Leaf Herbivory Research Articles

Drought stress drives sex-specific differences in plant resistance against herbivores between male and female poplars through changes in transcriptional and metabolic profiles

Drought stress poses adverse influence on plant growth and further alters plant-herbivore interactions. Such effect is enhanced as drought occurrence is reported to increase due to global warming. Although dioecious plant species have shown sex-specific response to drought stress through the changes in growth performance and stress tolerance, whether such changes will drive sex-specific differences in defense against herbivores between male and female plant conspecifics is barely studied. In the current study, female and male poplar full-siblings were submitted to moderate (75 % field water capacity) and severe drought (50 % field water capacity) stresses, followed by herbivore growth and feeding bioassays to test the effect of plant gender on herbivore growth and feeding performance of two specialist and two generalist leaf herbivores. The results showed that although the growth of both plant sexes was inhibited by the two drought levels, male plants performed better than female conspecifics. In the paired-choice bioassays, the specialist herbivores preferred female plants while the generalist herbivores fed more on the male plants without drought stress. Both the moderate and severe drought stresses reversed such preferences. In the triple-choice bioassays, the specialist herbivores preferred female control plants while the generalist herbivores fed more on female plants under severe drought. In addition, the specialist herbivores fed on female plants from severe drought stress grew the worst while the generalist herbivores gained the highest fresh weight. The transcriptomic and metabolomic profiling revealed that female plant leaves contained higher levels of flavonoids than males under control condition while severe drought stress remarkably reduced the levels of defensive metabolites such as flavonoids, isoflavonoids, neoflavonoids and alkaloids in female but not in male plant leaves.

Testing the role of local plant chemical diversity on plant-herbivore interactions and plant species coexistence.

Accumulating evidence suggests that herbivorous insects influence the local composition and richness of Neotropical plant species, particularly in species-rich genera. Species richness, phylogenetic diversity, and chemical diversity all influence the ability of insect herbivores to find and utilize their hosts. The relative impact of these components of diversity on species coexistence and plant-herbivore interactions is not well understood. We constructed 60 local communities of up to 13 species of Piper (Piperaceae) in native, mature forest at a lowland wet forest location in Costa Rica. The species composition of each community was chosen such that species richness, phylogenetic diversity, and GCMS-based chemical diversity were varied independently among communities. We predicted that chemical diversity would most strongly affect the communities across time, with smaller effects of taxonomic and phylogenetic diversity. At 13 months after the experimental planting, we assessed survivorship of each cutting, measured total leaf area loss of the survivors, leaf area loss to generalist and specialist herbivorous insect species, and local extinction of species. Generalist and specialist herbivory decreased with increasing levels of species richness and phylogenetic diversity, respectively. Surprisingly, there was no independent effect of chemical diversity on any of the three measures of herbivore damage. Nevertheless, plots with a higher chemical and phylogenetic diversity showed decreased plant mortality and local species extinction. Overall, our results suggested that both chemical and phylogenetic similarity are important factors in the assembly and maintenance of tropical plant communities. The fact that chemical diversity influences plant mortality suggests that leaf herbivores, and possibly other plant natural enemies, could increase plant diversity via the selective mortality of similar chemotypes.

Photosynthetic and defensive responses of two Mediterranean oaks to insect leaf herbivory.

Insect herbivory is a dominant interaction across virtually all ecosystems globally and has dramatic effects on plant function such as reduced photosynthesis activity and increased levels of defenses. However, most previous work assessing the link between insect herbivory, photosynthesis and plant defenses has been performed on cultivated model plant species, neglecting a full understanding of patterns in natural systems. In this study, we performed a field experiment to investigate the effects of herbivory by a generalist foliar feeding insect (Lymantria dispar) and leaf mechanical damage on multiple leaf traits associated with defense against herbivory and photosynthesis activity on two sympatric oak species with contrasting leaf habit (the evergreen Quercus coccifera L. and the deciduous Quercus pubescens Willd). Our results showed that, although herbivory treatments and oak species did not strongly affect photosynthesis and dark respiration, these two factors exerted interactive effects. Insect herbivory and mechanical damage (vs control) decreased photosynthesis activity for Q. coccifera but not for Q. pubescens. Insect herbivory and mechanical damage tended to increase chemical (increased flavonoid and lignin concentration) defenses, but these effects were stronger for Q. pubescens. Overall, this study shows that two congeneric oak species with contrasting leaf habit differ in their photosynthetic and defensive responses to insect herbivory. While the evergreen oak species followed a more conservative strategy (reduced photosynthesis and higher physical defenses), the deciduous oak species followed a more acquisitive strategy (maintained photosynthesis and higher chemical defenses).

Top‐down cascading effects of seed‐feeding beetles and their parasitoids on plants and leaf herbivores

Abstract When feeding on a plant, herbivorous insects alter the quality of the plant as a food source. This affects other organisms interacting with the same plant. These so‐called ‘plant‐mediated interactions’ can be altered by parasitoids that attack the herbivores. So far, this research area has mainly focussed on interactions at the leaf level, and very little is known about plant‐mediated interactions via seeds. It is still poorly understood if seeds that survive insect damage have fewer resources to allocate to plant growth and defence against leaf herbivores, and whether parasitoids that kill seed‐feeding insects mitigate such negative effects. Using seeds of wild lima bean plants Phaseolus lunatus, we studied the effect of the intensity of infestation by seed beetles Zabrotes subfasciatus and their parasitoids Stenocorse bruchivora on the following parameters under lab conditions: seed mass and germination, plant growth and defensive compounds (cyanogenic glycosides and flavonoids) and performance of a leaf herbivore species Spodoptera latifascia. In addition, we performed a field experiment using seeds with or without insect damage to investigate the consequences on plant performance and fitness in the wild. Seed beetle infestation had an overall negative impact on seed germination. Lab experiments revealed that damaged seeds produced plants with slower growth and reduced concentration of defensive compounds, which increased the performance of the leaf herbivores. Effects of seed‐feeding on seed germination and plant growth were attenuated by parasitism, resulting in a net increase of the number of viable offspring. In the field, we observed that seed damage impaired germination, delayed flowering time and increased leaf herbivory. Our results show that plant‐mediated interactions between insect herbivores are not limited to leaf herbivores, but extend to seed herbivores. In our study system, parasitoids had no apparent effect on these interactions, despite their strong beneficial effects on germination and plant performance. These findings confirm the long‐lasting consequences of indirect plant‐mediated interactions in a community‐wide ecological context. Furthermore, they contribute to a better understanding of the important but understudied effects of parasitoids on plant fitness. Read the free Plain Language Summary for this article on the Journal blog.

Leaf beetle herbivory shapes the subsequent flower-visiting insect community and impacts plant reproduction

ABSTRACT Herbivory can induce changes in flower traits influencing the community of flower-visiting insects and ultimately impacting the plant’s reproductive output. Here, we investigated how leaf herbivory on sweet pepper plants, Capsicum annuum L., by Diabrotica speciosa (Germar) adults influences the community of insect floral visitors and alters plant reproduction. In an experimental field, we found that flowers of herbivore-infested plants were less visited by insects than those of uninfested plants. A similar pattern was found for the abundance of the three most common species of floral visitors in the collections, Apis mellifera (Linnaeus), Toxomerus sp.1, and Trigona spinipes (Fabricius). The insect community associated with the flowers of herbivore-infested plants was distinct, less rich, and diverse than that of uninfested plants. Leaf herbivory also impacted flower abundance that likely influenced the visual attraction of insects. The changes in flower-visiting insect community associated with herbivore-infested plants coincided with a reduced number of fruits, which were smaller and contained fewer seeds than those from uninfested plants. Our results suggest that leaf herbivory by D. speciosa results in direct and indirect costs to the plants through modifications in abundance and composition of flower-visiting insect community.

Exploring the Volatiles Released from Roots of Wild and Domesticated Tomato Plants under Insect Attack.

Plants produce volatile organic compounds that are important in communication and defense. While studies have largely focused on volatiles emitted from aboveground plant parts upon exposure to biotic or abiotic stresses, volatile emissions from roots upon aboveground stress are less studied. Here, we investigated if tomato plants under insect herbivore attack exhibited a different root volatilome than non-stressed plants, and whether this was influenced by the plant’s genetic background. To this end, we analyzed one domesticated and one wild tomato species, i.e., Solanum lycopersicum cv Moneymaker and Solanum pimpinellifolium, respectively, exposed to leaf herbivory by the insect Spodoptera exigua. Root volatiles were trapped with two sorbent materials, HiSorb and PDMS, at 24 h after exposure to insect stress. Our results revealed that differences in root volatilome were species-, stress-, and material-dependent. Upon leaf herbivory, the domesticated and wild tomato species showed different root volatile profiles. The wild species presented the largest change in root volatile compounds with an overall reduction in monoterpene emission under stress. Similarly, the domesticated species presented a slight reduction in monoterpene emission and an increased production of fatty-acid-derived volatiles under stress. Volatile profiles differed between the two sorbent materials, and both were required to obtain a more comprehensive characterization of the root volatilome. Collectively, these results provide a strong basis to further unravel the impact of herbivory stress on systemic volatile emissions.

Leaf-chewing herbivores affect preference and performance of a specialist root herbivore

Plants interact with a diversity of phytophagous insects above- and belowground. By inducing plant defence, one insect herbivore species can antagonize or facilitate other herbivore species feeding on the same plant, even when they are separated in space and time. Through systemic plant-mediated interactions, leaf-chewing herbivores may affect the preference and performance of root-feeding herbivores. We studied how six different leaf-chewing herbivore species of Brassica oleracea plants affected oviposition preference and larval performance of the root-feeding specialist Delia radicum. We expected that female D. radicum flies would oviposit where larval performance was highest, in accordance with the preference–performance hypothesis. We also assessed how the different leaf-chewing herbivore species affected defence-related gene expression in leaves and primary roots of B. oleracea, both before and after infestation with the root herbivore. Our results show that leaf-chewing herbivores can negatively affect the performance of root-feeding D. radicum larvae, although the effects were relatively weak. Surprisingly, we found that adult D. radicum females show a strong preference to oviposit on plants infested with a leaf-chewing herbivore. Defence-related genes in primary roots of B. oleracea plants were affected by the leaf-chewing herbivores, but these changes were largely overridden upon local induction by D. radicum. Infestation by leaf herbivores makes plants more attractive for oviposition by D. radicum females, while decreasing larval performance. Therefore, our findings challenge the preference–performance hypothesis in situations where other herbivore species are present.

Effects of plant diversity and leaf traits on insect herbivory in plantation and natural forests

Conversion from natural forest to timber plantation is an important cause of pristine forests loss. These changes alter community structure and cause a decrease in the diversity of plant communities. Leaf functional traits, which are an important defensive strategy, might also be influenced by such alterations. Altogether, shifts from natural forest to timber plantation may lead to profound changes in plant-plant and plant-animal interactions, including herbivory and the relative abundance of different feeding guilds, an important aspect of forest ecosystem function and community dynamics. In this study, we assessed insect herbivore damage in saplings of four native tree species in the understory of natural forests and two types of ca. 80-year-old timber plantations. We measured leaf damage by the most common feeding guilds in over 9000 leaves from 200 saplings. We first compared herbivory between natural forest and plantations, and we then analyzed the drivers of herbivory and of the two most common guilds – chewers and miners – using several indices of forest structure and leaf traits as predictors. Total herbivory did not change among forest types, but it showed some variation in two of the four species. Herbivory decreased with increasing species richness and increased with increasing basal area of conspecific and heterospecific trees. Leaf damage caused by chewers increased with leaf thickness, while damage caused by miners showed the opposite relationship. On an ecological level, our findings support expectations from the resource concentration hypothesis and on the role of leaf traits in mediating the impact of insect feeding guilds on leaf herbivory. On an applied level, these results suggest that timber plantations can support similar levels of ecosystem processes than natural forests decades after their establishment. Allowing the regeneration of a diverse understory in plantation forests should be implemented to favor ecosystem dynamics close to those of the original forests.

Leafminer attack accelerates the development of soil-dwelling conspecific pupae via plant-mediated changes in belowground volatiles.

Summary Herbivore population dynamics are strongly influenced by the interactions established through their shared host. Such plant‐mediated interactions can occur between different herbivore species and different life developmental stages of the same herbivore. However, whether these interactions occur between leaf‐feeding herbivores and their soil‐dwelling pupae is unknown.We studied whether tomato (Solanum lycopersicum) leaf herbivory by the American serpentine leafminer Liriomyza trifolii affects the performance of conspecific pupae exposed to the soil headspace of the plant. To gain mechanistic insights, we performed insect bioassays with the jasmonate‐deficient tomato mutant def‐1 and its wild‐type, along with phytohormones, gene expression and root volatiles analyses.Belowground volatiles accelerated leafminer metamorphosis when wild‐type plants were attacked aboveground by conspecifics. The opposite pattern was observed for def‐1 plants, in which aboveground herbivory slowed metamorphosis. Leafminer attack induced jasmonate and abscisic acid accumulation and modulated volatile production in tomato roots in a def‐1‐dependent manner.Our results demonstrate that aboveground herbivory triggers changes in root defence signalling and expression, which can directly or indirectly via changes in soil or microbial volatiles, alter pupal development time. This finding expands the repertoire of plant–herbivore interactions to herbivory‐induced modulation of metamorphosis, with potential consequences for plant and herbivore community dynamics.

Seasonality and forest edge as drivers of Tradescantia zebrina Hort. ex Bosse invasion in the Atlantic Forest.

As a result of biodiversity and ecosystem service losses associated with biological invasions, there has been growing interest in basic and applied research on invasive species aiming to improve management strategies. Tradescantia zebrina is a herbaceous species increasingly reported as invasive in the understory of disturbed forest ecosystems. In this study, we assess the effect of spatial and seasonal variation on biological attributes of this species in the Atlantic Forest. To this end, we measured attributes of T. zebrina associated with plant growth and stress in the four seasons at the forest edge and in the forest interior of invaded sites in the Iguaçu National Park, Southern Brazil. The invasive plant had higher growth at the forest edge than in the forest interior and lower leaf asymmetry and herbivory in the winter than in the summer. Our findings suggest that the forest edge environment favours the growth of T. zebrina. This invasive species is highly competitive in the understory of semi-deciduous seasonal forests all over the year. Our study contributes to the management of T. zebrina by showing that the summer is the best season for controlling this species.

Soil cadmium stress reduced host plant odor selection and oviposition preference of leaf herbivores through the changes in leaf volatile emissions

The Elemental defense hypothesis suggested that metal accumulation in plant tissues could serve as direct defense to reduce herbivore feeding preference as metals are toxic to phytophagous insects. However, the indirectly defensive role of heavy metals on host plant odor selection and oviposition preference of leaf herbivores through the changes in leaf volatile organic compounds (VOCs) is still unknown. In this study, we used a local woody plant species, Populus yunnanensis, to investigate whether soil cadmium (Cd) stress could affect plant VOC production and whether Cd-mediated changes in leaf VOC emissions will further influence the host plant odor and oviposition preferences of female adults of a specialist and a generalist herbivore species. The results clearly showed that the soil Cd stress could prominently induce leaf total VOC emissions of P. yunnanensis and such induction was positively correlated with leaf Cd accumulation. Herbivore olfactometer bioassays further demonstrated that the VOCs released by P. yunnanensis under Cd exposure are far less attractive to both of the specialist and generalist female adults compared to control plants, leading to significant reduction in oviposition on Cd-treated plants. Moreover, the host plant odor selection and oviposition preference of the two herbivore species were all negatively correlated with leaf total VOC emissions, which confirmed the defensive role of Cd-induced VOCs for deterring the female insects. The result will extend the existing knowledge of the Elemental defense hypothesis and provide new insight into predicting the herbivore damage level of poplar species that naturally occurred in metal-polluted habitats.

Leaf Induction Impacts Behavior and Performance of a Pollinating Herbivore

Flowering plants use volatiles to attract pollinators while deterring herbivores. Vegetative and floral traits may interact to affect insect behavior. Pollinator behavior is most likely influenced by leaf traits when larval stages interact with plants in different ways than adult stages, such as when larvae are leaf herbivores but adult moths visit flowers as pollinators. Here, we determine how leaf induction and corresponding volatile differences in induced plants influence behavior in adult moths and whether these preferences align with larval performance. We manipulated vegetative induction in four Nicotiana species. Using paired induced and control plants of the same species with standardized artificial flowers, we measured foraging and oviposition choices by their ecologically and economically important herbivore/pollinator, Manduca sexta. In parallel, we measured growth rates of M. sexta larvae fed leaves from control or induced plants to determine if this was consistent with female oviposition preference. Lastly, we used plant headspace collections and gas chromatography to quantify volatile compounds from both induced and control leaves to link changes in plant chemistry with moth behavior. In the absence of floral chemical cues, vegetative defensive status influenced adult moth foraging preference from artificial flowers in one species (N. excelsior), where females nectared from induced plants more often than control plants. Plant vegetative resistance consistently influenced oviposition choice such that moths deposited more eggs on control plants than on induced plants of all four species. This oviposition preference for control plants aligned with higher larval growth rates on control leaves compared with induced leaves. Control and induced plants of each species had similar leaf volatile profiles, but induced plants had higher emission levels. Leaves of N. excelsior produced the most volatile compounds, including some inducible compounds typically associated with floral scent. We demonstrate that vegetative plant defensive volatiles play a role in host plant selection and that insects assess information from leaves differently when choosing between nectaring and oviposition locations. These results underscore the complex interactions between plants, their pollinators, and herbivores.

Climate change‐adaptive participatory field gene banking for a California endemic oak

Anthropogenic climate change is causing demographic shifts at species' range edges. Trailing edge populations, which may be genetically distinct and adapted to relative climate extremes, already are showing declines in some species. The associated loss of trailing edge genetic diversity may limit possibilities for future climate‐adaptive restoration. For plants with recalcitrant seed, such as oaks, that cannot tolerate conventional seed banking, we propose a novel approach to the conservation of climate‐threatened genetic diversity: dispersed, participatory field gene banking. In this collaborative model, trailing edge transplants are stewarded at dispersed sites across a species' projected regional refugia. In 2018, we initiated a pilot participatory field gene bank for the foundational, endemic California blue oak (Quercus douglasii), a species experiencing increasing climate‐related declines at its trailing edge. To evaluate seedling performance, the gene bank was designed as a set of 23 small, dispersed common gardens with paired local and trailing edge seeds. Trailing edge seedlings showed lower survival and growth relative to locals, yet they also showed lower levels of leaf disease and herbivory, traits that could confer an adaptive advantage in a more xeric future. The substantial early survival of translocated seeds suggests that participatory field gene banking may offer an effective means of preserving trailing edge genetic diversity for oaks, thereby maintaining genetic resources that could be critical for future climate change‐adaptive restoration. However, further observations are needed to confirm the strategy's longer‐term viability and evaluate evidence of local adaptation.

Leaf traits-mediated effects of tree diversity on insect herbivory on Populus laurifolia in a riparian forest ecosystem

Tree diversity and landscape features have long been considered as the main drivers of insect herbivory in forest ecosystems. However, relatively little is known about how local and landscape factors, directly and indirectly, acting at different spatial scales affect insect damage under natural, non-outbreak conditions. Here, 30 mixed and pure forest stands were selected in natural forests along the Irtysh river in Xinjiang, Northwest China. To assess the effects of landscape-scale forest isolation, tree diversity, stand position, tree size, understory vegetation cover, and leaf traits on leaf herbivory on Populus laurifolia, we measured three leaf traits (i.e., leaf area, specific leaf area, and leaf dry matter content) and defoliation intensity of insect herbivores in host poplars in 30 sampling plots within mixed and pure forest stands. We also explored the indirect effects of tree diversity on insect herbivory via changes in leaf traits. We found that both forest isolation and tree height had positive effects on insect herbivory, but vegetation cover negatively affected it. Insect herbivory was lower in mixed than in pure forest stands, however, this difference was only significant in stands at the near distance from the river. All leaf traits differed significantly between mixed and pure stands, and varied with tree height. In addition, insect herbivory was positively correlated with leaf area and specific leaf area. However, the influence of tree diversity and tree size on insect herbivory mainly act indirectly through changes in leaf area and specific leaf area. Our results indicate that insect herbivory can be driven by a complex system of ecological factors at multiple scales, and offer an insight into the key role of leaf traits in driving tree diversity-herbivory interactions in a natural forest ecosystem. Thus, these findings are crucial to improve risk assessment and potential prevention strategies of insect damage in riparian forests in real-world situations.

Sexual differences in above- and belowground herbivore resistance between male and female poplars as affected by soil cadmium stress

Dioecious plant species presented sexual differences in metal accumulation and allocation between male and female conspecifics that grown on metal contaminated soil. As the Elemental defense hypothesis postulates that metals accumulated in plant tissues could protect plants from herbivory, whether such sexual dimorphism in response to metal stress of a dioecious plant will lead to differences in herbivore resistance between male and female conspecifics is still unknown. In this study, we used female and male siblings of Populus deltoides to investigate the effect of plant sex on the growth and feeding preferences of four leaf herbivores and a root herbivore under soil cadmium (Cd) stress. The results showed that the male plants accumulated significantly higher Cd in the leaves while the females allocated more Cd in the roots. Leaf herbivores fed on male leaves grew worse than those fed on female leaves under Cd exposure, while the root herbivore showed the opposite results. In addition, all leaf herbivores strongly preferred the leaves from Cd-stressed female plants than male ones. The quantification of gene expression further showed that Cd stress could significantly upregulate more genes involved in Cd uptake, transport and detoxification pathways in male leaves and female roots. In combination with the correlation tests, we postulated that such sexual differences in herbivore resistance between the two plant sexes was most likely due to the different Cd allocation patterns in plant leaves and roots.

Comparative Metabolomics of Fruits and Leaves in a Hyperdiverse Lineage Suggests Fruits Are a Key Incubator of Phytochemical Diversification.

Interactions between plants and leaf herbivores have long been implicated as the major driver of plant secondary metabolite diversity. However, other plant-animal interactions, such as those between fruits and frugivores, may also be involved in phytochemical diversification. Using 12 species of Piper, we conducted untargeted metabolomics and molecular networking with extracts of fruits and leaves. We evaluated organ-specific secondary metabolite composition and compared multiple dimensions of phytochemical diversity across organs, including richness, structural complexity, and variability across samples at multiple scales within and across species. Plant organ identity, species identity, and the interaction between the two all significantly influenced secondary metabolite composition. Leaves and fruit shared a majority of compounds, but fruits contained more unique compounds and had higher total estimated chemical richness. While the relative levels of chemical richness and structural complexity across organs varied substantially across species, fruit diversity exceeded leaf diversity in more species than the reverse. Furthermore, the variance in chemical composition across samples was higher for fruits than leaves. By documenting a broad pattern of high phytochemical diversity in fruits relative to leaves, this study lays groundwork for incorporating fruit into a comprehensive and integrative understanding of the ecological and evolutionary factors shaping secondary metabolite composition at the whole-plant level.

Leaf herbivory counteracts nematode-triggered repression of jasmonate-related defenses in tomato roots.

Shoot herbivores may influence the communities of herbivores associated with the roots via inducible defenses. However, the molecular mechanisms and hormonal signaling underpinning the systemic impact of leaf herbivory on root-induced responses against nematodes remain poorly understood. By using tomato (Solanum lycopersicum) as a model plant, we explored the impact of leaf herbivory by Manduca sexta on the performance of the root knot nematode Meloidogyne incognita. By performing glasshouse bioassays, we found that leaf herbivory reduced M. incognita performance in the roots. By analyzing the root expression profile of a set of oxylipin-related marker genes and jasmonate root content, we show that leaf herbivory systemically activates the 13-Lipoxigenase (LOX) and 9-LOX branches of the oxylipin pathway in roots and counteracts the M. incognita-triggered repression of the 13-LOX branch. By using untargeted metabolomics, we also found that leaf herbivory counteracts the M. incognita-mediated repression of putative root chemical defenses. To explore the signaling involved in this shoot-to-root interaction, we performed glasshouse bioassays with grafted plants compromised in jasmonate synthesis or perception, specifically in their shoots. We demonstrated the importance of an intact shoot jasmonate perception, whereas having an intact jasmonate biosynthesis pathway was not essential for this shoot-to-root interaction. Our results highlight the impact of leaf herbivory on the ability of M. incognita to manipulate root defenses and point to an important role for the jasmonate signaling pathway in shoot-to-root signaling.

Squash Varieties Domesticated for Different Purposes Differ in Chemical and Physical Defense Against Leaf and Root Herbivores

Plant domestication often reduces plant defenses by selection on chemical and physical defense traits. Thus, it is expected that herbivorous insects perform better on crop varieties than on their wild relatives. However, recent studies show that this pattern is not ubiquitous. We examined how varieties of squash (Cucurbita spp.) domesticated for different purposes (for consumption or as ornamentals), differ in plant defense traits and in their interactions with a leaf and a root herbivore. Two types of defenses were measured: cucurbitacins, which are toxic phytochemicals, and trichomes that are physical barriers for most herbivores. We addressed the following questions: (i) what is the variation in cucurbitacin content and leaf trichome density among varieties? (ii) does purpose of domestication explain differences in defense traits among varieties? and (iii) are herbivore feeding preferences and performance altered by the defense traits of squash varieties? We found great variation in cucurbitacin content among varieties, but not according to their purpose of domestication. Cucurbitacins were found mostly in cotyledons and roots and in very small quantities in the leaves. In contrast, trichome density was greater on the varieties selected for consumption than on the ornamental varieties. The performance of a leaf herbivore (Spodoptera latifascia) and a root herbivore (Diabrotica balteata), was not different among squash varieties. Moreover, in a choice experiment, larvae of the root herbivore preferred to feed on squash varieties with high cucurbitacin content. Whereas, in the field, native leaf herbivores preferred to feed on varieties selected for consumption. Our results contribute to a better understanding on how varietal selection may differentially affect plant defenses. This knowledge could help in the development of crop varieties with enhanced insect resistance.

Ecological and evolutionary distances from neighbouring plants do not influence leaf herbivory by chewing insects in a Neotropical savanna

ABSTRACT Background Coexisting plant species frequently exhibit marked differences in leaf damage caused by chewing insects. Such variation in leaf herbivory has often been attributed to interspecific differences in leaf defensive traits, leaf nutritional quality and leaf abundance. Aims We aimed to investigate the hypothesis that plants surrounded by more similar neighbours tend to exhibit higher levels of herbivory than plants surrounded by less similar neighbours. Methods We sampled 27 tree and shrub species in 49 plots of 10 m2 located in a Neotropical savanna. For each of the 815 plants sampled, we quantified leaf damage, specific leaf area, leaf toughness, height, and conspecific abundance. We analysed the relationship between herbivory levels and plant traits comparing each individual with its neighbouring plants. The effect of phylogenetic similarity was addressed using the mean phylogenetic distance between a focal plant individual and its neighbours (i.e., the phylogenetic isolation). Results Leaf herbivory damage ranged from zero to 29.6%. We found that phylogenetic isolation, specific leaf area, plant height, and plant abundance were not related to differences in leaf herbivory at the individual level in a neighbourhood. Conclusions Our findings show that leaf herbivory damage of individual plants was not consistently influenced either by phylogenetic or by trait similarity with neighbours.

An experimental investigation of costs of tolerance against leaf and floral herbivory in the herbaceous weed horsenettle (Solanum carolinense, Solanaceae)

Background and aims – A plant’s tolerance of herbivory depends on its ability to endure and compensate for damage so as to lessen the impact that herbivores have on the plant’s performance (e.g. its growth, reproduction, or fitness). While tolerance of herbivory is beneficial to plants, it is rarely complete, and individuals in plant populations tend to vary in their levels of tolerance. The goal of this study was to investigate potential costs associated with tolerance of leaf and floral herbivory in horsenettle (Solanum carolinense), a perennial herbaceous weed that is often subjected to high levels of damage from a diversity of herbivores. Material and methods – We exposed 96 potted individuals across eight genets of horsenettle to factorial treatments of leaf herbivory by lace bugs and simulated floral herbivory by weevils. We quantified tolerance for each plant genet for both types of herbivory in terms of the impact of damage on the number of flowers opened, number of seeds produced, and root biomass (i.e. paternal, maternal, and vegetative tolerance, respectively).Key results – Plant genets ranged widely in their ability to compensate for leaf and flower damage. While there was little evidence for tradeoffs in tolerance through the different routes, there was strong evidence of tradeoffs in genets’ abilities to tolerate herbivore damage to leaves and damage to flowers.Conclusion – Tolerance is a useful defence strategy to cope with damage caused by herbivores, but its evolution may be constrained by concomitant costs and tradeoffs. The evolutionary role of the tradeoffs identified in this study are likely to be greater the more species of herbivores a plant hosts, and the more that herbivore levels vary both spatially and temporally.