How do two specialist butterflies determine growth and biomass of a shared host plant?

Although insect herbivory can modify subsequent quantity and quality of their host plants, change in plant quantity following herbivory has received less attention than plant quality. In particular, little is known about how previous herbivore damage determines plant growth and biomass in an insect species-specific manner. We explored whether herbivore species-specific food demand influences plant growth and biomass. To do this, we conducted a series of experiments and field survey using two specialist butterflies, Sericinus montela and Atrophaneura alcinous, and their host plant, Aristolochia debilis. It is known that A. alcinous larva requires four times more food resources to fulfill its development than S. montela larva. Despite that A. alcinous larvae imposed greater damage on plants than S. montela larvae, plant growth did not differ due to herbivory by these species both in single and multiple herbivory events. On the other hand, total aboveground biomass of the plants was reduced more by A. alcinous than S. montela feeding regardless of the number of herbivory events. Feeding on plants with a history of previous herbivory neither decreased nor increased larval growth. Our results suggest that food demand of the two butterfly species determined subsequent plant biomass, although the plant response may depend on tolerance of the host plant (i.e., ability to compensate for herbivore damage). Such difference in the effects of different herbivore species on host plant biomass is more likely to occur than previously thought, because food demand differs in most herbivore species sharing a host plant.     

Friend or foe?: a plant's induced response to an omnivore

Omnivorous natural enemies of herbivores consume plant-based resources and may elicit induced resistance in their host plant. A greater induction threshold for damage produced by omnivorous predators than for strict herbivores might be expected if omnivore performance is enhanced on noninduced plants, allowing them to reduce future levels of herbivory. Currently, it is not known if a plant responds to feeding by omnivorous predators and by herbivores similarly. To examine this question, we chose herbivore and omnivore species that produce the same kind of quantifiable damage to cotton leaves, enabling us to control statistically for the intensity of plant damage, and ask whether plant responses differed depending on the identity of the damaging species. We first compared changes in plant peroxidase activity, gossypol gland number and density, and leaf area in response to feeding by the spider mite Tetranychus turkestani (Ugarov and Nikolski) (an herbivore) and by one of the mite's principal natural enemies, the western flower thrips Frankliniella occidentalis (Pergande) (an omnivore). Both species increased the activity of peroxidase, but when we controlled for the amount of damage, the peroxidase activity of mite-damaged plants was higher than that of thrips-damaged plants. We also found that thrips, but not spider mites, increased the density of gossypol glands in the second true leaf. In a second experiment we included an additional herbivore, the bean thrips Caliothrips fasciatus (Pergande), to see if the different responses of cotton to thrips and mite herbivory we first observed were attributable to differences in trophic function (herbivore versus omnivore) or to other differences in feeding generated by thrips versus mites. Cotton plants exhibited the same pattern of induced responses (elevated peroxidase, increased number of glands, reduced leaf area) to herbivory generated by the bean thrips (an herbivore) and western flower thrips (an omnivore), suggesting that trophic function was not a key determinant of plant response. Thrips-damaged plants again showed a significantly higher density of gossypol glands than did mite-damaged plants. Overall, our results suggest that (1) an omnivorous predator systemically induces resistance traits in cotton and (2) whereas there is evidence of taxonomic specificity (thrips versus mites), there is little support for trophic specificity (herbivorous thrips versus omnivorous thrips) in the elicitation of induced responses.     

Colonization by nitrogen-fixing <Emphasis Type="Italic">Frankia</Emphasis> bacteria causes short-term increases in herbivore susceptibility in red alder (<Emphasis Type="Italic">Alnus rubra</Emphasis>) seedlings

Carbon allocation demands from root-nodulating nitrogen-fixing bacteria (NFB) can modulate the host plant’s chemical phenotype, with strong bottom–up effects on herbivores. In contrast to well-studied rhizobia, the effects of other important NFB on plant chemistry and herbivory are much less understood. Here, combining field surveys in the Oregon Coast Range, USA with laboratory experiments, we analyzed how N₂-fixing Frankia bacteria influenced plant growth, chemistry, and herbivory on Alnus rubra (red alder) seedlings. In the field, we quantified Frankia nodulation, herbivore damage, and plant size. In the laboratory, we grew seedlings with Frankia (F+), Frankia-free but nitrogen-fertilized (N+), or both uncolonized and unfertilized (F?N?) and assessed growth and leaf chemistry. We further conducted choice trials with black slugs, Arion rufus, a natural red alder herbivore. In the field, Frankia nodulation was significantly positively correlated with herbivory and negatively with seedling height. In contrast, in the lab, F+ as well as N+ seedlings were significantly taller than the F?N? controls. Seedlings from both treatments also had significantly increased leaf protein concentration compared to controls, whereas carbon-based nutritive compounds (carbohydrates) as well as leaf palatability-decreasing condensed tannins, lignin, and fiber were decreased in F+ but not in N+ treatments. In the choice assays, slugs preferred leaf material from F+ seedlings, but the effects were only significant in young leaves. Our study indicates that colonization by Frankia causes short-term ecological costs in terms of susceptibility to herbivory. However, the ubiquity of this symbiosis in natural settings suggests that these costs are outweighed by benefits beyond the seedling stage.     

No evolution of reduced resistance and compensation for psyllid herbivory by the invasive <Emphasis Type="Italic">Genista monspessulana</Emphasis>

The evolution of redirecting resources from plant defense to growth or reproduction may explain why some exotic species are successful invaders in new environments. For example, the evolution of increased competitive ability hypothesis posits that escape from herbivores by invasive plants results in the selection of more vigorous genotypes that reduce their allocation of resources to defense. In addition, understanding the defense strategy of an invasive plant may help forecast the likely impact of herbivory. We tested the prediction of reduced defense (i.e., resistance) in Genista monspessulana, measured indirectly as the performance of a specialist psyllid herbivore, by comparing five native and introduced plant populations. We also examined the ability of G. monspessulana to compensate for herbivory in the presence and the absence of psyllids for a single plant population from the native and introduced regions. Plant origin (native or introduced) did not influence the psyllid’s abundance and population growth rate, suggesting no change in resistance to herbivory for introduced plants. Similarly, we found no overall difference in plant performance between individuals in the presence and the absence of psyllid herbivory, suggesting that G. monspessulana was able to fully compensate for herbivory. Damaged plants compensated by changing the pattern of branching, which also resulted in greater dry leaf biomass. We conclude that evolution of reduced defenses does not explain the success of G. monspessulana as an invader and that compensation for herbivory may limit the efficacy of the psyllid as a biological control agent.     

Associational effects against a leaf beetle mediate a minority advantage in defense and growth between hairy and glabrous plants

Based on the accumulation of evidence, the risk of herbivory depends not only on the traits of a plant but also on those of neighboring plants. Despite the potential importance of frequency-dependent interactions in the evolutionary stability of anti-herbivore defense, we know little about such associational effects between defended and undefended plants within a species. In this study, we determined whether the intraspecific associational effects against the oligophagous leaf beetle, Phaedon brassicae, caused a minority advantage in defense and growth between trichome-producing (hairy) and trichomeless (glabrous) plants of Arabidopsis halleri subsp. gemmifera. We experimentally demonstrated that the magnitude of herbivory and the number of adult beetles on hairy plants decreased when hairy plants were a minority, whereas the leaf damage and the beetle abundance did not differ between hairy and glabrous plants when glabrous plants were a minority. By contrast, the larvae of P. brassicae occurred less when hairy plants were a majority. We also found a reciprocal minority advantage in the biomass production for both hairy and glabrous plants. Additionally, the adults tended to attack glabrous leaves more rapidly than hairy ones, particularly when the beetles were starved or experienced glabrous diets. Furthermore, in the absence of herbivory, the growth of hairy plants tended to be slower than glabrous plants, which indicated a cost for the production of trichomes. Our study suggests that associational effects are a mechanism for the maintenance of trichome dimorphism by contributing to negative frequency-dependent growth.     

Enhanced leaf nitrogen status stabilizes omnivore population density

Plant traits can mediate the strength of interactions between omnivorous predators and their prey through density effects and changes in the omnivores’ trophic behavior. In this study, we explored the established assumption that enhanced nutrient status in host plants strengthens the buffering effect of plant feeding for omnivorous predators, i.e., prevents rapid negative population growth during prey density decline and thereby increases and stabilizes omnivore population density. We analyzed 13 years of field data on population densities of a heteropteran omnivore on Salix cinerea stands, arranged along a measured leaf nitrogen gradient and found a 195 % increase in omnivore population density and a 63 % decrease in population variability with an increase in leaf nitrogen status from 26 to 40 mgN × g^?1. We recreated the leaf nitrogen gradient in a greenhouse experiment and found, as expected, that increasing leaf nitrogen status enhanced omnivore performance but reduced per capita prey consumption. Feeding on high nitrogen status host plants can potentially decouple omnivore–prey population dynamics and allow omnivores to persist and function effectively at low prey densities to provide “background level” control of insect herbivores. This long-term effect is expected to outweigh the short-term effect on per capita prey consumption—resulting in a net increase in population predation rates with increasing leaf nitrogen status. Conservation biological control of insect pests that makes use of omnivore background control could, as a result, be manipulated via management of crop nitrogen status.     

Herbivory on planted oak seedlings across a habitat edge created by timber harvest

Edge habitats create environmental gradients that affect plant community composition and herbivore behavior. Silvicultural disturbance creates edge habitat with direct (via changes in light) and indirect (via changes in herbivore behavior) consequences for the growth and survival of tree seedlings, and thus, the composition of the future forest stands. Herbivores, particularly ungulates, can be a major limiting factor in oak regeneration, and silvicultural disturbance may alter the abundance or behavior of herbivores following harvest. We measured the severity of herbivory on experimentally planted white (Quercus alba) and black oak (Quercus velutina) seedlings by white-tailed deer (Odocoileus virginianus) and eastern cottontail rabbits (Sylvilagus floridanus), as well as foliar damage from insects, across gradients created by clearcuts in a deciduous forest in Indiana, USA. Overall browse pressure on oaks was low in our study. Nonetheless, spatial variation in herbivory depended on herbivore taxa; herbivory by rabbits was highest inside harvest openings, whereas foliar damage by insects peaked in the forest. Intensity of deer herbivory was constant across the edge. In addition, we observed indirect interactions among herbivore species mediated by a seedling’s browsing history. Herbivore damage by deer was positively related to past browsing by rabbits, and foliar damage from insects was positively related to past browsing by both deer and rabbits. Increasing woody plant competition reduced herbivory on seedlings by both deer and rabbits. Given the lack of spatial variability in deer herbivory and low overall herbivory by rabbits, we suspect that interactions between timber harvesting and herbivory did not have a strong impact on oak seedlings at our study sites.     

The Impacts of Above- and Belowground Plant Input on Soil Microbiota: Invasive <Emphasis Type="Italic">Spartina alterniflora</Emphasis> Versus Native <Emphasis Type="Italic">Phragmites australis</Emphasis>

Invasive plants affect soil food webs through various resource inputs including shoot litter, root litter and living root input. The net impact of invasive plants on soil biota has been recognized; however, the relative contributions of different resource input pathways have not been quantified. Through a 2 × 2 × 2 factorial field experiment, a pair of invasive and native plant species (Spartina alterniflora vs. Phragmites australis) was compared to determine the relative impacts of their living roots or shoots and root litter on soil microbial and nematode communities. Living root identity affected bacteria-to-fungi PLFA ratios, abundance of total nematodes, plant-feeding nematodes and omnivorous nematodes. Specifically, the plant-feeding nematodes were 627% less abundant when living roots of invasive S. alterniflora were present than those of native P. australis. Likewise, shoot and root biomass (within soil at 0–10 cm depth) of S. alterniflora was, respectively, 300 and 100% greater than those of P. australis. These findings support the enemy release hypothesis of plant invasion. Root litter identity affected other components of soil microbiota (that is, bacterial-feeding nematodes), which were 34% more abundant in the presence of root litter of P. australis than S. alterniflora. Overall, more variation associated with nematode community structure and function was explained by differences in living roots than root or shoot litter for this pair of plant species sharing a common habitat but contrasting invasion degrees. We conclude that belowground resource input is an important mechanism used by invasive plants to affect ecosystem structure and function.     

To Smell you Better: Prior Food Deprivation Increases Herbivore Insect Responsiveness to Host Plant Odor Cues

Hunger plays a crucial role in insect feeding behavior, however food deprivation is rarely considered when insect responses to plant host and related chemical stimuli are investigated. Here we assessed, by means of experiments with Y-tube olfactometer, the effect of food deprivation time on the response of a specialist (Xanthogaleruca luteola) and a generalist (Diabrotica speciosa) herbivore beetle species (Coleoptera: Chrysomelidae) to odor cues of their respective host plants. Increasing food deprivation periods enhanced responses to host plant odor in both species, with insects remaining for longer in the olfactometer arm carrying plant odor than in the control, moving less frequently between olfactometer arms, and being more efficient in moving towards the plant odor as their first choice. These trends were less significant in the generalist species, which also required a longer fasting threshold (48 h) in comparison with the specialist (8 h). Our results, showing that prior food deprivation time can influence insect herbivore responsiveness to plant stimuli and that those effects may vary between species, highlight the risk of neglecting this factor in studies involving insect responses to host or chemical stimuli.     

Histological evidence that diploid hybrids of <Emphasis Type="Italic">Cobitis taenia</Emphasis> and <Emphasis Type="Italic">C. elongatoides</Emphasis> (Teleostei,Cobitidae) develop into fertile females and sterile males

Rising temperatures likely affect the trophic interactions in temperate regions as global warming progresses. An open question is how a temperature rise may affect consumer pressure and plant abundance in shallow aquatic ecosystems, where most consumers are omnivorous. Interestingly, herbivory (plant-eating) is more prevalent toward low latitudes in ectotherms such as fish and aquatic invertebrates, and this may be temperature driven. We used pond snails (Lymnaea stagnalis L.) as a model aquatic ectotherm species and tested their consumption of both animal prey (Gammarus pulex L.) and plant material (Potamogeton lucens L.) at three different temperatures (15, 20, and 25°C). Higher temperatures led to higher consumption rates by the omnivore on both plant food and animal prey when fed separately. When the food was offered simultaneously, the pond snails consistently preferred animal prey over plant material at all tested temperatures. However, the omnivore did consume plant material even though they had enough animal prey available to them. Based on our experiments, we conclude that with increasing temperatures, L. stagnalis will only increase their consumption rates but not change food preference. Further studies are needed to test the generality of our findings across aquatic species to predict the effect of warming on aquatic plant consumption.     

Oviposition Preferences of <Emphasis Type="Italic">Plutella xylostella</Emphasis> are Influenced by the Type of Plant Induction and Glucosinolate Hydrolysis Profiles

Effects of inducing plants by exposing them to insect herbivory, mechanical damage or damaged neighboring plants were evaluated on the oviposition preferences of Plutella xylostella. The role of plant genotypes differing in their glucosinolate hydrolysis profiles was also evaluated using a wild ecotype (Col-0) and a genetically modified line (tgg1tgg2) of Arabidopsis thaliana. While the Col-0 line has normal production of glucosinolate hydrolysis products, the double myrosinase knockout (tgg1tgg2) is defective in the production of these volatiles. Dual choice oviposition assays were performed using naïve P. xylostella females, and the two A. thaliana lines, which were exposed to the three types of induction treatments. Female oviposition preferences were significantly influenced by both the type of plant induction and the plant genotypes differing in their volatile profiles. Plutella xylostella females significantly preferred to oviposit on herbivore-damaged plants (versus undamaged controls) when Col-0 plants were used, but chose control plants over the double myrosinase knockout tgg1tgg2. However, plant genotype did not influence oviposition choices between plant-plant primed or mechanically damaged plants and paired undamaged controls. Given the prevalent use of genetically modified plants and the potential differences in their responses to different types of induction, these factors may be important to consider in the management of specialist pests such as the diamondback moth P. xylostella.     

Differences in interactions of aboveground and belowground herbivores on the invasive plant <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis> and native host <Emphasis Type="Italic">A. sessilis</Emphasis>

Plant invasions may result in novel plant-herbivore interactions. However, we know little about whether and how invasive plants can mediate native above- and belowground herbivore interactions. In this study, we conducted greenhouse experiments to examine the interaction between a native defoliating beetle, Cassida piperata, and a native root-knot nematode, Meloidogyne incognita, on the invasive alligator weed, Alternanthera philoxeroides. We also included their native host A. sessilis in the experiments to examine whether the patterns of above- and belowground herbivore interaction vary with host plants (invasive vs. native). We analyzed total carbon and nitrogen in leaves and roots attacked by M. incognita and C. piperata. M. incognita slightly negatively affected feeding by C. piperata on A. philoxeroides, and the leaf area damaged decreased as the number of M. incognita increased. M. incognita had a negative impact on total leaf nitrogen, but had no impact on total leaf carbon. M. incognita egg production on A. philoxeroides roots decreased as the amount of damage caused by C. piperata increased. Herbivory by C. piperata did not affect total root carbon or nitrogen. M. incognita and C. piperata did not affect each other on the native plant A. sessilis. These results suggest that invasive plants can mediate native above- and belowground herbivore interactions. The knowledge of how invasive plants affect those interactions is crucial for better understanding the impacts of biological invasions on native above- and belowground organisms.     

Soybean defense induction to <Emphasis Type="Italic">Spodoptera cosmioides</Emphasis> herbivory is dependent on plant genotype and leaf position

Plants have evolved a diverse array of defensive mechanisms against biotic and abiotic stresses, which can be either constitutive or inducible. Variation in plant-intrinsic factors such as the genotype and the leaf position coupled with insect herbivory can affect the expression of resistance to insects. We investigated if soybean defense induction triggered by Spodoptera cosmioides herbivory varies in function of the genotype and leaf position. This hypothesis was tested in two bioassays using leaf discs or entire leaflets collected from the upper and lower trifoliates of S. cosmioides-injured and uninjured V3-V4 soybean plants. We used one genotype that was constitutively resistant and one that was constitutively susceptible to S. cosmioides based on previous screening. Third-instar larvae were fed one of the treatments and assayed for leaf consumption, larval growth, and efficiency of conversion of ingested food. Genotype and leaf position significantly interacted with herbivory and affected soybean-induced resistance to S. cosmioides. Negative responses on S. cosmioides larvae consumption and growth rates were only observed when leaf material was originated from the upper soybean trifoliate. The susceptible soybean genotype did not exhibit induced resistance characteristics. Food offered as leaf disc was better at demonstrating induced resistance in previously injured soybean, whereas offering entire leaflet the induced effects were less pronounced. Here we provide new findings on soybean resistance by demonstrating that resistance induction to S. cosmioides herbivory is dependent on the plant genotype and leaf position where injury took place, with negative effects better evinced in bioassays using leaf discs than entire leaflets.     

Herbivore-induced infochemicals influence foraging behaviour in two intertidal predators

Herbivore-induced defences appear ubiquitous across most biomes and habitats. Yet the direct correlation between induced changes in host plant chemistry and the population dynamics of the herbivore remain untested in many systems. In plant–herbivore interactions in the terrestrial environment, indirect or tritrophic interactions appear a successful way in which changes in the host plant chemistry induced by prior herbivory can impact on herbivore populations via increased success of natural enemies. This set of interactions remains untested in the marine system. Here, we present work from experiments using orthogonal contrasts of plants with different prior treatments (control, mechanical damage or herbivory) and the presence or absence of herbivores on the foraging behaviour of a crab, Carcinus maenas, and a fish, Lipophrys pholis. These experiments were carried out using a novel flow-through flume, i.e. as a choice chamber supplied by turbulent water from independent cue sources. Our results show that in the Ascophyllum nodosum (plant)–Littorina obtusata (herbivore) system infochemicals from induced plants can directly influence predator foraging behaviour. L. pholis was attracted to the presence of a feeding L. obtusata, but was also more attracted to odours from herbivore-induced tissue than odours from mechanically damaged or naïve A. nodosum. C. maenas was more attracted to odours from herbivore-induced tissue compared to naïve tissue, regardless of the presence of L. obtusata. This is the first demonstration of such behavioural consequences of herbivore-induced changes in plants for marine systems.     

Genetic determination of tannins and herbivore resistance in <Emphasis Type="Italic">Quercus ilex</Emphasis>

Genetic variability of trees influences the chemical composition of tissues. This determines herbivore impact and, consequently, herbivore performance. We evaluated the independent effects of plant genotype and provenance on the tannin content of holm oak (Quercus ilex) and their consequences for herbivory and performance of gypsy moth (Lymantria dispar) larvae. Oak seedlings of 48 open-pollinated families from six populations were grown in a common garden in central Spain. Half the plants were subjected to defoliation by gypsy moth larvae and the other half were destructively sampled for chemical analysis. Tannin content of leaves did not differ significantly among populations but differed significantly among families. Estimates of heritability (h ²) and quantitative genetic differentiation among populations for tannin content (Q _ST) were 0.83 and 0.12, respectively. Defoliation was not related to the tannin content of plants nor to spine and trichome densities of leaves, although positive family–mean associations were observed between defoliation and both seed weight and plant height (P < 0.003). Among the oak populations, differential increase in larval weight gain with defoliation was observed. Leaf tannin content in Q. ilex is genetically controlled but does not influence defoliation or predict performance of the larvae. Different efficiencies of food utilisation depending on the oak genotypes indicate that other plant traits are influencing the feeding patterns and fitness of L. dispar and consequent population dynamics.     

Strong effects of hydrologic environment and weak effects of elevated CO<Subscript>2</Subscript> on the invasive weed <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis> and the biocontrol beetle <Emphasis Type="Italic">Agasicles hygrophila</Emphasis>

Global change, such as elevated CO₂, may alter interactions between invasive plants and biocontrol agents, impacting biocontrol efficacy. Here, we conducted four experiments in Texas, USA to test how elevated CO₂ influences an invasive plant (Alternanthera philoxeroides) and its interactions with an introduced biocontrol beetle (Agasicles hygrophila) in terrestrial (well-watered) and flooded environments. We grew plants for 9 months in ambient or elevated CO₂ (800 ppm) chambers in continuously flooded or well-watered conditions. In no-choice trials, flooding increased leaf toughness and decreased beetle consumption but beetles only oviposited on ambient CO₂ leaves. In choice trials, beetles preferred to feed and oviposit on terrestrial plants but were also less likely to damage elevated CO₂ leaves. Caged beetle populations were larger in terrestrial conditions than aquatic conditions for a second set of plants grown in the chambers. With a third set of plants grown in the ambient or elevated CO₂ chambers, damage for plants placed in the field (aquatic setting) was higher for plants grown in terrestrial conditions vs. flooded conditions at ambient CO₂. Our results suggest that elevated CO₂ will have minor effects on the efficacy of this biocontrol agent by decreasing oviposition and number of leaves damaged, and hydrologic environment may affect invasive plant performance by altering herbivore oviposition and feeding preferences. A broader understanding of the effects of global change on biocontrol will help prevent and manage future spread of invasive plants.     

Omnivores as plant bodyguards—A model of the importance of plant quality

The importance of omnivores in ecological systems is increasingly being recognized, not least due to their intensified use as biocontrol agents in crop production. We model a simple plant–herbivore–omnivore (predator) system to explore the effects of plant suitability as food for omnivores on the outcome of omnivore–herbivore interactions. The model predicts that increasing plant suitability relative to herbivore suitability for the omnivore will catalyze the extinction of herbivores or omnivores, depending on the relative growth rate of omnivores feeding solely on plants or herbivores. When omnivore growth is higher on plants, either the omnivore or the herbivore goes extinct. When omnivore growth is higher on herbivores, the possible consequences are extinction, stable coexistence, and limit cycles, depending on the combination of species properties. Our results suggest that plants in some situations may evolve towards becoming more suitable to omnivores to escape detrimental herbivores and that breeders could manipulate crop suitability to omnivore species to reach a desired outcome of omnivore–herbivore interactions.     

Insect herbivory on water mint: you can't get there from here?

Aquatic plants are thought to have fewer herbivore species than their terrestinal counterparts, and possibly to suffer less herbivory I examined herbivory on water mint Mentha aquatica growing in and out of water and tested possible processes determining the observed pattern of leaf damage Plants growing on land had much more herbivore damage than those growing in water The most common herbivore of Mentha at the site (a chrysomelid beetle) showed no p reference for leaves from terrestrial plants over those from aquatic plants Caging aquatic plants to exclude moorhens suggested that these predators were not having a strong effect in removing insect herbivores (though this conclusion is tentative due to low insect numbers) Transplanting aquatic plants to a terrestrial location, while keeping their roots in water, resulted in marked increases in herbivore damage, relative to control aquatic plants The results suggest that the water barrier may prevent effective exploitation of emergent aquatic plants by terrestrial herbivores This may have consequences for observed patterns of herbivore richness on such plants, plant fitness, and a more speculative suggestion, for the mode of reproduction in aquatic plants     

Effects of insect attack to stems on plant survival,growth, reproduction and photosynthesis

Studies of insect herbivory have mostly focused on leaf‐feeding even though most woody plant biomass is stem tissue. Attack to stems has the potential to be more detrimental to plant performance than attack to leaves. Here we asked how severe is the impact of insect stem herbivory on plant performance. We quantify the effect of insect stem herbivory via a meta‐analysis of 119 papers in 100 studies (papers by the same authors were treated as the same study). These studies involved 92 plant species and 70 species of insect herbivore (including simulated herbivory). Attack to plant stems reduced plant performance by an average of approximately 22%. Stem herbivory had greatest impacts on plant and branch survival, which was reduced by 63%. Measures of plant reproduction and vegetative biomass were reduced by 33% and 16% respectively, while measurements of photosynthetic rate were not significantly different between plants with and without stem herbivore attack. Stem herbivory led to a decline in leader performance but an increase in performance of laterals, highlighting the importance of plant compensation. Juvenile plants were more severely affected by stem herbivory than adult plants, and studies conducted in greenhouses found more severe effects than studies conducted in the field. Stem herbivory did not have a significant effects on any of the non‐performance responses measured (defence compounds, SLA, root:shoot, phenology and plant carbon and nitrogen). We compare our results with results from various meta‐analyses considering herbivory on other plant parts. The impact of insect herbivory to stems on plant performance appears at least as severe as insect herbivory to roots and leaves, if not more.