Direct Defense Research Articles

α-Linolenic acid in Papilio machaon larvae regurgitant induces a defensive response in Apiaceae

Papilio machaon hippocrates C. Felder et R. Felder, 1864 (Papilionidae) larvae are pests of plants of the family Apiaceae. It is unclear whether Apiaceae plants show induced defensive responses against P. machaon hippocrates larvae, and if so, how these responses are induced. Comparison of the fatty acid (FA) composition of the leaves of host plants and the regurgitant of P. machaon hippocrates larvae by LC–MS revealed a great increase in α-linolenic acid (α-LA) in the regurgitant compared with the FAs contained in the leaves. However, specific FA amino acid conjugates, known as elicitor compounds, such as volicitin, were not detected. Sterile host plants (Saposhnikovia divaricata (Turcz.) Schischk., Apiaceae) were treated with α-LA to mimic the damage made by P. machaon hippocrates larvae. After α-LA treatment to leaves, induced defensive reactions, i.e., release of volatile compounds such as α- and β-pinene and camphene (possible induced indirect defense) and the accumulation of specialized metabolites such as (R)-falcarinol and bergapten (possible induced direct defense) were observed. These findings highlight the role of α-LA in the interaction between P. machaon hippocrates larvae and Apiaceae host plants.

Dispensing a Synthetic Green Leaf Volatile to Two Plant Species in a Common Garden Differentially Alters Physiological Responses and Herbivory

Herbivore-induced plant volatile (HIPV)-mediated eavesdropping by plants is a well-documented, inducible phenomenon that has practical agronomic applications for enhancing plant defense and pest management. However, as with any inducible phenomenon, responding to volatile cues may incur physiological and ecological costs that limit plant productivity. In a common garden experiment, we tested the hypothesis that exposure to a single HIPV would decrease herbivore damage at the cost of reduced plant growth and reproduction. Lima bean (Phaseolus lunatus) and pepper (Capsicum annuum) plants were exposed to a persistent, low dose (~10 ng/h) of the green leaf volatile cis-3-hexenyl acetate (z3HAC), which is a HIPV and damage-associated volatile. z3HAC-treated pepper plants were shorter, had less aboveground and belowground biomass, and produced fewer flowers and fruits relative to controls, while z3HAC-treated lima bean plants were taller and produced more leaves and flowers than did controls. Natural herbivory was reduced in z3HAC-exposed lima bean plants, but not in pepper. Cyanogenic potential, a putative direct defense mechanism in lima bean, was lower in young z3HAC-exposed leaves, suggesting a growth–defense tradeoff from z3HAC exposure alone. Plant species-specific responses to an identical volatile cue have important implications for agronomic costs and benefits of volatile-mediated interplant communication under field conditions.

Direct defense of common bean accessions against two-spotted spider mite (Tetranychus urticae Koch.) attack

To find the direct defense of seedling resistance of common beans, by resistant mechanisms, morphological and physiological attributes of ten cultivars (Naz, Dorsa, Akhtar,KS41128, 65-062-107, 65-071-98, 65-071-306, 65-071-410, 65-071-400, and 65-071-405) were evaluated against two-spotted spider mite in 2017 at Bu-Ali Sina university, Hamedan, Iran. Among four kinds of resistant mechanisms such as antixenosis, antibiosis, tolerant tests and PRI index, both antixenosis and tolerance mechanisms determined to be the most accurate tests in the evaluating of common bean resistance against TSSM attack. Germination delay, development and fast growth, early maturity, erected posture, small cotyledon area, the more leaf thickness along with the dark-colored demonstrated were the escape mechanisms of common beans tolerant genotypes against TSSM attack. Some epidermal traits such as the first defense barrier on common bean like hook-shaped and high density of trichome especially on abaxial epidermis by having trapping behavior showed high relation with tolerant genotypes. In fact, in tolerant beans, related-traits to trichome on leaves entrapped the body parts of TSSM such as leg tarsi, mouthpart and ovipositor and prevented to move, feed and reproduction of mites and therefore, these features decreased damage to leaf area of Phaseolus vulgaris as well. The 65-071-98, 65-062-107 genotypes and NAZ, were certainly categorized as the most tolerant cultivars while Akhtar and 65-071-400 were introduced as the most susceptible accessions of common beans, respectively.

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

BackgroundMaize (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.ResultsIn 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.ConclusionsThis study provided further insights to understand the role of defense signaling networks in Mp708’s resistance to CLA.

Functions of ROS in Macrophages and Antimicrobial Immunity.

Reactive oxygen species (ROS) are a chemically defined group of reactive molecules derived from molecular oxygen. ROS are involved in a plethora of processes in cells in all domains of life, ranging from bacteria, plants and animals, including humans. The importance of ROS for macrophage-mediated immunity is unquestioned. Their functions comprise direct antimicrobial activity against bacteria and parasites as well as redox-regulation of immune signaling and induction of inflammasome activation. However, only a few studies have performed in-depth ROS analyses and even fewer have identified the precise redox-regulated target molecules. In this review, we will give a brief introduction to ROS and their sources in macrophages, summarize the versatile roles of ROS in direct and indirect antimicrobial immune defense, and provide an overview of commonly used ROS probes, scavengers and inhibitors.

The Induced Resistance Lexicon: Do's and Don'ts.

To be protected from biological threats, plants have evolved an immune system comprising constitutive and inducible defenses. For example, upon perception of certain stimuli, plants can develop a conditioned state of enhanced defensive capacity against upcoming pathogens and pests, resulting in a phenotype called 'induced resistance' (IR). To tackle the confusing lexicon currently used in the IR field, we propose a widely applicable code of practice concerning the terminology and description of IR phenotypes using two main phenotypical aspects: local versus systemic resistance, and direct versus primed defense responses. Our general framework aims to improve uniformity and consistency in future scientific communication, which should help to avoid further misinterpretations and facilitate the accessibility and impact of this research field.

Plant defense responses triggered by phytoseiid predatory mites (Mesostigmata: Phytoseiidae) are species-specific, depend on plant genotype and may not be related to direct plant feeding

Zoophytophagous arthropods can elicit plant defense responses affecting potential prey beyond predation. Phytophagy prevails as the main trigger for these responses, as in the case of Euseius stipulatus (Athias-Henriot) (Mesostigmata: Phytoseiidae), a predator occurring in citrus. Because other triggers cannot be excluded, our aim was to examine whether other phytoseiids co-occurring with E. stipulatus but not engaged in plant feeding [Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot] could induce similar responses (in terms of herbivore induced plant volatiles, HIPVs, and main defensive pathways), and how these affected the behavior of conspecifics and the shared prey, Tetranychus urticae Koch (Prostigmata: Tetranychidae). N. californicus triggered plant genotype-specific defense responses, including the production of different HIPVs compared to clean plants. However, we could not observe these effects for P. persimilis. T. urticae avoided better protected plants, because of stronger direct or indirect defense. As plants with weaker direct defense levels should offer higher prey densities, and those harboring conspecific predators represent higher risk of cannibalism, predators were expected to behave similarly. However, they did not. Our results demonstrate that plant defense triggered by phytoseiids is species-specific, depend on plant genotype and can be triggered by non-feeding activities. As N. californicus is a highly efficient predator used worldwide, further studies with this species are needed. Likewise, cineol, one of the volatiles identified in the blends triggered by this phytoseiid, could be used to manipulate the prey. These studies could pave the way for a more efficient use of phytoseiids in agroecosystems.

Vitamin D is a strategic blow to coronavirus infection

The world is in the grip of the pandemic of the new viral infection COVID-19. The number of patients around the world is not only not decreasing, but also progressively increasing. Treatment and prevention of SARS-CoV-2 is a major global healthcare challenge. Effective and safe methods of treatment and prevention are urgently needed that can reduce the risk of infection, reduce the risk of developing the infectious process and mortality from this serious disease in addition to quarantine. Vitamin D is known for its classic role in maintaining bone mineral density. Currently, his contribution has been more and more studied. For example, the immune system is important, as well as adaptive immunity and regulation of the inflammatory cascade. In these reviews, the mechanisms of the effect of vitamin D on cellular and humoral immunity and direct antiviral defense of the body were discovered, and its potential modules – the role in vaccine immunogenicity. The data of observational and randomized clinical trials proving the positive effect of colecalciferol on the frequency and severity of seasonal viral respiratory diseases are presented. The mechanism of penetration and development of coronavirus in the human body, changes in the immune system and humoral factors of the body’s defense against the background of the course of SARS-CoV-2. Coronavirus and more severe course is an infectious process depending on age and associated diseases. In this article, we analyze and summarize the data of modern studies, in which it is proved that the level of vitamin D in the blood has a beneficial effect on the content of vitamins D in the body’s immune and antiviral defense and its role in reducing the risk of infection and the severity of pathological diseases, including COVID-19. Discussion of the doses and regimens of vitamin D therapy against viral infections, including COVID-19, is based on the experience of previous and ongoing studies and guidelines.

Zucchini Plants Alter Gene Expression and Emission of (E)-β-Caryophyllene Following Aphis gossypii Infestation.

Zucchini (Cucurbita pepo L.) is widely cultivated in temperate regions. One of the major production challenges is the damage caused by Aphis gossypii (Homoptera: Aphididae), a polyphagous aphid, which can negatively affect its host plant, both directly by feeding and indirectly by vectoring viruses. To gain insights into the transcriptome events that occur during the zucchini–aphid interaction and to understand the early-to-late defense response through gene expression profiles, we performed RNA-sequencing (RNA-Seq) on zucchini leaves challenged by A. gossypii (24, 48, and 96 h post-infestation; hpi). Data analysis indicated a complex and dynamic pattern of gene expression and a transient transcriptional reconfiguration that involved more than 700 differentially expressed genes (DEGs), including a large number of defense-related genes. The down-regulation of key genes of plant immunity, such as leucine-rich repeat (LRR) protein kinases, transcription factors, and genes associated with direct (i.e., protease inhibitors, cysteine peptidases, etc.) and indirect (i.e., terpene synthase) defense responses, suggests the aphid ability to manipulate plant immune responses. We also investigated the emission of volatile organic compounds (VOCs) from infested plants and observed a reduced emission of (E)-β-caryophyllene at 48 hpi, likely the result of aphid effectors, which reflects the down-regulation of two genes involved in the biosynthesis of terpenoids. We showed that (E)-β-caryophyllene emission was modified by the duration of plant infestation and by aphid density and that this molecule highly attracts Aphidius colemani, a parasitic wasp of A. gossypii. With our results we contributed to the identification of genes involved in cucurbit plant interactions with phloem feeders. Our findings may also help pave the way toward developing tolerant zucchini varieties and to identify molecules for sustainable management of harmful insect populations.

PACAP is a pathogen-inducible resident antimicrobial neuropeptide affording rapid and contextual molecular host defense of the brain.

Defense of the central nervous system (CNS) against infection must be accomplished without generation of potentially injurious immune cell-mediated or off-target inflammation which could impair key functions. As the CNS is an immune-privileged compartment, inducible innate defense mechanisms endogenous to the CNS likely play an essential role in this regard. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide known to regulate neurodevelopment, emotion, and certain stress responses. While PACAP is known to interact with the immune system, its significance in direct defense of brain or other tissues is not established. Here, we show that our machine-learning classifier can screen for immune activity in neuropeptides, and correctly identified PACAP as an antimicrobial neuropeptide in agreement with previous experimental work. Furthermore, synchrotron X-ray scattering, antimicrobial assays, and mechanistic fingerprinting provided precise insights into how PACAP exerts antimicrobial activities vs. pathogens via multiple and synergistic mechanisms, including dysregulation of membrane integrity and energetics and activation of cell death pathways. Importantly, resident PACAP is selectively induced up to 50-fold in the brain in mouse models of Staphylococcus aureus or Candida albicans infection in vivo, without inducing immune cell infiltration. We show differential PACAP induction even in various tissues outside the CNS, and how these observed patterns of induction are consistent with the antimicrobial efficacy of PACAP measured in conditions simulating specific physiologic contexts of those tissues. Phylogenetic analysis of PACAP revealed close conservation of predicted antimicrobial properties spanning primitive invertebrates to modern mammals. Together, these findings substantiate our hypothesis that PACAP is an ancient neuro-endocrine-immune effector that defends the CNS against infection while minimizing potentially injurious neuroinflammation.

Elevational gradients in constitutive and induced oak defences based on individual traits and their correlated expression patterns

Elevational gradients are useful ecological settings for revealing the biotic and abiotic drivers of plant trait variation and plant–insect interactions. However, most work focusing on plant defences has looked at individual traits and few studies have assessed multiple traits simultaneously, their correlated expression patterns, and abiotic factors associated with such patterns across elevations. To address this knowledge gap, we studied elevational variation in direct (phenolic compounds) and indirect (volatile organic compounds) constitutive defences and their inducibility after feeding by a specialist beetle Altica quercetorum in saplings of 18 wild populations of Quercus pyrenaica. We tested for: 1) clines in each defensive trait individually, 2) their patterns of correlated expression and 3) associations between any such clines and climatic factors. We found that constitutive direct defences (lignins and hydrolysable tannins) decreased with increasing elevation. We observed no elevational gradient for constitutive indirect defences (volatile organic compounds) or the inducibility of direct or indirect defensive traits when looking at groups of compounds. However, at individual tree‐level, increased induction of two monoterpenes (α‐fenchene and camphene) at higher elevation was shown. Furthermore, we show a significant pattern of co‐expression of constitutive and induced phenolics across populations, which weakened with increasing elevation. Finally, we found no evidence that climatic factors were associated with either individual or correlated trait expression patterns across elevations. Overall, these findings call for moving beyond elevational clines in individual plant defences, and argue that assessing elevational shifts in trait correlated expression patterns and their underlying mechanisms can increase our understanding of plant defence evolution and plant–herbivore interactions along environmental gradients.

European defence policy at a crossroads – Germany preserving the status quo and France seeking change?

ABSTRACT The combination of an increasingly assertive Russia with growing uncertainty over long-term US commitment to Europe's security has resulted in calls for new efforts to be made in European defence cooperation. Post-Brexit, France and Germany become the two remaining significant defence actors within the EU policy framework. Given this reconfiguration, an important question to has to be answered. Which state, France or Germany, is currently gaining more influence in European defence cooperation? A critical conceptual framework is utilised to explore the nature of Franco-German rivalry and to determine which nation is likely to obtain more influence in this policy area. Firstly, the article explores the clash between France's desire to direct European defence cooperation towards the stabilisation of Europe's southern neighbourhood with Germany's preference to minimise its own military involvement outside Europe. The article then focuses on non-EU defence solutions separately proposed by France and Germany, those being the European Intervention Initiative and the Framework Nations Concept respectively. The article finds that Germany's preferences are a considerable obstacle to attempts to create a more autonomous form of European defence cooperation and that dependence on US military strength and NATO structures continues to be an unavoidable reality.

Chris Hanretty, A Court of Specialists: Judicial Behavior on the UK Supreme Court, New York: Oxford University Press, 2020, 304 pp, hb £64.00

Chris Hanretty, A Court of Specialists: Judicial Behavior on the UK Supreme Court, New York: Oxford University Press, 2020, 304 pp, hb £64.00

Pepper domestication enhances parasitoid recruitment to herbivore-damaged plants

Plant breeding has improved traits such as fruit flavor and yield but may have compromised direct and indirect defenses to herbivores compared to their wild ancestors. This has been termed the plant domestication-reduced defense hypothesis. We present evidence that domestication of Capsicum annuum (the chili pepper) from its wild progenitor, Capsicum annuum var. glabriusculum, has not affected resistance to the insect herbivore, Manduca sexta (the tobacco hornworm). Caterpillars performed equally well on the domesticated and wild pepper. Subsequent behavioral choice assays with one of the main natural enemies of M. sexta, the parasitoid wasp Cotesia congregata, showed that parasitoids preferentially chose herbivore-damaged domesticated pepper plants over their wild relative. To investigate this tri-trophic interaction further, we then assessed the efficiency of C. congregata to parasitize M. sexta on numerous wild pepper accessions and domesticated pepper cultivars in a large foraging enclosure. We found that herbivores feeding on domesticated plants were parasitized at more than twice the rate of those on wild genotypes. These results imply that pepper domestication has not changed resistance to herbivorous insects (i.e., leaf palatability as a direct defense), but rather has improved volatile attraction to recruit natural enemies.

A comparison of the direct and indirect defence abilities of cultivated maize versus perennial and annual teosintes

The transition from a perennial to an annual life cycle, as well as domestication, are expected to increase plant growth and reproduction at the same time that anti-herbivore defences are reduced. Here, we investigated the effects of the life-history transition (the perennial teosinte Zea diploperennis to the annual teosinte Z. mays ssp. mexicana) and domestication of Zea (annual teosinte to the modern maize Z. mays ssp. mays) on direct and indirect defences against the fall armyworm Spodoptera frugiperda. The direct defence of Zea was assessed by larval survival and nutritional indices based on food intake and utilisation. Indirect defence was measured in terms of the olfactory preference of the night-active predatory earwig Doru luteipes for nocturnal herbivore-induced plant volatiles (HIPVs) from the teosintes and maize. Larval growth and survival were reduced on teosintes relative to maize. Whilst larvae fed on perennial teosinte had lower food intake indices, those on annual teosinte showed lower food utilisation indices relative to maize. The earwig preferred HIPVs emitted by teosintes over those by maize, but it did not discriminate between odours of herbivore-damaged annual and perennial teosinte. The nocturnal HIPV blend from maize contained the lowest total amount of fatty acid derivatives, while it had higher total amounts of terpenes compared to teosintes. Our study shows that the teosintes are better defended than maize in terms of direct and indirect defences; however, the perennial teosinte have stronger direct defences against the fall armyworm than the annual teosinte.

Multiple Infestations Induce Direct Defense of Maize to Tetranychus urticae (Acari: Tetranychidae)

Plants present constitutive or induced defense mechanisms against herbivory. In addition, studies show that there are interactions between these different defense mechanisms when multiple species infestations occur. This study investigated the interaction between maize defensive mechanisms to control two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) under single and double species infestations with this spider mite and fall armyworm, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae). The experiment was carried out in a greenhouse with the following treatments: uninfested Bt (Bacillus thuringiensis Berliner; Bacillaceae) and conventional maize, single infestation with spider mite on Bt and conventional maize, and both maize types with infestations of spider mite and fall armyworm. Two d after infestation, all treatments were re-infested with spider mite. The number of eggs, immatures, and adult females (alive and dead) were recorded for re-infested populations. In addition, a leaf sample was taken from all maize plants for spectrometric analysis. There was no significant difference of biological variables of spider mite between Bt and conventional plants, as well as the ones from pre-infested and non-infested plants. The same chemical pattern of ions was observed on plants in these 4 groups. In the conventional pre-infested plants with spider mite and fall armyworm, the population of re-infested mite showed reduced survival and fertility. Defensive compounds detected were HMBOA-Glc, Linoleoyl-GPI, and kaempferol rutinose. It was suggested that there is direct induced defense against spider mite in conventional maize in multiple infestations with spider mite and fall armyworm.

Effects of soil salinity on the expression of direct and indirect defences in wild cotton Gossypium hirsutum

Abstract Previous studies have frequently reported effects of abiotic factors on herbivore‐induced plant defences based on effects on single plant traits. However, plants commonly express multiple defences simultaneously and these traits are often correlated. Thus, a fuller understanding of abiotic‐context dependency in plant defence requires measuring multiple traits and addressing their patterns of correlated expression. We evaluated the effects of soil salinity on the expression of direct (phenolic compounds, gossypol gland density) and indirect (volatile organic compounds, extrafloral nectar) defensive traits in wild cotton Gossypium hirsutum. Specifically, we asked whether soil salinity affects the induction of these traits, and whether it shapes trait correlations potentially underlying altered patterns of trait induction. We conducted a factorial experiment with 16 cotton genotypes where we manipulated soil salinity and defence induction by applying artificial leaf damage (25% mechanical damage and caterpillar oral secretions) and measured defence levels at different time points post damage. Leaf damage induced most traits except gossypol gland density, whereas salinity did not have a mean effect (across constitutive and induced levels) on any of the measured traits. Nonetheless, salinity prevented the induction of phenolic compounds (condensed and hydrolysable tannins), and also affected trait correlations. Specifically, phenolic compounds were negatively associated with nectar production only under salinized conditions, an apparent trade‐off that could affect the induction of phenolic compounds. In addition, positive correlations between phenolic compounds and gland density and root biomass observed under control conditions were lost under salinized conditions. Synthesis. By investigating the effects of soil salinity on the expression of multiple direct and indirect defensive traits and their underlying correlations, these findings build towards a better understanding of how abiotic context dependency shapes plant allocation to and expression of multiple defensive traits.

Identification and characterization of two sesquiterpene synthase genes involved in volatile-mediated defense in tea plant (Camellia sinensis)

Terpenes and their derivatives are vital components of tea aroma. Their constitution and quantity are highly important criteria for the sensory evaluation of teas. Biologically, terpenes are involved in chemical resistance of tea plant against biotic and/or abiotic stresses. The goal of this study is to identify volatile terpenes of tea plants implicated in defense against herbivores and to identify terpene synthase (TPS) genes for their biosynthesis. Upon herbivory by tea geometrid (Ectropis obliqua Prout), tea plants were found to emit two sesquiterpenes, (E, E)-α-farnesene and (E)-nerolidol, which were undetectable in intact tea plants. The induced emission of (E, E)-α-farnesene and (E)-nerolidol suggests that they function in either direct or indirect defense of tea plants against the tea geometrid. Candidate TPS genes were identified from the transcriptomes of tea plants infested by tea geometrids. Two dedicated sesquiterpene synthases, CsAFR and CsNES2, were identified. CsAFR belongs to the TPS-b clade and can catalyze the formation of (E, E)-α-farnesene from (E, E)-FPP. CsNES2 belongs to the TPS-g clade and can synthesize (E)-nerolidol using (E, E)-FPP. The two genes were also both dramatically upregulated by herbivore damage. In summary, we showed that two novel sesquiterpene synthase genes CsAFR and CsNSE2 are inducible by herbivory and responsible for the elevated emission of herbivore-induced (E, E)-α-farnesene and (E)-nerolidol, which are implicated in tea plant defense against herbivores.

Two farnesyl pyrophosphate synthases, GhFPS1–2, in Gossypium hirsutum are involved in the biosynthesis of farnesol to attract parasitoid wasps

Sesquiterpenoids play an import role in the direct or indirect defense of plants. Farnesyl pyrophosphate synthases (FPSs) catalyze the biosynthesis of farnesyl pyrophosphate, which is a key precursor of farnesol and (E)-β-farnesene. In the current study, two FPS genes in Gossypium hirsutum, GhFPS1 and GhFPS2, were heterologously cloned and functionally characterized in a greenhouse setting. The open reading frames for full-length GhFPS1 and GhFPS2 were each 1 029 nucleotides, and encoded two proteins of 342 amino acids with molecular weights of 39.4 kDa. The deduced amino acid sequences of GhFPS1–2 showed high identity to FPSs of other plants. Quantitative real-time PCR analysis revealed that GhFPS1 and GhFPS2 were highly expressed in G. hirsutum leaves, and were upregulated in methyl jasmonate (MeJA)-, methyl salicylate (MeSA)- and aphid infestation-treated cotton plants. The recombinant proteins of either GhFPS1 or GhFPS2 plus calf intestinal alkaline phosphatase could convert geranyl diphosphate (GPP) or isopentenyl diphosphate (IPP) to one major product, farnesol. Moreover, in electrophysiological response and Y-tube olfactometer assays, farnesol showed obvious attractiveness to female Aphidius gifuensis, which is an important parasitic wasp of aphids. Our findings suggest that two GhFPSs are involved in farnesol biosynthesis and they play a crucial role in indirect defense of cotton against aphid infestation.

Luca Incurvati* Conceptions of Set and the Foundations of Mathematics.

On one level, the book under review is, as the author indicates in his very brief concluding chapter, a defense of the iterative conception of set. But exposition of that conception and its direct defense against criticisms take up only two of its seven substantive chapters. For the defense mainly consists of chapter-length examinations of rival conceptions, denominated the naïve, the limitation-of-size, the stratified, and the graph conceptions, examinations that begin in each case with the examiner not unsympathetic, but finish with him unconvinced, so that the iterative conception wins in the end by what he calls ‘inference to the best conception’. It is the book’s role as a one-stop source for both technical information and philosophical commentary on the various conceptions just listed, never before treated at length and with comparisons all in one place, that makes the book an indispensable reference work for anyone interested in the philosophy of set theory. But though the book is much more thorough than, say, [Holmes, 2017], the article on alternative set theories in the Stanford Encyclopedia, still Incurvati’s work does not pretend to be — well, encyclopedic. There are minor topics he leaves out that in their day excited flashes of interest, notably Vopenkism, about which one used to hear a lot, and more importantly coverage of the topics that are included does not pretend to be exhaustive. On the contrary, one of the book’s virtues is that, for all the information it provides, it shows also how open-ended investigation of the different conceptions remains: almost every paragraph raises further issues for future exploration, and it is bound to generate discussion for years to come.