Performance Of Insect Herbivores Research Articles

Effects of simulated winter browsing on mountain birch foliar chemistry and on the performance of insect herbivores

Winter browsing by mammalian herbivores is known to induce a variety of morphological and physiological changes in plants. Browsing has been suggested to decrease the carbohydrate reserves in woody plants, which might lead to reduced tannin production in leaves during the following summer, and consequently, to increased herbivore damage on leaves. We conducted a clipping experiment with mature mountain birch trees and measured the effects of clipping on birch growth, leaf chemistry and toughness, as well as on the performance of insect herbivores. Leaves grew larger and heavier per unit area in the clipped ramets and had a higher content of proteins than leaves in the control trees. Clipping treatment did not affect the total content of sugars in the leaves (mg g−1), suggesting that a moderate level of clipping did not significantly reduce the carbohydrate pools of fully‐grown mountain birch trees. Furthermore, the contents of proanthocyanidins (condensed tannins) and gallotannins were slightly higher in the leaves of clipped ramets, contrary to the hypothesis of reduced tannin production. The effects of clipping treatment on leaf and shoot growth and on foliar chemistry were mainly restricted to the clipped ramets, without spreading to untreated ramets within the same tree individual. The effects of clipping on leaf characters varied during the growing season; for instance, leaf toughness in clipped ramets was higher than toughness in control trees and ramets only when leaves were mature. Accordingly, clipping had inconsistent effects on insect herbivores feeding at different times of the growing season. The generally small impact of clipping on herbivore performance suggests that the low intensity of natural browsing at the study area, simulated by our clipping treatment, does not have strong consequences for the population dynamics of insect herbivores on mountain birch via enhanced population growth caused by browsing‐induced changes in food quality.

Does lignin modification affect feeding preference or growth performance of insect herbivores in transgenic silver birch (Betula pendula Roth)?

Transgenic silver birch (Betula pendula Roth) lines were produced in order to modify lignin biosynthesis. These lines carry COMT (caffeate/5-hydroxyferulate O-methyltransferase) gene from Populus tremuloides driven by constitutive promoter 35S CaMV (cauliflower mosaic virus) or UbB1 (ubiquitin promoter from sunflower). The decreased syringyl/guaiacyl (S/G) ratio was found in stem and leaf lignin of 35S CaMV-PtCOMT transgenic silver birch lines when compared to non-transformed control or UbB1-PtCOMT lines. In controlled feeding experiments the leaves of transgenic birch lines as well as controls were fed to insect herbivores common in boreal environment, i.e., larvae of Aethalura punctulata, Cleora cinctaria and Trichopteryx carpinata (Lepidoptera: Geometridae) as well as the adults of birch leaf-feeding beetles Agelastica alni (Coleoptera: Chrysomelidae) and Phyllobius spp. (Coleoptera: Curculionidae). The feeding preferences of these herbivores differed in some cases among the tested birch lines, but these differences could not be directly associated to lignin modification. They could as well be explained by other characteristics of leaves, either natural or caused by transgene site effects. Growth performance of lepidopteran larvae fed on transgenic or control leaves did not differ significantly.

Elevated atmospheric CO(2) affects the chemical quality of brassica plants and the growth rate of the specialist, Plutella xylostella, but not the generalist, Spodoptera littoralis.

Cabbage, Brassica oleracea subsp. capitata (cv. Lennox and Rinda), and oilseed rape, Brassica rapa subsp. oleifera (cv. Valo and Tuli), plants were grown under ambient CO(2) (360 ppm) or elevated CO(2) (720 ppm) at 23/18 degrees C and under a photoperiod of 22/2 h light (250 micromol m(-)(2) s(-)(1))/dark regime for up to 5 weeks. Afterward, the performance of the crucifer specialist Plutella xylostella (Lepidoptera: Plutellidae) and the generalist Spodoptera littoralis (Lepidoptera: Noctuidae) on those plants was studied. The mean relative growth rate (RGR) of P. xylostella larvae, feeding on both cultivars of oilseed rape or on the Lennox cultivar of cabbage leaves grown at an elevated CO(2) concentration, was significantly reduced as compared to ambient CO(2). A negative larval growth rate at elevated CO(2) was observed for P. xylostella on both oilseed rape cultivars, but the growth rate was reduced but positive on cabbage. Conversely, the RGR of S. littoralis on either plant species was not affected by CO(2) treatment but was lower on cabbage cv. Rinda than on cv. Lennox. The mortality of the larvae was not affected by CO(2) treatment either. At the same time, elevated CO(2) significantly decreased the concentrations of leaf phytochemical constituents in oilseed rape, i.e., total phenolics and total nitrogen, but not in cabbage. The effect of elevated CO(2) on the leaf glucosinolate concentrations of both plant species was marginal. In addition, the observed significant changes in individual glucosinolate concentrations of oilseed rape leaves were not consistent among cultivars. However, our results demonstrate for the first time quite strong effects of CO(2) enrichment on the larval performance of P. xylostella, which is an important pest of Brassica plants around the world. Further studies are still required to increase our understanding of why elevated CO(2) differently affects the performance of specialist and generalist insect herbivores on Brassica plants.

Damage‐induced changes in woody plants and their effects on insect herbivore performance: a meta‐analysis

We conducted a meta‐analysis of 68 studies published between 1982 and 2000 in which the responses of woody plants to natural or simulated herbivore damage and/or insect herbivore performance on control and damaged plants were measured. Cumulative meta‐analyses revealed dramatic temporal changes in the magnitude and direction of the plant and herbivore responses reported during the last two decades. Studies conducted in the 1980s reported increase in phenolic concentrations, reduction in nutrient concentrations and negative effect on herbivore performance, consistently with the idea of induced resistance. In contrast, in the early 1990s when the idea that some types of plant damage may result in induced susceptibility was generally accepted, studies reported non‐significant results or induced susceptibility, and smaller effects on herbivores. The above changes may reflect paradigm shifts in the theory of induced defenses and/or the differences between study systems used in the early and the more recent studies. Overall, plant growth and carbohydrate concentrations were reduced in damaged plants despite enhanced photosynthetic rates. Damage increased the concentrations of carbon and phenolics, while terpene concentrations tended to decrease after damage; changes in nutrient concentrations after damage varied according to nutrient mobility, inherent plant growth rate, ontogenetic stage and plant type (deciduous/evergreen). Early season damage caused more pronounced changes in plants than late season damage, which is in accordance with the assumption that vigorously growing foliage has a greater capacity to respond to damage. Insect growth rate and female pupal weight decreased on previously damaged plants, while herbivore survival, consumption and male pupal weight were not significantly affected. The magnitude and direction of herbivore responses depended on the type of plant, the type of damage, the time interval between the damage and insect feeding (rapid/delayed induced resistance), and the timing of the damage.

Cascading effects of variation in plant vigour on the relative performance of insect herbivores and their parasitoids

Abstract1. Consequences of variation in food plant quality were estimated for a system consisting of two monophagous noctuid herbivores and three ichneumonid parasitoids.2. In a natural population, pupal weights of the herbivores in this system,Nonagria typhaeandArchanara sparganii, were found to be highly variable. Pupal weights increased strongly and consistently with the increase in the vigour of the host plant,Typha latifolia, providing support for the plant vigour hypothesis. Correspondingly, as the moths do not feed as adults, a strong, positive correlation between host vigour and fecundity of the herbivores would be expected.3. There were strong and positive relationships between adult body sizes of the parasitoids and the sizes of their lepidopteran hosts. Moreover, a direct, positive link between plant quality and parasitoid size was documented.4. For all three parasitoids, cascading effects of plant quality on body size were weaker than for the herbivores. Differences in the importance of adult feeding and oviposition behaviour suggest that dependence of fitness on body size is also weaker in the parasitoids than in the moths. It is therefore concluded that the numerical response of the herbivore population to a change in plant quality should exceed the corresponding response in the parasitoids.5. The results of this work imply that variation in plant variables may affect performance of different trophic levels to a different extent. It is suggested that the importance of adult feeding for the reproductive success (capital vs. income breeding strategies) in both herbivores and parasitoids is an essential aspect to consider when predicting responses of such a system to changes in plant quality.

Co2and O3Effects on Paper Birch (Betulaceae:Betula papyrifera) Phytochemistry and Whitemarked Tussock Moth (Lymantriidae:Orgyia leucostigma) Performance

Elevated atmospheric concentrations of CO2 and O3 are known to alter the chemical composition of foliage, which in turn may affect the performance of herbivorous insects. We investigated the independent and interactive effects of CO2 and O3 on foliar quality of paper birch (Betula papyrifera Marshall) and the consequences of chemical changes for performance of the whitemarked tussock moth Orgyia leucostigma (J. E. Smith). The experimental design wa sa2b y 2 factorial, with ambient and elevated levels of CO2 and O3, respectively. Foliage was analyzed for concentrations of nitrogen, starch, and condensed tannins. CO2 and O3 independently and inter- actively affected nitrogen concentrations, with the elevated CO2 O3 treatment reducing nitrogen concentrations more than either treatment alone. Elevated CO2 and O3 had no signiÞcant effect on starch and tannin concentrations when administered alone but increased starch concentrations by 17% over ambient when administered together. Larvae were reared on experimental trees from egg hatch through pupation to determine treatment effects on development time and pupal mass. Larval performance measures were not statistically different among fumigation treatments, although fe- males tended to have reduced pupal mass under the elevated CO2 O3 treatment. These results demonstrate that chemical responses of some plant species to elevated levels of CO2 (560 lL 1 ) and O3 (1.5 ambient) may be of insufÞcient magnitude to signiÞcantly alter standard measures of individual insect performance.

Relationships between sulfonylurea herbicide treatment of host plants and the performance of herbivorous insects.

Previous work had shown that the sulfonylurea herbicide chlorsulfuron affected the survival of a herbivorous insect species dwelling on a sub-lethally exposed host plant. Further experiments have been conducted to establish whether this negative effect was a single occurrence characteristics for the specific insect-plant interaction and the specific herbicide tested. Three insect-plant interactions were tested for the effects of selected sulfonylurea herbicides, i.e. metsulfuron-methyl, chlorsulfuron and tribenuron-methyl. The species pairs tested were Pieris brassicae/Brassica napus, Gastrophysa polygoni/Fallopia convolvulus and Sitobium avenae/Triticum aestivium. No significant effects on survival and relative growth rate of P brassicae or G polygoni were found when treating the host plants with sulfonylurea herbicides. However, the host plants had a significantly reduced root and shoot growth rate when treated with herbicide. Treating T aestivium with the recommended field rate of metasulfuron-methyl did not cause any change in development time, growth rate or fecundity of S avenae feeding on the host plants. The data presented suggest that the increased mortality observed for G polygoni larvae feeding on chlorsulfuron-treated host plants observed earlier was characteristic for this herbicide and for the specific plant-insect interaction only.

Response of the copper butterfly Lycaena tityrus to increased leaf nitrogen in natural food plants: evidence against the nitrogen limitation hypothesis.

This study examined the effects of increased leaf N in natural food plants on oviposition, preimaginal survival, growth, and adult size of the butterfly Lycaena tityrus. Female butterflies did not discriminate between leaves of high and low N content. In accordance with previous studies, we found higher growth rates and concomitantly decreased development times at a high N level. However, because of high pupal (and larval) mortality (overall 73.0%) as well as a reduction in adult size (by ca. 8%) this was, overall, not beneficial to the butterflies. Thus, our results were not consistent with the broad interspecific trend that insect herbivore performance is positively correlated with leaf N. These findings undermine the general applicability of the N limitation hypothesis. As the detrimental effects were largely confined to the pupal and adult stages, results obtained from the larval phase only may not yield reliable results and must therefore be interpreted with caution. If negative effects of N enrichment are found more frequently in declining species inhabiting nutrient poor grassland, this will have major implications for the conservation of these species.

Choice, performance and heritability of performance of specialist and generalist insect herbivores towards cacalol and seneciphylline, two allelochemicals of Adenostyles alpina (Asteraceae)

Abstract We compared the effects of a sesquiterpene (ST, cacalol) and a pyrrolizidine alkaloid (PA, seneciphylline), both occurring in Adenostyles alliariae, on food choice and performance of specialist and generalist insect herbivores which are all known to feed or live on A. alliariae. In choice experiments we investigated whether the compounds were preferred, deterrent or had no effect. All specialist species Aglaostigma discolor (Hymenoptera, Tenthredinidae), Oreina cacaliae (Coleoptera, Chrysomelidae) and O. speciosissima avoided feeding when confronted with the combination of compounds. Only larvae of A. discolor avoided the single ST treatment as well. Larvae of the generalist species Callimorpha dominula (Lepidoptera, Arctiidae), Cylindrotoma distinctissima (Diptera, Tipulidae) and Miramella alpina (Caelifera, Acrididae) generally avoided feeding from PA, ST and PAST treatments. The only exception were caterpillars of C. dominula which were indiscriminate towards PA when naive, and preferred to feed on the PA treatment when they had experienced the compound before. Performance, measured as the growth of larvae on the different treatments in a no choice situation over a period of 10–17 days, was not different between treatments in the specialist leaf beetles O. cacaliae and O. speciosissima. Their avoidance of the combination treatment in the choice experiments had no obvious effect on growth when forced to feed from the treatment. In the generalist C. dominula only the high concentration combination treatment (PAST) reduced growth of the larvae due to decreased consumption. In C. distinctissima we found reduced growth in all treatments except one (PA3%). Poor growth performance in C. distinctissima was due to postingestive physiological effects of all treatments and additionally to consumption reduction in high-dose ST treatments. Genetic variability (broad sense heritability) of growth performance metabolism varied in accordance with the specialization degree of the species. O. cacaliae, the most specialized species, had no significant heritability; O. speciosissima, the less specialized specialist, had a heritability of 0.46; C. dominula, the PA adapted generalist species, had a heritability of 0.64; C. distinctissima, the generalist with no apparent adaptations, had a heritability of 0.84.

Phytochemical Changes during Recurrent Selection for Resistance to the European Corn Borer

Feeding performance of herbivorous insects is influenced by host plant nutritional quality which can be improved for insect resistance by artificial selection. This study was conducted to determine which biochemical constituents in maize (Zea mays L.) change during recurrent selection for resistance to first‐ and second‐generation European corn borer (ECB) [Ostrinia nubilalis (Hübner)]. Four cycles of selection (C0, C2, C4, and C5) from the BS9 population were field grown, artificially and naturally infested with ECB, and the following tissues sampled for biochemical analysis: immature and mature leaf blade, leaf sheath, rind, node, and pith. Tissue was analyzed for percent protein, DIMBOA [2,4‐dihydroxy‐7‐methoxy 2H‐l,4‐benzoxazin‐3 (4H)‐one], fiber, and cell wall‐bound phenolics, which included p‐coumaric acid (pCA), ferulic acid (FA), cyclobutane dimers (CBD), and diferulic acid (DFA). Leaf and stalk toughness were also determined and showed significant increases over cycles of selection. Protein content was lowest in stalk tissues with advanced cycles having lower levels, but leaf protein content did not differ significantly. DFA reached high levels in the rind (0.85 mg/g) and leaf sheath (1.35 mg/g) tissues, and increased significantly in immature leaf tissue (0.55–1.02 mg/g) over cycles of selection and may serve to fortify tender whorl tissue. Number of tunnels per stalk was negatively correlated with DFA content in the pith (r = − 77, P = 0.02). Microspectrophotometer determinations of epidermal cell wall absorbance for leaf blade and rind tissue showed increased absorbances (23 and 27%, respectively) in the spectral region characteristic of phenolic acids over cycles of selection. Phenolic acids, in particular DFA, have increased over cycles of selection to render maize tissue more resistant through fortification of cell walls, especially in leaf and rind epidermal tissue.

Interactions between arbuscular mycorrhizal fungi and foliar-feeding insects in Plantago lanceolata L.

A field experiment was conducted to investigate whether infection by arbuscular mycorrhizal (AM) fungi has any effect on herbivory by foliar-feeding insects. Plants of PI ant ago laureolata L. were grown in a randomized block design and natural levels of mycorrhizal infection reduced by the application of the granular fungicide iprodione. Plant growth responses were examined and herbivore bioassays performed by rearing both a chewing and sucking insect on the leaves of mycorrhizal and fungicide-treated plants. Fungicide application successfully reduced mycorrhizal infection, and this led to reductions in foliar biomass, caused by lower leaf number. However, fungicide-treated plants suffered consistently higher levels of damage by centralist chewing and leaf-mining insects, which colonized the plants. The chewing insect bioassay confirmed the field results, in that larvae of Arttia caja L. (Lepidoptera: Arctiidae) consumed more leaf material from plants in which infection was reduced. There was no evidence that AM fungi altered food quality for the chewing insect. Instead, infection caused an increase in the carbon/nutrient balance, which in turn led to increased levels of the carbon-based feeding deterrents, aucubin and catalpol, The sucking insect, Mvzus perskae (Sulzer) reacted in an opposite fashion to the ehewtr. with performance being greater on mycorrhizal plants. Again, there was no evidence that an alteration in food Quality was the cause, and in this case infection may result in changes in leaf morphology which benefit the insect. We suggest that under conditions of high light and low nutrient availability. AM infection can alter the carbon/nutrient balance of plants, leading to an increased allocation to carbon-based defences. This can have important consequences for insect herbivore performance and the patterns of herbivory in field situations.

Interactive effects of rutin and constant versus alternating temperatures on performance of Manduca sexta caterpillars

AbstractThe effects of different concentrations of rutin and constant temperature (20 °C) versus alternating temperatures (23:15 °C) on growth, molting and food utilization efficiencies of third instar tobacco hornworms (Manduca sexta) were determined. Relative consumption rate (RCR) and relative growth rate (RGR) were significantly higher for larvae at the alternating thermal regime compared to those at the constant (representing the average) temperature. With increasing concentrations of rutin, the negative effect of rutin on RCR and RGR increased for the larvae in the alternating thermal regime; however, at the constant temperature, rutin had little effect. The alternating thermal regime promoted synchrony in the timing of spiracle apolysis (the earliest morphological marker of molt). Rutin disrupted that synchrony. I discuss how patterns of host plant resistance may be altered with a decrease in amplitude of diurnal temperatures (as has been documented recently for temperate regions) through the uncoupling of herbivore performance and allelochemical concentration. I conclude that simultaneous consideration of fluctuating temperatures and allelochemicals is advisable when assessing the effects of temperature and allelochemicals on performance of insect herbivores because interactive effects between temperature and dietary components occur and perhaps are common.

Performance of Insect Herbivores on Hybridizing Trees: The Case of the Subarctic Birches

The consequences of hybridization between two related birch species, the mountain and the dwarf birch (Betula pubescens ssp. tortuosa and B. nana), on the performance of insect herbivores were studied in Finnish Lapland. Leaf quality of both arboretum-grown birches and birches of a natural stand was bioassayed with 14 insect species (one geometrid lepidopteran, one argid, one cimbicid, and 11 tenthredinid sawflies). All the herbivore species belonged to the local birch leaf-chewer guild. There were considerable differences among the herbivore species in the relative suitability of the two parent birch species. Larvae of different species grew equally well on the pure mountain birches and on the hybrids, irrespective of the mother tree

Responses of Diciduous Trees to Elevated Atmospheric CO2: Productivity, Phytochemistry, and Insect Performance

Although rising levels of atmospheric carbon dioxide are expected to directly affect forest ecosystems, little is known of how specific ecological interactions will be modified. This research evaluated the effects of enriched CO2 on the productivity and phytochemistry of forest trees and performance of associated insects. Our experimental system consisted of three tree species (quaking aspen [Populus tremuloides], red oak [Quercus rubra], sugar maple [Acer saccharum]) that span a range from fast to slow growing, and two species of leaf—feeding insects (gypsy moth [Lymantria dispar] and forest tent caterpillar [Malacosoma disstria]). Carbon—nutrient balance theory provided a framework for tests of three hypotheses; in response to enriched CO2: (1) relative increases in tree growth rates will be greatest for aspen and least for maple, (2) relative decreases in protein and increases in carbon—based compounds will be greatest for aspen and least for maple, and (3) relative reductions in performance will be greatest for insects fed aspen and least for insects fed maple. We grew 1—yr—old seedlings for 60 d under ambient (385 ± 5 μL/L) or elevated (642 ± 2 μL/L) CO2 regimes at the University of Wisconsin Biotron. After 50 d, we conducted feeding trials with penultimate—instar gypsy moth and forest tent caterpillars. After 60 d, a second set of trees was harvested and partitioned into root, stem, and leaf tissues. We subsequently analyzed leaf material for a variety of compounds known to affect performance of insect herbivores. In terms of actual dry—matter production, aspen responded the most to enriched CO2 atmopheres whereas maple responded the least. Proportional growth increases (relative to ambient plants), however were highest for oak and lest for maple. Effects of elevated CO2 on biomass allocation patterns differed among the three species; root—to—shoot ratios increased in aspen, decreased in oak, and did not change in maple. Enriched CO2 altered concentrations of primary and secondary metabolites in leaves, but the magnitude and direction of effects were species—specific. Aspen showed the largest change in storage carbon compounds (starch), whereas maple experienced the largest change in defensive carbon compounds (condensed and hydrolyzable tannins). Consumption rates of insects fed high—CO2 aspen increased dramatically, but growth rates declined. The two species of insects differed in response to oak and maple grown under enriched CO2. Gypsy moths grew better on high—CO2 oak, whereas forest tent caterpillars were unaffected; tent caterpillars tended to grow less on high—CO2 maple, whereas gypsy moths were unaffected. Changes in insect performance parameters were related to changes in foliar chemistry. Responses of plants and insects agreed with some, but not all, of the predictions of carbon—nutrient balance theory. This study illustrates that tree productivity and chemistry, and the performance of associated insects, will change under CO2 atmospheres predicted for the next century. Changes in higher level ecological processes, such as community structure and nutrient cycling, are also implicated.

Response of Western Spruce Budworm (Lepidoptera: Tortricidae) to Increased Nitrogen in Artificial Diets

The western spruce budworm, Choristoneura occidentalis Freeman, was used to test the hypothesis that insect herbivore performance is dependent on dietary nitrogen in a positively linear or convex manner. Artificial diets with seven levels of N were tested both with or without mineral supplements to determine if minerals had important effects on the budworm's response to N. A three-generation bioassay quantified survival rates for all life stages and pupal weights for insects reared on diets with 1.2–7.6% N dry mass. Data were used to estimate population growth over three generations by determining the number of F1 F2, and F3 offspring produced (i.e., fitness). The budworm's response to increased dietary N was neither positively linear nor convex. Larvae reared on diets with very high (3.9 and 7.6%) concentrations of N, compared with N levels in Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, foliage, had good survival and reproduction, whereas larvae on diets with N levels near foliage quantities (1.2–3.0%) had very poor performance, with the exception that performance was good on the mineral-limited 1.2% N diet. The addition of minerals to the diets had important effects on responses to N, implicating an interaction between N and minerals. Regression analysis of data on estimated population growth on the 14 diets tested indicated that the ratio of Zn to N was the best predictor of budworm fitness, not the actual N content of the diet. The response to Zn/N ratios was concave, implying proportions ≤0.00085 or ≥0.00282 had positive effects on fitness, whereas ratios from 0.001 to 0.0025 had negative effects. It was hypothesized that host plant N determines the amount of food ingested, which in tum affects the amounts of other nutrients consumed. Thus, a proper balance of many different nutrients appears to be the most important factor in the nutritional ecology of insect herbivores.

The Effects of Leaf Damage on the Performance of Insect Herbivores on Birch, Betula pubescens

The Effects of Leaf Damage on the Performance of Insect Herbivores on Birch, Betula pubescens