Direct Defense Research Articles

Zoophytophagous mirids provide pest control by inducing direct defences, antixenosis and attraction to parasitoids in sweet pepper plants.

In addition to their services as predators, mirid predators are able to induce plant defences by phytophagy. However, whether this induction occurs in sweet pepper and whether it could be an additional benefit to their role as a biological control agent in this crop remain unknown. Here, these questions were investigated in two model insects, the mirids Nesidiocoris tenuis and Macrolophus pygmaeus. Plant feeding behaviour was observed in both N. tenuis and M. pygmaeus on sweet pepper and occupied 33% and 14% of total time spent on the plant, respectively. The punctures caused by mirid plant feeding induced the release of a blend of volatile organic compounds (VOCs) which repelled the herbivore pests Frankliniella occidentalis and Bemisia tabaci and attracted the whitefly parasitoid Encarsia formosa. The repellent effect on B. tabaci was observed for at least 7 days after initial exposure of the plant to N. tenuis, and attraction of E. formosa remained functional for 14 days. Plant defences induced by the feeding of mirid predators, their subsequent effects on the behaviour of both pests and natural enemies, and the persistence of these observed effects open the door to new control strategies in the sweet pepper crop. Further application of this research is discussed, such as the vaccination of plants by zoophytophagous mirids in the nursery before transplantation. © 2017 Society of Chemical Industry.

Vicia faba plants respond to oviposition by invasive Halyomorpha halys activating direct defences against offspring

The invasive stink bug Halyomorpha halys is established in many European and American agro-ecosystems, where it causes severe crop losses. Potential control measures might include enhancement of plant defences. When attacked by herbivorous insects that oviposit on it, the plant may respond by priming direct defences, which might affect the development of future brood. Halyomorpha halys attacks numerous plant species in the invaded areas. Here, we investigated whether Vicia faba plants challenged by H. halys females can impair the development of its offspring through the activation of induced direct defences. We measured the weight and dimension of nymphs that developed on oviposition-experienced plants after 7 and 17 days from hatching. Nymphs that developed on oviposition-experienced plants weighed less compared to those that developed either on control plants or on plants solely subjected to H. halys feeding, and third instars showed shorter dimensions (tibia length). In addition, when oviposition-experienced plants were attacked by nymphs, higher and more rapid expression of two jasmonic acid-dependent genes (cysteine proteinase inhibitor gene and NAI1) was detected, possibly due to a mechanism of priming. Increased expression of the salicylic acid-responsive PR1 gene was also detected in egg-experienced plants, although the response was delayed compared to JA-dependent genes. Our results suggest that V. faba plants recognize H. halys oviposition as a warning signal and pre-activate defences against future nymphal herbivory.

Direct Threat and Business Necessity: Understanding and Untangling Two ADA Defenses

The article provides a comprehensive examination of the ADA’s direct threat and business necessity defenses. These two defenses share common attributes in terms of enabling employers to reduce workplace health and safety risks, and some courts tend to apply them as if they were interchangeable in nature. But, the two defenses are distinct in focus. The direct threat defense provides a narrow view that analyzes whether a specific individual poses a significant threat of substantial harm to safety or health. The business necessity defense, on the other hand, takes a broader view and examines whether an impairment or attribute generally correlates with unacceptable job performance. After presenting an overview of the regulatory underpinnings of these two defenses as well as the judiciary’s construction and application, this article turns to three issues on which the courts have expressed conflicting views and recommends policy-based solutions for each issue. First, the burden of proof on the direct threat issue should be borne by the employer rather than the employee. Second, employers should refrain from requiring employees to provide diagnostic information when returning from sick leave and focus less intrusively on the need for leave and the anticipated date of return. Finally, an employer policy that disqualifies individuals with a history of addiction should be permissible only if an individualized assessment supports the exclusion. These solutions appropriately focus on the reality of risks rather than on the undesirable impact of stereotypical assumptions.

270: Commensal microbes confer protection against Zika virus infection in a murine gnotobiotic model of congenital Zika syndrome

Recent findings reveal that commensal microbiota may play a role in protection against viral infections. For example, bacteria isolated from the human stomach confer resistance against rotavirus infection in mice. Vertical transmission of ZIKV has been shown cause IUGR in mice. Here we sought to determine the contribution of commensal bacteria in protecting against ZIKV infection, vertical transmission, and IUGR. Current pandemic ZIKV was isolated from a traveler returning from Central America and propagated in Vero cells (ZIKV HN16). Pregnant germ-free (GF) and conventional (CONV) Swiss-Webster mice were intravenously inoculated with 104 PFU of second passage ZIKV (n=11) or a mock (n=10) injection on embryonic day 6 (e6), then daily until day e9 (Figure 1). Mice (n=2) were given anti-IFNI1 ab prior to and after infection as positive infection controls. On e18, Cesareans were performed and mice assessed for intrauterine reabsorption and demise as well as embryonic pup weight. Tissues were assessed for ZIKV infection by TaqMan viral qPCR assay. Inoculated mice were asymptomatic based on daily assessment of mobility and paralysis. Overall, GF-ZIKV pups had a greater rate of in utero demise with ZIKV infection (p< 0.01), while there was no difference for conventional controls (Fig 2A). In GF-ZIKV dams, ZIKV was detected in 3 of 4 spleens assessed, but only detected in 1 of 4 spleens from GF-ZIKV mice, and with 100-fold less viral load (B). The uterus was positive for ZIKV in 75% (3/4) GF-ZIKV dams in comparison to 50% (2/4) CONV-ZIKV dams, also with 100-fold less viral load (B). Of the mice positive for ZIKV in the uterus, 3 of 4 had associated in utero demise, while all pregnancies with undetectable levels of ZIKV in the uterus had no incidences of in utero demise (Fig A/B?). Pups of Zika infected conventional mothers showed no difference in fetal weight compared to mock, while germ free mothers were 25% smaller by weight (Fig C) (p<0.0001), indicating protection of the native flora. The findings demonstrate that commensal bacteria confer protection against fetal/placental ZIKV infection and transmission either through direct host defense or mediated through adaptive immunity.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Plant-arthropod interactions: who is the winner?

Herbivorous arthropods have interacted with plants for millions of years. During feeding they release chemical cues that allow plants to detect the attack and mount an efficient defense response. A signaling cascade triggers the expression of hundreds of genes, which encode defensive proteins and enzymes for synthesis of toxic metabolites. This direct defense is often complemented by emission of volatiles that attract beneficial parasitoids. In return, arthropods have evolved strategies to interfere with plant defenses, either by producing effectors to inhibit detection and downstream signaling steps, or by adapting to their detrimental effect. In this review, we address the current knowledge on the molecular and chemical dialog between plants and herbivores, with an emphasis on co-evolutionary aspects.

Expression of Defensive Genes Responsible for Direct and Indirect Defense Against Spider Mite Tetranychus urticae in Black Bean

Expression of Defensive Genes Responsible for Direct and Indirect Defense Against Spider Mite Tetranychus urticae in Black Bean

The terpene synthase gene family in Gossypium hirsutum harbors a linalool synthase GhTPS12 implicated in direct defence responses against herbivores.

Herbivore-induced terpenes have been reported to function as ecological signals in plant-insect interactions. Here, we showed that insect-induced cotton volatile blends contained 16 terpenoid compounds with a relatively high level of linalool. The high diversity of terpene production is derived from a large terpene synthase (TPS) gene family. The TPS gene family of Gossypium hirsutum and Gossypium raimondii consist of 46 and 41 members, respectively. Twelve TPS genes (GhTPS4-15) could be isolated, and protein expression in Escherichia coli revealed catalytic activity for eight GhTPS. The upregulation of the majority of these eight genes additionally supports the function of these genes in herbivore-induced volatile biosynthesis. Furthermore, transgenic Nicotiana tabacum plants overexpressing GhTPS12 were generated, which produced relatively large amounts of (3S)-linalool. In choice tests, female adults of Helicoverpa armigera laid fewer eggs on transgenic plants compared with non-transformed controls. Meanwhile, Myzus persicae preferred feeding on wild-type leaves over leaves of transgenic plants. Our findings demonstrate that transcript accumulation of multiple TPS genes is mainly responsible for the production and diversity of herbivore-induced volatile terpenes in cotton. Also, these genes might play roles in plant defence, in particular, direct defence responses against herbivores.

Orthogonal fitness benefits of nitrogen and ants for nitrogen-limited plants in the presence of herbivores.

Predictable effects of resource availability on plant growth-defense strategies provide a unifying theme in theories of direct anti-herbivore defense, but it is less clear how resource availability modulates plant indirect defense. Ant-plant-hemipteran interactions produce mutualistic trophic cascades when hemipteran-tending ants reduce total herbivory, and these interactions are a key component of plant indirect defense in most terrestrial ecosystems. Here we conducted an experiment to test how ant-plant-hemipteran interactions depend on nitrogen (N) availability by manipulating the presence of ants and aphids under different N fertilization treatments. Ants increased plant flowering success by decreasing the densities of herbivores, and the effects of ants on folivores were positively related to the density of aphids. Unexpectedly, N fertilization produced no changes in plant N concentrations. Plants grown in higher N grew and flowered more, but aphid honeydew chemistry stayed the same, and neither the density of aphids nor the rate of ant attraction per aphid changed with N addition. The positive effects of ants and N addition on plant fitness were thus independent of one another. We conclude that N was the plant's limiting nutrient and propose that addition of the limiting nutrient is unlikely to alter the strength of mutualistic trophic cascades.

What happens in the pith stays in the pith: tissue-localized defense responses facilitate chemical niche differentiation between two spatially separated herbivores.

Herbivore attack is known to elicit systemic defense responses that spread throughout the host plant and influence the performance of other herbivores. While these plant-mediated indirect competitive interactions are well described, and the co-existence of herbivores from different feeding guilds is common, the mechanisms of co-existence are poorly understood. In both field and glasshouse experiments with a native tobacco, Nicotiana attenuata, we found no evidence of negative interactions when plants were simultaneously attacked by two spatially separated herbivores: a leaf chewer Manduca sexta and a stem borer Trichobaris mucorea. T.mucorea attack elicited jasmonic acid (JA) and jasmonoyl-l-isoleucine bursts in the pith of attacked stems similar to those that occur in leaves when M. sexta attacks N. attenuata leaves. Pith chlorogenic acid (CGA) levels increased 1000-fold to levels 6-fold higher than leaf levels after T.mucorea attack; these increases in pith CGA levels, which did not occur in M.sexta-attacked leaves, required JA signaling. With plants silenced in CGA biosynthesis (irHQT plants), CGA, as well as other caffeic acid conjugates, was demonstrated in both glasshouse and field experiments to function as a direct defense protecting piths against T.mucorea attack, but not against leaf chewers or sucking insects. T.mucorea attack does not systemically activate JA signaling in leaves, while M.sexta leaf-attack transiently induces detectable but minor pith JA levels that are dwarfed by local responses. We conclude that tissue-localized defense responses allow tissue-specialized herbivores to share the same host and occupy different chemical defense niches in the same hostplant.

α-Farnesene and ocimene induce metabolite changes by volatile signaling in neighboring tea (Camellia sinensis) plants

Herbivore-induced plant volatiles (HIPVs) act as direct defenses against herbivores and as indirect defenses by attracting herbivore enemies. However, the involvement of HIPVs in within-plant or plant-to-plant signaling is not fully clarified. Furthermore, in contrast to model plants, HIPV signaling roles in crops have hardly been reported. Here, we investigated HIPVs emitted from tea (Camellia sinensis) plants, an important crop used for beverages, and their involvement in tea plant-to-plant signaling. To ensure uniform and sufficient exposure to HIPVs, jasmonic acid combined with mechanical damage (JAMD) was used to simulate herbivore attacks. Metabonomics techniques based on ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry and gas chromatography-mass spectrometry were employed to determine metabolite changes in undamaged tea plants exposed to JAMD-stimulated volatiles. JAMD-stimulated volatiles mainly enhanced the amounts of 1-O-galloyl-6-O-luteoyl-α-d-glucose, assamicain C, 2,3,4,5-tetrahydroxy-6-oxohexyl gallate, quercetagitrin, 2-(2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4-oxo-4H-chromen-8-yl)-4,5-dihydroxy-6-(hydroxymethyl)-tetrahydro-2H-pyran-3-yl, 3,4-dimethoxybenzoate, 1,3,4,5,6,7-hexahydroxyheptan-2-one, and methyl gallate in neighboring undamaged tea leaves. Furthermore, α-farnesene and β-ocimene, which were produced after JAMD treatments, were identified as two main JAMD-stimulated volatiles altering metabolite profiles of the neighboring undamaged tea leaves. This research advances our understanding of the ecological functions of HIPVs and can be used to develop crop biological control agents against pest insects in the future.

Plant response to butterfly eggs: inducibility, severity and success of egg-killing leaf necrosis depends on plant genotype and egg clustering

Plants employ various defences killing the insect attacker in an early stage. Oviposition by cabbage white butterflies (Pieris spp.) on brassicaceous plants, including Brassica nigra, induces a hypersensitive response (HR) - like leaf necrosis promoting desiccation of eggs. To gain a deeper insight into the arms race between butterflies and plants, we conducted field and greenhouse experiments using different B. nigra genotypes. We investigated variation in HR and consequent survival of P. brassicae egg clusters. Impact of egg density, distribution type and humidity on HR formation and egg survival was tested. HR differed among plant genotypes as well as plant individuals. Egg density per plant did not affect HR formation. Remarkably, egg survival did not depend on the formation of HR, unless butterflies were forced to lay single eggs. Larval hatching success from single eggs was lower on plants expressing HR. This may be due to increased vulnerability of single eggs to low humidity conditions at necrotic leaf sites. We conclude that effectiveness of HR-like necrosis in B. nigra varies with plant genotype, plant individual and the type of egg laying behaviour (singly or clustered). By clustering eggs, cabbage white butterflies can escape the egg-killing, direct plant defence trait.

Methyl jasmonate induction of cotton: a field test of the 'attract and reward' strategy of conservation biological control.

Natural or synthetic elicitors can affect plant physiology by stimulating direct and indirect defence responses to herbivores. For example, increased production of plant secondary metabolites, a direct response, can negatively affect herbivore survival, development and fecundity. Indirect responses include increased emission of plant volatiles that influence herbivore and natural enemy behaviour, and production of extrafloral nectar that serves as a food source for natural enemies after their arrival on induced plants. Therefore, the use of elicitors has potential for the study of basic aspects of tritrophic interactions, as well as application in biorational pest control, i.e. an 'attract and reward' strategy. We conducted a field study to investigate the effects of methyl jasmonate, an elicitor of plant defence responses, on three trophic levels: the plant, herbivores and natural enemies. We made exogenous applications of methyl jasmonate to transgenic cotton and measured volatile emission, extrafloral nectar production and plant performance (yield). We also assessed insect abundance, insect performance, and parasitism and predation of brown stink bug, Euschistus servus, eggs in methyl jasmonate-treated and untreated control plots. Application of methyl jasmonate increased emission of volatiles, in particular, (+)-limonene and (3E)-4,8-dimethyl-1,3,7-nonatriene, and production of extrafloral nectar, but not yield, compared with the control treatment. Despite increased volatile and extrafloral nectar production, methyl jasmonate application did not affect plant bug performance, or mortality of E. servus egg masses, and only marginally influenced insect abundance. Mortality of E. servus eggs varied over the course of the study. Overall, methyl jasmonate treatment affected cotton plant-induced responses, but not the insects that inhabit the plants. Our results were probably influenced by reduced natural enemy colonization of cotton from adjacent non-crop habitats, and subsequent low within-field population recruitment. Much remains to be learned about the effects of exogenous application of plant-produced 'enhancers' on the behaviour of natural enemies before crop physiology can be manipulated to enhance pest control.

In vitro and in vivo antimicrobial activity of a synthetic peptide derived from the C-terminal region of human chemokine CCL13 against Pseudomonas aeruginosa

Chemokines are important mediators of immunological responses during inflammation and under steady-state conditions. In addition to regulating cell migration, some chemotactic cytokines have direct effects on bacteria. Here, we characterized the antibacterial ability of the synthetic oligopeptide CCL1357-75, which corresponds to the carboxyl-terminal region of the human chemokine CCL13. In vitro measurements indicated that CCL1357-75 disrupts the cell membrane of Pseudomonas aeruginosa through a mechanism coupled to an unordered-helicoidal conformational transition. In a murine pneumonic model, CCL1357-75 improved mouse survival and bacterial clearance and decreased neutrophil recruitment, proinflammatory cytokines and lung pathology compared with that observed in untreated infected animals. Overall, our study supports the ability of chemokines and/or chemokine-derived oligopeptides to act as direct defense agents against pathogenic bacteria and suggests their potential use as alternative antibiotics.

Root symbionts: Powerful drivers of plant above‐ and belowground indirect defenses

Soil microbial mutualists of plants, including mycorrhizal fungi, non-mycorrhizal fungi and plant growth promoting rhizobacteria, have been typically characterized for increasing nutrient acquisition and plant growth. More recently, soil microbes have also been shown to increase direct plant defense against above- and belowground herbivores. Plants, however, do not only rely on direct defenses when attacked, but they can also recruit pest antagonists such as predators and parasitoids, both above and belowground, mainly via the release of volatile organic compounds (i.e., indirect defenses). In this review, we illustrate the main features and effects of soil microbial mutualists of plants on plant indirect defenses and discuss possible applications within the framework of sustainable crop protection against root- and shoot-feeding arthropod pests. We indicate the main knowledge gaps and the future challenges to be addressed in the study and application of these multifaceted interactions.

What signals do herbivore-induced plant volatiles provide conspecific herbivores?

Herbivore-induced plant volatiles (HIPVs) have been opined as ‘indirect or direct defenses’ of plants and are extensively studied. In contrast, HIPVs may also indicate that plant defenses have been overcome by herbivores infesting the plant; however, studies on this aspect have so far received little attention. Using the interaction of Capsicum annum (Bell pepper) with its pest Scirtothrips dorsalis (Chilli thrips) as a model system, we studied the role of HIPVs in this selected insect–plant interaction. Multiple-choice olfactometer assays with headspace volatiles collected from different growth stages of un-infested C. annum plants represented by pre-flowering (PF), flowering (FL) and fruiting stages (FR) proved FR volatiles to be highly attractive to S. dorsalis. Further, FR plants were infested with S. dorsalis adults and HIPVs released by infested plants were collected and subjected to multiple-choice olfactometer bioassays. Thrips were significantly attracted to HIPVs than to headspace volatiles of un-infested FR plants or thrips body odour. Coupled GC-EAG with S. dorsalis and HIPVs or FR plant volatile revealed specific compounds that elicited an EAG response. Individual EAG-active compounds were less attractive to thrips, however, synthetic blends of EAG-active compounds at the ratio similar to headspace samples were found to be highly attractive. However, when given a choice between synthetic blends of HIPVs and FR, thrips were significantly attracted to synthetic blend of HIPVs. Our study provides empirical data on signals HIPVs may provide to conspecific herbivores and suggests that the role of HIPVs, mostly generalized as defense, may vary based on the interaction and must be studied closely to understand their ecological functions.

Ecological Importance of Cyanogenesis and Extrafloral Nectar in Invasive English Laurel,Prunus laurocerasus

Abstract English laurel (Rosaceae: Prunus laurocerasus L.) is an evergreen shrub to small tree that is native to Asia but widely used in landscaping in temperate zones. In the Pacific Northwest this plant has become an important invasive species. However, surprisingly little is known about its ecology—in particular, its chemical defenses and interaction with herbivores and organisms of higher trophic levels. In the present field study, we quantitatively measured cyanogenesis (a constitutive direct chemical defense) and secretion of extrafloral nectar (EFN; an inducible indirect defense), and analyzed the effects of these defenses on insect herbivores (black vine weevil [Otiorhynchus sulcatus]) and predators (sugar ants [Tapinoma sessile]). To induce EFN production, English laurel leaves were mechanically damaged at different intensities and in a way to mimic feeding damage by the black vine weevil, which represents the only observed insect herbivore feeding on this plant at our study site near Portland, O...

Caterpillar-Induced Plant Volatiles Attract Adult Tortricidae

Binary and ternary combinations of volatile organic compounds identified earlier from caterpillar-infested apple foliage caught more than one thousand individuals of both sexes of several adult tortricid leafroller species in several days of trials conducted in apple orchards in southern British Columbia. A series of combinations with phenylacetonitrile, benzyl alcohol, and/or 2-phenylethanol and acetic acid enabled substantial catches of both sexes of eye-spotted budmoth, Spilonota ocellana, oblique-banded leafroller, Choristoneura rosaceana and three-lined leafroller, Pandemis limitata. These findings suggest that new monitoring aides can be developed to seasonally track populations, enabling practical applications in surveillance of female leafroller populations for the first time. It may also be possible to develop suppression tools based on combinations of kairomone compounds originally identified from leafroller larval-damaged apple trees, given the level of attraction. The discovery of these adult tortricid attractants (aromatic compounds plus acetic acid) raises new ecological questions about evolved direct plant defences against herbivores. Larval feeding-induced attraction of adult herbivores produces signals that are potentially harmful to the plant by increasing herbivory in the same family and probably feeding guild, but evidence for effects on plant fitness is needed.

Indirect plant defense against insect herbivores: a review.

Plants respond to herbivore attack by launching 2 types of defenses: direct defense and indirect defense. Direct defense includes all plant traits that increase the resistance of host plants to insect herbivores by affecting the physiology and/or behavior of the attackers. Indirect defense includes all traits that by themselves do not have significant direct impact on the attacking herbivores, but can attract natural enemies of the herbivores and thus reduce plant loss. When plants recognize herbivore-associated elicitors, they produce and release a blend of volatiles that can attract predators, parasites, and other natural enemies. Known herbivore-associated elicitors include fatty acid-amino acid conjugates, sulfur-containing fatty acids, fragments of cell walls, peptides, esters, and enzymes. Identified plant volatiles include terpenes, nitrogenous compounds, and indoles. In addition, constitive traits including extrafloral nectars, food bodies, and domatia can be further induced to higher levels and attract natural enemies as well as provide food and shelter to carnivores. A better understanding of indirect plant defense at global and componential levels via advanced high throughput technologies may lead to utilization of indirect defense in suppression of herbivore damage to plants.

Social buffering in a eusocial invertebrate: termite soldiers reduce the lethal impact of competitor cues on workers.

While the impact of predator-induced stress on prey has received considerable attention, there has been far less research into the effect of competitors. Cues from aggressive competitors should be particularly likely to evoke behavioral and/or physiological responses, since they may be indicative of both direct (interference) and indirect (exploitative) threats. The danger posed by such competitors, and the "fear" they evoke, should be reduced at lower competitor densities and by the presence of individual conspecifics specialized for defense. We assessed how Reticulitermes flavipes termite workers and soldiers were affected by cues from conspecific nestmates, conspecific non-nestmates, and the heterospecific competitor R.virginicus. Competitor cues altered flavipes worker and soldier behavior, decreasing worker growth and increasing their mortality. The presence of flavipes soldiers largely ameliorated these negative impacts: adding even a single soldier (5% of flavipes individuals) decreased worker mortality by 50-80%. Although worker mortality increased with competitor density, increased soldier densities did not increase the benefit to workers. The small number of soldiers required to substantially alter cue-mediated interactions suggests that this caste, in addition to providing direct defense, also occupies a "keystone role" by providing homeostatic feedback to workers functioning in stressful environments.

Antipredator responses to alarm pheromone in groups of young and/or old thrips larvae

AbstractMany prey species suffer from different predators in the course of their ontogeny. Hence, the alarm signal a small prey individual sends can have a different meaning than the signal a large prey individual sends, both for small and for large receivers. Larvae of Western Flower Thrips face predators that attack only small larvae, or predators that attack small larvae and large larvae. Furthermore, thrips larvae release a two‐component alarm pheromone, which varies in composition with larval age. Here, we study whether their response to alarm pheromone varies with composition of the pheromone. First, we confirmed that large and small larvae respond when nearby larvae of both sizes were prodded with a brush to induce alarm pheromone excretion. Subsequently, we tested whether thrips larvae of a given size respond differentially to alarm pheromone excreted by a small or large companion larva. We analyzed two types of behavior used in direct defense against a predator and one type of escape response. Only small (not large) larvae attempted to escape more frequently in response to excretions from a large larva. This difference in response could have been due to the alarm pheromone or to the companion larva in the vicinity. We subsequently tested for, but did not find, an effect of size of the companion larva on the behavior of the test larva when exposed to synthetic pheromone mimicking that of a large larva. Finally, we tested how pheromone composition affects antipredator behavior by exposing thrips larvae to synthetic pheromones differing in amount and ratio of the two components. Only for small larvae, we found significant changes in escape behavior with pheromone amount, and a trend with the ratio. Overall, we conclude that small thrips larvae respond differentially to alarm pheromones excreted by small and large larvae and that this differential response is due to differences in pheromone quantity and possibly also quality. Our results suggest that responses to alarm signals can vary with the chemical composition of those alarm signals.