agroecological contexts. Empirical studies suggest significant but highly variable responses of natural pest control to land-use change. Current ecological models are either too specific to provide insight across agroecosystems or too generic to guide management with actionable predictions. We suggest obtaining the full benefit of available empirical, theoretical, and methodological knowledge by combining trait-mediated understanding from correlative studies with the explicit representation of causal relationships achieved by mechanistic modeling. To link these frameworks, we adapt the concept of archetypes, or context-specific generalizations, from sustainability science. Similar responses of natural pest control to land-use gradients across cases that share key attributes, such as functional traits of focal organisms, indicate general processes that drive system behavior in a context-sensitive manner. Based on such observations of natural pest control, a systematic definition of archetypes can provide the basis for mechanistic models of intermediate generality that cover all major agroecosystems worldwide. Example applications demonstrate the potential for upscaling understanding and improving predictions of natural pest control, based on knowledge transfer and scientific synthesis. A broader application of this mechanistic archetype approach promises to enhance ecology's contribution to natural resource management across diverse regions and social-ecological contexts.

An aggressive nonconsumptive effect mediates pest control and multipredator interactions in a coffee agroecosystem.

Natural pest control is an alternative to pesticide use in agriculture, and may help to curb insect declines and promote crop production. Nonconsumptive interactions in natural pest control that historically have received far less attention than consumptive interactions, may have distinct impacts on pest damage suppression and may also mediate positive multipredator interactions. Additionally, when nonconsumptive effects are driven by natural enemy aggression, variation in alternative resources for enemies may impact the strength of pest control. Here we study control of the coffee berry borer (CBB), Hypothenemus hampei, by a keystone arboreal ant species, Azteca sericeasur, which exhibits a nonconsumptive effect on CBB by throwing them off coffee plants. We conducted two experiments to investigate: (1) if the strength of this behavior is driven by spatial or temporal variability in scale insect density (an alternative resource that Azteca tends for honeydew), (2) if this behavior mediates positive interactions between Azteca and other ground-foraging ants, and (3) the effect this behavior has on the overall suppression of CBB damage in multipredator scenarios. Our behavioral experiment showed that nearly all interactions between Azteca and CBB are nonconsumptive and that this behavior occurs more frequently in the dry season and with higher densities of scale insects on coffee branches. Our multipredator experiment revealed that borers thrown off coffee plants by Azteca can survive and potentially damage other nearby plants but may be suppressed by ground-foraging ants. Although we found no non-additive effects between Azteca and ground-foraging ants on overall CBB damage, together, both species resulted in the lowest level of plant damage with the subsequent reduction in "spillover" damage caused by thrown CBB, indicating spatial complementarity between predators. These results present a unique case of natural pest control, in which damage suppression is driven almost exclusively by nonconsumptive natural enemy aggression, as opposed to consumption or prey behavioral changes. Furthermore, our results demonstrate the variability that may occur in nonconsumptive pest control interactions when natural enemy aggressive behavior is impacted by alternative resources, and also show how these nonconsumptive effects can mediate positive interactions between natural enemies to enhance overall crop damage reduction.

The distribution of covert microbial natural enemies of a globally invasive crop pest, fall armyworm, in Africa: Enemy release and spillover events.

Invasive species pose a significant threat to biodiversity and agriculture world-wide. Natural enemies play an important part in controlling pest populations, yet we understand very little about the presence and prevalence of natural enemies during the early invasion stages. Microbial natural enemies of fall armyworm Spodoptera frugiperda are known in its native region, however, they have not yet been identified in Africa where fall armyworm has been an invasive crop pest since 2016. Larval samples were screened from Malawi, Rwanda, Kenya, Zambia, Sudan and Ghana for the presence of four different microbial natural enemies; two nucleopolyhedroviruses, Spodoptera frugiperda NPV (SfMNPV) and Spodoptera exempta NPV (SpexNPV); the fungal pathogen Metarhizium rileyi; and the bacterium Wolbachia. This study aimed to identify which microbial pathogens are present in invasive fall armyworm, and determine the geographical, meteorological and temporal variables that influence prevalence. Within 3 years of arrival, fall armyworm was exposed to all four microbial natural enemies. SfMNPV probably arrived with fall armyworm from the Americas, but this is the first putative evidence of host spillover from Spodoptera exempta (African armyworm) to fall armyworm for the endemic pathogen SpexNPV and for Wolbachia. It is also the first confirmed incidence of M. rileyi infecting fall armyworm in Africa. Natural enemies were localised, with variation being observed both nationally and temporally. The prevalence of SfMNPV (the most common natural enemy) was predominantly explained by variables associated with the weather; declining with increasing rainfall and increasing with temperature. However, virus prevalence also increased as the growing season progressed. The infection of an invasive species with a natural enemy from its native range and novel pathogens specific to its new range has important consequences for understanding the population ecology of invasive species and insect-pathogen interactions. Additionally, while it is widely known that temporal and geographic factors affect insect populations, this study reveals that these are important in understanding the distribution of microbial natural enemies associated with invasive pests during the early stages of invasion, and provide baseline data for future studies.

Identification of entomopathogenic fungus Metarhizium rileyi infested in fall armyworm in the cornfield of Korea, and evaluation of its virulence.

The fall armyworm (FAW) Spodoptera frugiperda is an important invasive pest in Africa and Asia. It is a polyphagous pest with at least 353 recorded host plant species, including corn. Chemical control of this pest is unsuccessful because of a developed resistance and harmful effects on the environment. Entomopathogenic fungi are potential biological control agents for FAW. In this study, the native strain of Metarhizium rileyi (KNU-Ye-1), collected from a cornfield at Yeongcheon, Korea, was identified by morphological and molecular characterization. The susceptibility of the fourth-instar larvae of FAW to the native strain M. rileyi was examined in the laboratory. The results showed that the Korean strain of M. rileyi (KNU-Ye-1) was highly virulent to FAW larvae, causing 89% mortality 7 days posttreatment. Therefore, M. rileyi (KNU-Ye-1) identified in this study is highly valuable for the biological control of FAW in the field.

Toxicity of Photorhabdus luminescens and Xenorhabdus bovienii bacterial metabolites to pecan aphids (Hemiptera: Aphididae) and the lady beetle Harmonia axyridis (Coleoptera: Coccinellidae).

Toxicity of the metabolites of two bacteria, Photorhabdus luminescens and Xenorhabdus bovienii, symbionts of entomopathogenic nematodes, were tested in the laboratory against the multicolored Asian lady beetle, Harmonia axyridis, the black pecan aphid, Melanocallis caryaefoliae, and the blackmargined aphid, Monellia caryella. Bacterial broth prepared from both P. luminescens and X. bovienii demonstrated high levels of toxicity equivalent to the pyrethroid insecticide bifenthrin and caused higher insect mortality than tryptic soy broth plus yeast extract (TSY) (blank control) against M. caryella; broth culture of P. luminescens was more effective than TSY against M. caryaefoliae. At the levels tested, the metabolites were not toxic to H. axyridis.

Effect of Different Wheat-Based Diets and Corn Meal Addition on Development Parameters of Ephestia kuehniella (Zeller, 1879) (Lepidoptera: Pyralidae).

The expansion of Integrated Pest Management (IPM), including biological control, has had several positive consequences for the agricultural environment and participants in the production chain. To enable successful operation and applications of biological control, production of insects used for rearing natural enemies (parasitoids and predators) must be optimized to reduce time and costs and improve production both qualitatively and quantitatively. The present study evaluated the effect of wheat varieties, the main component of artificial diets for Ephestia kuehniella, on the reproductive performance and biological parameters of this flour moth, which is used for mass production of Trichogramma spp. (Hymenoptera: Trichogrammatidae) and other parasitoids and predators. Four varieties of wheat were compared: BRS 327, BRS Marcante, BRS Parrudo, and KBR, with and without the addition of corn E. kuehniella reared on 97% BRS 327 wheat flour + 3% nutritional yeast had the best biological parameters and substitution of corn for about half of the wheat increased the number of eggs per female.

Characterizing the Complete Mitochondrial Genome of Arma custos and Picromerus lewisi (Hemiptera: Pentatomidae: Asopinae) and Conducting Phylogenetic Analysis.

We characterized the mitochondrial genome (mitogenome) and conducted phylogenetic analyses of 48 Hemiptera species by sequencing and analyzing the mitogenome of Arma custos (Fabricius) and Picromerus lewisi (Scott). The complete mitogenomes of the two predators were 16,024 bp and 19,587 bp in length, respectively, and it contained 37 classical genes, including 13 protein-coding genes (PCGs), 2 ribosomal RNA genes (rRNAs), and 22 transfer RNA genes (tRNAs), and a control region. Most PCGs in these predators use ATN as the start codon. This research revealed that the genes of the two natural enemy species have an A + T content of 75.40% and all tRNAs have a typical cloverleaf structure, with the exception of trnS1, which lacks a dihydrouridine arm. This is the first study to compare the mitochondrial genetic structure of two predatory insects; the mitochondrial genetic structure of individual predatory insects has been sequenced in previous studies. Here, phylogenetic analysis on the basis of amino acid and nucleotide sequences of 13 mitochondrial PCGs using Bayesian inference and maximum likelihood methods were conducted to generate similar tree topologies, which suggested that the two predators with close genetic relationships belong to Asopinae subfamily. Furthermore, the monophyly of the Pentatomoidea superfamily is well accepted despite limited taxon and species sampling. Finally, their complete mitogenome provided data to establish a predator-prey food web, which is the foundation of effective pest management. Our results also enhanced the database of natural enemy insects.

The Role of Experiments in Monarch Butterfly Conservation: A Review of Recent Studies and Approaches.

Monarch butterflies (Danaus plexippus) (Lepidoptera Danaidae Danaus plexippus (Linnaeus)) are an iconic species of conservation concern due to declines in the overwintering colonies over the past twenty years. Because of this downward trend in overwintering numbers in both California and Mexico, monarchs are currently considered 'warranted-but-precluded' for listing under the Endangered Species Act. Monarchs have a fascinating life history and have become a model system in chemical ecology, migration biology, and host-parasite interactions, but many aspects of monarch biology important for informing conservation practices remain unresolved. In this review, we focus on recent advances using experimental and genetic approaches that inform monarch conservation. In particular, we emphasize three areas of broad importance, which could have an immediate impact on monarch conservation efforts: 1) breeding habitat and host plant use, 2) natural enemies and exotic caterpillar food plants, and 3) the utility of genetic and genomic approaches for understanding monarch biology and informing ongoing conservation efforts. We also suggest future studies in these areas that could improve our understanding of monarch behavior and conservation.

Plant Secondary Metabolites as Defense Tools against Herbivores for Sustainable Crop Protection.

Plants have evolved several adaptive strategies through physiological changes in response to herbivore attacks. Plant secondary metabolites (PSMs) are synthesized to provide defensive functions and regulate defense signaling pathways to safeguard plants against herbivores. Herbivore injury initiates complex reactions which ultimately lead to synthesis and accumulation of PSMs. The biosynthesis of these metabolites is regulated by the interplay of signaling molecules comprising phytohormones. Plant volatile metabolites are released upon herbivore attack and are capable of directly inducing or priming hormonal defense signaling pathways. Secondary metabolites enable plants to quickly detect herbivore attacks and respond in a timely way in a rapidly changing scenario of pest and environment. Several studies have suggested that the potential for adaptation and/or resistance by insect herbivores to secondary metabolites is limited. These metabolites cause direct toxicity to insect pests, stimulate antixenosis mechanisms in plants to insect herbivores, and, by recruiting herbivore natural enemies, indirectly protect the plants. Herbivores adapt to secondary metabolites by the up/down regulation of sensory genes, and sequestration or detoxification of toxic metabolites. PSMs modulate multi-trophic interactions involving host plants, herbivores, natural enemies and pollinators. Although the role of secondary metabolites in plant-pollinator interplay has been little explored, several reports suggest that both plants and pollinators are mutually benefited. Molecular insights into the regulatory proteins and genes involved in the biosynthesis of secondary metabolites will pave the way for the metabolic engineering of biosynthetic pathway intermediates for improving plant tolerance to herbivores. This review throws light on the role of PSMs in modulating multi-trophic interactions, contributing to the knowledge of plant-herbivore interactions to enable their management in an eco-friendly and sustainable manner.