Undamaged Control Plants Research Articles

The wheat dioxygenase BX6 is involved in the formation of benzoxazinoids in planta and contributes to plant defense against insect herbivores

Benzoxazinoids are plant specialized metabolites with defense properties, highly abundant in wheat (Triticum), one of the world’s most important crops. The goal of our study was to characterize dioxygenase BX6 genes in tetraploid and hexaploid wheat genotypes and to elucidate their effects on defense against herbivores. Phylogenetic analysis revealed four BX6 genes in the hexaploid wheat T. aestivum, but only one ortholog was found in the tetraploid (T. turgidum) wild emmer wheat and the cultivated durum wheat. Transcriptome sequencing of durum wheat plants, damaged by either aphids or caterpillars, revealed that several BX genes, including TtBX6, were upregulated upon caterpillar feeding, relative to the undamaged control plants. A virus-induced gene silencing approach was used to reduce the expression of BX6 in T. aestivum plants, which exhibited both reduced transcript levels and reduced accumulation of different benzoxazinoids. To elucidate the effect of BX6 on plant defense, bioassays with different herbivores feeding on BX6-silenced leaves were conducted. The results showed that plants with silenced BX6 were more susceptible to aphids and the two-spotted spider mite than the control. Overall, our study indicates that wheat BX6 is involved in benzoxazinoid formation in planta and contributes to plant resistance against insect herbivores.

Herbivore-induced plant volatiles mediate behavioral interactions between a leaf-chewing and a phloem-feeding herbivore

Plants respond adaptively to herbivore stress in order to maintain fitness. Upon herbivore attack, plants emit blends of volatile organic compounds (VOCs) that differ from those that are constitutively emitted. These defense responses are typically specific to the identity of the attacking herbivore and often linked to the herbivore's feeding guild (e.g. chewing, phloem-feeding). Herbivores use plant volatiles to locate suitable host plants and changes in volatile emissions can affect host-plant location. Therefore, herbivores from separate feeding guilds can interact indirectly through the modulation of plant responses. In this study we tested how damage by an herbivore from one feeding guild affected the host-plant choice of an herbivore from a separate feeding guild, and vice versa. A chewing herbivore, the Colorado potato beetle (Leptinotarsa decemlineata), and a phloem feeding herbivore, the green peach aphid (Myzus persicae), were assayed in olfactometers to assess behavioral responses to odors emitted by potato plants (Solanum tuberosum) that were damaged by herbivores from the other feeding guild. Leptinotarsa decemlineata oriented more frequently towards undamaged plants compared to M. persicae damaged plants. Surprisingly, M. persicae preferred plants that were damaged by L. decemlineata, although previous studies had shown that they perform worse on these plants. Distinct differences were detected in the volatile profiles of herbivore-damaged and undamaged plants. Leptinotarsa decemlineata induced stronger volatile emissions compared to undamaged control plants, while M. persicae tended to suppress volatile emissions. These herbivores demonstrate contrasting induction of plant volatiles and behavioral responses. Exploring the nature of co-occurring herbivores and how they perceive potential hosts can play a significant role in understanding the ecological functions and community dynamics of plant plasticity and interactions with a variety of herbivores.

Herbivory and inbreeding affect growth, reproduction, and resistance in the rhizomatous offshoots of Solanum carolinense (Solanaceae)

Resource sharing within clonal plant networks can occur via the translocation of water, nutrients, and photoassimilates through rhizomes and stolons. Similar mechanisms may mediate the sharing of information (e.g., about herbivory or other environmental stressors) among ramets via molecular or biochemical signals. The storage of such information in belowground structures could facilitate the transmission of appropriate phenotypic responses across growing seasons in perennial species. However, few previous studies have explored the potential transfer of ecologically relevant information within such networks. This study addresses the effects of foliar herbivory and belowground overwintering on the growth and flowering, physical defenses, and herbivore resistance in the clonally spreading species Solanum carolinense L. (Solanaceae). We used rhizomes from inbred and outbred plants that were repeatedly exposed to feeding damage by Manduca sexta L. (Sphingidae) caterpillars and rhizomes from undamaged control plants. These rhizomes were either planted immediately or exposed to overwintering conditions and allowed to produce new ramets (rhizomatous offshoots). We then assessed offshoot emergence, flowering, physical defense traits, and herbivore performance. Relative to controls, offshoots of herbivore-damaged plants exhibited greater spine and trichome densities, and reduced performance of M. sexta larvae. However, they also emerged and flowered significantly later, and produced fewer flowers than offshoots of undamaged plants. Inbreeding also negatively affected offshoot emergence, flowering, trichome production, and herbivore resistance. These effects of parental herbivory were more pronounced in outbred offshoots, indicating that inbreeding may compromise the trans-seasonal induction of plant defenses. Finally, exposure to overwintering conditions increased trichome production and reduced caterpillar performance on offshoots. Together, these results show that induced defenses can be transmitted through rhizomes and affect offshoot growth, flowering, defensive traits, and herbivore resistance. They also document fitness-related costs associated with defense induction in offshoots and suggest that the transfer of defenses across seasons can be compromised by inbreeding.

Terpenoids dominate the bouquet of volatile organic compounds produced by Passiflora edulis in response to herbivory by Heliconius erato phyllis (Lepidoptera: Nymphalidae)

In response to injury, plants produce volatile organic compounds (VOCs) that usually differ depending on the type of damage they have suffered (e.g., mechanical damage, herbivory, and oviposition). The objectives of this study were to identify and compare the bouquet of volatiles emitted by passion vine plants (Passiflora edulis) after injury caused by mechanical damage (MD), herbivory (HB), and oviposition (OV) by the lepidopteran, Heliconius erato phyllis. Following injury, extracts of plant emissions were collected from each treatment every 24 h for three days and were analyzed by GC and GC/MS. Results show that plants emitted 12 volatiles before and after damage, namely terpenoids, ketones, and aldehydes. Although no significant differences were detected between the three treatments individually, if the entire bouquet of volatiles is analyzed, samples collected at 24 h were different from samples collected at 48 and 72 h. However, terpenoid emission increased significantly in HB plants after 24 h. HB plants emitted approximately 6300, 50, 46, 11, 6, and 3.6 times more (3E,7E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), (E)-β-ocimene, (Z)-β-farnesene, (E)-β-caryophyllene, and farnesane, respectively, compared to control plants. OV plants displayed a peak of emission of (E)-β-ocimene after 72 h, which distinguished them from HB plants. MD plants showed a general increase of VOCs versus undamaged control plants. Furthermore, it has been suggested that (E)-β-ocimene may be sequestered by larvae of H. erato phyllis as a component of the odoriferous bouquet of the abdominal scent glands present in adult males, which play a role in sexual communication.

Latitudinal Gradients in Induced and Constitutive Resistance against Herbivores

Plants are hypothesized to evolve increased defense against herbivores at lower latitudes, but an increasing number of studies report evidence that contradicts this hypothesis. Few studies have examined the evolution of constitutive and induced resistance along latitudinal gradients. When induction is not considered, underlying patterns of latitudinal clines in resistance can be obscured because plant resistance represents a combination of induced and constitutive resistance, which may show contrasting patterns with latitude. Here, we asked if there are latitudinal gradients in constitutive versus induced resistance by using genotypes of Oenothera biennis (Onagraceae) sampled along an 18° latitudinal gradient. We conducted two bioassay experiments to compare the resistance of plant genotypes against one generalist (Spodoptera exigua) and one specialist (Acanthoscelidius acephalus) herbivore. These insects were assayed on: i) undamaged control plants, ii) plants that had been induced with jasmonic acid, and iii) plants induced with herbivore damage. Additionally, we examined latitudinal gradients of constitutive and induced chemical resistance by measuring the concentrations of total phenolics, the concentration of oxidized phenolics, and the percentage of phenolics that were oxidized. Spodoptera exigua showed lower performance on plants from lower latitudes, whereas A. acephalus showed no latitudinal pattern. Constitutive total phenolics were greater in plants from lower latitudes, but induced plants showed higher total phenolics at higher latitudes. Oxidative activity was greatest at higher latitudes regardless of induction. Overall, both latitude and induction have an impact on different metrics of plant resistance to herbivory. Further studies should consider the effect of induction and herbivore specialization more explicitly, which may helpto resolve the controversy in latitudinal gradients in herbivory and defense.

Low tolerance to simulated herbivory in Hawaiian seedlings despite induced changes in photosynthesis and biomass allocation.

Seedling herbivory is an important factor underlying plant community diversity and structure. While considerable research has characterized seedling defence in terms of resistance, very little is known about seedling tolerance of herbivory. Moreover, few studies have attempted to identify mechanisms of tolerance across a range of plant species. Seedling tolerance of simulated herbivory was tested in a diverse pool of ten Hawaiian plant species, including several lobeliad species (family Campanulaceae), a grass, a herb and common woody trees and shrubs. Tolerance was measured as the relative survival and growth of damaged plants receiving 50% defoliation with simultaneous jasmonic acid application compared with undamaged control plants, assessed 1·5 and 5weeks after damage. Putative mechanisms of tolerance were measured, including photosynthetic parameters, light use efficiency, and biomass allocation reflecting growth priorities, and analysed using species-level regression analyses on tolerance indices. No species fully tolerated 50% defoliation at either harvest date, and simulated herbivory significantly reduced shoot as well as root biomass. Lobeliad species had particularly low tolerance. Species varied considerably in size, biomass allocation parameters and their constitutive (pre-damage) and induced (post-damage) photosynthetic parameters. However, only constitutive levels of non-photochemical quenching were significantly related to tolerance, indicating that species with more efficient light use (and less heat dissipation) are better at tolerating damage than species with high levels of heat dissipation. Native Hawaiian plants expressed low tolerance to a conservative level of simulated herbivory. Root growth decreased in response to damage, but this was not associated with greater tolerance, suggesting this response may be due to allocation constraints following defoliation and not due to adaptive plasticity. Conservation of native island plants threatened by invasive herbivores should prioritize protection for seedlings for improved regeneration and the persistence of native plants in disturbed habitats.

Regrowth patterns and rosette attributes contribute to the differential compensatory responses of Arabidopsis thaliana genotypes to apical damage.

A plant's compensatory performance refers to its ability to maintain or increase its reproductive output following damage. The ability of a plant to compensate depends on numerous factors including the type, severity, frequency and timing of damage, the environmental conditions and the plant's genotype. Upon apical damage, a cascade of hormonal and genetic responses often produces dramatic changes in a plant's growth, development, architecture and physiology. All else being equal, this response is largely dependent on a plant's genotype, with different regrowth patterns displayed by different genotypes of a given species. In this study, we compare the architectural and growth patterns of two Arabidopsis thaliana genotypes following apical damage. Specifically, we characterise regrowth patterns of the genotypes Columbia-4 and Landsberg erecta, which typically differ in their compensation to apical meristem removal. We report that Landsberg erecta suffered reductions in the number of stems produced, maximum elongation rate, a delay in reaching this rate, lower average rosette quality throughout the growing period, and ultimately, less aboveground dry biomass and seed production when damaged compared to undamaged control plants. Columbia-4 had no reductions in any of these measures and maintained larger rosette area when clipped relative to when unclipped. Based on the apparent influence of the rosette on these genotypes' compensatory performances, we performed a rosette removal experiment, which confirmed that the rosette contributes to compensatory performance. This study provides a novel characterisation of regrowth patterns following apical damage, with insights into those measures having the largest effect on plant performance.

Interaction ofAnthonomus grandisand cotton genotypes: biological and behavioral responses

AbstractThe boll weevil,Anthonomus grandisBoheman (Coleoptera:Curculionidae), is a key pest of cotton,Gossypium hirsutumL. (Malvaceae). Knowledge about boll weevil feeding and oviposition behavior and its response to plant volatiles can underpin our understanding of host plant resistance, and contribute to improved monitoring and mass capture of this pest. Boll weevil oviposition preference and immature development in four cotton genotypes (CNPA TB90,TB85,TB15, andBRSRubi) were investigated in the laboratory and greenhouse. Volatile organic compounds (VOCs) produced byTB90 and Rubi genotypes were obtained from herbivore‐damaged and undamaged control plants at two phenological stages – vegetative (prior to squaring) and reproductive (during squaring) – and four collection times – 24, 48, 72, and 96 h following herbivore damage. The boll weevil exhibited similar feeding and oviposition behavior across the four tested cotton genotypes. The chemical profiles of herbivore‐damaged plants of both genotypes across the two phenological stages were qualitatively similar, but differed in the amount of volatiles produced. Boll weevil response toVOCextracts was studied using a Y‐tube olfactometer. The boll weevil exhibited similar feeding and oviposition behavior at the four tested cotton genotypes, although delayed development and production of smaller adults was found when fedTB85. The chemical profile of herbivore‐damaged plants of both genotypes at the two phenological stages and time periods (24–96 h) was similar qualitatively, with 30 identified compounds, but differed in the amount of volatiles produced. Additionally, boll weevil olfactory response was positive to herbivory‐induced volatiles. The results help to understand the interaction betweenA. grandisand cotton plants, and why it is difficult to obtain cotton genotypes possessing constitutive resistance to this pest.

Volatile Organic Compounds of Conspecific-Damaged Eucalyptus benthamii Influence Responses of Mated Females of Thaumastocoris peregrinus

Plants respond to herbivory by synthesizing and releasing novel blends of volatile organic compounds (VOCs). Natural enemies are attracted to these VOCs, but little is known about the effects of these chemicals on the herbivores themselves. We studied the effect of Thaumastocoris peregrinus herbivory on VOCs released by Eucalyptus benthamii plants and the responses of this herbivore to the VOCs. In total, 12 compounds released by E. benthamii were identified. Five compounds (β-pinene, linalool, 9-epi-(E)-caryophyllene, viridiflorol, and one unidentified compound) emitted after herbivore and mechanical damage were not detected in collections from undamaged plants. The three most abundant VOCs, α-pinene, aromadendrene, and globulol, were released in greater quantities from herbivore-damaged plants compared to plants with mechanical damage, which, in turn, released greater amounts than undamaged (control) plants. The VOCs emitted after herbivore damage did not differ during the photophase and scotophase in either quantity or quality. In an olfactometer, mated female T. peregrinus showed a preference for undamaged plants over herbivore-damaged plants, and also for hexane over α-pinene at an amount equivalent to that released by a herbivore-damaged plant. In the olfactometer, virgin females did not exhibit any preference between conspecific-damaged or undamaged plants.

Experimental Infection of Plants with an Herbivore-Associated Bacterial Endosymbiont Influences Herbivore Host Selection Behavior

Although bacterial endosymbioses are common among phloeophagous herbivores, little is known regarding the effects of symbionts on herbivore host selection and population dynamics. We tested the hypothesis that plant selection and reproductive performance by a phloem-feeding herbivore (potato psyllid, Bactericera cockerelli) is mediated by infection of plants with a bacterial endosymbiont. We controlled for the effects of herbivory and endosymbiont infection by exposing potato plants (Solanum tuberosum) to psyllids infected with “Candidatus Liberibacter solanacearum” or to uninfected psyllids. We used these treatments as a basis to experimentally test plant volatile emissions, herbivore settling and oviposition preferences, and herbivore population growth. Three important findings emerged: (1) plant volatile profiles differed with respect to both herbivory and herbivory plus endosymbiont infection when compared to undamaged control plants; (2) herbivores initially settled on plants exposed to endosymbiont-infected psyllids but later defected and oviposited primarily on plants exposed only to uninfected psyllids; and (3) plant infection status had little effect on herbivore reproduction, though plant flowering was associated with a 39% reduction in herbivore density on average. Our experiments support the hypothesis that plant infection with endosymbionts alters plant volatile profiles, and infected plants initially recruited herbivores but later repelled them. Also, our findings suggest that the endosymbiont may not place negative selection pressure on its host herbivore in this system, but plant flowering phenology appears correlated with psyllid population performance.

Consequences of constitutive and induced variation in the host’s food plant quality for parasitoid larval development

Constitutive and induced changes in plant quality impact higher trophic levels, such as the development of parasitoids, in different ways. An efficient way to study how plant quality affects parasitoids is to examine how the parasitoid larva is integrated within the host during the growth process. In two experiments, we investigated the effects of varying nutritional quality of Brassica oleracea on parasitoid larval development inside the host, the diamondback moth (Plutella xylostella). First, we compared larval growth of the specialist Diadegma semiclausum and the generalist Diadegma fenestrale, when the host was feeding on Brussels sprout plants that were either undamaged or were previously induced by caterpillar damage. Larvae of the generalist D. fenestrale showed lower growth rates than larvae of the specialist D. semiclausum, and this difference was more pronounced on herbivore-induced plants, suggesting differences in host-use efficiency between parasitoid species. The growth of D. semiclausum larvae was also analyzed in relation to herbivore induction on Brussels sprouts and on a wild B. oleracea strain. Parasitoid growth was more depressed on induced than on undamaged control plants, and more on wild cabbage than on Brussels sprouts, which was largely explained by differences in host mass. The effects of induction of wild Brassica on parasitoid development were pronounced early on, but as P. xylostella feeding began inducing the previously undamaged control plants, the effect of induction disappeared, revealing a temporal component of plant–parasitoid interactions. This study demonstrates how insights into the physiological aspects of host–parasitoid interactions can improve our understanding of the effects of plant-related traits on parasitoid wasps.

Differentiation of Mechanical Damages of Rice Plants Using E-Nose

Abstract Plants change the emission of induced volatiles in response to damage and herbivore attack, and monitoring the change of such volatiles could provide a nondestructive means of plant health measurement. Current monitoring techniques for plant volatiles are time-consuming and costly. The main objective of this research is to figure out whether electronic nose (e-nose) technique can be used to differentiate rice plants with different degrees of mechanical damage. A portable e-nose (PEN2) is used to characterize and classify rice plants subjected to three degrees of mechanical damage compared with undamaged control plants. Principle component analysis (PCA), Linear discriminant analysis (LDA), Stepwise discriminant analysis (SDA), and Back-propagation neural network (BPNN) are applied to evaluate the data. Different degrees of damaged rice plants are better distinguished using LDA than using PCA. The average correction ratio of testing set of BPNN is 75%. The results obtained indicate that it is poss...

Do Leaf Cutting Ants Cut Undetected? Testing the Effect of Ant-Induced Plant Defences on Foraging Decisions in Atta colombica

Leaf-cutting ants (LCAs) are polyphagous, yet highly selective herbivores. The factors that govern their selection of food plants, however, remain poorly understood. We hypothesized that the induction of anti-herbivore defences by attacked food plants, which are toxic to either ants or their mutualistic fungus, should significantly affect the ants' foraging behaviour. To test this “induced defence hypothesis,” we used lima bean (Phaseolus lunatus), a plant that emits many volatile organic compounds (VOCs) upon herbivore attack with known anti-fungal or ant-repellent effects. Our results provide three important insights into the foraging ecology of LCAs. First, leaf-cutting by Atta ants can induce plant defences: Lima bean plants that were repeatedly exposed to foraging workers of Atta colombica over a period of three days emitted significantly more VOCs than undamaged control plants. Second, the level to which a plant has induced its anti-herbivore defences can affect the LCAs' foraging behaviour: In dual choice bioassays, foragers discriminated control plants from plants that have been damaged mechanically or by LCAs 24 h ago. In contrast, strong induction levels of plants after treatment with the plant hormone jasmonic acid or three days of LCA feeding strongly repelled LCA foragers relative to undamaged control plants. Third, the LCA-specific mode of damaging leaves allows them to remove larger quantities of leaf material before being recognized by the plant: While leaf loss of approximately 15% due to a chewing herbivore (coccinelid beetle) was sufficient to significantly increase VOC emission levels after 24 h, the removal of even 20% of a plant's leaf area within 20 min by LCAs did not affect its VOC emission rate after 24 h. Taken together, our results support the “induced defence hypothesis” and provide first empirical evidence that the foraging behaviour of LCAs is affected by the induction of plant defence responses.

Discrimination of different types damage of rice plants by electronic nose

The profiles of volatile compounds emitted by plants varies in response to damage or herbivore attack. The potential of electronic nose technology to monitor such changes, with the aim of diagnosing plant health was investigated. An electronic nose (E-nose) was used to analyse rice plants that were subjected to different types of treatments causing damage, and the results were compared to those of undamaged control plants. Principal component analysis (PCA), linear discrimination analysis (LDA), cluster analysis (CA), back-propagation neural network (BPNN), and learning vector quantisation (LVQ) network were used to evaluate the E-nose data. The results indicated that the E-nose can successfully discriminate between rice plants with different types of damage. The discrimination was more pronounced after the LDA than after the PCA. The front 5 principal component values of the PCA were extracted and they acted as the input date for the neural network analyses. Good discrimination results were obtained using these front 5 principal component values in LVQ and BPNN. The results demonstrated that it is plausible to use E-nose technology as a method for monitoring rice cultivation practices.

Parasitoid load affects plant fitness in a tritrophic system

AbstractPlants attacked by herbivorous insects emit volatile compounds that attract predators or parasitoids of the herbivores. Plant fitness increases when these herbivorous insects are parasitized by solitary parasitoids, but whether gregarious koinobiont parasitoids also confer a benefit to plant fitness has been disputed. We investigated the relationship between parasitoid load of the gregarious Cotesia glomerata (L.) (Hymenoptera: Braconidae), food consumption by larvae of their host Pieris brassicae L. (Lepidoptera: Pieridae), and seed production in a host plant, Brassica nigra L. (Brassicaceae), in a greenhouse experiment. Plants damaged by caterpillars containing single parasitoid broods produced a similar amount of seeds as undamaged control plants and produced significantly more seeds than plants with unparasitized caterpillars feeding on them. Increasing the parasitoid load to levels likely resulting from superparasitization, feeding by parasitized caterpillars was significantly negatively correlated with plant seed production. Higher parasitoid brood sizes were negatively correlated with pupal weight of Cotesia glomerata, revealing scramble competition leading to a fitness trade‐off for the parasitoid. Our results suggest that in this tritrophic system plant fitness is higher when the gregarious parasitoid deposits a single brood into its herbivorous host. A prediction following from these results is that plants benefit from recruiting parasitoids when superparasitization is prevented. This is supported by our previous results on down‐regulation of synomone production when Brassica oleracea was fed on by parasitized caterpillars of P. brassicae. We conclude that variable parasitoid loads in gregarious koinobiont parasitoids largely explain existing controversies about the putative benefit of recruiting these parasitoids for plant reproduction.

Host plant selection by a monophagous herbivore is not mediated by quantitative changes in unique plant chemistry: Agonopterix alstroemeriana and Conium maculatum

Host plant selection by ovipositing females is a key process determining the success of phytophagous insects. In oligophagous lepidopterans, host-specific plant secondary chemicals are expected to be dominant factors governing oviposition behavior; distinctive compounds can serve as high-contrast signals that clearly differentiate confamilial hosts from non-hosts increasing the accuracy of host quality evaluation. Agonopterix alstroemeriana (Clerk) (Lepidoptera: Oecophoridae) and Conium maculatum L. (Apiaceae) form an extremely specialized plant-herbivore system, with A. alstroemeriana monophagous on C. maculatum, a plant with few other insect herbivores at least in part due to its virtually unique capacity among plants to produce piperidine alkaloids. Here we have studied the response of A. alstroemeriana oviposition to unique host plant secondary metabolites, piperidine alkaloids, and widespread compounds, mono- and sesquiterpenes, in a concentration-dependent fashion. Rates of oviposition were negatively correlated with Z-ocimene concentrations. To confirm the deterrent properties of this monoterpene for A. alstroemeriana oviposition, we conducted a choice experiment using artificially damaged C. maculatum plants, with higher emission of volatiles, and undamaged control plants. Damaged plants were less preferred as oviposition sites compared to the controls. The lack of association between oviposition and piperidine alkaloids, defenses unique to Conium species, suggests that quantitative changes of these species-specific chemicals do not play a predominant role in host selection by the monophagous A. alstroemeriana.

The role of the plant in attracting parasitoids: response to progressive mechanical wounding

AbstractBased on the model system of Brussels sprouts [Brassica oleracea var. gemmifera (Brassicaceae)], the herbivore cabbage white caterpillar, Pieris brassicae (L.) (Lepidoptera: Pieridae), and the parasitoid wasp, Cotesia glomerata (L.) (Hymenoptera: Braconidae), the influence of plant damage type, and damage duration were assessed on plant volatile emission and subsequent recruitment of natural antagonists of the herbivore. Plants were damaged by three methods for a period of either 3 or 8 h: herbivore damage (HD), progressive mechanical damage, and final mechanical damage inflicted in a single event. Wind‐tunnel bioassays evaluated whether the mode of damage affected female parasitoid oriented flight. After both periods of damage, all treatments were highly significantly preferred by naïve C. glomerata to undamaged control plants. After 3 h, herbivore‐damaged plants were significantly preferred to plants with final damage (FD). Most remarkably, following 8‐h damage, the parasitoid preferred both herbivore‐damaged and progressively damaged plants to plants with FD and did not significantly discriminate between herbivore and progressively damaged plants, thus indicating a similarity in plant response to herbivore and progressive mechanical damage. In addition to wind‐tunnel bioassays, emitted plant volatiles were collected and analysed by thermal desorption gas chromatography/mass spectrometry, following 3 and 8 h of damage in order to correlate volatiles released from different damage types with the attraction of the parasitoid. Differences in volatile profiles from all damage types were similar following both 3 and 8 h of damage, with only (Z)‐3‐hexenyl acetate found to be emitted in significantly higher quantities by final mechanical damage compared with HD after 3 h. In conclusion, the plant's response to progressive mechanical damage was more similar to HD than final mechanical damage deployed at a single point in time, irrespective of damage duration, and C. glomerata did not significantly discriminate between progressive damage and HD.

Host-locating response by the aphid parasitoid Aphidius ervi to tomato plant volatiles

The blend of volatile compounds emitted by tomato plants (Solanum lycopersicum) infested with the potato aphid (Macrosiphum euphorbiae) has been studied comparatively with undamaged plants and aphids themselves. Aphid-infested plants were significantly more attractive towards Aphidius ervi than undamaged plants and aphids themselves. Oriented response towards host-damaged plant, from which aphids were removed just before running the bioassay, did not differ from that recorded for infested plants. Collection of the volatiles and analysis by gas chromatography revealed only quantitative differences between uninfested and aphid-infested plants. Nine compounds, α-pinene, (Z)-3-hexen-1-ol, α-phellandrene, limonene, (E)-β-ocimene, p-cymene, methyl salicylate, (E)-β-caryophyllene and an unknown compound, were emitted at higher levels from aphid-infested plants than from undamaged control plants, whilst no differences were noted for hexanal, 6-methyl-5-hepten-2-one, and humulene (=α-caryophyllene). Synthetic standards of these compounds were tested in wind tunnel bioassays and all elicited a significant increase in oriented flight and landings on the target by the aphid parasitoid Aphidius ervi. (E)-β-caryophyllene resulted the most attractive towards female wasps. These results corroborate the hypothesis that the volatiles produced by the plant in response to aphid attack derive from both jasmonic and salicylic acid pathways, and are exploited by A. ervi as olfactory cues to locate its hosts.

P.2.04 A rat model predicting sexual side effects of antidepressants

Plants respond adaptively to herbivore stress in order to maintain fitness. Upon herbivore attack, plants emit blends of volatile organic compounds (VOCs) that differ from those that are constitutively emitted. These defense responses are typically specific to the identity of the attacking herbivore and often linked to the herbivore's feeding guild (e.g. chewing, phloem-feeding). Herbivores use plant volatiles to locate suitable host plants and changes in volatile emissions can affect host-plant location. Therefore, herbivores from separate feeding guilds can interact indirectly through the modulation of plant responses. In this study we tested how damage by an herbivore from one feeding guild affected the host-plant choice of an herbivore from a separate feeding guild, and vice versa. A chewing herbivore, the Colorado potato beetle (Leptinotarsa decemlineata), and a phloem feeding herbivore, the green peach aphid (Myzus persicae), were assayed in olfactometers to assess behavioral responses to odors emitted by potato plants (Solanum tuberosum) that were damaged by herbivores from the other feeding guild. Leptinotarsa decemlineata oriented more frequently towards undamaged plants compared to M. persicae damaged plants. Surprisingly, M. persicae preferred plants that were damaged by L. decemlineata, although previous studies had shown that they perform worse on these plants. Distinct differences were detected in the volatile profiles of herbivore-damaged and undamaged plants. Leptinotarsa decemlineata induced stronger volatile emissions compared to undamaged control plants, while M. persicae tended to suppress volatile emissions. These herbivores demonstrate contrasting induction of plant volatiles and behavioral responses. Exploring the nature of co-occurring herbivores and how they perceive potential hosts can play a significant role in understanding the ecological functions and community dynamics of plant plasticity and interactions with a variety of herbivores.

Rapid response to shoot removal by the invasive wetland plant, alligator weed ( Alternanthera philoxeroides)

Resprouting plants provide an interesting test to the generality of plant allometric relationships. The ability to rapidly resprout after disturbance also makes weeds more difficult to control. We performed a glasshouse experiment to investigate regrowth of an invasive plant (alligator weed, Alternanthera philoxeroides (Martius) Grisebach) after an experimental mowing treatment. Nutrient levels and biomass accumulation were measured weekly for five weeks, and carbohydrate levels were measured when regrowth was quickest. After five weeks, the biomass of treatment plants was similar to that expected from a growth curve fitted to undamaged control plants. Treatment plants, however, had a higher below-ground biomass, and a higher ratio of stem to leaf biomass than expected. The regrowing material also had a lower nutrient concentration. Both the rapid regrowth and the change in morphology make the mechanical control of alligator weed more difficult, and may, in part, be responsible for the invasiveness of this plant.