Differences In Plant Quality Research Articles

Alfalfa (Medicago sativa L.) quality is improved from tractor traffic implemented during harvest

Studies documenting the consequences of harvest traffic in alfalfa production have addressed soil and plant growth parameters. One response was larger leaf/stem ratios in plants that were trafficked, which suggests higher quality. To fully understand how harvest traffic affects alfalfa quality a need for further analysis is warranted. Our objectives were to quantify differences in plant quality between trafficked and non-trafficked plants through 4 years of alfalfa production and to determine when these differences occur. The experimental units were furrow-irrigated raised beds with four harvests per year in Youngston clay loam soil in Fruita, Colorado. A John Deere 2280 swather and a John Deere 2955 tractor, driven over the alfalfa 7 days after swathing, were used to create four traffic treatments; plants that were never trafficked, plants trafficked only by the swather, plants trafficked only by the tractor, and plants trafficked by both the swather and the tractor. Quality was determined by measuring relative feed value, acid detergent fiber, neutral detergent fiber, and crude protein using near infrared reflectance spectroscopy. Alfalfa trafficked by the tractor had increased quality throughout the 4 years of production.

Effects of plant-mediated differences in host quality on the development of two related endoparasitoids with different host-utilization strategies

Among parasitoids that develop inside the bodies of feeding, growing hosts (so-called ‘koinobiont’ endoparasitoids), two strategies have evolved to dispose of host resources. The larvae of one group consumes most host tissues before pupation, whereas in the other the parasitoid larvae consume only host hemolymph and fat body and at maturity emerge through the host cuticle to pupate externally. Here we compared development and survival (to adult emergence) of two related larval endoparasitoids (Braconidae: Microgastrinae) of the diamondback moth, Plutella xylostella. Larvae of Dolichogenidea sicaria are tissue feeders whereas larvae of Cotesia vestalis are hemolymph feeders. Here, development of P. xylostella and the two parasitoids was compared on three populations (one cultivar [Cyrus], two wild, [Winspit and Kimmeridge]) of cabbage that have been shown to vary in direct defense and hence quality. Survival of P. xylostella and C. vestalis (to adult eclosion) did not vary with cabbage population, but did so in D. sicaria, where survival was lower when reared on the wild populations than on the cultivar. Furthermore, adult herbivore mass was significantly higher and development was significantly shorter in moths reared on the cultivar. The tissue-feeing D. sicaria was larger but took longer to develop than the hemolymph-feeder C. vestalis. The performance of both parasitoids was better on the cabbage cultivar than on the wild populations, although the effects were less apparent than in the host. Our results show that (1) differences in plant quality are diffused up the food chain, and (2) the effects of host quality are reflected on the development of both parasitoids.

Effects of intraspecific and intra-individual differences in plant quality on preference and performance of monophagous aphid species.

Plant chemistry is one of the main drivers of herbivore distribution. Monophagous herbivore species are highly specialized, but even within their only host species the chemistry varies. The herbivore's choice is initially mainly guided by volatile plant compounds. Once on the plant, particularly for aphids the phloem quality affects their performance. However, little is known about the intraspecific and intra-individual variation in phloem sap and their influences on monophagous aphids. To determine potential mechanisms involved in aphid colonization, we tested the effects of intraspecific chemical variation in Tanacetum vulgare, which produces different chemotypes, on the preference of two monophagous aphid species. Moreover, we measured the performance of the aphids on different plant parts (stem close to the inflorescence, young and old leaves) of these chemotypes and analyzed their phloem sap composition. Both species preferred the β-thujone (THU) over the trans-carvyl acetate (CAR) chemotype in dual-choice assays. Survival of Macrosiphoniella tanacetaria was neither affected by intraspecific nor intra-individual variation, whereas the reproduction was highest on stems. In contrast, Uroleucon tanaceti survived and reproduced best on old leaves of the preferred chemotype. The sugar, organic acid and amino acid composition pronouncedly differed between phloem exudates of different plant parts, but less between chemotypes. Unexpectedly, high concentrations of amino acids did not necessarily enhance aphid performance. These different performance optima may cause niche differentiation and, therefore, enable co-existence. In conclusion, the tremendous variation in plant chemistry even within one species can affect the distribution of highly specialized aphids at various scales aphid species-specifically.

Effects of population-related variation in plant primary and secondary metabolites on aboveground and belowground multitrophic interactions.

Insects feeding on aboveground and belowground tissues can influence each other through their shared plant and this is often mediated by changes in plant chemistry. We examined the effects of belowground root fly (Delia radicum) herbivory on the performance of an aboveground herbivore (Plutella xylostella) and its endoparasitoid wasp (Cotesia vestalis). Insects were reared on three populations of wild cabbage (Brassica oleracea) plants, exhibiting qualitative and quantitative differences in root and shoot defense chemistry, that had or had not been exposed to root herbivory. In addition, we measured primary (amino acids and sugars) and secondary [glucosinolate (GS)] chemistry in plants exposed to the various plant population-treatment combinations to determine to what extent plant chemistry could explain variation in insect performance variables using multivariate statistics. In general, insect performance was more strongly affected by plant population than by herbivory in the opposite compartment, suggesting that population-related differences in plant quality are larger than those induced by herbivory. Sugar profiles were similar in the three populations and concentrations only changed in damaged tissues. In addition to population-related differences, amino acid concentrations primarily changed locally in response to herbivory. Whether GS concentrations changed in response to herbivory (indole GS) or whether there were only population-related differences (aliphatic GS) depended on GS class. Poor correlations between performance and chemical attributes made biological interpretation of these results difficult. Moreover, trade-offs between life history traits suggest that factors other than food nutritional quality contribute to the expression of life history traits.

Drought stress and leaf herbivory affect root terpenoid concentrations and growth of Tanacetum vulgare.

Plant responses of both shoots and roots to combined abiotic and biotic stress have been rarely investigated. However, stresses such as drought and aboveground herbivory might lead to conflicting resource allocation patterns and pronounced shifts in shoot vs. root defenses. In the present study, the effects of water availability and leaf herbivory by caterpillars of a generalist on various shoot and root traits of the aromatic plant Tanacetum vulgare L. were investigated. This species contains terpenoids in leaves and roots, which can differ in composition among individuals, forming so-called chemotypes. To test for intraspecific variation, responses were investigated in two chemotypes, the thujone and the carvyl acetate chemotype. Furthermore, effects of differences in plant quality on the herbivores were studied. Shoot biomass significantly decreased due to drought and herbivory, whereas the root/shoot ratio increased following drought but was unaffected by herbivory. No shifts in C/N ratios were found. In contrast to our expectation, leaf terpenoid concentrations decreased only slightly due to drought, whereas root terpenoids were significantly induced by both drought and herbivory. Chemotypes showed distinct responses to drought at least in the root/shoot ratio, with a higher drought sensitivity of the carvyl acetate chemotype. The body mass of the caterpillars was unaffected by the irrigation treatment but depended on chemotype and terpenoid concentration of the plants. Thus, both qualitative and quantitative defenses strongly affect herbivore development. The present results offer new insights into the above- and belowground organ-specific responses of plants. They highlight the importance of roots in response to various environmental challenges.

Preference and Performance in Plant–Herbivore Interactions across Latitude–A Study in U.S. Atlantic Salt Marshes

High-latitude plants are often more palatable to herbivores than low-latitude conspecifics. Does increased plant palatability lead to better herbivore performance? Our field and laboratory work investigated (A) whether high-latitude plants have traits indicating that they should be higher-quality foods for herbivores; (B) whether geographic differences in plant quality are more important than local adaptation of herbivores. We studied 3 plant species and 6 invertebrate herbivores in U.S. Atlantic Coast. Past studies had shown high-latitude individuals of these plants are more palatable than low-latitude conspecifics. We documented plant traits and herbivore performance (body size) in the field across latitude. We collected individuals from different latitudes for factorial (plant region x herbivore region) laboratory experiments, examining how herbivore performance was affected by plant region, herbivore region, and their interaction (i.e., local adaptation). Field surveys suggested high-latitude plants were likely of higher quality to herbivores. Leaf nitrogen content in all plant species increased toward high latitudes, consistent with lower leaf C/N and higher leaf chlorophyll content at high latitudes. Furthermore, leaf toughness decreased toward higher latitudes in 1 species. The body size of 4 herbivore species increased with latitude, consistent with high-latitude leaves being of higher quality, while 2 grasshopper species showed the opposite pattern, likely due to life-history constraints. In the laboratory, high-latitude plants supported better performance in 4 herbivore species (marginal in the 5th). The geographic region where herbivores were collected affected herbivore performance in all 6 species; however, the pattern was mixed, indicating a lack of local adaptation by herbivores to plants from their own geographic region. Our results suggest that more-palatable plants at high latitudes support better herbivore growth. Given that geographic origin of either plants or herbivores can affect herbivore performance, the nature of plant-herbivore interactions is likely to change if climate change “reshuffles” plant and herbivore populations across latitude.

Development of Mamestra brassicae and its solitary endoparasitoid Microplitis mediator on two populations of the invasive weed Bunias orientalis

AbstractThe warty cabbage Bunias orientalis is an invasive pest in much of central Europe, including much of Germany since the 1980s, whereas in other countries, such as The Netherlands, it is a less common exotic species. Here, healthy larvae of Mamestra brassicae, which has been found feeding on B. orientalis plants in Germany, and larvae parasitized by one of its major larval endoparasitoids Microplitis mediator, were reared on both herbivore‐induced and noninduced leaves of B. orientalis originating from single large populations growing in The Netherlands and central Germany. Herbivore performance was less negatively affected than parasitoid performance by differences in plant quality. Development times in both M. brassicae and Mi. mediator were shorter on Dutch than German plants and also shorter on noninduced than induced plants. Moreover, survival and body size of the parasitoid was more strongly affected by plant population and induction than survival of healthy M. brassicae. Chemical analyses of defensive secondary metabolites [glucosinolates (GS)] revealed that concentrations of the major GS sinalbin were constitutively expressed in German plants whereas they were induced in Dutch plants. However, in separate feeding bioassays in which preference for induced and noninduced leaves was compared separately, L3 instars of M. brassicae preferred noninduced German plants over Dutch plants but induced Dutch plants over German plants, revealing that changes in primary metabolites or an unidentified non‐GS compound mediates population‐related differences in plant quality. The results reveal asymmetric effects of plant quality in exotic plants on organisms in the second and third trophic level.

Intraspecific plant chemical diversity and its relation to herbivory

Several aromatic plant species are well known for their high intraspecific variation in terpene composition. Within these species, different chemotypes can be distinguished, which are characterised by one major metabolite and distinct satellite compounds in lower abundance. Such intraspecific differences in plant quality should have major effects on herbivorous insects but may also be partly shaped by their feeding activities. In the present study, the effects of selected Tanacetum vulgare L. chemotypes on herbivore presence and preferences were investigated, and the naturally occurring diversity of T. vulgare was explored at a small spatial scale. A distinct distribution pattern of aphids and miners was found on different chemotypes of different origin of T. vulgare, with species-specific preferences of different herbivorous species. Larvae of two generalist noctuid species performed worse on most chemotypes of T. vulgare than on other plant species. Furthermore, the specific terpene composition of T. vulgare influenced larval development of these two generalist species. The naturally occurring chemical diversity of T. vulgare plants in an area smaller than 3 km(2) was extremely high, exhibiting 14 different chemotypes. Several individual patches of T. vulgare consisted of more than one chemotype. In conclusion, the existing chemotypical pattern of T. vulgare plants leads to a species-specific distribution of herbivores but may in turn be the result of contrasting selection pressures of various specialist and generalist herbivores.

Manejo da cobertura de ambientes protegidos: radiação solar e seus efeitos na produção da gérbera

Este trabalho propôs avaliar a influência das malhas de sombreamento (termorrefletora) instaladas externa e internamente em ambiente protegido coberto com polietileno de baixa densidade (PEBD), cultivado com gérbera, na radiação solar global (Qg) e nos parâmetros da planta: crescimento, desenvolvimento e qualidade da gérbera. O experimento foi conduzido em dois ciclos no ano de 2004, na ESALQ/USP, em Piracicaba, SP, em ambiente protegido, dividido em dois módulos de produção. Os ambientes foram diferenciados um do outro pela instalação da malha termorrefletora (50%): malha externa (ambiente 1 - A1) e malha interna (ambiente 2 - A2). Nesses ambientes, os resultados dos dois ciclos mostraram alteração na Qg; nos ambientes A1 e A2 as Qg foram respectivamente 33,6 e 21,7 (1º ciclo) e 27,2 e 17,9% (2º ciclo) em relação à observada externamente. Considerando-se os dois ciclos conclui-se que os resultados indicaram que não houve diferenças na qualidade das plantas nos dois ambientes, mas, analisando-se separadamente os dois ciclos da cultura, o A1 (malha externa) foi o que mais favoreceu a qualidade das plantas de gérbera e somente as gérberas presentes no A1 (malha externa) atenderam às exigências mercadológicas, quanto aos números de botões florais.

Spatial, bottom‐up, and top‐down effects on the abundance of a leaf miner

Many plant and animal species have higher densities at the centre of their distribution, with a gradual decline in abundance towards the edge of the range, though reasons for this pattern is not well known. We examined the abundance of the leaf miner Cameraria sp. nova over the range of its host plant Quercus myrtifolia in Florida and addressed how bottom‐up and top‐down factors varied over its whole distribution. Leaf miner densities, plant quality and natural enemy effects on mine survivorship were evaluated in 40 sites and spatially structured models were used to determine the effects of spatial location on the abundance of Cameraria and effects of both bottom‐up (tannin concentration, foliar nitrogen, soil nitrogen, and leaf area) and top‐down factors (larval parasitism and predation) on abundance and survivorship. Cameraria mines were, on average, three times more abundant on edge/coastal sites compared to centre/inland sites and did not support the hypothesis of higher abundance on the centre of the distribution. Differences in plant quality, larval parasitism and successful emergence of mines on edge versus central sites might be partially responsible for this finding. A trend surface equation with latitude and longitude combined explained almost 52% of the variation in Cameraria density and a trend surface map also revealed peaks of Cameraria abundance on the edges of the plant distribution. Correlograms also indicated a significant spatial structure of Cameraria as mines were positively spatially autocorrelated at small distances (≈122 km). Partial regression analyses indicated that 69% of the variation in Cameraria abundance was explained by the effects of latitude, longitude, elevation and percentage of foliar nitrogen. Our results indicated that variation in Cameraria abundance was mostly explained by spatial position and significant effects of bottom‐up and top‐down factors were not detected in our large‐scale study.

Are population differences in plant quality reflected in the preference and performance of two endoparasitoid wasps?

In recent years, increasing attention has been paid in exploring the role of direct plant defence, through the production of allelochemicals, on the performance of parasitoid wasps and their hosts. However, few studies have determined if parasitoids can detect differences in plant quality and thus preferentially attack hosts on which their progeny develop most successfully. In this study we examined the development and preference of two endoparasitoids, Diadegmasemiclausum and Cotesia glomerata, developing in larvae of their respective hosts, Plutella xylostella and Pieris brassicae. In turn, these were reared on different wild populations of black mustard Brassica nigra originating in the Netherlands and Sicily (Italy), as well as single cultivated strains of B. nigra and brown mustard, B. juncea. Chemical analyses of foliar glucosinolates and volatile emissions by P. xylostella‐damaged plants revealed large differences between B. nigra and B. juncea plants, with smaller differences among the B. nigra populations. The four mustard populations differentially affected development time and body mass of the herbivores and parasitoids. Contrasts among the means revealed significant differences mainly between B. nigra and B. juncea. Both parasitoids, however, preferred to alight on plants in which their progeny developed most successfully. In behavioural bioassays, D. semiclausum did not discriminate among the B. nigra populations and preferred to alight on B. juncea, which was the best plant population for parasitoid development. By contrast, C. glomerata females exhibited the lowest preference for Italian B. nigra populations, on which adult parasitoid size was the smallest. These results reveal that parasitoids can detect even small differences in plant quality presumably through their volatile blends and that plant preference and offspring performance in the two species are ‘optimally synchronized’.

Coastal dunes as important strongholds for the survival of the rare Niobe fritillary (Argynnis niobe)

We studied the oviposition and larval habitat preferences of the Niobe fritillary (Argynnis niobe) in the dunes of the east Frisian Island Langeoog (German North Sea). By ascertaining habitat quality we are able to assess the minimum habitat size for populations of A. niobe in dune islands. The preferred oviposition and larval habitats were best characterised by a combination of (1) host-plant abundance, (2) host-plant quality and (3) vegetation structure. The oviposition and larval habitats of A. niobe were characterised by low-growing vegetation with bare ground and a warm microclimate. In contrast to the also common V. tricolor ssp. curtisii, the leaves of the host plant V. canina showed a lower C/N ratio, suggesting that differences in plant quality may account for host-plant use. A. niobe seems to depend on very large areas of potential larval habitat, thus explaining its ongoing decline in the increasingly fragmented Central European landscape. Our data indicate that grass encroachment is a major threat for A. niobe in coastal dunes due to its negative impact on microclimate and violet germination. Mosaic top-soil removal and low-intensity grazing should be suitable tools to promote rejuvenation of V. canina.

Fertilizer Concentration Affects Growth and Foliar Elemental Concentration of Strobilanthes dyerianus

Grown as an annual in most of the United States, Strobilanthes dyerianus Mast. has become increasingly popular in summer landscapes partially due to its superior performance in hot and humid conditions. At present, there is no published research on the nutritional requirements of S. dyerianus. Our study examined growth and foliar elemental response to different levels of fertilizer. Rooted cuttings were transplanted and grown with 0, 100, 200, 300, and 400 mg·L–1 N from 5N–2.2 P–12.4 K fertilizer as constant liquid feed. Plants were irrigated whenever the volumetric water content of the substrate was <20% as determined with a Theta Probe moisture meter. Weekly pH and electrical conductivity (EC) were monitored using the pour through method. Eight weeks after initiation of treatment, dry weight and leaf area was measured. Recently mature leaf tissue was analyzed for total N, P, K, Ca, Mg, S, Fe, Mn, B, Cu, Zn, and Mo. There were no significant differences in plant quality under the 100, 200, 300, or 400 mg·L–1 N treatments. The largest plants, based on leaf area and shoot dry weight, were produced with 200 mg·L–1 N. Compared to recommended EC levels for bedding plants, the treatments receiving 300 and 400 mg·L–1 N had excessively high levels of substrate soluble salts though overall plant quality was not reduced. The increase in fertilizer concentration yielded a linear increase in tissue concentration of N, P, and K and a linear decrease in tissue concentration of Ca and Mg.

The relative feeding value of a new pasture legume, eastern star clover (Trifolium dasyurum), compared with subterranean clover (Trifolium subterraneum)

An accession of eastern star clover (Trifolium dasyurum C. Presl.), a new species to agriculture, has been identified by the National Annual Pasture Legume Improvement Program for commercial release in Australia. This paper reports the findings of an experiment designed to assess the feeding value of eastern star clover compared with a commercial cultivar of subterranean clover (T. subterraneum L. cv. Dalkeith). The hypothesis tested in this experiment is that sheep grazing eastern star clover will have similar growth rates, condition scores, and wool production to sheep grazing subterranean clover. Additionally, it is hypothesised that the sheep grazing the different clover species will have similar health and meat quality. The relative feeding value of the 2 clover species was tested using 14-month-old Merino wethers, grazing 8 by 0.5 ha plots (4 of each species). Stocking rates were such that herbage mass availability would not have limited feed intake. Liveweight, wool growth, and animal health were monitored. After 10 weeks of grazing, 2 animals from each plot were slaughtered for sensory analysis of meat. Although there were generally no differences in liveweight change, condition, or wool growth between sheep grazing eastern star or subterranean clovers, sheep in the subterranean clover plots grew faster during the first month of grazing. There were no differences in meat eating quality (tenderness, juiciness, or flavour), animal health, or vegetable matter contamination of wool. The data suggest that the clovers had the same relative feeding value despite herbage mass from the eastern star clover plots having lower in vitro digestibility, crude protein, and higher fibre than herbage mass from the subterranean clover plots. Given that there was a minimum of 1000 kg/ha of herbage mass in the plots, it is likely that sheep gazing the two clovers were able to maintain the same weight by selecting the high quality components of the pasture. Differences in plant quality are associated with differences in reproductive strategies of the clovers.

RESOURCE TRACKING BY BUMBLE BEES: RESPONSES TO PLANT-LEVEL DIFFERENCES IN QUALITY

This study considers how a forager moves through its environment when food is patchily distributed and the patches differ in quality. One possibility is to move directionally among patches, staying longer in the best patches (the Hypothesis). Additionally, when foragers reuse patches in a regenerating environment, they can potentially benefit from remembering the most profitable patches, and return preferentially to these (the Hypothesis). Both hypotheses were tested with foraging bumble bees (Bombus spp.) collecting nectar in the foothills and mountains of southwest Alberta, Canada. Individually marked worker bumble bees were observed visiting flowers on focal plants of five species visited primarily by bumble bees. In three plant species (Epilobium angustifolium, Hedysarum alpinum, and Penstemon confertus), variation in nectar secretion rate was experimentally induced by defoliation and fertilization of individual plants. In the other two species (H. sulphurescens and Oxytropis monticola), bees' responses to natural variation in plant-level nectar secretion were measured. Consid- ering the bee population as a whole, plants with higher nectar production rates attracted more bees (three of five plant species) and had more of their flowers visited (three of five plant species). The Local-Experience Hypothesis was supported in three of the five plant species: individual bees stayed longer by visiting more flowers on plants with higher rates of nectar production. The Memory Hypothesis was supported in four of the five plant species; individual bees were more likely to return to plants with higher rates of nectar secretion. Overall, there was a positive correlation between the extent to which individual plants differed in their rate of nectar secretion (a species-level trait), and the strength of support for the Memory Hypothesis (measured as a standardized effect size). That is, individual bumble bees more strongly adjusted their visitation rate based on plant quality as the magnitude of natural differences in plant quality increased. Support for the Memory Hypothesis may explain why bumble bees often revisit the same plants on successive foraging trips: memory for good plants gives them a fitness advantage over naive bees using the same area. Bumble bees appear to use a relatively sophisticated spatial memory in resource tracking, which may constrain the evolution of empty-flower strategies of plant nectar secretion.

Micro‐fungi and invertebrate herbivores on birch trees: fungal mediated plant–herbivore interactions or responses to host quality?

AbstractWe studied interactions between microfungi and herbivores sharing a host tree. In a series of experiments and field observations over a 3‐year period, we compared phenotypic and genetic correlations of fungal frequencies and performance of invertebrate herbivores growing on mature half‐sib progenies of mountain birches (Betula pubescens ssp. czerepanovii) in two environments, a forested river valley and an adjacent higher‐elevation mountain birch woodland. We found little support for direct relation between fungal frequencies and performance of herbivore species. Instead, genetic correlations, particularly between autumnal moth (Epirrita autumnata) and rust fungus (Melampsoridium betulinum), suggest that herbivore performance may be caused by (1) genetic differences in plant quality for fungi and herbivores, or (2) genetic differences in responses to environmental conditions.

Localized outbreak of a willow leaf beetle: plant vigor or natural enemies?

AbstractThe possible roles of plant quality (vigor) and natural enemies in the development of a localized out‐break of the leaf beetle Galerucella lineola (Coleoptera: Chrysomelidae) in a stand of Salix cinerea were investigated. Caged and uncaged larvae on six bushes in the outbreak area were compared with caged and uncaged larvae on six bushes in an adjacent nonoutbreak area in terms of performance. In 1997, when the studies were performed, the natural density of the insect (beetles plus eggs) was six times higher in the outbreak area compared with the nonoutbreak area. Even though the vigor (measured as shoot length) of bushes in the outbreak was 72% higher than that of bushes in the nonoutbreak area, we found no difference between areas in the performance (survival, developmental time, pupal weight) of caged larvae or in the willingness of caged females to lay eggs. Among larvae exposed to natural enemies, the disappearance rate was significantly higher in the nonoutbreak area. The density of generalist predators was significantly higher in the nonoutbreak than in the outbreak area. We conclude that differences in plant quality, despite the observed difference in plant vigor, could not explain the observed difference in beetle density between areas. Lower predation pressure in the outbreak area could, however, not be excluded as a possible reason for the higher density of leaf beetles in this area.

Preference–performance linkage in the neotropical spittlebug Deois flavopicta, and its relation to the Phylogenetic Constraints Hypothesis

Summary1. Predictions from the Phylogenetic Constraints Hypothesis were tested for the first time in a tropical system using the pasture pest Deois flavopicta Stal, which oviposits into the ground and not into plant tissues. The prediction that there is no oviposition preference–larval performance linkage was supported. The absence of such a link provides an evolutionary basis for eruptive population dynamics.2. The effects of host species and host plant quality on the preference of ovipositing females of D. flavopicta and performance of their offspring on the selected host plants were tested at the population level.3. Female oviposition behaviour was affected by the presence of the host plant. Females of D. flavopicta showed a strong preference to oviposit close to host plants. The number of eggs was higher in pots containing Brachiaria ruziziensis (121.88 ± 13.70) than in pots containing only the wet oviposition substrate (5.2 ± 1.98) or dry oviposition substrate (0.067 ± 0.067). Ovipositing females did not, however, discriminate between plants of Brachiaria decumbens and Axonopus marginatus and did not show a strong oviposition preference in relation to differences in plant quality (protein and fibre content). They did show oviposition preference for plants under the high watering regime. The mean number of eggs collected from pots with non water‐stressed plants was 60% higher than the mean number of eggs collected on pots with water‐stressed plants.4. Although females did not show ovipositional preference, spittlebug larval performance, measured as percentage survival and duration of nymphal period, was better on plants of high protein and low fibre content. These results indicate that there is not a linkage between female oviposition preference and subsequent nymphal performance in relation to differences in protein and fibre content in the host plants. There was, however, a limited linkage between oviposition preference and nymphal performance in relation to plant water content. Females showed preference for moist sites that have high survival of newly hatched nymphs.5. Evidence indicates that for D. flavopicta, the influences of natality and female oviposition behaviour in response to plant quality are not the major factors driving population outbreaks, which is in accordance with the Phylogenetic Constraints Hypothesis.

Quality of plant species utilized by northern white-tailed deer in summer along a climatic gradient

During two growing seasons, we evaluated forage quality (in terms of digestibility and nitrogen content) of eight (five woody and three herbaceous) native species of plants commonly consumed by white-tailed deer (Odocoileus virginianus) at four sites along a climatic gradient. At one site, we also compared the composition of native forages of deer with that of three cultivated species consumed occasionally by deer. We predicted that forage quality would improve with increasing latitude because the cool climate and short growing season should allow forage to remain more digestible during the period of availability. We also predicted that the quality of cultivated plants should be higher than that of forest plants throughout the growing season, and particularly towards its end, because of successive harvesting of cultivated plants. Depending on the plant species, estimated dry-matter digestibility varied between 55.2% and 79.2%, whereas nitrogen content averaged between 0.7% and 5.7%. Both variables decreased progressively throughout the summer. Our results did not support the first prediction despite a reduction of 50% in the number of degree-days between the southern and the northern extremes of the climatic gradient. Inter-annual climate variations may have masked subtle differences in plant quality between sites. As predicted, cultivated forages tended to be of higher quality than native species growing in neighboring woodlots, and particularly at the end of the summer because of mowing and regrowth. Our results indicated that white-tailed deer living at the northern fringe of their range cannot count on highly digestible forage to compensate for the short growing season.

The Use of Crumb Rubber as a Container Component for Lantana Production

Lantana camara `New Gold', `Irene', and `Patriot Dove Wings' were planted in five pine bark-based media containing 0%, 12.5%, 25%, 37.5%, and 50% crumb rubber. Each medium was amended with 7.14 kg·m-3 dolomite lime, 0.892 kg·m-3 of Micromax, and 4.76 kg·m-3 of 17-6-12 Nutricote fertilizer. Height and visual quality ratings were taken at 4 and 8 weeks. Dry weights were taken when the experiment was terminated. There were no significant differences in height, visual quality, and dry weight of `New Gold' lantana for all crumb rubber rates. `Irene' grew taller and had higher visual quality rating in the 4th week with 12.5% and 25% crumb rubber. This trend continued in the 8th week with taller plants grown in 25% crumb rubber. However, there were no differences in plant quality. Dry weight of plants grown in 37.5% and 50% crumb rubber was reduced when compared to the control. There were no differences in growth or quality of `Patriot Dove Wings' at week four. At week eight a reduction in both height and visual quality occurred with 37.5% and 50% crumb rubber. Plant dry weights were also significantly reduced at >37.5% crumb rubber.