Terpenes from herbivore-induced tomato plant volatiles attract Nesidiocoris tenuis (Hemiptera: Miridae), a predator of major tomato pests

The oviposition of cotton bollworms stimulates the defense against its eggs and larvae in tomato plants

BACKGROUND

Herbivorous insects sustain their populations by oviposition. To reduce the damage caused by herbivores, the host plant triggers a defensive response upon detection of egg deposition. However, the specific impact of the egg deposition time of the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae), on the tomato plant defense remains obscure.

RESULTS

This study investigated the effects of tomato plant defenses on cotton bollworm eggs and larvae at different time intervals following egg deposition. The study revealed that tomato plant defense triggered by egg deposition did not directly affect the hatchability of the eggs. Nevertheless, it attracted Trichogramma chilonis 48 h after the egg deposition. Gas chromatography-mass spectrometry analysis of the oviposition-induced plant volatiles (OIPVs) revealed a considerable increase in the amount of α-pinene released by tomato plants 48 h after egg deposition. The olfactory results from Y-tube experiments showed that α-pinene exhibited a substantial attraction towards T. chilonis. In addition, it was found that the defense response induced by egg deposition for 24 and 48 h significantly inhibited the growth and development of the larvae. Metabolomics analysis revealed that the egg deposition of cotton bollworm altered the metabolite composition and caused significant modifications in the metabolic pathways of tomato plants.

CONCLUSION

These findings provide novel insights into pest management by using egg-induced plant defenses to reduce egg hatching, and impede larval growth and development in herbivorous insects. © 2024 Society of Chemical Industry.

Tritrophic Interactions Mediated by Zoophytophagous Predator-Induced Host Plant Volatiles

The zoophytophagous mirid predator Nesidiocoris tenuis and the ectoparasitoid Stenomesius japonicus are important biological control agents for several agricultural pests including the invasive leafminer, Phthorimaea absoluta, a destructive pest of Solanaceous crops especially tomato in sub-Saharan Africa. However, little is known about how feeding by N. tenuis can influence the tritrophic interactions in the tomato plant. Here, we tested the hypothesis that N. tenuis phytophagy would influence the tritrophic olfactory interactions between the host plant tomato and pest, predator, and parasitoid. In olfactometer assays, P. absoluta females and N. tenuis adults were both attracted to constitutive volatiles released by the tomato plant. Whereas females of P. absoluta avoided volatiles released by N. tenuis-infested plants, S. japonicus females and N. tenuis adults were attracted to the induced volatiles. In coupled gas chromatography-electroantennographic detection (GC-EAD) recordings of intact and N. tenuis-infested plant volatiles, antennae of P. absoluta and S. japonicus females both detected eight components, whereas N. tenuis adults detected seven components which were identified by GC-mass spectrometry (GC-MS) as terpenes and green leaf volatiles (GLVs). Dose-response olfactometer bioassays revealed that the responses of P. absoluta, N. tenuis, and S. japonicus varied with the composition and concentration of blends and individual compounds tested from N tenuis-induced volatiles. Females of P. absoluta showed no preference for an eight-component blend formulated from the individual repellents including hexanal, (Z)-3-hexenyl butanoate, and δ-elemene identified in the volatiles. On the other hand, S. japonicus females were attracted to an eight-component blend including the attractants (E)-2-hexenal, (Z)-3-hexenol, methyl salicylate, β-phellandrene, and (E)-caryophyllene. Likewise, N. tenuis adults were attracted to a seven-component blend including the attractants β-phellandrene, δ-elemene, and (E)-caryophyllene identified in the volatiles. Our findings suggest that there is potential for the use of terpenes and GLVs to manage the insects in the tritrophic interaction.

Tomato yellow leaf curl virus manipulates Bemisia tabaci, MEAM1 both directly and indirectly through changes in visual and volatile cues

The sweetpotato whitefly, Bemisia tabaci MEAM1, is one of the most devastating pests of row-crop vegetables worldwide, damaging crops directly through feeding and indirectly through the transmission of many different viruses, including the geminivirus Tomato yellow leaf curl virus (TYLCV). Y-tube olfactometer tests were conducted at different stages of TYLCV infection in tomatoes to understand how TYLCV affects B. tabaci behavior. We also recorded changes in tomato hosts' color and volatile profiles using color spectrophotometry and gas chromatography-mass spectrometry (GC-MS). We found that the infection status of B. tabaci and the infection stage of TYLCV influenced host selection, with uninfected whiteflies showing a preference for TYLCV-infected hosts, especially during the late stages of infection. Viruliferous B. tabaci attraction to visual targets significantly differed from non-viruliferous B. tabaci. Late-stage infected hosts had larger surface areas reflecting yellow-green wavelengths and higher emissions of methyl salicylate in their volatile profiles. These findings shed new light on several critical mechanisms involved in the viral manipulation of an insect vector and its economically important host.

Plants recruit insecticidal bacteria to defend against herbivore attacks

Pest feeding affects the rhizobacteria community. The rhizomicrobiota activates salicylic acid and jasmonic acid signaling pathways to help plants deal with pest infestation. However, whether plants can recruit special pesticidal microorganisms to deal with attack from herbivores is unclear. A system composed of peanuts and first-instar larvae of Holotrichia parallela were used to analyze whether peanuts truly enrich the insecticidal bacteria after feeding by larvae, and whether inoculation of the enriched bacteria promotes the resistance of plants to herbivore. In this study, high-throughput sequencing of 16 S rRNA gene amplicons was used to demonstrate that infestation of the subterranean pest H. parallela quickly changed the rhizosphere bacterial community structure within 24 h, and the abundance of Enterobacteriaceae, especially Enterobacter, was manifestly enriched. Root feeding induced rhizobacteria to form a more complex co-occurrence network than the control. Rhizosphere bacteria were isolated, and 4 isolates with high toxicity against H. parallela larvae were obtained by random forest analysis. In a back-inoculation experiment using a split-root system, green fluorescent protein (GFP)-labeled Enterobacter sp. IPPBiotE33 was observed to be enriched in uneaten peanut roots. Additionally, supplementation with IPPBiotE33 alleviated the adverse effects of H. parallela on peanuts. Our findings indicated that herbivore infestation could induce plants to assemble bacteria with specific larvicidal activity to address threats.

Validating Indigenous Farmers' Practice in the Management of the Fall Armyworm Spodoptera frugiperda (J. E. Smith) in Maize Cropping Systems in Africa

Before the invasion of the fall armyworm (FAW) Spodoptera frugiperda into Africa, smallholder farmers had been using indigenous practices such as applying fish soup to plants to manage stemborer pests. Although farmers have since begun adapting this practice against FAW, no attempt has been made to scientifically evaluate this practice. Therefore, we assessed the efficacy of applying fish soup to maize plants that were artificially infested with FAW under semi-field conditions. Our results showed that foliar damage is inversely correlated with the concentration of a fish soup and sugar solution, with the highest (100%) concentration resulting in the lowest foliar damage and the highest plant recovery. The FAW foliar damage results for maize plants treated with 100%, 50%, 10% fish soup and sugar, and distilled water were 46.3 ± 5.6, 51.1 ± 5.0, 71.6 ± 5.2, and 99.4 ± 0.4%, respectively, whereas plant recovery results from the same treatments were 35.2 ± 3.7, 31.1 ± 5.4, 20.0 ± 4.6, and 0.0 ± 0.0%, respectively. A concentration of fish soup and sugar solution of at least 25.9% was required to achieve the lowest foliar damage of 17.8% and peak plant recovery of 73.6%. Fish soup and sugar solutions attracted a wide range of insects, including potential natural enemies (predators and parasitoids) of FAW, in a dose-dependent manner. Maize plants treated with fish soup and sugar showed higher chlorophyll content and better growth than the control did. Proximate and chemical analysis showed that fish soup contains essential plant growth nutrients (e.g., nitrogen, phosphorus, and calcium). Through GC-MS analyses, we identified 76 volatile organic compounds in fish soup, of which 16 have been reported as insect attractants, highlighting their potential ecological significance. Therefore, the indigenous pest management practices for FAW, such as the use of fish soup, deserve particular attention. These practices could contribute to food security and improve the livelihoods of vulnerable communities. Further field validation studies, economic analyses, product development, and optimisation are therefore required to optimise the use of fish soup based on fish waste.

Better Together: Volatile-Mediated Intraguild Effects on the Preference of Tuta absoluta and Trialeurodes vaporariorum for Tomato Plants

Plant-herbivore interactions have been extensively studied in tomato plants and their most common pests. Tomato plant chemical defenses, both constitutive and inducible, play a role in mediating these interactions. Damaged tomato plants alter their volatile profiles, affecting herbivore preferences between undamaged and damaged plants. However, previous studies on tomato volatiles and herbivore preferences have yielded conflicting results, both in the volatile chemistry itself as well as in the attraction/repellent herbivore response. This study revisits the volatile-mediated interactions between tomato plants and two of their main herbivores: the leafminer Tuta absoluta and the whitefly Trialeurodes vaporariorum. Tomato plant volatiles were analyzed before and after damage by each of these herbivores, and the preference for oviposition (T. absoluta) and settling (T. vaporariorum) on undamaged and damaged plants was assessed both after conspecific and heterospecific damage. We found that both insects consistently preferred damaged plants over undamaged plants. The emission of herbivore-induced plant volatiles (HIPVs) increased after T. absoluta damage but decreased after T. vaporariorum damage. While some of our findings are in line with previous reports, T. absoluta preferred to oviposit on plants damaged by conspecifics, which differs from earlier studies. A comparison of HIPVs emitted after damage by T. absoluta and T. vaporariorum revealed differences in up- or down-regulation, as well as significant variations in specific compounds (12 for T. absoluta and 26 for T. vaporariorum damaged-plants). Only two compounds, β-caryophyllene and tetradecane, significantly varied because of damage by either herbivore, in line with the overall variation of the HIPV blend. Differences in HIPVs and herbivore preferences may be attributed to the distinct feeding habits of both herbivores, which activate different defensive pathways in plants. The plant's challenge in simultaneously activating both defensive pathways may explain the preference for heterospecific damaged plants found in this study, which are also in line with our own observations in greenhouses.

Induction of Glandular Trichomes to Control Bemisia tabaci in Tomato Crops: Modulation by the Natural Enemy Nesidiocoris tenuis

Whitefly-transmitted viruses are one of the biggest threats to tomato (Solanum lycopersicum) growing worldwide. Strategies based on the introgression of resistance traits from wild relatives are promoted to control tomato pests and diseases. Recently, a trichome-based resistance characterizing the wild species Solanum pimpinellifolium was introgressed into a cultivated tomato. An advanced backcross line (BC5S2) exhibiting the presence of acylsugar-associated type IV trichomes, which are lacking in cultivated tomatoes, was effective at controlling whiteflies (Hemiptera: Aleyrodidae) and limiting the spread of whitefly-transmitted viruses. However, at early growth stages, type IV trichome density and acylsugar production are limited; thus, protection against whiteflies and whitefly-transmitted viruses remains irrelevant. In this work, we demonstrate that young BC5S2 tomato plants feeding-punctured by the zoophytophagous predator Nesidiocoris tenuis (Hemiptera: Miridae) displayed an increase (above 50%) in type IV trichome density. Acylsugar production was consistently increased in N. tenuis-punctured BC5S2 plants, which was more likely associated with upregulated expression of the BCKD-E2 gene related to acylsugar biosynthesis. In addition, the infestation of BC5S2 plants with N. tenuis effectively induced the expression of defensive genes involved in the jasmonic acid signaling pathway, resulting in strong repellence to Bemisia tabaci and attractiveness to N. tenuis. Thus, through preplant release of N. tenuis in tomato nurseries carried out in some integrated pest management programs, type IV trichome-expressing plants can be prepared to control whiteflies and whitefly-transmitted viruses at early growth stages. This study emphasizes the advantage of reinforcing constitutive resistance using defense inducers to guarantee robust protection against pests and transmitted viruses.

Dynamic distress calls: volatile info chemicals induce and regulate defense responses during herbivory

Plants are continuously threatened by a plethora of biotic stresses caused by microbes, pathogens, and pests, which often act as the major constraint in crop productivity. To overcome such attacks, plants have evolved with an array of constitutive and induced defense mechanisms- morphological, biochemical, and molecular. Volatile organic compounds (VOCs) are a class of specialized metabolites that are naturally emitted by plants and play an important role in plant communication and signaling. During herbivory and mechanical damage, plants also emit an exclusive blend of volatiles often referred to as herbivore-induced plant volatiles (HIPVs). The composition of this unique aroma bouquet is dependent upon the plant species, developmental stage, environment, and herbivore species. HIPVs emitted from infested and non-infested plant parts can prime plant defense responses by various mechanisms such as redox, systemic and jasmonate signaling, activation of mitogen-activated protein (MAP) kinases, and transcription factors; mediate histone modifications; and can also modulate the interactions with natural enemies via direct and indirect mechanisms. These specific volatile cues mediate allelopathic interactions leading to altered transcription of defense-related genes, viz., proteinase inhibitors, amylase inhibitors in neighboring plants, and enhanced levels of defense-related secondary metabolites like terpenoids and phenolic compounds. These factors act as deterrents to feeding insects, attract parasitoids, and provoke behavioral changes in plants and their neighboring species. This review presents an overview of the plasticity identified in HIPVs and their role as regulators of plant defense in Solanaceous plants. The selective emission of green leaf volatiles (GLVs) including hexanal and its derivatives, terpenes, methyl salicylate, and methyl jasmonate (MeJa) inducing direct and indirect defense responses during an attack from phloem-sucking and leaf-chewing pests is discussed. Furthermore, we also focus on the recent developments in the field of metabolic engineering focused on modulation of the volatile bouquet to improve plant defenses.

Herbivore-Dependent Induced Volatiles in Pear Plants Cause Differential Attractive Response by Lacewing Larvae

Biological control may benefit from the behavioral manipulation of natural enemies using volatile organic compounds (VOCs). Among these, herbivore-induced plant volatiles (HIPVs) provide potential tools for attracting or retaining predators and parasitoids of insect pests. This work aimed to characterize the VOCs emitted by pear plants in response to attack by Cacopsylla bidens (Hemiptera: Psyllidae), a major pest in pear orchards, to compare these with VOCs induced by a leaf chewing insect, Argyrotaenia sphaleropa (Lepidoptera: Tortricidae), and to evaluate the behavioral response of Chrysoperla externa (Neuroptera: Chrysopidae) to HIPVs from pear plants damaged by either herbivore. The results demonstrated that plants damaged by the pear psylla emitted VOC blends with increased amounts of aliphatic aldehydes. Leafroller damage resulted in increased amounts of benzeneacetonitrile, (E)-4,8-dimethylnona-1,3,7-triene, β-ocimene and caryophyllene. In olfactometer bioassays, larvae of C. externa were attracted to herbivore-damaged plants when contrasted with undamaged plants. When plant odors from psylla-damaged were contrasted with those of leafroller-damaged plants, C.externa preferred the former, also showing shorter response lag-times and higher response rates when psylla-damaged plants were present. Our results suggest that pear plants respond to herbivory by modifying their volatile profile, and that psylla-induced volatiles may be used as prey-specific chemical cues by chrysopid larvae. Our study is the first to report HIPVs in pear plants attacked by C. bidens, as well as the attraction of C. externa to psyllid-induced volatiles.

Chemosensory Protein 2 of Male Athetis lepigone Is Involved in the Perception of Sex Pheromones and Maize Volatiles

In moths, the interactions between chemosensory proteins (CSPs) and sex pheromones have yet to be comprehensively investigated. Here, we examined the function of AlepCSP2 in male Athetis lepigone based on protein expression, molecular docking, site-directed mutagenesis, fluorescence competitive binding analyses, and RNA interference (RNAi) experiments. We found that AlepCSP2 showed strong binding affinity for two sex pheromones and five maize volatiles and that binding was optimal under neutral conditions. Furthermore, we identified six amino acids as being key residues involved in the interaction between AlepCSP2 and multiple ligands. Further RNAi showed that siCSP2 males displayed consistently lower electroantennography responses to two sex pheromones and three maize volatiles at different dosages tested, and the mating rate also decreased significantly by 37.50%. These findings will contribute to characterizing the binding mechanisms of moth CSPs to sex pheromones and host volatiles and also identify unique targets for developing novel pest behavior disruptors.

Non-host plant odors influence the tritrophic interaction between tomato, its foliar herbivore Tuta absoluta and mirid predator Nesidiocoris tenuis

The tomato leafminer, Tuta absoluta is a destructive invasive pest of cultivated tomato and other Solanaceae plants, with yield losses of 80-100%. Mirid predators are key natural enemies of T. absoluta, but they also feed on host plants in the absence of their prey. Management of T. absoluta is a challenge due to its high biotic potential, resistance to many insecticides and the absence of sufficiently adapted auxiliary fauna in its new dispersion zones. Olfaction plays an important role in the tritrophic interaction between tomato, its herbivore pest T. absoluta and its mirid predators, which can be influenced by non-host plant odors. However, how non-host odours shape this interaction is poorly understood. Previously, we had demonstrated belowground crop protection properties of certain Asteraceae plants against the root-knot nematode Meloidogyne incognita, pest of tomato and other Solanaceae plants. Additionally, Asteraceae plants impact negatively on feeding behavior of above-ground pests of Solanaceae plants, including the greenhouse whitefly (Trialeurodes vaporariorum) and green peach aphid (Myzus persicae). Here, we tested the hypothesis that foliar volatiles from some of these non-host Asteraceae plants can influence the tomato-T. absoluta-mirid predator tritrophic interaction. In olfactometer assays, T. absoluta females were attracted to volatiles of the Solanaceae host plants tomato and giant nightshade but avoided volatiles of the Asteraceae plants, blackjack and marigold, and the positive control, wild tomato, when tested alone or in combination with the host plants. Coupled gas chromatography-mass spectrometry analysis showed that host and non-host plants varied in their emission of volatiles, mainly monoterpenes and sesquiterpenes. Random forest analysis combined with behavioral assays identified monoterpenes as the host plant attractive blend to T. absoluta and its mirid predator, with sesquiterpenes identified as the non-host plant repellent blend against T. absoluta. Contrastingly, the mirid predator was indifferent to the non-host plant repellent sesquiterpenes. Our findings indicate that terpenes influence the tomato-T. absoluta-mirid predator tritrophic interaction. Further, our results emphasize the importance of studying crop protection from a holistic approach to identify companion crops that serve multi-functional roles.

Plants strike back: Plant volatiles and their role in indirect defence against aphids

As sessile organisms, plants have evolved different strategies to defend themselves against various biotic stressors. An important aspect of the complex response of plants to biotic stress is the emission of volatile compounds (VOCs), which are involved in direct and indirect plant defence mechanisms. Indirect plant defences include a range of plant traits that mediate defence against herbivores and play an important ecological role by not only utilising plants' own capabilities, but also signalling and attracting natural enemies of herbivores. Often the combination of volatiles emitted is specific to herbivores; they are consequently recognised by parasites and other predators, providing a clear link between the volatile signature and the prey. In this review, we focus on indirect plant defence and summarise current knowledge and perspectives on relationships between plants, aphids and parasitic wasps.

Differential responses of Bactrocera dorsalis and its parasitoids to headspaces of different varieties of tree-attached mango fruits and the associated chemical profiles

Bactrocera dorsalis (Hendel) is a major pest of fruits and vegetables worldwide with documented losses of up to 100%. Various management techniques including the use of parasitoids, such as Fopius arisanus (Sonan) and Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) within the context of the Integrated Pest Management (IPM) approach have been deployed for its control. The effectiveness of parasitoids is well understood, but knowledge of the semiochemicals that mediate their behavior, as well as that of the host fruit fly to tree-attached mangoes, is lacking. Here, we first compared the attractiveness of the above-mentioned fruit fly and its parasitoids to volatiles of different treatments (non-infested physiologically mature unripe and ripe mangoes, mangoes newly exposed to ovipositing B. dorsalis, and mangoes on day 7 and day 9 post-oviposition) of tree-attached Kent, Apple, and Haden mango varieties relative to control (clean air). The fruit fly was significantly more attracted to the mango volatiles (up to 93% of responsive insects) compared to the control (clean air). Fopius arisanus was significantly more attracted to mangoes with ovipositing fruit flies (68–76%) while D. longicaudata was significantly more attracted to day 9 post-oviposited mangoes (64–72%) compared to the control. Secondly, we elucidated the headspace volatile profiles of the non-infested and infested tree-attached mangoes using gas chromatography linked to mass spectrometry (GC-MS). The volatiles revealed various types of organic compounds with qualitative and quantitative differences. The majority of the compounds were esters making 33.8% of the total number, followed by sesquiterpenes-16.4%, and monoterpenes-15.4% among others. Most compounds had higher release rates in headspace volatiles of fruit fly-infested mangoes. Lastly, we harvested the infested mangoes and incubated them for puparia recovery. The number of puparia recovered varied according to the mango variety with Apple mango registering 81.7% of the total, while none was recovered from Kent. These results represent the first report of the changes in the headspace components of non-infested and infested tree-attached mangoes and the associated differential responses of the mentioned insects. A follow-up study can reveal whether there is a convergence in olfactomes which is significant when developing baits that selectively attract the fruit fly and not its natural enemies and fill the knowledge gap from an evolutionary ecological perspective.

Molecular mechanisms, genetic mapping, and genome editing for insect pest resistance in field crops

Improving crop resistance against insect pests is crucial for ensuring future food security. Integrating genomics with modern breeding methods holds enormous potential in dissecting the genetic architecture of this complex trait and accelerating crop improvement. Insect resistance in crops has been a major research objective in several crop improvement programs. However, the use of conventional breeding methods to develop high-yielding cultivars with sustainable and durable insect pest resistance has been largely unsuccessful. The use of molecular markers for identification and deployment of insect resistance quantitative trait loci (QTLs) can fastrack traditional breeding methods. Till date, several QTLs for insect pest resistance have been identified in field-grown crops, and a few of them have been cloned by positional cloning approaches. Genome editing technologies, such as CRISPR/Cas9, are paving the way to tailor insect pest resistance loci for designing crops for the future. Here, we provide an overview of diverse defense mechanisms exerted by plants in response to insect pest attack, and review recent advances in genomics research and genetic improvements for insect pest resistance in major field crops. Finally, we discuss the scope for genomic breeding strategies to develop more durable insect pest resistant crops.

Alpha-Phellandrene and Alpha-Phellandrene-Rich Essential Oils: A Systematic Review of Biological Activities, Pharmaceutical and Food Applications

Alpha-phellandrene is a very common cyclic monoterpene found in several EOs, which shows extensive biological activities. Therefore, the main focus of the present systematic review was to provide a comprehensive and critical analysis of the state of the art regarding its biological activities and pharmaceutical and food applications. In addition, the study identified essential oils rich in alpha-phellandrene and summarized their main biological activities as a preliminary screening to encourage subsequent studies on their single components. With this review, we selected and critically analyzed 99 papers, using the following bibliographic databases: PubMed, SciELO, Wiley and WOS, on 8 July 2022. Data were independently extracted by four authors of this work, selecting those studies which reported the keyword "alpha-phellandrene" in the title and/or the abstract, and avoiding those in which there was not a clear correlation between the molecule and its biological activities and/or a specific concentration from its source. Duplication data were removed in the final article. Many essential oils have significant amounts of alpha-phellandrene, and the species Anethum graveolens and Foeniculum vulgare are frequently cited. Some studies on the above-mentioned species show high alpha-phellandrene amounts up to 82.1%. There were 12 studies on alpha-phellandrene as a pure molecule showed promising biological functions, including antitumoral, antinociceptive, larvicidal and insecticidal activities. There were 87 research works on EOs rich in alpha-phellandrene, which were summarized with a focus on additional data concerning potential biological activities. We believe this data is a useful starting point to start new research on the pure molecule, and, in particular, to distinguish between the synergistic effects of the different components of the OEs and those due to alpha-phellandrene itself. Toxicological data are still lacking, requiring further investigation on the threshold values to distinguish the boundary between beneficial and toxic effects, i.e., mutagenic, carcinogenic and allergenic. All these findings offer inspiration for potential applications of alpha-phellandrene as a new biopesticide, antimicrobial and antitumoral agent. In particular, we believe our work is of interest as a starting point for further studies on the food application of alpha-phellandrene.

Electroantennogram and machine learning reveal a volatile blend mediating avoidance behavior by Tuta absoluta females to a wild tomato plant

Tomato cultivation is threatened by the infestation of the nocturnal invasive tomato pinworm, Tuta absoluta. This study was based on field observations that a wild tomato plant, Solanum lycopersicum var. cerasiforme, grown in the Mount Kenya region, Kenya, is less attacked by T. absoluta, unlike the cultivated tomato plants like S. lycopersicum (var. Rambo F1). We hypothesized that the wild tomato plant may be actively avoided by gravid T. absoluta females because of the emission of repellent allelochemical constituents. Therefore, we compared infestation levels by the pest in field monocrops and intercrops of the two tomato genotypes, characterized the headspace volatiles, then determined the compounds detectable by the insect through gas chromatography-linked electroantennography (GC-EAG), and finally performed bioassays using a blend of four EAG-active compounds unique to the wild tomato. We found significant reductions in infestation levels in the monocrop of the wild tomato, and intercrops of wild and cultivated tomato plants compared to the monocrop of the cultivated tomato plant. Quantitative and qualitative differences were noted between volatiles of the wild and cultivated tomato plants, and between day and night volatile collections. The most discriminating compounds between the volatile treatments varied with the variable selection or machine learning methods used. In GC-EAG recordings, 16 compounds including hexanal, (Z)-3-hexenol, α-pinene, β-myrcene, α-phellandrene, β-phellandrene, (E)-β-ocimene, terpinolene, limonene oxide, camphor, citronellal, methyl salicylate, (E)-β-caryophyllene, and others tentatively identified as 3,7,7-Trimethyl-1,3,5-cycloheptatriene, germacrene D and cis-carvenone oxide were detected by antennae of T. absoluta females. Among these EAG-active compounds, (Z)-3-hexenol, α-pinene, α-phellandrene, limonene oxide, camphor, citronellal, (E)-β-caryophyllene and β-phellandrene are in the top 5 discriminating compounds highlighted by the machine learning methods. A blend of (Z)-3-hexenol, camphor, citronellal and limonene oxide detected only in the wild tomato showed dose-dependent repellence to T. absoluta females in wind tunnel. This study provides some groundwork for exploiting the allelochemicals of the wild tomato in the development of novel integrated pest management approaches against T. absoluta.

Plant Volatiles and Herbivore Induced Plant Volatiles from Chili Pepper Act as Attractant of the Aphid Parasitoid Aphelinus varipes (Hymenoptera: Aphelinidae)

Plants have evolved a number of different chemical defenses, covering nearly all classes of (secondary) metabolites, that represent a major barrier to herbivory: some are constitutive; others are induced after attacks from herbivores (HIPVs) and may elicit the attraction of predators and parasitoids. Here, we studied how the female solitary endoparasitoid Aphelinus varipes responds to plant and host aphid volatiles in a series of experiments on five commercially important vegetables that were either healthy or infested with the aphid Myzus persicae: chili pepper, eggplant, crown daisy, Chinese cabbage and cabbage. The results for the olfactory responses of A. varipes showed that the presence of M. persicae increased the attraction of the endoparasitoid to the infested plants. In a second experiment, volatiles from highly attractive and repellent plants were obtained via headspace collection to investigate volatiles from healthy and aphid-damaged plants. The results for the differences in volatile profiles in response to aphid infestation in chili pepper cultivar were dominated by the volatile blends, including α-pinene, decanal and phthalic acid, while in cabbage they were dominated by isophorone. Moreover, when HIPVs with different concentrations were compared, α-pinene at a dose rate of 100 ng/μL attracted more parasitoids, and the comparison was useful to understand the mechanisms of plant secondary volatiles during aphid infestation and to provide new resources to control this insect pest. Overall our study shows how HIPVs can bolster tritrophic interactions by enhancing the attractiveness of parasitoids.

The Endophyte Trichoderma asperellum M2RT4 Induces the Systemic Release of Methyl Salicylate and (Z)-jasmone in Tomato Plant Affecting Host Location and Herbivory of Tuta absoluta

The use of endophytic fungi has dramatically increased plant performance through the enhancement of plant protection against abiotic and biotic stressors. We previously demonstrated that the endophytic fungus Trichoderma asperellum M2RT4 improves tomato defenses against the tomato leafminer Tuta absoluta through the reduction of oviposition, leafmining, pupation, and adult emergence. However, the underlying mechanism by which the presence of this endophytic fungus within tomato host plant affects T. absoluta host selection and life-history traits is unknown. We tested the behavioral responses of T. absoluta in Y-tube olfactometer bioassays and found that females preferred non-inoculated tomato plants against those inoculated by endophytes. Additionally, T. absoluta females were not attracted to non-inoculated infested nor to inoculated-infested tomato plants. Chemical analysis revealed the emission of methyl salicylate in inoculated tomato plant and an increase in the amounts of monoterpenes emitted from non-inoculated infested plants. Additionally, we found that upon herbivory, T. asperellum M2RT4 modulates tomato plant chemistry through the production of (Z)-jasmone thus activating both salicylic and jasmonic acid defense pathways. Further, T. absoluta females were attracted to monoterpernes including α-pinene, 2-carene, and β-phellandrene but repelled by methyl salicylate. Methyl salicylate could therefore be considered as a good semiochemical-based candidate for sustainable T. absoluta management using a "push-pull" approach. However, in dose-response bioassays, females of T. absoluta did not show any preference to the four component-blend (α-pinene, 2-carene, β-phellandrene, and methyl salicylate). (Z)-jasmone-treated tomato leaflets significantly reduced the leafmining activity of the pest at the concentration of 10 ng/μL and causing the highest larval mortality rate (83%) with the shortest LT₅₀ (1.73 days) 7 days post-treatment. T. asperellum M2RT4 effect on herbivore performance was then (Z)-jasmone-mediated. These findings expand our understanding of how the endophytic fungus T. asperellum M2RT4 could mediate chemical interactions between T. absoluta and its host plant which are potentially important for development of environmentally friendly T. absoluta management programs.