Effect of methyl salicylate-based lures on beneficial and pest arthropods in strawberry

Harnessing Phytohormones: Advancing Plant Growth and Defence Strategies for Sustainable Agriculture

Phytohormones, pivotal regulators of plant growth and development, are increasingly recognized for their multifaceted roles in enhancing crop resilience against environmental stresses. In this review, we provide a comprehensive synthesis of current research on utilizing phytohormones to enhance crop productivity and fortify their defence mechanisms. Initially, we introduce the significance of phytohormones in orchestrating plant growth, followed by their potential utilization in bolstering crop defences against diverse environmental stressors. Our focus then shifts to an in-depth exploration of phytohormones and their pivotal roles in mediating plant defence responses against biotic stressors, particularly insect pests. Furthermore, we highlight the potential impact of phytohormones on agricultural production while underscoring the existing research gaps and limitations hindering their widespread implementation in agricultural practices. Despite the accumulating body of research in this field, the integration of phytohormones into agriculture remains limited. To address this discrepancy, we propose a comprehensive framework for investigating the intricate interplay between phytohormones and sustainable agriculture. This framework advocates for the adoption of novel technologies and methodologies to facilitate the effective deployment of phytohormones in agricultural settings and also emphasizes the need to address existing research limitations through rigorous field studies. By outlining a roadmap for advancing the utilization of phytohormones in agriculture, this review aims to catalyse transformative changes in agricultural practices, fostering sustainability and resilience in agricultural settings.

Methyl Salicylate Can Benefit Ornamental Pest Control, and Does Not Alter Per Capita Predator Consumption at Close-Range

Methyl salicylate (MeSA) is an herbivore-induced plant volatile widely tested for attracting natural enemies for pest control. MeSA is commercially sold as slow-release lures or as a spray. While MeSA application has increased the abundance of natural enemies in numerous food crops, its ability to reduce pests for crop protection is not as frequently demonstrated. Our first objective was to test MeSA lures in ornamental fields where few studies have been done, and monitor natural enemies, pests, and crop protection. A 2-year study in spruce container yards revealed more aphid parasitoids (Pseudopraon sp.), fewer aphids (Mindarus obliquus) on shoot tips, and less shoot tip damage in MeSA plots during the first year. A 2-year study in red maple fields revealed more predatory lady beetles and rove beetles, and parasitic Ceraphronidae, Diapriidae, and Chalcidoidea in one or both years with MeSA. Fewer pest thrips were also captured in MeSA plots, though it is not clear whether this was due to enhanced predation or reduced colonization. Maple growth as measured by stem diameter change did not differ with MeSA use. A 2-year study examining predation on sentinel Halyomorpha halys eggs in various mature ornamental stock blocks found no increase in predation except for 1 month, though green lacewings, lady beetles, and predatory thrips occurred more in MeSA plots in the first year. While MeSA is expected to enhance biological control by herding in natural enemies, the impacts that applied volatiles have on predator efficiency is mostly unknown. Thus, our second objective examined how volatiles would impact feeding rates at close-range. Adult carabid Pterostichus melanarius, adult coccinellids Coccinella septempunctata and Harmonia axyridis, and larval lacewing Chrysoperla rufilabris consumed their prey at similar rates in the presence/absence of MeSA when food was presented directly in a 28 cm2 or 30 ml arena, or when foraging in a 520 cm2 outdoor soil arena or 946 ml arena with aphids on leaves.

New slow release mixture of (E)-β-farnesene with methyl salicylate to enhance aphid biocontrol efficacy in wheat ecosystem

Semiochemical use is a promising way to reduce damage from pests by improving natural control in agro-ecosystems. The aphid alarm pheromone (E)-β-farnesene (EβF) and herbivore-induced methyl salicylate (MeSA) are two volatile cues to induce changes in aphid behavior with functional significance. Because of limitations related to the volatility and oxidization of EβF and MeSA under natural conditions, slow-release and antioxidant techniques should be developed and optimized before application. Here, a slow-release alginate bead of EβF mixed with MeSA was first designed and manufactured. We hypothesized that a mixture of these two semiochemicals could be effective in controlling Sitobion miscanthi in wheat crops. Both MeSA and EβF in alginate beads were released stably and continuously for at least 15 days in the laboratory, whereas EβF in paraffin oil and pure MeSA were released for only 2 and 7 days, respectively. In 2018 field experiments, EβF and MeSA alone or in association significantly decreased the abundance of alate and apterous aphids. An increased abundance of mummified aphids enhanced by higher parasitism rates was observed when using EβF and MeSA in association, with a significant reduction of apterous abundance, more so than EβF or MeSA alone. In 2019, plots treated with a mixture of EβF and MeSA showed significantly decreased abundance of alate and apterous aphids with higher parasitism rates compared with the control. The new slow-release alginate bead containing a mixture of EβF with MeSA could be the most efficient formulation to control S. miscanthi population by attracting parasitoids in the wheat agro-ecosystem. © 2021 Society of Chemical Industry. © 2021 Society of Chemical Industry.

Methyl Salicylate Fails to Enhance Arthropod Predator Abundance or Predator to Pest Ratios in Cotton

Conservation biological control is a fundamental tactic in integrated pest management (IPM). Greater biological control services can be achieved by enhancing agroecosystems to be more favorable to the presence, survival, and growth of natural enemy populations. One approach that has been tested in numerous agricultural systems is the deployment of synthetic chemicals that mimic those produced by the plant when under attack by pests. These signals may attract arthropod natural enemies to crop habitats and thus potentially improve biological control activity locally. A 2-yr field study was conducted in the cotton agroecosystem to evaluate the potential of synthetic methyl salicylate (MeSA) to attract native arthropod natural enemies and to enhance biological control services on two key pests. Slow-release packets of MeSA were deployed in replicated cotton plots season long. The abundance of multiple taxa of natural enemies and two major pests were monitored weekly by several sampling methods. The deployment of MeSA failed to increase natural enemy abundance and pest densities did not decline. Predator to prey ratios, used as a proxy to estimate biological control function, also largely failed to increase with MeSA deployment. One exception was a season-long increase in the ratio of Orius tristicolor (White) (Hemiptera: Anthocoridae) to Bemisia argentifolii Bellows and Perring (= Bemisia tabaci MEAM1) (Hemiptera: Aleyrodidae) adults within the context of biological control informed action thresholds. Overall results suggest that MeSA would not likely enhance conservation biological control by the natural enemy community typical of U.S. western cotton production systems.

Exploring the Kairomone-Based Foraging Behaviour of Natural Enemies to Enhance Biological Control: A Review

Kairomones are chemical signals that mediate interspecific interactions beneficial to organisms that detect the cues. These attractants can be individual compounds or mixtures of herbivore-induced plant volatiles (HIPVs) or herbivore chemicals such as pheromones, i.e., chemicals mediating intraspecific communication between herbivores. Natural enemies eavesdrop on kairomones during their foraging behaviour, i.e., location of oviposition sites and feeding resources in nature. Kairomone mixtures are likely to elicit stronger olfactory responses in natural enemies than single kairomones. Kairomone-based lures are used to enhance biological control strategies via the attraction and retention of natural enemies to reduce insect pest populations and crop damage in an environmentally friendly way. In this review, we focus on ways to improve the efficiency of kairomone use in crop fields. First, we highlight kairomone sources in tri-trophic systems and discuss how these attractants are used by natural enemies searching for hosts or prey. Then we summarise examples of field application of kairomones (pheromones vs. HIPVs) in recruiting natural enemies. We highlight the need for future field studies to focus on the application of kairomone blends rather than single kairomones which currently dominate the literature on field attractants for natural enemies. We further discuss ways for improving kairomone use through attract and reward technique, olfactory associative learning, and optimisation of kairomone lure formulations. Finally, we discuss why the effectiveness of kairomone use for enhancing biological control strategies should move from demonstration of increase in the number of attracted natural enemies, to reducing pest populations and crop damage below economic threshold levels and increasing crop yield.

Assessment of Attractant Lures and Monitoring Traps for Drosophila suzukii (Diptera: Drosophidae) Using Electrophysiology, Laboratory Choice Assays, and Field Trials

Monitoring is critical to control efforts for Drosophila suzukii Matsumura, an invasive polyphagous fly that has the potential to cause significant losses in commercial soft fruit and berry production worldwide. We used an iterative process to identify trap colors, trap designs, and volatile mixtures to improve monitoring efforts in commercial blueberry, raspberry, and blackberry crops. Our results suggest that the selection of trap color and design and attractant lures should be customized to the crop in which they are deployed. In raspberries grown in high tunnel systems, DrosaLure paired with Drosal traps painted green and purple were highly specific to D. suzukii although actual capture counts were low. However, in field grown raspberries, BioLure and Multilure traps were most effective, but with significant nontarget bycatch. In blueberries, we had greatest success with a 5 µg:50 ng mixture of ethyl acetate-acetoin in a green/purple-colored jar-style trap with large (5 cm) mesh covered openings.

Interactive Effects of an Herbivore-Induced Plant Volatile and Color on an Insect Community in Cranberry

Simple Summary

Plants often increase their odor emissions after herbivore feeding damage, which in turn attract natural enemies of the herbivores such as insect predators. Synthetic versions of these so-called herbivore-induced plant volatiles (HIPVs) can be used to monitor populations of beneficial insects in agriculture. In addition, HIPVs can potentially attract the herbivores themselves. However, whether synthetic HIPVs interact with color to affect insect communities in farms is unknown. In this study, we tested a lure containing the HIPV methyl salicylate (named ‘PredaLure’) in combination with five different colored sticky traps to monitor insect populations in cranberry fields (also known as bogs). We found that hoverflies (also called flower flies or syrphid flies), whose larvae are predators of several insect pests including aphids and thrips, were attracted to PredaLure but this attraction was affected by the color of the trap. In fact, the numbers of hoverflies were 2–4 higher on yellow and white traps baited with PredaLure than on unbaited traps. Irrespective of trap color, plant-feeding thrips were also more attracted to PredaLure-baited than unbaited traps. Our study provides guidelines for the use of odor-baited colored sticky traps to monitor natural enemies such as hoverflies in an agricultural system like cranberries.

Abstract

Synthetic herbivore-induced plant volatiles (HIPVs) could be used to monitor insect populations in agroecosystems, including beneficial insects such as natural enemies of herbivores. However, it is unknown whether insect responses to HIPVs are influenced by visual cues, e.g., color. We hypothesized that the HIPV methyl salicylate (MeSA) interacts with color to affect insect captures on sticky traps. To test this, we conducted a 5 × 2 factorial field experiment in a commercial cranberry farm to monitor numbers of insect predators, parasitoids, and herbivores by using five colored sticky traps that were either baited with a MeSA lure (named ‘PredaLure’) or unbaited. At the community level, PredaLure increased captures of predators. At the individual-taxon level, captures of the hoverfly Toxomerus marginatus (Diptera: Syrphidae) and thrips (Thysanoptera: Thripidae) were higher on PredaLure-baited traps. However, only captures of T. marginatus on PredaLure-baited traps interacted significantly with color such that the numbers of this hoverfly on yellow and white traps were 2–4 times higher when baited with PredaLure. This study is the first to document the interactive effects of synthetic HIPVs and color on an insect community. Our findings have implications for optimal selection of HIPV-baited colored traps to monitor natural enemy populations in agroecosystems.

Attracting Chrysopidae With Plant Volatiles for Lace Bug (Hemiptera: Tingidae) Control in Rhododendrons and Azaleas

The azalea lace bug (Stephanitis pyrioides Scott) (Hemiptera: Tingidae) is an invasive pest of rhododendrons and azaleas (Ericaceae: Rhododendron), which feeds on the underside of leaves causing chlorosis, reduced photosynthesis, and even plant death. While insecticides can control this pest, growers, landscape managers, and homeowners have requested softer alternatives. Augmentative release of predatory green lacewing Chrysoperla sp. (Neuroptera: Chrysopidae) eggs and larvae has reduced S. pyrioides, but large-scale implementation may not be practical nor cost-effective. Attracting naturally occurring Chrysopidae with plant volatiles may be an economical and convenient option. In this study, we tested whether volatile blends 1) attracted Chrysoperla sp., and 2) controlled S. pyrioides populations on Rhododendron spp. in farm or urban landscapes. Experimental plots contained different multicomponent lures placed aboveground next to infested plants. Adult Chrysoperla sp., other natural enemies, and S. pyrioides from egg to adult stages were monitored in both farm and urban landscapes for two summers. Overall, two out of three volatile blends consistently attracted Chrysoperla sp. to sticky traps near baited plants. Methyl salicylate + acetic acid + 2-phenylethanol (methyl salicylate blend) and acetophenone + acetic acid + 2-phenylethanol (acetophenone blend) captured more adult Chrysoperla sp. than control traps in farm landscapes. However, only the acetophenone blend was associated with a slight reduction of S. pyrioides. Additional research is needed to determine whether the phenology of the first generation of both species are synchronized for effective season biological control in the Pacific Northwest.

Electrophysiological and behavioural response of Philaenus spumarius to essential oils and aromatic plants

The meadow spittlebug, Philaenus spumarius, is a highly polyphagous widespread species, playing a major role in the transmission of the bacterium Xylella fastidiosa subspecies pauca, the agent of the “Olive Quick Decline Syndrome”. Essential oils (EOs) are an important source of bio-active volatile compounds that could interfere with basic metabolic, biochemical, physiological, and behavioural functions of insects. Here, we report the electrophysiological and behavioural responses of adult P. spumarius towards some EOs and related plants. Electroantennographic tests demonstrated that the peripheral olfactory system of P. spumarius females and males perceives volatile organic compounds present in the EOs of Pelargonium graveolens, Cymbopogon nardus and Lavandula officinalis in a dose-dependent manner. In behavioral bioassays, evaluating the adult responses towards EOs and related plants, both at close (Y-tube) and long range (wind tunnel), males and females responded differently to the same odorant. Using EOs, a clear attraction was noted only for males towards lavender EO. Conversely, plants elicited responses that varied upon the plant species, testing device and adult sex. Both lavender and geranium repelled females at any distance range. On the contrary, males were attracted by geranium and repelled by citronella. Finally, at close distance, lavender and citronella were repellent for females and males, respectively. Our results contribute to the development of innovative tools and approaches, alternative to the use of synthetic pesticides, for the sustainable control of P. spumarius aiming to contrasting the expansion of X. fastidiosa.

The NALCN Channel Regulator UNC-80 Functions in a Subset of Interneurons To Regulate Caenorhabditis elegans Reversal Behavior

NALCN (Na⁺leak channel, non-selective) is a conserved, voltage-insensitive cation channel that regulates resting membrane potential and neuronal excitability. UNC79 and UNC80 are key regulators of the channel function. However, the behavioral effects of the channel complex are not entirely clear and the neurons in which the channel functions remain to be identified. In a forward genetic screen for C. elegans mutants with defective avoidance response to the plant hormone methyl salicylate (MeSa), we isolated multiple loss-of-function mutations in unc-80 and unc-79. C. elegans NALCN mutants exhibited similarly defective MeSa avoidance. Interestingly, NALCN, unc-80 and unc-79 mutants all showed wild type-like responses to other attractive or repelling odorants, suggesting that NALCN does not broadly affect odor detection or related forward and reversal behaviors. To understand in which neurons the channel functions, we determined the identities of a subset of unc-80-expressing neurons. We found that unc-79 and unc-80 are expressed and function in overlapping neurons, which verified previous assumptions. Neuron-specific transgene rescue and knockdown experiments suggest that the command interneurons AVA and AVE and the anterior guidepost neuron AVG can play a sufficient role in mediating unc-80 regulation of the MeSa avoidance. Though primarily based on genetic analyses, our results further imply that MeSa might activate NALCN by direct or indirect actions. Altogether, we provide an initial look into the key neurons in which the NALCN channel complex functions and identify a novel function of the channel in regulating C. elegans reversal behavior through command interneurons.

Plant-Plant Communication: Is There a Role for Volatile Damage-Associated Molecular Patterns?

Damage-associated molecular patterns (DAMPs) are an ancient form of tissue-derived danger or alarm signals that initiate cellular signaling cascades, which often initiate defined defense responses. A DAMP can be any molecule that is usually not exposed to cells such as cell wall components, peptides, nucleic acid fragments, eATP and other compounds. DAMPs might be revealed upon tissue damage or during attack. Typically, DAMPs are derived from the injured organism. Almost all eukaryotes can generate and respond to DAMPs, including plants. Besides the molecules mentioned, certain volatile organic compounds (VOCs) can be considered as DAMPs. Due to their chemical nature, VOCs are supposed to act not only locally and systemically in the same plant but also between plants. Here, we focus on damage-induced volatiles (DIVs) that might be regarded as DAMPs; we will review their origin, chemical nature, physiochemical properties, biological relevance and putative function in plant-plant communications. Moreover, we discuss the possibility to use such airborne DAMPs as eco-friendly compounds to stimulate natural defenses in agriculture in order to avoid pesticides.

Methyl Salicylate Increases Attraction and Function of Beneficial Arthropods in Cranberries

Methyl salicylate (MeSA) is an herbivore-induced plant volatile (HIPV) known to attract the natural enemies of herbivores in agro-ecosystems; however, whether this attraction leads to an increase in natural enemy functioning, i.e., predation, remains largely unknown. Here, we monitored for 2 years (2011-2012) the response of herbivores and natural enemies to MeSA lures (PredaLure) by using sticky and pitfall traps in cranberry bogs. In addition, European corn borer, Ostrinia nubilalis, egg masses were used to determine whether natural enemy attraction to MeSA leads to higher predation. In both years, MeSA increased adult hoverfly captures on sticky traps and augmented predation of O. nubilalis eggs. However, MeSA also attracted more phytophagous thrips and, in 2012, more plant bugs (Miridae) to sticky traps. Furthermore, we used surveillance cameras to record the identity of natural enemies attracted to MeSA and measure their predation rate. Video recordings showed that MeSA lures increase visitation by adult lady beetles, adult hoverflies, and predatory mites to sentinel eggs, and predation of these eggs doubled compared to no-lure controls. Our data indicate that MeSA lures increase predator attraction, resulting in increased predation; thus, we provide evidence that attraction to HIPVs can increase natural enemy functioning in an agro-ecosystem.

The Ecology of Salicylic Acid Signaling: Primary, Secondary and Tertiary Effects with Applications in Agriculture

The salicylic acid pathway is one of the primary plant defense pathways, is ubiquitous in vascular plants, and plays a role in rapid adaptions to dynamic abiotic and biotic stress. Its prominence and ubiquity make it uniquely suited for understanding how biochemistry within plants can mediate ecological consequences. Induction of the salicylic acid pathway has primary effects on the plant in which it is induced resulting in genetic, metabolomic, and physiologic changes as the plant adapts to challenges. These primary effects can in turn have secondary consequences for herbivores and pathogens attacking the plant. These secondary effects can both directly influence plant attackers and mediate indirect interactions between herbivores and pathogens. Additionally, stimulation of salicylic acid related defenses can affect natural enemies, predators and parasitoids, which can recruit to plant signals with consequences for herbivore populations and plant herbivory aboveground and belowground. These primary, secondary, and tertiary ecological consequences of salicylic acid signaling hold great promise for application in agricultural systems in developing sustainable high-yielding management practices that adapt to changing abiotic and biotic environments.

Bringing Ecology Back: How Can the Chemistry of Indirect Plant Defenses Against Herbivory Be Manipulated to Improve Pest Management?

Research on insect-plant interactions has highlighted the intricacies of constitutive and induced plant defenses. Of particular interest has been the relationship of natural enemies (especially parasitic hymenoptera) to herbivore induced changes to plants, especially their responses to herbivore induced plant volatiles (HIPVs). In recent decades this has been a fertile area for research, with elegant experiments showing that HIPVs are important in attracting natural enemies to plants. We critically appraise the application of work on HIPVs in plant-insect-natural enemy interactions. The promise of applications to improve pest management has not been forthcoming. We attribute this to a failure to include the multifaceted aspects of natural enemy-prey interactions - attraction, location, subjugation and experience. Attraction in an olfactometer by naïve parasitoids has not been translated to methodologically sound field-based estimates of higher parasitism rates. We highlight what needs to be done to better understand the information that HIPVs convey, how this is utilized by parasitoids and how a greater understanding of these interactions might lead to the development of new strategies so that this knowledge can be effectively deployed for improved pest management.

Cascading effects of combining synthetic herbivore-induced plant volatiles with companion plants to manipulate natural enemies in an agro-ecosystem

BACKGROUND

Whether tactics to manipulate natural enemies in agro-ecosystems enhance their ecosystem function and services remains debatable. We conducted field experiments in 2015-2016 to test the hypothesis that attraction of natural enemies to herbivore-induced plant volatiles (HIPVs), alone or in combination with companion plants, increases crop productivity. Our treatments consisted of bean plants alone or baited with methyl salicylate (MeSA; an HIPV), or combined with coriander (a companion plant), or with both MeSA and coriander. Numbers of arthropods were visually sampled in each treatment. Sentinel aphids were used to measure ecosystem function (i.e. predation). Plant damage and biomass, and the number and weight of pods and seeds, were measured as a proxy for ecosystem services.

RESULTS

MeSA and coriander, when alone or combined, increased the abundance of insect predators from six families, reduced herbivore (e.g. spider mite and thrips) populations, and increased aphid predation. MeSA and coriander also reduced damage by spider mites. MeSA with or without coriander did not, however, increase crop biomass or any yield parameters.

CONCLUSIONS

MeSA alone or combined with coriander attracted different predator communities, altered pest communities, and reduced damage; however, these results did not cascade down to improve crop productivity. © 2018 Society of Chemical Industry.

Field Trapping of Predaceous Insects With Synthetic Herbivore-Induced Plant Volatiles in Cotton Fields

Nine herbivore-induced plant volatiles (HIPVs) and one methyl jasmonate were field-tested for their attractiveness to the main predators in cotton fields of North China in 2 yr. The main predators including ladybird beetles (Propylaea japonica (Thunberg), Harmonia axyridis (Pallas)), green lacewings (Chrysoplera sinica (Tjeder), Chrysopa spp.), predatory bugs (Geocoris pallidipennis (Costa), Orius spp., Nabis spp.) and spiders (Misumenops tricuspidatus (Fabricius), Erigonidium graminicolum (Sundevall)) were investigated. Two-way ANOVA indicated that the volatile compound, year, and the volatile compound × year interaction affected the behavioral responses of predators. It was found that indole significantly attracted the ladybird beetle P. japonica, H. axyridis. Linalool could attract P. japonica. Green lacewing C. sinica was significantly attracted by α-pinene and β-pinene, whereas indole significantly attracted Chrysopa spp. Methyl jasmonate and α-pinene showed significant attraction to small-flower bug Orius spp. In addition, the attraction of α-humulene to C. sinica, attractiveness of β-pinene to Orius spp. and Chrysopa spp., were observed only in one of the two years. However, the big-eyed bug G. pallidipennis, damsel bug Nabis spp., spiders M. tricuspiata and E. graminicolum did not respond to any of the tested HIPVs. These results are discussed with respect to possible applications of a synthetic attractant for main predators in cotton fields.

Tritrophic Interactions Mediated by Herbivore-Induced Plant Volatiles: Mechanisms, Ecological Relevance, and Application Potential

Tritrophic interactions between plants, herbivores, and their natural enemies are an integral part of all terrestrial ecosystems. Herbivore-induced plant volatiles (HIPVs) play a key role in these interactions, as they can attract predators and parasitoids to herbivore-attacked plants. Thirty years after this discovery, the ecological importance of the phenomena is widely recognized. However, the primary function of HIPVs is still subject to much debate, as is the possibility of using these plant-produced cues in crop protection. In this review, we summarize the current knowledge on the role of HIPVs in tritrophic interactions from an ecological as well as a mechanistic perspective. This overview focuses on the main gaps in our knowledge of tritrophic interactions, and we argue that filling these gaps will greatly facilitate efforts to exploit HIPVs for pest control.

Cucumber Plants Baited with Methyl Salicylate Accelerates Scymnus (Pullus) sodalis (Coleoptera: Coccinellidae) Visiting to Reduce Cotton Aphid (Hemiptera: Aphididae) Infestation

The cotton aphid, Aphis gossypii (Glover) (Hemiptera: Aphididae), is a major pest of many crops worldwide and a major cucumber plant pest in Taiwan. Because cotton aphids rapidly develop insecticide resistance and because of the insecticide residue problem, a safe and sustainable method is required to replace conventional chemical control methods. Methyl salicylate (MeSA), a herbivore-induced plant volatile, has been shown to affect aphids' behavior and attract the natural enemies of aphids for reducing their population. Therefore, this study examined the direct effects of MeSA on cotton aphids' settling preference, population development, and attractiveness to natural enemies. The efficiency of using MeSA and the commercial insecticide pymetrozine for reducing the cotton aphid population in laboratory and outdoor cucumber plant pot was also examined. The results showed no difference in winged aphids' settling preference and population development between the MeSA and blank treatments. Cucumber plants infested with cotton aphids and baited with 0.1% or 10% MeSA contained significantly higher numbers of the natural enemy of cotton aphids, namely Scymnus (Pullus) sodalis (Weise) (Coleoptera: Coccinellidae), and MeSA-treated cucumber plants contained a lower number of aphids. Significantly lower cotton aphid numbers were found on cucumber plants within a 10-m range of MeSA application. In addition, fruit yield showed no difference between the MeSA and pymetrozine treatments. According to our findings, 0.1% MeSA application can replace insecticides as a cotton aphid control tool. However, large-scale experiments are necessary to confirm its efficiency and related conservation biological control strategies before further use.

Carnivore Attractant or Plant Elicitor? Multifunctional Roles of Methyl Salicylate Lures in Tomato Defense

Synthetic plant volatile lures attract natural enemies, but may have non-target effects due to the multifunctional nature of volatile signals. For example, methyl salicylate (MeSA) is used to attract predators, yet also serves as a signaling hormone involved in plant pathogen defense. We investigated the consequences of deploying MeSA lures to attract predators for tomato (Solanum lycopersicum) defense against herbivores. To understand the spatial distribution of the lure's effect, we exposed tomatoes in the field to MeSA along a linear distance gradient and induced defenses by simulating feeding by hornworm caterpillars in a fully crossed factorial design (+/- MeSA, +/- herbivory). Subsequently, we analyzed activity of several defensive proteins (protease inhibitors, polyphenol oxidase, peroxidase), development of hornworm larvae (Manduca sexta), growth of fungal pathogens (Cladosporium and Alternaria), and attractiveness to herbivores and predators. Overall, MeSA-exposed plants were more resistant to both insects and pathogens. Secondary pathogen infection was reduced by 25% in MeSA exposed plants, possibly due to elevated polyphenol oxidase activity. Interestingly, we found that lures affected plant pathogen defenses equivalently across all distances (up to 4 m away) indicating that horizontal diffusion of a synthetic volatile may be greater than previously assumed. While thrips avoided colonizing hornworm- damaged tomato plants, this induced resistance was not observed upon pre-exposure to MeSA, suggesting that MeSA suppresses the repellant effect induced by herbivory. Thus, using MeSA lures in biological control may inadvertently protect crops from pathogens, but has mixed effects on plant resistance to insect herbivores.

Use of slow-release plant infochemicals to control aphids: a first investigation in a Belgian wheat field

Using infochemicals to develop a push–pull strategy in pest control is a potential way to promote sustainable crop production. Infochemicals from plant essential oils were mixed with paraffin oil for slow release in field experiments on wheat to control the population density of cereal aphids and to enhance their natural enemies. (Z)-3-Hexenol (Z3H) attracted Metopolophum dirhodum and Sitobion avenae, the predominant species on wheat in Belgium, and may be a useful infochemical for aphid control by attracting aphids away from field plots. Release of (E)-β-farnesene (EBF) or a garlic extract (GE) led to a significant decrease in the abundance of wheat aphids. The main natural enemies of cereal aphids found were lacewings (47.8%), hoverflies (39.4%), and ladybirds (12.8%). Ladybird abundance varied little before the end of the wheat-growing season. Our results suggest that these chemicals can form the basis of a “push–pull” strategy for aphid biological control, with GE and EBF acting as a pest- and beneficial-pulling stimulus and Z3H for aphid pulling.

Acarine attractants: Chemoreception, bioassay, chemistry and control

The Acari are of significant economic importance in crop production and human and animal health. Acaricides are essential for the control of these pests, but at the same time, the number of available pesticides is limited, especially for applications in animal production. The Acari consist of two major groups, the mites that demonstrate a wide variety of life strategies, i.e., herbivory, predation and ectoparasitism, and ticks which have evolved obligatory hematophagy. The major sites of chemoreception in the acarines are the chelicerae, palps and tarsi on the forelegs. A unifying name, the "foretarsal sensory organ" (FSO), is proposed for the first time in this review for the sensory site on the forelegs of all acarines. The FSO has multiple sensory functions including olfaction, gustation, and heat detection. Preliminary transcriptomic data in ticks suggest that chemoreception in the FSO is achieved by a different mechanism from insects. There are a variety of laboratory and field bioassay methods that have been developed for the identification and characterization of attractants but minimal techniques for electrophysiology studies. Over the past three to four decades, significant progress has been made in the chemistry and analysis of function for acarine attractants in mites and ticks. In mites, attractants include aggregation, immature female, female sex and alarm pheromones; in ticks, the attraction-aggregation-attachment, assembly and sex pheromones; in mites and ticks host kairomones and plant allomones; and in mites, fungal allomones. There are still large gaps in our knowledge of chemical communication in the acarines compared to insects, especially relative to acarine pheromones, and more so for mites than ticks. However, the use of lure-and-kill and lure-enhanced biocontrol strategies has been investigated for tick and mite control, respectively, with significant environmental advantages which warrant further study.

Chemical Ecology of Neuroptera

With 6,000 species, Neuroptera (lacewings, antlions, dustywings, and allies) is a relatively small order; however, most larval neuropterans are predacious, often in agricultural systems, lending added importance to this group. Advances in neuropteran phylogeny, most recently through genomic studies, stabilized the nomenclature of this ancestral order of Holometabola, facilitating basic and applied research on these important and interesting insects. The first pheromones for green lacewings (Chrysopidae) have been identified; this, and other research on antlions (Myrmeleontidae), suggests that male-produced long-range pheromones are the norm for the order. Characterizations of the myriad neuropteran exocrine gland systems, including prothoracic, metathoracic, abdominal, dermal, and anal glands, are revealing unforeseen trophic relationships with biological control implications. For examples, males of Chrysopa and other lacewing genera evidently must sequester specific chemical precursors from prey or plants to produce their attractant pheromones, and larval antlion venoms are potentially important genetic leads for insecticidal peptides.

Testing for phytochemical synergism: arthropod community responses to induced plant volatile blends across crops

Using herbivore-induced plant volatiles (HIPVs) to attract specific natural enemies in the field has proven challenging, partly because of a poor understanding of: (i) which compound(s) to manipulate to attract specific taxa, and (ii) the ecological conditions over which HIPVs are effective. To address these issues, we quantified the response of a complex arthropod community to three common HIPVs (methyl salicylate, cis-3-hexen-1-ol, and phenylethyl alcohol) as individual compounds and equal part blends in corn and soybean fields. Of 119 arthropod taxa surveyed, we found significant responses by four species in corn fields (2 parasitoids, 1 herbivore, and 1 detritivore) and 16 in soybean fields (8 parasitoids, 3 predators, 4 herbivores, and 1 detritivore), with both attractive and repellent effects of the HIPVs observed. For example, tachinid flies were highly attracted to cis-3-hexen-1-ol (ca. 3-fold increase), but repelled by methyl salicylate (ca. 60 % decrease). Surprisingly, we found very few cases in which HIPVs acted synergistically; only two arthropod groups (ichneumonid wasps and phorid flies) were more attracted by a blend of the HIPVs than by the individual compounds composing the blend. Crop type, however, had a strong impact on the strength of arthropod responses to HIPVs. A few arthropod species were broadly affected across both crops (i.e., the herbivore Halticus bractatus was repelled by most of our treatments, regardless of crop background), but overall more arthropod groups responded to HIPVs released in soybean fields compared with corn. This was true despite the fact that taxa responding to HIPVs were present and abundant in both systems, suggesting that crop-based outcomes were likely driven by the plant matrix rather than mere differences in taxonomic composition of the arthropod community in corn vs. soybean fields. As a whole, these results suggest that: (i) repellent effects of HIPVs on natural enemies of herbivorous insects can be observed as frequently as attractive effects; (ii) odor blends may be no more effective than single-compound lures for some taxa; and (iii) crop background alters the magnitude of attraction to HIPVs, depending on the species being targeted.

Evaluation of airborne methyl salicylate for improved conservation biological control of two-spotted spider mite and hop aphid in Oregon hop yards

The use of synthetic herbivore-induced plant volatiles (HIPV) to attract natural enemies has received interest as a tool to enhance conservation biological control (CBC). Methyl salicylate (MeSA) is a HIPV that is attractive to several key predators of two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and hop aphid, Phorodon humuli (Schrank) (Homoptera: Aphididae). A 2-year study was conducted to evaluate the recommended commercial use of MeSA in hop yards in Oregon. Slow-release MeSA dispensers were stapled to supporting poles in 0.5 ha plots and these plots were compared to a paired non-treated plot on each of three farms in 2008 and 2009. Across both years, there was a trend for reduced (range 40-91%) mean seasonal numbers of T. urticae in five of the six MeSA-baited plots. Stethorus spp., key spider mite predators, tended to be more numerous in MeSA-baited plots compared to control plots on a given farm. Mean seasonal densities of hop aphid and other natural enemies (e.g., Orius spp. and Anystis spp.) were similar between MeSA-treated and control plots. Variability among farms in suppression of two-spotted spider mites and attraction of Stethorus spp. suggests that the use of MeSA to enhance CBC of spider mites in commercial hop yards may be influenced by site-specific factors related to the agroecology of individual farms or seasonal effects that require further investigation. The current study also suggests that CBC of hop aphid with MeSA in this environment may be unsatisfactory.

Dispensing synthetic green leaf volatiles in maize fields increases the release of sesquiterpenes by the plants, but has little effect on the attraction of pest and beneficial insects

Maize plants respond to feeding by arthropod herbivores by producing a number of secondary plant compounds, including volatile organic compounds (VOCs). These herbivore-induced VOCs are not only known to attract natural enemies of the herbivores, but they may also prime inducible defences in neighbouring plants, resulting in stronger and faster defence responses in these VOC-exposed plants. Among the compounds that cause this priming effect, green leaf volatiles (GLVs) have received particular attention, as they are ubiquitous and rapidly emitted upon damage. In this study, we investigated their effects under realistic conditions by applying specially devised dispensers to release four synthetic GLVs at physiologically relevant concentrations in a series of experiments in maize fields. We compared the VOC emission of GLV-exposed maize plants to non-exposed plants and monitored the attraction of herbivores and predators, as well as parasitism of the caterpillar Spodoptera frugiperda, the most common herbivore in the experimental maize fields. We found that maize plants that were exposed to GLVs emitted increased quantities of sesquiterpenes compared to non-exposed plants. In several replicates, herbivorous insects, such as adult Diabrotica beetles and S. frugiperda larvae, were observed more frequently in GLV-treated plots and caused more damage to GLV-exposed plants than to non-exposed plants. Parasitism of S. frugiperda was only weakly affected by GLVs and overall parasitism rates of S. frugiperda were similar in GLV-exposed and non-exposed plots. The effects on insect presence depended on the distance from the GLV-dispensers at which the plants were located. The results are discussed in the context of strategies to improve biological control by enhancing plant-mediated attraction of natural enemies.