Extreme acidity in a cynipid gall: a potential new defensive strategy against natural enemies.

The morphology of insect-induced galls contributes to defences of the gall-inducing insect species against its natural enemies. In terms of gall chemistry, the only defensive compounds thus far identified in galls are tannins that accumulate in many galls, preventing damage by herbivores. Intrigued by the fruit-like appearance of the translucent oak gall (TOG; Amphibolips nubilipennis, Cynipidae, Hymenoptera) induced on red oak (Quercus rubra), we hypothesized that its chemical composition may deviate from other galls. We found that the pH of the gall is between 2 and 3, making it among the lowest pH levels found in plant tissues. We examined the organic acid content of TOG and compared it to fruits and other galls using high-performance liquid chromatography and gas chromatography-mass spectrometry. Malic acid, an acid with particularly high abundance in apples, represents 66% of the organic acid detected in TOGs. The concentration of malic acid was two times higher than in other galls and in apples. Gall histology showed that the acid-containing cells were enlarged and vacuolized just like fruits mesocarp cells. Accumulation of organic acid in gall tissues is convergent with fruit morphology and may constitute a new defensive strategy against predators and parasitoids.

Nutrition vs association: plant defenses are altered by arbuscular mycorrhizal fungi association not by nutritional provisioning alone.

BACKGROUND: While it is known that arbuscular mycorrhizal fungi (AMF) can improve nutrient acquisition and herbivore resistance in crops, the mechanisms by which AMF influence plant defense remain unknown. Plants respond to herbivory with a cascade of gene expression and phytochemical biosynthesis. Given that the production of defensive phytochemicals requires nutrients, a commonly invoked hypothesis is that the improvement to plant defense when grown with AMF is simply due to an increased availability of nutrients. An alternative hypothesis is that the AMF effect on herbivory is due to changes in plant defense gene expression that are not simply due to nutrient availability. In this study, we tested whether changes in plant defenses are regulated by nutritional provisioning alone or the response of plant to AMF associations. Maize plants grown with or without AMF and with one of three fertilizer treatments (standard, 2 × nitrogen, or 2 × phosphorous) were infested with fall armyworm (Spodoptera frugiperda; FAW) for 72 h. We measured general plant characteristics (e.g. height, number of leaves), relative gene expression (rtPCR) of three defensive genes (lox3, mpi, and pr5), total plant N and P nutrient content, and change in FAW mass per plant. RESULTS: We found that AMF drove the defense response of maize by increasing the expression of mpi and pr5. Furthermore, while AMF increased the total phosphorous content of maize it had no impact on maize nitrogen. Fertilization alone did not alter upregulation of any of the 3 induced defense genes tested, suggesting the mechanism through which AMF upregulate defenses is not solely via increased N or P plant nutrition. CONCLUSION: This work supports that maize defense may be optimized by AMF associations alone, reducing the need for artificial inputs when managing FAW.

Transcriptomic and volatile signatures associated with maize defense against corn leaf aphid.

BACKGROUND: Maize (Zea mays L.) is a major cereal crop, with the United States accounting for over 40% of the worldwide production. Corn leaf aphid [CLA; Rhopalosiphum maidis (Fitch)] is an economically important pest of maize and several other monocot crops. In addition to feeding damage, CLA acts as a vector for viruses that cause devastating diseases in maize. We have shown previously that the maize inbred line Mp708, which was developed by classical plant breeding, provides heightened resistance to CLA. However, the transcriptomic variation conferring CLA resistance to Mp708 has not been investigated. RESULTS: In this study, we contrasted the defense responses of the resistant Mp708 genotype to those of the susceptible Tx601 genotype at the transcriptomic (mRNA-seq) and volatile blend levels. Our results suggest that there was a greater transcriptomic remodeling in Mp708 plants in response to CLA infestation compared to the Tx601 plants. These transcriptomic signatures indicated an activation of hormonal pathways, and regulation of sesquiterpenes and terpenoid synthases in a constitutive and inducible manner. Transcriptomic analysis also revealed that the resistant Mp708 genotype possessed distinct regulation of ethylene and jasmonic acid pathways before and after aphid infestation. Finally, our results also highlight the significance of constitutive production of volatile organic compounds (VOCs) in Mp708 and Tx601 plants that may contribute to maize direct and/or indirect defense responses. CONCLUSIONS: This study provided further insights to understand the role of defense signaling networks in Mp708's resistance to CLA.

Chemical Cues from Entomopathogenic Nematodes Vary Across Three Species with Different Foraging Strategies, Triggering Different Behavioral Responses in Prey and Competitors.

Chemical cues play important roles in predator-prey interactions. Semiochemicals can aid predator foraging and alert prey organisms to the presence of predators. Previous work suggests that predator traits differentially influence prey behavior, however, empirical data on how prey organisms respond to chemical cues from predator species with different hunting strategies, and how foraging predators react to cues from potential competitors, is lacking. Furthermore, most research in this area has focused on aquatic and aboveground terrestrial systems, while interactions among belowground, soiling-dwelling organisms have received relatively little attention. Here, we assessed how chemical cues from three species of entomopathogenic nematodes (EPNs), each with a different foraging strategy, influenced herbivore (cucumber beetle) and natural enemy (EPN) foraging behavior. We predicted these cues could serve as chemical indicators of increased predation risk, prey availability, or competition. Our findings revealed that foraging cucumber beetle larvae avoided chemical cues from Heterorhabditis bacteriophora (active-foraging cruiser EPNs), but not Steinernema carpocapsae (ambusher EPNs) or Steinernema riobrave (intermediate-foraging EPNs). In contrast, foraging H. bacteriophora EPNs were attracted to cues produced by the two Steinernema species but not conspecific cues. Notably, the three EPN species produced distinct blends of olfactory cues, with only a few semi-conserved compounds across species. These results indicate that a belowground insect herbivore responds differently to chemical cues from different EPN species, with some EPN species avoiding prey detection. Moreover, the active-hunting EPNs were attracted to heterospecific cues, suggesting these cues indicate a greater probability of available prey, rather than strong interspecific competition.

Generalising indirect defence and resistance of plants.

Indirect defence, the adaptive top-down control of herbivores by plant traits that enhance predation, is a central component of plant-herbivore interactions. However, the scope of interactions that comprise indirect defence and associated ecological and evolutionary processes has not been clearly defined. We argue that the range of plant traits that mediate indirect defence is much greater than previously thought, and we further organise major concepts surrounding their ecological functioning. Despite the wide range of plant traits and interacting organisms involved, indirect defences show commonalities when grouped. These categories are based on whether indirect defences boost natural enemy abundance via food or shelter resources, or, alternatively, increase natural enemy foraging efficiency via information or alteration of habitat complexity. The benefits of indirect defences to natural enemies should be further explored to establish the conditions in which indirect defence generates a plant-natural enemy mutualism. By considering the broader scope of plant-herbivore-natural enemy interactions that comprise indirect defence, we can better understand plant-based food webs, as well as the evolutionary processes that have shaped them.

The role of toxic nectar secondary compounds in driving differential bumble bee preferences for milkweed flowers.

While morphological differences such as tongue length are often featured as drivers of pollinator floral preferences, differences in chemical detection and tolerance to secondary compounds may also play a role. We sought to better understand the role of secondary compounds in floral preference by examining visitation of milkweed flowers, which can contain toxic cardenolides in their nectar, by bumble bees (Bombus spp.), some of their most abundant and important pollinators. We examine bumble bee species visitation of common milkweed (Asclepias syriaca) compared to other flowers in the field and test whether observed preferences may be influenced by avoidance and tolerance of cardenolides, as measured by the cardenolide ouabain, in the lab. We reveal that common milkweed is visited predominantly by one bumble bee species, Bombus griseocollis, in a ratio much higher than the abundance of this species in the community. We confirmed the presence and toxicity of cardenolides in A. syriaca nectar. Lab experiments revealed that B. griseocollis, compared to the common bumble bees B. impatiens and B. bimaculatus, exhibit greater avoidance of cardenolides, but only at levels that start to induce illness, whereas the other species exhibit either no or reduced avoidance of cardenolides, resulting in illness and mortality in these bees. Toxicity experiments reveal that B. griseocollis also has a substantially higher tolerance for cardenolides than B. impatiens. Together, these results support a potential evolutionary association between B. griseocollis and milkweed that may involve increased ability to both detect and tolerate milkweed cardenolides.

Asymmetry in Herbivore Effector Responses: Caterpillar Frass Effectors Reduce Performance of a Subsequent Herbivore.

Multiple species of phytophagous insects may co-occur on a plant and while plants can defend themselves from insect herbivory, plant responses to damage by different species and feeding guilds of insects may be asymmetric. Plants can trigger specific responses to elicitors/effectors in insect secretions altering herbivore performance. Recently, maize chitinases present in fall armyworm (FAW, Spodoptera frugiperda) frass were shown to act as effectors suppressing caterpillar-induced defenses in maize while increasing caterpillar performance. We investigated the effect of frass chitinase-mediated suppression of herbivore defenses in maize on the performance and preference of a subsequent insect herbivore from a different feeding guild, corn leaf aphid (Rhopalosiphum maidis). Aphid performance was highest on plants with FAW damage without frass chitinases compared to damaged plants with frass chitinases or undamaged plants. Plant exposure to frass chitinases post FAW damage also altered the production of herbivore-induced volatile compounds compared to damaged, buffer-treated plants. However, aphid preference to damaged, frass chitinase-treated plants was not different from damaged, buffer-treated plants or undamaged plants. This study suggests that frass effector-mediated alteration of plant defenses affects insect herbivores asymmetrically; while it enhances the performance of caterpillars, it suppresses the performance of subsequent herbivores from a different feeding guild.

Induced Plant Defenses Against Herbivory in Cultivated and Wild Tomato.

Crop domestication and selective breeding have altered plant defense mechanisms, influencing insect-plant interactions. A reduction in plant resistance/tolerance against herbivory is generally expected in domesticated species, however, limited efforts have been made to compare inducibility of plant defenses between wild and domesticated genotypes. In the present study, the inducibility of several plant defense mechanisms (e.g. defensive chemicals, trichomes, plant volatiles) were investigated, and the performance and preference of the herbivore Helicoverpa zea were measured in three different tomato genotypes; a) wild tomato, Solanum pimpinellifolium L. (accession LA 2093), b) cherry tomato, S. lycopersicum L. var. cerasiforme (accession Matts Wild Cherry), and c) cultivated tomato, S. lycopersicum L. var. Better Boy). Enhanced inducibility of defensive chemicals, trichomes, and plant volatiles in the cultivated tomato, and a higher level of constitutive plant resistance against herbivory in the wild genotype was observed. When comparing the responses of damaged vs. undamaged leaves, the percent reduction in larval growth was higher on damaged leaves from cultivated tomato, suggesting a higher induced resistance compared to other two genotypes. While all tomato genotypes exhibited increased volatile organic compound (VOCs) emissions in response to herbivory, the cultivated variety responded with generally higher levels of VOCs. Differences in VOC patterns may have influenced the ovipositional preferences, as H. zea female moths significantly preferred laying eggs on the cultivated versus the wild tomato genotypes. Selection of traits during domestication and selective breeding could alter allocation of resources, where plants selected for higher yield performance would allocate resources to defense only when attacked.

Induced release of a plant-defense volatile 'deceptively' attracts insect vectors to plants infected with a bacterial pathogen.

Transmission of plant pathogens by insect vectors is a complex biological process involving interactions between the plant, insect, and pathogen. Pathogen-induced plant responses can include changes in volatile and nonvolatile secondary metabolites as well as major plant nutrients. Experiments were conducted to understand how a plant pathogenic bacterium, Candidatus Liberibacter asiaticus (Las), affects host preference behavior of its psyllid (Diaphorina citri Kuwayama) vector. D. citri were attracted to volatiles from pathogen-infected plants more than to those from non-infected counterparts. Las-infected plants were more attractive to D. citri adults than non-infected plants initially; however after feeding, psyllids subsequently dispersed to non-infected rather than infected plants as their preferred settling point. Experiments with Las-infected and non-infected plants under complete darkness yielded similar results to those recorded under light. The behavior of psyllids in response to infected versus non-infected plants was not influenced by whether or not they were carriers of the pathogen. Quantification of volatile release from non-infected and infected plants supported the hypothesis that odorants mediate psyllid preference. Significantly more methyl salicylate, yet less methyl anthranilate and D-limonene, was released by infected than non-infected plants. Methyl salicylate was attractive to psyllids, while methyl anthranilate did not affect their behavior. Feeding on citrus by D. citri adults also induced release of methyl salicylate, suggesting that it may be a cue revealing location of conspecifics on host plants. Infected plants were characterized by lower levels of nitrogen, phosphorus, sulfur, zinc, and iron, as well as, higher levels of potassium and boron than non-infected plants. Collectively, our results suggest that host selection behavior of D. citri may be modified by bacterial infection of plants, which alters release of specific headspace volatiles and plant nutritional contents. Furthermore, we show in a laboratory setting that this apparent pathogen-mediated manipulation of vector behavior may facilitate pathogen spread.

Divergent impacts of the neonicotinoid insecticide, clothianidin, on flight performance metrics in two species of migratory butterflies.

Long-distance flight is crucial for the survival of migratory insects, and disruptions to their flight capacity can have significant consequences for conservation. In this study, we examined how a widely used insecticide, clothianidin (class: neonicotinoid), impacted the flight performance of two species of migratory butterflies, monarchs (Danaus plexippus) and painted ladies (Vanessa cardui). To do this, we quantified the free-flight energetics and tethered-flight velocity and distance of the two species using flow-through respirometry and flight mill assays. Our findings show differential effects of the pesticide on the two species. For painted ladies, we found that clothianidin exposure reduced average free-flight metabolic rates, but did not affect either average velocity or total distance during tethered flight. Other studies have linked low flight metabolic rates with reduced dispersal capacity, indicating that clothianidin exposure may hinder painted lady flight performance in the wild. Conversely, for monarchs, we saw no significant effect of clothianidin exposure on average free-flight metabolic rates but did observe increases in the average velocity, and for large individuals, total distance achieved by clothianidin-exposed monarchs in tethered flight. This suggests a potential stimulatory response of monarchs to low-dose exposures to clothianidin. These findings indicate that clothianidin exposure has the potential to influence the flight performance of butterflies, but that not all species are impacted in the same way. This highlights the need to be thoughtful when selecting performance assays, as different assays can evaluate fundamentally distinct aspects of physiology, and as such may yield divergent results.

An amino acid substitution inhibits specialist herbivore production of an antagonist effector and recovers insect-induced plant defenses.

Plants respond to insect herbivory through the production of biochemicals that function as either direct defenses or indirect defenses via the attraction of natural enemies. While attack by closely related insect pests can result in distinctive levels of induced plant defenses, precise biochemical mechanisms responsible for differing responses remain largely unknown. Cowpea (Vigna unguiculata) responds to Fall armyworm (Spodoptera frugiperda) herbivory through the detection of fragments of chloroplastic ATP synthase γ-subunit proteins, termed inceptin-related peptides, present in larval oral secretions (OS). In contrast to generalists like Fall armyworm, OS of the legume-specializing velvetbean caterpillar (VBC; Anticarsia gemmatalis) do not elicit ethylene production and demonstrate significantly lower induced volatile emission in direct herbivory comparisons. Unlike all other Lepidoptera OS examined, which preferentially contain inceptin (Vu-In; +ICDINGVCVDA-), VBC OS contain predominantly a C-terminal truncated peptide, Vu-In(-A) (+ICDINGVCVD-). Vu-In(-A) is both inactive and functions as a potent naturally occurring antagonist of Vu-In-induced responses. To block antagonist production, amino acid substitutions at the C terminus were screened for differences in VBC gut proteolysis. A valine-substituted peptide (Vu-In(ΔV); +ICDINGVCVDV-) retaining full elicitor activity was found to accumulate in VBC OS. Compared with the native polypeptide, VBC that previously ingested 500 pmol of the valine-modified chloroplastic ATP synthase γ-subunit precursor elicited significantly stronger plant responses in herbivory assays. We demonstrate that a specialist herbivore minimizes the activation of defenses by converting an elicitor into an antagonist effector and identify an amino acid substitution that recovers these induced plant defenses to a level observed with generalist herbivores.

Sending mixed messages: a trophic cascade produced by a belowground herbivore-induced cue.

Plants defend themselves against herbivores both directly (chemical toxins and physical barriers) and indirectly (attracting natural enemies of their herbivores). Previous work has shown that plant roots of citrus defend against root herbivores by releasing an herbivore-induced plant volatile (HIPV), pregeijerene (1,5-dimethylcyclodeca-1,5,7-triene), that attracts naturally occurring entomopathogenic nematodes (EPNs) to Diaprepes abbreviatus larvae when applied in the field. However, the soil community is complex and contains a diversity of interspecific relationships that modulate food web assemblages. Herein, we tested the hypothesis that other nematode types beyond EPNs, as well as, nematophagous fungi are affected by the same HIPV that attracts EPNs to herbivore-damaged roots. We employed molecular probes designed to detect and quantify nematodes from the Acrobeloides-group (free-living bacterivorous nematodes, FLBNs), some of which compete with EPNs by 'hyperparasitizing' insect cadavers, and five species of nematophagous fungi (NF), which attack and kill EPNs. In two different agricultural systems (citrus and blueberry), we detected diverse species of nematodes and fungi; however, only the behavior of FLBNs was affected in a manner similar to that reported previously for EPNs. Although detected, NF abundance was not statistically affected by the presence of the belowground HIPV. We provide the first evidence showing subterranean HIPVs behave much the same as those aboveground, attracting not only parasitoids, but also hyperparasites and other food web members.

Chemical ecology in conservation biocontrol: new perspectives for plant protection.

Threats to food security require novel sustainable agriculture practices to manage insect pests. One strategy is conservation biological control (CBC), which relies on pest control services provided by local populations of arthropod natural enemies. Research has explored manipulative use of chemical information from plants and insects that act as attractant cues for natural enemies (predators and parasitoids) and repellents of pests. In this review, we reflect on past strategies using chemical ecology in CBC, such as herbivore-induced plant volatiles and the push-pull technique, and propose future directions, including leveraging induced plant defenses in crop plants, repellent insect-based signaling, and genetically engineered crops. Further, we discuss how climate change may disrupt CBC and stress the importance of context dependency and yield outcomes.

Impacts of larval host plant species on dispersal traits and free-flight energetics of adult butterflies.

Animals derive resources from their diet and allocate them to organismal functions such as growth, maintenance, reproduction, and dispersal. How variation in diet quality can affect resource allocation to life-history traits, in particular those important to locomotion and dispersal, is poorly understood. We hypothesize that, particularly for specialist herbivore insects that are in co-evolutionary arms races with host plants, changes in host plant will impact performance. From their coevolutionary arms-race with plants, to a complex migratory life history, Monarch butterflies are among the most iconic insect species worldwide. Population declines initiated international conservation efforts involving the replanting of a variety of milkweed species. However, this practice was implemented with little regard for how diverse defensive chemistry of milkweeds experienced by monarch larvae may affect adult fitness traits. We report that adult flight muscle investment, flight energetics, and maintenance costs depend on the host plant species of larvae, and correlate with concentration of milkweed-derived cardenolides sequestered by adults. Our findings indicate host plant species can impact monarchs by affecting fuel requirements for flight.

Stomata-mediated interactions between plants, herbivores, and the environment.

Stomata play a central role in plant responses to abiotic and biotic stresses. Existing knowledge regarding the roles of stomata in plant stress is centered on abiotic stresses and plant-pathogen interactions, but how stomata influence plant-herbivore interactions remains largely unclear. Here, we summarize the functions of stomata in plant-insect interactions and highlight recent discoveries of how herbivores manipulate plant stomata. Because stomata are linked to interrelated physiological processes in plants, herbivory-induced changes in stomatal dynamics might have cellular, organismic, and/or even community-level impacts. We summarize our current understanding of how stomata mediate plant responses to herbivory and environmental stimuli, propose how herbivores may influence these responses, and identify key knowledge gaps in plant-herbivore interactions.

Cover Crop Soil Legacies Alter Phytochemistry and Resistance to Fall Armyworm (Lepidoptera: Noctuidae) in Maize.

Plant-soil feedbacks can mediate aboveground plant-herbivore interactions by impacting plant chemistry. Given that soil legacies and agricultural practices are closely tied, a better understanding of soil legacy cascades and their application in pest management are needed. We tested how cover crop legacies alter resistance to fall armyworm (Spodoptera frugiperda Smith, Lepidoptera: Noctuidae) in maize (Zea mays L., Poales: Poaceae). We compared herbivore performance and behavior of fall armyworm larvae on maize grown after four cover crop treatments: a leguminous mycorrhizal cover crop (pea: Pisum sativum L., Fabales: Fabaceae), a nonleguminous mycorrhizal cover crop (triticale: x Triticosecale Wittm. Ex A. Camus, Poales: Poaceae), a nonleguminous nonmycorrhizal cover crop (radish: Raphanus sativus L., Brassicales: Brassicaceae), and no cover crops (fallow). Soil inorganic N was highest in pea treatments and lowest in triticale treatments, while maize AMF colonization was greatest when grown after mycorrhizal cover crops compared to nonmycorrhizal or no cover crops. Cover crop legacies altered the emission of maize volatiles and fall armyworm larvae oriented toward odors emitted by maize grown after radish more frequently than triticale in olfactometer assays. Additionally, larvae performed better and consumed more leaf tissue when feeding on maize grown after radish and poorest on plants grown after triticale. When damaged by fall armyworm, maize grown after triticale expressed higher levels of lipoxygenase-3 (lox3), while plants grown after radish upregulated maize proteinase inhibitor (mpi) gene expression. Our results highlight the importance of appropriate cover crop selection and suggest that triticale could strengthen maize resistance to fall armyworm.

Subterranean herbivore-induced volatiles released by citrus roots upon feeding by Diaprepes abbreviatus recruit entomopathogenic nematodes.

Herbivore-induced volatile emissions benefit plant hosts by recruiting natural enemies of herbivorous insects. Such tritrophic interactions have been examined thoroughly in the above-ground terrestrial environment. Recently, similar signals have also been described in the subterranean environment, which may be of equal importance for indirect plant defense. The larvae of the root weevil, Diaprepes abbreviates, are a serious pest of citrus. Infestations can be controlled by the use of entomopathogenic nematodes, yet the interactions between the plant, insect and nematode are poorly understood and remain unpredictable. In bioassays that used a root zone six-arm olfactometer, citrus roots ('Swingle citrumelo' rootstock) recruited significantly more entomopathogenic nematodes (Steinernema diaprepesi) when infested with root weevil larvae than non-infested roots. Infested plants were more attractive to nematodes than larvae alone. Roots damaged by weevil larvae attracted more nematodes than mechanically damaged roots and sand controls. By dynamic in situ collection and GC-MS analysis of volatiles from soil, we determined that four major terpene compounds were produced by infested plant roots that were not found in samples from non-infested roots or soil that contained only larvae. Solvent extracts of weevil-infested roots attracted more nematodes than extracts of non-infested roots in a two choice sand-column bioassay. These findings suggest that Swingle citrus roots release induced volatiles as an indirect defense in response to herbivore feeding, and that some of these induced volatiles function as attractants for entomopathogenic nematodes.

Specialist versus generalist insect herbivores and plant defense.

There has been a long-standing hypothesis that specialist and generalist insects interact with plants in distinct ways. Although many tests exist, they typically compare only one species of each, they sometimes confound specialization and feeding guild, and often do not link chemical or transcriptional measures of the plant to actual resistance. In this review, we synthesize current data on whether specialists and generalists actually differ, with special attention to comparisons of their differential elicitation of plant responses. Although we find few consistencies in plant induction by specialists versus generalists, feeding guilds are predictive of differential plant responses. We outline a novel set of predictions based on current coevolutionary hypotheses and make methodological suggestions for improved comparisons of specialists and generalists.

Interspecific nematode signals regulate dispersal behavior.

BACKGROUND: Dispersal is an important nematode behavior. Upon crowding or food depletion, the free living bacteriovorus nematode Caenorhabditis elegans produces stress resistant dispersal larvae, called dauer, which are analogous to second stage juveniles (J2) of plant parasitic Meloidogyne spp. and infective juveniles (IJ)s of entomopathogenic nematodes (EPN), e.g., Steinernema feltiae. Regulation of dispersal behavior has not been thoroughly investigated for C. elegans or any other nematode species. Based on the fact that ascarosides regulate entry in dauer stage as well as multiple behaviors in C. elegans adults including mating, avoidance and aggregation, we hypothesized that ascarosides might also be involved in regulation of dispersal behavior in C. elegans and for other nematodes such as IJ of phylogenetically related EPNs. METHODOLOGY/PRINCIPAL FINDINGS: Liquid chromatography-mass spectrometry analysis of C. elegans dauer conditioned media, which shows strong dispersing activity, revealed four known ascarosides (ascr#2, ascr#3, ascr#8, icas#9). A synthetic blend of these ascarosides at physiologically relevant concentrations dispersed C. elegans dauer in the presence of food and also caused dispersion of IJs of S. feltiae and J2s of plant parasitic Meloidogyne spp. Assay guided fractionation revealed structural analogs as major active components of the S. feltiae (ascr#9) and C. elegans (ascr#2) dispersal blends. Further analysis revealed ascr#9 in all Steinernema spp. and Heterorhabditis spp. infected insect host cadavers. CONCLUSIONS/SIGNIFICANCE: Ascaroside blends represent evolutionarily conserved, fundamentally important communication systems for nematodes from diverse habitats, and thus may provide sustainable means for control of parasitic nematodes.