Comparing the attraction of two parasitoids to herbivore-induced volatiles of maize and its wild ancestors, the teosintes

Attracting Scelionidae egg parasitoids to enhance stink bug egg parasitisation in soybean crops using methyl salicylate and (E,E)-α-farnesene

BACKGROUND

Plant volatile organic compounds (VOCs) play a crucial role in mediating interactions between plants, herbivores and natural enemies. Among these VOCs, methyl salicylate and (E,E)-α-farnesene are emitted as herbivore-induced plant volatiles (HIPVs) by soybean plants in response to feeding by the brown stink bug Eushistus heros. These HIPVs function as synomones, influencing the foraging behaviour of the egg parasitoid, Telenomus podisi, the main natural enemy of E. heros, one of the major soybean pests in Brazil.

RESULTS

Laboratory experiments showed that two soybean cultivars, BRS 7580 and BRS 7880, produced similar qualitative blends of HIPVs, with methyl salicylate, (E,E)-α-farnesene and (Z)-3-hexenyl acetate being produced by both cultivars. Soybean cultivar BRS 7580 produced a significant lower amount of HIPVs compared to BRS 7880 but this difference did not affect the attractiveness of the egg parasitoid Telenomus podisi. Field experiments using these two cultivars and synthetic applications of methyl salicylate and (E,E)-α-farnesene showed a substantial increase in egg parasitism in all treated areas. Parasitism rates ranged from 50% to 80% in areas where these HIPVs were deployed, compared to only 10% in untreated control areas.

CONCLUSIONS

The egg parasitoid Telenomus podisi demonstrated an adept ability in recognising between HIPVs in soybean blends, even in the presence of significant quantitative differences. The results from the field experiment showed the potential of HIPVs in attracting natural enemies to specific target areas within fields. (E,E)-α-Farnesene showed an improved action during the later stages of soybean growth, notably at R6. In addition, this volatile attracted other families of natural enemies. © 2024 Society of Chemical Industry.

The push-pull intercrop Desmodium does not repel, but intercepts and kills pests

Over two decades ago, an intercropping strategy was developed that received critical acclaim for synergizing food security with ecosystem resilience in smallholder farming. The push-pull strategy reportedly suppresses lepidopteran pests in maize through a combination of a repellent intercrop (push), commonly Desmodium spp., and an attractive, border crop (pull). Key in the system is the intercrop's constitutive release of volatile terpenoids that repel herbivores. However, the earlier described volatile terpenoids were not detectable in the headspace of Desmodium, and only minimally upon herbivory. This was independent of soil type, microbiome composition, and whether collections were made in the laboratory or in the field. Furthermore, in oviposition choice tests in a wind tunnel, maize with or without an odor background of Desmodium was equally attractive for the invasive pest Spodoptera frugiperda. In search of an alternative mechanism, we found that neonate larvae strongly preferred Desmodium over maize. However, their development stagnated and no larva survived. In addition, older larvae were frequently seen impaled and immobilized by the dense network of silica-fortified, non-glandular trichomes. Thus, our data suggest that Desmodium may act through intercepting and decimating dispersing larval offspring rather than adult deterrence. As a hallmark of sustainable pest control, maize-Desmodium push-pull intercropping has inspired countless efforts to emulate stimulo-deterrent diversion in other cropping systems. However, detailed knowledge of the actual mechanisms is required to rationally improve the strategy, and translate the concept to other cropping systems.

Comparative analysis of defensive secondary metabolites in wild teosinte and cultivated maize under flooding and herbivory stress

Climate change is driving an alarming increase in the frequency and intensity of abiotic and biotic stress factors, negatively impacting plant development and agricultural productivity. To survive, plants respond by inducing changes in below and aboveground metabolism with concomitant alterations in defensive secondary metabolites. While plant responses to the isolated stresses of flooding and insect herbivory have been extensively studied, much less is known about their response in combination. Wild relatives of cultivated plants with robust stress tolerance traits provide an excellent system for comparing how diverse plant species respond to combinatorial stress, and provide insight into potential germplasms for stress-tolerant hybrids. In this study, we compared the below and aboveground changes in the secondary metabolites of maize (Zea mays) and a flood-tolerant wild relative Nicaraguan teosinte (Zea nicaraguensis) in response to flooding, insect herbivory, and their combination. Root tissue was analyzed for changes in belowground metabolism. Leaf total phenolic content and headspace volatile organic compound emission were analyzed for changes in aboveground secondary metabolism. Results revealed significant differences in the root metabolome profiles of teosinte and maize. Notably, the accumulation of the flavonoids apigenin, naringenin, and luteolin during flooding and herbivory differentiated teosinte from maize. Aboveground, terpenes, including trans-α-bergamotene and (E)-4,8-dimethylnona-1,3,7-triene, shaped compositional differences in their volatile profiles between flooding, herbivory, and their combination. Taken together, these results suggest teosinte may be more tolerant than maize due to dynamic metabolic changes during flooding and herbivory that help relieve stress and influence plant-insect interactions.

Plant Variety, Mycorrhization, and Herbivory Influence Induced Volatile Emissions and Plant Growth Characteristics in Tomato

Plants produce a range of volatile organic compounds (VOCs) that mediate vital ecological interactions between herbivorous insects, their natural enemies, plants, and soil dwelling organisms including arbuscular mycorrhizal fungi (AMF). The composition, quantity, and quality of the emitted VOCs can vary and is influenced by numerous factors such as plant species, variety (cultivar), plant developmental stage, root colonization by soil microbes, as well as the insect developmental stage, and level of specialization of the attacking herbivore. Understanding factors shaping VOC emissions is important and can be leveraged to enhance plant health and pest resistance. In this greenhouse study, we evaluated the influence of plant variety, mycorrhizal colonization, herbivory, and their interactions on the composition of emitted volatiles in tomato plants (Solanum lycopersicum L.). Four tomato varieties from two breeding histories (two heirlooms and two hybrids), were used. Tomato plants were inoculated with a commercial inoculum blend consisting of four species of AMF. Plants were also subjected to herbivory by Manduca sexta (Lepidoptera: Sphingidae L.) five weeks after transplanting. Headspace volatiles were collected from inoculated and non-inoculated plants with and without herbivores using solid phase-microextraction. Volatile profiles consisted of 21 different volatiles in detectable quantities. These included monoterpenes, sesquiterpenes, and alkane hydrocarbons. We documented a strong plant variety effect on VOC emissions. AMF colonization and herbivory suppressed VOC emissions. Plant biomass was improved by colonization of AMF. Our results show that mycorrhization, herbivory and plant variety can alter tomato plant VOC emissions and further shape volatile-mediated insect and plant interactions.

Effects of wild, local, and cultivated tobacco varieties on the performance of Spodoptera litura and its parasitoid Meteorus pulchricornis

BACKGROUND

Plant domestication can alter plant and insect interactions and influence bottom-up and top-down effects. However, little is known about the effects of wild, local, and cultivated varieties of the same plant species in the same region on herbivores and their parasitoids. Here, six tobacco varieties were selected: wild Bishan and Badan tobaccos, local Liangqiao and Shuangguan sun-cured tobaccos, and cultivated Xiangyan 5 and Cunsanpi. We examined how wild, local, and cultivated tobacco types affect the tobacco cutworm herbivore Spodoptera litura and its parasitoid Meteorus pulchricornis.

RESULTS

Levels of nicotine and trypsin protease inhibitor in leaves and the fitness of S. litura larvae varied significantly among the varieties. Wild tobacco had the highest levels of nicotine and trypsin protease inhibitor, which reduced the survival rate and prolonged the development period of S. litura. The tobacco types significantly influenced the life history parameters and host selection of M. pulchricornis. The cocoon weight, cocoon emergence rate, adult longevity, hind tibia length, and offspring fecundity of M. pulchricornis increased, whereas the development period decreased from wild to local to cultivated varieties. The parasitoids were more likely to select wild and local varieties than cultivated varieties.

CONCLUSION

Domestication of tobacco resulted in reduced resistance to S. litura in cultivated tobacco. Wild tobacco varieties suppress S. litura populations, adversely affect M. pulchricornis, and may enhance bottom-up and top-down control of S. litura. © 2023 Society of Chemical Industry.

Herbivory Damage Increased VOCs in Wild Relatives of Murtilla Plants Compared to Their First Offspring

Murtilla (Ugni molinae) is a shrub native to Chile that has undergone an incipient domestication process aimed at increasing its productivity. The reduction in intrinsic chemical defenses due to the domestication process has resulted in a decrease in the plant's ability to defend itself against mechanical or insect damage. In response to this damage, plants release volatile organic compounds (VOCs) as a means of defense. To understand how domestication has impacted the production of VOCs in the first offspring of murtilla, we hypothesized that their levels would be reduced due to the induction of mechanical and herbivore damage. To test this hypothesis, we collected VOCs from four offspring ecotypes and three wild relatives of murtilla. We induced mechanical and herbivore damage in the plants and then enclosed them in a glass chamber, where we captured the VOCs. We identified 12 compounds using GC-MS. Our results showed that wild relative ecotypes had a higher VOC release rate of 624.6 µg/cm²/day. Herbivore damage was the treatment that produced the highest release of VOCs, with 439.3 µg/cm²/day in wild relatives. These findings suggest that herbivory triggers defenses through the emission of VOCs, and that domestication has influenced the production of these compounds in murtilla. Overall, this study contributes to bridging the gap in the incipient domestication history of murtilla and highlights the importance of considering the impact of domestication on a plant's chemical defenses.

The effects of plant domestication on the foraging and performance of parasitoids

Domestication-related changes in the chemical traits of crop plants affect parasitoid foraging success, development, and survival. For example, herbivore-induced changes in the production of volatiles by domesticated plants can enhance or reduce parasitoid attraction. While the trade-off between nutrient content and chemical defense in cultivated plants can increase the suitability of hosts for parasitoids, their increased health and size can positively affect their immune response against parasitoids. Overall, plant domestication is expected to significantly affect their relationship with parasitoids due to altered plant morphology, physical characteristics, chemical defenses, and new plant associations. This review highlights the need for research on the effects of plant domestication on host-parasitoid interactions in the interest of better controlling insect pests.

Molecular ecology of plant volatiles in interactions with insect herbivores

Plant-derived volatile organic compounds (VOCs) play pivotal roles in interactions with insect herbivores. Individual VOCs can be directly toxic or deterrent, serve as signal molecules to attract natural enemies, and/or be perceived by distal plant tissues as a priming signal to prepare for expected herbivory. Environmental conditions, as well as the specific plant-insect interaction being investigated, strongly influence the observed functions of VOC blends. The complexity of plant-insect chemical communication via VOCs is further enriched by the sophisticated molecular perception mechanisms of insects, which can respond to one or more VOCs and thereby influence insect behavior in a manner that has yet to be fully elucidated. Despite numerous gaps in the current understanding of VOC-mediated plant-insect interactions, successful pest management strategies such as push-pull systems, synthetic odorant traps, and crop cultivars with modified VOC profiles have been developed to supplement chemical pesticide applications and enable more sustainable agricultural practices. Future studies in this field would benefit from examining the responses of both plants and insects in the same experiment to gain a more complete view of these interactive systems. Furthermore, a molecular evolutionary study of key genetic elements of the ecological interaction phenotypes could provide new insights into VOC-mediated plant communication with insect herbivores.

Influence of wild, local and cultivated tobacco varieties on the oviposition preference and offspring performance of Spodoptera litura

The influences of different plants on herbivores have recently attracted research interest; however, little is known regarding the effects of wild, local and cultivated varieties of the same plant from the same origin on herbivores. This study aimed to examine the effects of different tobacco varieties from the same origin on the oviposition preference and offspring performance of Spodoptera litura. We selected two wild ('Bishan wild tobacco' and 'Badan wild tobacco'), two local ('Liangqiao sun-cured tobacco' and 'Shuangguan sun-cured tobacco') and two cultivated ('Xiangyan No. 5' and 'Cunsanpi') tobacco varieties from Hunan Province, China. We found that female S. litura varied in oviposition preferences across the tobacco varieties. They preferred to lay eggs on the cultivated varieties, followed by the local varieties, with the wild varieties being the least preferred. Furthermore, different tobacco varieties significantly influenced the life history parameters of S. litura. Survival rate, pupal weight, emergence rate and adult dry weight decreased in the following order: cultivated varieties > local varieties > wild varieties. Conversely, the pupal stage and development period decreased in the following order: wild varieties > local varieties > cultivated varieties. Therefore, we conclude that wild tobacco varieties have higher resistance to S. litura than cultivated and local varieties, reflecting the evolutionary advantages of wild tobacco varieties.

Modern Maize Hybrids Have Lost Volatile Bottom-Up and Top-Down Control of Dalbulus maidis, a Specialist Herbivore

Following damage by herbivores, many plants release volatiles that dissuade future conspecifics from feeding. In many crop plants however, induced volatiles mediating this kind of interactions among plants, herbivores and also their natural enemies have been altered through the process of domestication. The selection of crops for increased yield may have gone at a cost of defense, possibly including defense-related volatiles. Dalbulus maidis (Hemiptera: Cicadellidae), a specialist leafhopper that only feeds on Zea spp., is a vector of Corn Stunt Spiroplasma, a serious maize disease. Here, we compared the volatiles released following D. maidis attack by a maize landrace and two maize hybrids of temperate and tropical background. Also, we performed behavioral assays with the leafhopper contrasting healthy non-attacked maize seedlings versus attacked seedlings. The maize landrace produced more than 6-fold larger quantities of induced volatiles compared to the maize hybrids after herbivory. Corn leafhopper females were able to detect and significantly preferred the odors of healthy seedlings over the attacked ones only in the landrace. They did not discriminate between the attacked and non-attacked hybrids. Additionally, we found that the attraction of the parasitoid wasp Anagrus virlai (Hymenoptera: Mymaridae) to its host was diminished in the tested hybrids. The parasitoid was able to detect the odors of the attacked landrace, however it was unable to discriminate between healthy and attacked maize hybrid plants. These results suggest that those more domesticated germplasms may have lost the ability not only to release volatiles that avoid colonization of future herbivores, but also to attract their natural enemies in a tritrophic system.

Spodoptera frugiperda Caterpillars Suppress Herbivore-Induced Volatile Emissions in Maize

The vast spectrum of inducible plant defenses can have direct negative effects on herbivores, or indirect effects, for instance in the form of herbivore-induced plant volatiles (HIPVs) that attract natural enemies. Various arthropods have evolved ways to suppress plant defenses. To test whether this is the case for caterpillar-induced HIPVs, we compared the volatile induction by Spodoptera frugiperda (Lepidoptera: Noctuidae), which is particularly well adapted to feed on maize (Zea mays), with the induction by three more generalist noctuid larvae. We tested the hypothesis that S. frugiperda suppresses HIPV emissions in maize, and thereby reduces attractiveness to natural enemies. HIPV emissions triggered by S. frugiperda when feeding on maize were indeed found to be significantly weaker than by Spodoptera littoralis, Spodoptera exigua, and Helicoverpa armigera. The suppression seems specific for maize, as we found no evidence for this when S. frugiperda caterpillars fed on cotton (Gossypium herbaceum). Artificially damaged maize plants treated with larval regurgitant revealed that HIPV suppression may be related to factors in the caterpillars' oral secretions. We also found evidence that differential physical damage that the caterpillars inflict on maize leaves may play a role. The suppressed induction of HIPVs had no apparent consequences for the attraction of a common parasitoid of S. frugiperda, Cotesia marginiventris (Hymenoptera: Braconidae). Nevertheless, the ability to manipulate the defenses of its main host plant may have contributed to the success of S. frugiperda as a major pest of maize, especially in Africa and Asia, which it has recently invaded.

A Return to the Wild: Root Exudates and Food Security

Challenges to food security under conditions of global change are forcing us to increase global crop production. Focussing on belowground plant traits, especially root exudation, has great promise to meet this challenge. Root exudation is the release of a vast array of compounds into the soil. These exudates are involved in many biotic and abiotic interactions. Wild relatives of crops provide a large potential source of information and genetic material and have desirable traits that could be incorporated into modern breeding programs. However, root exudates are currently underexploited. Here, we highlight how the traits of root exudates of crop wild relatives could be used to improve agricultural output and reduce environmental impacts, particularly by decreasing our dependence on pesticides and fertilisers.

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.

Agro-ecological options for fall armyworm (Spodoptera frugiperda JE Smith) management: Providing low-cost, smallholder friendly solutions to an invasive pest

Fall armyworm (FAW), a voracious agricultural pest native to North and South America, was first detected on the African continent in 2016 and has subsequently spread throughout the continent and across Asia. It has been predicted that FAW could cause up to $US13 billion per annum in crop losses throughout sub-Saharan Africa, thereby threatening the livelihoods of millions of poor farmers. In their haste to respond to FAW governments may promote indiscriminate use of chemical pesticides which, aside from human health and environmental risks, could undermine smallholder pest management strategies that depend to a large degree on natural enemies. Agro-ecological approaches offer culturally appropriate low-cost pest control strategies that can be readily integrated into existing efforts to improve smallholder incomes and resilience through sustainable intensification. Such approaches should therefore be promoted as a core component of integrated pest management (IPM) programmes for FAW in combination with crop breeding for pest resistance, classical biological control and selective use of safe pesticides. Nonetheless, the suitability of agro-ecological measures for reducing FAW densities and impact need to be carefully assessed across varied environmental and socio-economic conditions before they can be proposed for wide-scale implementation. To support this process, we review evidence for the efficacy of potential agro-ecological measures for controlling FAW and other pests, consider the associated risks, and draw attention to critical knowledge gaps. The evidence indicates that several measures can be adopted immediately. These include (i) sustainable soil fertility management, especially measures that maintain or restore soil organic carbon; (ii) intercropping with appropriately selected companion plants; and (iii) diversifying the farm environment through management of (semi)natural habitats at multiple spatial scales. Nevertheless, we recommend embedding trials into upscaling programmes so that the costs and benefits of these interventions may be determined across the diverse biophysical and socio-economic contexts that are found in the invaded range.

Genotypic Variation and Phenotypic Plasticity in Gene Expression and Emissions of Herbivore-Induced Volatiles, and their Potential Tritrophic Implications, in Cranberries

Herbivorous insects are important problems in cranberry (Vaccinium macrocarpon Ait.) production. The use of chemical pesticides is common practice, but beneficial insects such as natural enemies of herbivores (e.g. predators and parasitoids) could be affected as well. Therefore, we studied the defensive mechanisms that cranberry plants use to combat pests, focusing on herbivore-induced plant volatiles (HIPVs), which can be used to recruit predators and parasitoids foraging for prey or hosts. Then, we used synthetic HIPVs to test the attraction of natural enemies. In a greenhouse, we assessed nine cranberry genotypes for expression of genes involved in HIPV biosynthesis and/or emission of HIPVs. In an experimental field, we assessed whether baiting traps with individual or combinations of HIPVs increased attractiveness to natural enemies. The results showed that different cranberry genotypes vary in their emission of monoterpenes and sesquiterpenes but not in their expression of two genes associated with terpene biosynthesis, α-humulene/β-caryophyllene synthase and (3S,6E)-nerolidol/R-linalool synthase. Induction with methyl jasmonate or herbivore (gypsy moth, Lymantria dispar L.) feeding increased the expression of these genes and emission of HIPVs. The HIPV methyl salicylate (MeSA), alone or in combination with other HIPVs, increased syrphid attraction by 6-fold in the field, while (Z)-3-hexenyl acetate and MeSA repelled ladybeetles and megaspilids, respectively. Linalool and β-caryophyllene elicited no behavioral responses of natural enemies. Elucidating the mechanisms of pest resistance, as well as experimentally augmenting plant defenses such as HIPVs, may contribute to the development of more sustainable pest management practices in crops, including cranberries.

Crop domestication: anthropogenic effects on insect-plant interactions in agroecosystems

Although crop domestication is considered a model system for understanding evolution, the eco-evolutionary effects of domesticated crops on higher trophic levels have rarely been discussed. Changes in size, shape, quality, or timing of plant traits during domestication can influence entire arthropod communities. The plant traits specific to crop plants can be rare in nature. In the face of such novelty, it is important to understand how species and trophic levels vary in their responses. Although the evidence is still limited, crop domestication can influence the ecology, genetics, and evolution of plants, insect herbivores, natural enemies, and pollinators. We call for more study on how eco-evolutionary processes operate under domestication to provide new insight on the sustainability of species interactions within agroecosystems.

Indirect Root Defenses Cause Induced Fitness Costs in Bt-Resistant Western Corn Rootworm

Plants genetically modified to produce insecticidal toxins from the bacterium Bacillus thuringiensis Berliner (Bt) have been extensively used to manage the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) in the United States. Evolution of WCR resistance to Bt toxins has forced the consideration of alternative pest management and improved insect resistance management. Entomopathogenic nematodes (EPNs), obligate insect parasites, are attracted toward volatile organic compounds (VOCs) emitted by maize roots after WCR herbivory. The production of VOCs of two types of Bt maize (MON88017 and MIR604) and their near-isolines was evaluated after induction with Bt-susceptible and resistant WCR. The attraction of EPNs toward the Bt hybrids was tested in the laboratory and the field. Bt hybrids emitted VOCs when induced by Bt-resistant insects whereas induction by Bt-susceptible WCR did not elicit a plant response. Survival of Bt-resistant WCR was lower on the hybrid attracting EPNs and similar to the survival of Bt-susceptible WCR without EPNs. This trade-off of Bt-resistance is defined here as an induced fitness cost, and offers a viable tool to management of Bt-resistant WCR.

Nocturnal herbivore-induced plant volatiles attract the generalist predatory earwig Doru luteipes Scudder

Numerous studies have demonstrated that entomophagous arthropods use herbivore-induced plant volatile (HIPV) blends to search for their prey or host. However, no study has yet focused on the response of nocturnal predators to volatile blends emitted by prey damaged plants. We investigated the olfactory behavioral responses of the night-active generalist predatory earwig Doru luteipes Scudder (Dermaptera: Forficulidae) to diurnal and nocturnal volatile blends emitted by maize plants (Zea mays) attacked by either a stem borer (Diatraea saccharalis) or a leaf-chewing caterpillar (Spodoptera frugiperda), both suitable lepidopteran prey. Additionally, we examined whether the earwig preferred odors emitted from short- or long-term damaged maize. We first determined the earwig diel foraging rhythm and confirmed that D. luteipes is a nocturnal predator. Olfactometer assays showed that during the day, although the earwigs were walking actively, they did not discriminate the volatiles of undamaged maize plants from those of herbivore damaged maize plants. In contrast, at night, earwigs preferred volatiles emitted by maize plants attacked by D. saccharalis or S. frugiperda over undamaged plants and short- over long-term damaged maize. Our GC-MS analysis revealed that short-term damaged nocturnal plant volatile blends were comprised mainly of fatty acid derivatives (i.e., green leaf volatiles), while the long-term damaged plant volatile blend contained mostly terpenoids. We also observed distinct volatile blend composition emitted by maize damaged by the different caterpillars. Our results showed that D. luteipes innately uses nocturnal herbivore-induced plant volatiles to search for prey. Moreover, the attraction of the earwig to short-term damaged plants is likely mediated by fatty acid derivatives.

Plant volatile-mediated signalling and its application in agriculture: successes and challenges

856 I. 856 II. 857 III. 858 IV. 859 V. 860 VI. 862 VII. 863 VIII. 864 IX. 866 866 References 866 SUMMARY: The mediation of volatile secondary metabolites in signalling between plants and other organisms has long been seen as presenting opportunities for sustainable crop protection. Initially, exploitation of interactions between plants and other organisms, particularly insect pests, foundered because of difficulties in delivering, sustainably, the signal systems for crop protection. We now have mounting and, in some cases, clear practical evidence for successful delivery by companion cropping or next-generation genetic modification (GM). At the same time, the type of plant signalling being exploited has expanded to signalling from plants to organisms antagonistic to pests, and to plant stress-induced, or primed, plant-to-plant signalling for defence and growth stimulation.