Interactions between Apion species (Coleoptera: Curculionidae) and Polygonaceae. I. Apion curtirostre Germ, and Rumex acetosa L.

Abstract.

• 1 Apion curtirostre is the commonest weevil attacking Rumex acetosa in the Lancaster area.
• 2 The ovipositional behaviour, larval development, emergence and hibernation of A. curtirostre are described.
• 3 From dissection of samples of stems of R. acetosa, abundance curves for the stages of A. curtirostre and its chalcid parasitoids were constructed and the between-stage mortalities determined.
• 4 There is an exponential relationship between R. acetosa stem height and number of A. curtirostre eggs laid.
• 5 Male stems of R. acetosa appear earlier and are smaller than female stems. Taller stems, at least in female plants, live longer than shorter ones.
• 6 Apion survival is lower in male than in female stems.
• 7 Stem sex is the primary determinant of opposition choice with stem thickness a secondary determinant.
• 8 A. curtirostre eggs introduced experimentally into stems of four Rumex species survived significiantly better in R. acetosa than in any other species. Survival in R. acetosa female plants was twice that in males.
• 9 Survival of A. curtirostre eggs at densities of 4, 8 and 16 per R. acetosa stem was twice that at densities of 32 and 64 per stem.
• 10 The stem size of female R. acetosa was reduced as the number of attacking weevils increased. There was no significant effect in males. No adverse effect on seed production was detected.
• 11 The nature of the relationship between A. curtirostre and R. acetosa is discussed.

     

Structural refuges in two stem-boring weevils on Rumex crispus

Abstract.

• 1 Differences in feeding positions, parasitoid complexes and parasitization rates of the two dominant insect species in stems of Rumex crispus were investigated. Apion miniatum (inhabiting the lower 10% of the stem) and Apion violaceum (occurring all along the stem) exploited distinctly different feeding positions, partly due to differences in time of oviposition.
• 2 A.miniatum suffered less parasitization thanA.violaceum, measured both by number of parasitoid species and parasitization rates. Its feeding position constitutes a refuge.
• 3 Parasitization of A.violaceum was least in individuals feeding in basal, thick parts of the stem. There is a trend that the developed refuge increases with increasing stem diameter.
• 4 The refuge of A.violaceum in basal positions only affected idiobiont ectoparasitoids, because koinobiont endoparasitoids attack the weevils before they enter the stem. Moreover, the koinobiont did benefit from the refuge itself by avoiding hyperparasitism.
• 5 Densities of A.violaceum increased with plant size, whereas percentage parasitism did not differ. Its three most abundant parasitoid species showed small-scale density-independent patterns of attack over all plants. Therefore a constant proportion of weevil larvae mine within the refuge independent of its potential size.
• 6 Synchronization between weevils and plants, as well as between parasitoids and hosts, appears to be the dominant factor for the spatial community structure of the stem borers of Rumex crispus and their enemies.

     

The effect of a foliar disease (rust) on the development of Gastrophysa viridula (Coleoptera: Chrysomelidae)

Abstract.

• 1 Gastrophysa viridula Degeer (Coleoptera: Chrysomelidae) and the pathogenic rust fungus Uromyces rumicis (Schum.) Wint. both occur on leaves of Rumex crispus L. and R.obtusifolius L. Individual stages of beetle development, and egg laying, were compared on healthy and infected leaves of each plant species in the laboratory. Oviposition choice was investigated in the field and laboratory.
• 2 Beetles reared on infected leaves of each species had greater larval mortality and slower development than those reared on healthy leaves. Although larvae feeding on infected leaves consumed up to 2.5 times more dry weight than those reared on healthy leaves, they had a lower relative growth rate and pupated at a lower weight. These changes were consistent with the reduced nutritive quality of rust-infected Rumex leaves.
• 3 Fecundity of beetles reared on infected leaves of both species was considerably reduced. Eggs laid by beetles feeding on infected R.crispus leaves also had a reduced viability.
• 4 The beetle developed consistently poorer on healthy R.crispus than on healthy R.obtusifolius throughout its life-cycle. Differences in larval performance were greater between host species than between infected and healthy leaves.
• 5 Oviposition was similar on infected and healthy R.crispus in both the laboratory and field. However, adults consumed less, and laid fewer eggs on infected than on healthy R.obtusifolius. The pattern of egg laying on different aged leaves was affected by rust infection: a greater proportion of eggs was laid on the older, infected leaves, than on the equivalent aged leaves on the healthy plants. Few larvae survived from eggs laid on rusted leaves in the field.

     

Clutch size in a leaf-mining fly (Pegomya nigritarsis: Anthomyiidae)

ABSTRACT.

• 1 Pegomya nigritarsis Zetterstedt is a gregarious leaf-mining fly attacking Rumex sp. The larvae from one clutch of eggs all inhabit the same mine.
• 2 Egg-batch size varies between host plants and is correlated with leaf size.
• 3 On Rumex obtusifolius L. larval survival as a function of clutch size was measured in the field. This measure was incorporated in an optimal clutch size model and a clutch size prediction obtained.
• 4 The predicted optimal clutch size, three, is that most frequently found in the field.

     

Biochemical recognition in seeds: Germination of Rumex obtusifolius is promoted by leaves of facilitative adult conspecifics

Seeds express various germination behaviors in response to competitor plants. However, germination behaviors in response to facilitator plants are not yet well understood. Rumex obtusifolius seedlings usually appear on the ground near adult conspecific plants, and their survival rate under the canopy of adult conspecifics is higher than that outside the canopy, indicating that adult R. obtusifolius plants facilitate their seedling establishments. We hypothesized that emergence of R. obtusifolius seedlings is promoted by cues from adult conspecifics, but emergence of heterospecific seedlings is not. To test this, we investigated emergence responses of seedlings of R. obtusifolius and three other species that grow with R. obtusifolius in the presence of R. obtusifolius leaf phytochemicals. Emergence of R. obtusifolius seedlings was promoted by the presence of R. obtusifolius leaves. In contrast, emergence of other species seedlings was not promoted by R. obtusifolius leaves. We conclude that germination of R. obtusifolius seeds is facilitated in the presence of conspecifics, via water-soluble chemical exposure, and that recognizing these chemicals has adaptive value.     

Maternal behaviours may explain riffle‐scale variations in some stream insect populations

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Sheep grazing vs. cutting: regeneration and soil nutrient exploitation of the grassland weed Rumex obtusifolius

Broad-leaved dock (Rumex obtusifolius L., Polygonaceae) is an agronomically important perennial weed causing decreases in pasture yields and fodder quality. Non-chemical control measures for dock are often limited to frequent pulling and cutting, additionally it is usually avoided by grazing animals. Here, the regeneration of R. obtusifolius in a Rumex-infested grassland grazed by a sheep breed that explicitly feeds on dock (Ovis aries L. cv. East Prussian Skudden) was compared to cutting. Therefore, regeneration of 90 R. obtusifolius plants of three different size classes was monitored in three plots during three grazing and cutting cycles. Plant height and number of fruit-stands of regrown R. obtusifolius was significantly lower, number of leaves significantly higher after grazing than after cutting, while plant diameter was unaffected. Initially medium and large-sized plants (>40 cm diameter) were significantly more sensitive to grazing or cutting than initially smaller sized plants. Soil nitrate and ammonium concentrations in the vicinity of R. obtusifolius correlated with some regrowth parameters but were not affected by grazing or cutting. Sheep-grazed grassland communities comprised fewer legumes (p = 0.002), more grasses (p = 0.010) and fewer sward gaps (p = 0.025) than cut grassland. At the end of the experiment, abundance of R. obtusifolius in sheep grazed plots was lower than in cut plots (p = 0.089) suggesting that regrowth potential of this weed was depleted by continuous grazing and higher sward density. In conclusion, these data suggest that sheep could be considered in grassland management schemes to both directly and indirectly control Rumex infestations.     

The effects of chrysomelid beetle grazing and plant competition on the growth of Rumex obtusifolius

Summary The interaction between grazing by Gastrophysa viridula and interspecific plant competition was investigated for Rumex obtusifolius growing in the field. During an eight-month growing season non-competing R. obtusifolius grew larger than competing plants although herbivore loads (beetle productivity per unit leaf area) were similar for competing and non-competing plants. However, grazing significantly reduced the growth of R. obtusifolius only in competing plants thus demonstrating a synergism between plant competition and invertebrate herbivory. The relevance of these findings for the distribution of plant species is discussed.     

Biological Activity of the Constituents in Roots of Ezo-no-gishigishi (Rumex obtusifolius)

The roots of Ezo-no-gishigishi (Rumex obtusifolius) contained a high concentration of malonic acid (more than 100 mg/100 g fr.wt) and oxalic acid (15-45 mg/100g fr.wt). The effect of several compounds isolated from the roots of R. obtusifolius on the growth of some fungi, bacteria and lettuce seedlings was examined. It is suggested that one reason for the resistance to decomposition of roots of R. obtusifolius in soil is the existence of organic acids and derivatives of naphthalene and anthraquinone in the tissue.     

Ontogenetic variation in response to temperature change in the control of seed dormancy of Rumex obtusifolius L. and Rumex crispus L.

Abstract After the onset of imbibition, the dormant seeds of Rumex obtusifolius and R. crispus are stimulated to germinate by a change from an initial low temperature to a warmer temperature for a relatively brief period: the warmer that temperature the shorter is the optimum period spent at it, and this optimum value is unaffected by the initial temperature. The optimum period is more critical in R. crispus than in R. obtusifolius (about 1 h and 2.5 to 4 h, respectively, for a warmer temperature of 35°C in the dark); in the light the length of the period at the warmer temperature is less critical in both species. The sensitivity of the seeds to the change to the warmer temperature increases with time from the start of imbibition at a rate which is positively related to the initial temperature. In R. obtusifolius maximum sensitivity was typically reached after 3 to 5 d when the initial temperature was 20°C and then remained constant, or declined only slightly, over the period investigated (10 d). At the same initial temperature, however, R. crispus showed a cyclical pattern of sensitivity with peaks occurring at 3–4 d intervals from the start of imbibition.     

Effects of low temperatures on the loss of innate dormancy and the development of induced dormancy in seeds of Rumex obtusifolius L. and Rumex crispus L.

Abstract It is possible to remove the innate dormancy of seeds of Rumex crispus L and Rumex obtusifolius L. by an initial period of low-temperature stratification, providing the seeds are then transferred to a higher temperature. The lower the initial temperature within the range 1.5°-15°C, the greater the germination; there is no stratification effect at 20°C. Although 10°C and 15°C were shown to be suitable for both stratification and for the process of germination itself, neither temperature results in any germination if given constantly: a change from a lower to a higher temperature is essential. The optimum period for stratification depends on two separate processes which occur during the treatment–a rapid loss of innate or primary dormancy and a slower development of induced or secondary dormancy. Within the range 1.5°-15°C the rate of loss of innate dormancy appears to be independent of light and is probably independent of temperature. In contrast, the rate of induction of secondary dormancy increases with increase in temperature, and is more rapid in the dark than the light. The rate of induction of secondary dormancy during stratification is greater in R. crispus than in R. obtusifolius. As a consequence, maximum germination was obtained in both species after stratification at 1.5°C in the light, the optimum period of treatment being about 4 weeks in R. Obtusifolius and 6 weeks in R. crispus, while the maximum germination obtained and the optimal period of stratification decrease in both species with increase in stratification temperature.     

Age‐specific maternal effects interact with larval food supply to modulate life history in Coleomegilla maculata

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The effect of invertebrate and vertebrate predators on the foraging movements of Ischnura elegans larvae (Odonata: Zygoptera)

SUMMARY.

• 1 The foraging movements of late instar Ischnura elegans larvae were monitored in laboratory experiments to study the effects of predators on larval feeding behaviour.
• 2 Ischnura larvae are sit-atid-wait, or ambush, foragers, moving occasionally between perches in search of profitable feeding sites. Larval foraging movements, monitored at different densities of Daphnia prey, increased significantly when prey were absent.
• 3 In experiments without prey, larval movement was inhibited by the presence of fish predators, as well as by invertebrate predators (Notonecta glauca), but not by closely related, non-predatory invertebrates (Corixa punctata) or physical disturbance of the water (intermittent air bubbles).
• 4 Further experiments varied Ischnura hunger levels (0–8 days without food) and illumination (light or dark) with and without notonectid predators. Hunger had no consistent effect on penultimate instar behaviour but final instar foraging activity was significantly modified: movements increased after 4 days starvation and decreased again after 8 days. This response was suppressed by the presence of predators. Both larval instars moved significantly less often in the light, even when predators were absent.
• 5 These phenotypically flexible predator-avoidance responses are likely to decrease the risk of predation by both visual and tactile predators. However, predators clearly have an important influence on the feeding niche of Ischnura larvae, and may decrease the overall feeding efficiency, growth rate, and survival of larvae by constraining their movement in search of profitable feeding sites.

     

Seed survival and periodicity of seedling emergence in some species of Atriplex, Chenopodium, Polygonum and Rumex

Seeds or fruits of 10 weed species were collected in each of 3 years and mixed with the top 7·5 cm of sterilised soil which was confined in cylinders sunk in the ground outdoors and cultivated three times yearly. The numbers of seedlings emerging were recorded for 5 yr and the numbers of viable seeds remaining then determined. Few, if any, seedlings of Atriplex, Chenopodium or Polygonum spp. emerged in the autumn of sowing; the main emergence was consistently in March–May (A. hastata, A. patula), April–May (P. lapathifolium, P. persicaria), April–June (C. polyspermum), May–June (C. rubrum) or June–August (C. hybridum). When sown before November, some seedlings of Rumex crispus, R. obtusifolius and R. sanguineus appeared immediately. Most emerged in April in subsequent years. Seedling emergence was usually greatest in the first year; thereafter, with all species, seedling numbers decreased approximately exponentially from year to year. The mean numbers of seeds found to be viable after 5 yr ranged from 2·5% (R. sanguineus) to 16·6% (C. rubrum) of those sown.     

Effects of Poa trivialis, Stellaria media and Rumex obtusifolius on the growth of Lolium perenne in the glasshouse

In glasshouse experiments shoot dry weight, leaf area and tiller number of Lolium perenne, cv. S. 24, were compared when grown in monoculture and in competition with Poa trivialis, Stellaria media or Rumex obtusifolius at a range of densities and for different time intervals. The results showed that S. media and R. obtusifolius were more competitive than P. trivialis. Competition effects with S. media and R. obtusifolius appeared between the 4 and 6 wk stage, coinciding with the production of the first S. 24 tillers. Spraying with 2,4-D (0·84 kg acid equivalent/ha) for control of R. obtusifolius did not decrease grass yield whereas mecoprop (2·80 kg a.e./ha) for control of S. media damaged young L. perenne. It appeared that the optimum time for mecoprop treatment was between 4 and 6 wk after sowing when tillering had commenced. At this stage weed competition was only beginning and crop tolerance to the herbicide was adequate.     

The effects of prey density on survival and growth of damselfly larvae

Abstract.

• 1 Instar 10, 11 and 12 Ischnura larvae were maintained throughout the instar on a constant food supply (Daphnia magna of a standard size).
• 2 A very narrow range of prey availability separated cohorts in which all the larvae successfully moulted to the next instar, from those in which all the larvae died (less than one Daphnia per day in the case of instar 10).
• 3 Larvae were able to survive long periods without food at 16°C.
• 4 Prey availability had a marked effect on development rates, which continued to increase at prey densities well in excess of 100% survival by the larvae.
• 5 The data on Ischnura survival and development rates are compared with previously published general models of these two components of the predators' rate of increase.
• 6 We conclude that starvation is very unlikely to be a significant cause of mortality in the field for Ischnura (or indeed most other Odonata larvae), but that prey availability undoubtedly influences development rates. Natural selection should therefore favour larvae that forage optimally to minimize development times.

     

Lepidopteran pest populations and crop yields in row intercropped broccoli

Abstract

• 1 To determine how the presence of non‐host plants impact populations of lepidopteran pests and yield of broccoli, Brassica oleracea var. italica L., broccoli was intercropped with tomato, Lycopersicon esculentum Miller, or yellow sweetclover (YSC), Melilotus officinalis L., and compared with broccoli monoculture grown at two densities (high and low).
• 2 During a 1997 study, numbers of early instar imported cabbageworm, Artogeia rapae L., were greater in broccoli monoculture compared with intercropped plantings. In contrast, late instar A. rapae numbers were significantly higher in intercropped broccoli during most of the season, indicating greater survival of early instar stages in intercropped habitats.
• 3 Cabbage looper, Trichoplusia ni Hübner, eggs and larvae were more abundant in broccoli monoculture than intercropped broccoli in 1997. In addition, T. ni populations were found at significantly lower levels in broccoli‐YSC compared with broccoli‐tomato habitat throughout the season.
• 4 During a 1998 study, numbers of early and late A. rapae instars were greater in intercropped broccoli on most sampling dates.
• 5 The mean percentages of harvested broccoli heads infested with insects and associated frass were higher in monocultures than intercropped treatments in 1997. Additionally, a significantly lower number of contaminants were found in the crowns of broccoli harvested from broccoli‐YSC (YSC) compared with broccoli‐tomato (tomato) habitat. However, broccoli heads were significantly smaller in intercropped habitats.
• 6 Variations in insect responses and challenges to using crop diversification as a management tool are discussed.

     

Population dynamics of insects associated with Rumex obtusifolius in different habitats

The effect of different habitats on insect communities associated with Rumex obtusifolius was studied in detail. Study sites were selected for their variety of environmental characteristics (vegetation and habitat): shaded woodland, disturbed wasteland and pasture. The results of this study were that insect populations associated with R. obtusifolius responded differently to the different habitats. The observed differences in population dynamics among the insects showed quite clearly their responses to different habitats. There was also a pattern of time partitioning in the exploitation of the host‐plant among the insect species observed. Philaenus spumarius at nymphal stage had a peak density on approximately 20 June, Apion frumentarium and Apion spp. (Apion species other than A. frumentarium) had a peak density on approximately 30 June and Aphis rumicis had a peak density on approximately 28 July. This pattern of shift in time for peak population density (time‐shift) among the insects sharing a common host‐plant may guarantee each insect the opportunity to exploit the plant to a maximum.     

Fate of 13C in metabolic pathways and effects of high CO2 on the alteration of metabolites in Rumex obtusifolius L.

In present study, in vivo turn-over of ¹³CO₂ to organic acids such as oxalate and citrate in Rumex obtusifolius L. was explored. Conversion of fixed carbon to oxalate was studies using “new leaves”, i.e., leaves removed from 2-month-old-plants grown under different environmental conditions. Collected new leaves and stems were subjected to metabolomic analyses using capillary electrophoresis mass spectrometry. The results showed the mobilization of metabolites from stems to new leaves, where active TCA cycle and oxalate pathways occurred. The ¹³C labeling experiments also indicated that these pathways are active in new leaves. Subsequently, we compared the effects of high carbon dioxide level (1000 ppm) and nutrients (Hoagland’s formulation) on the metabolite accumulation in R. obtusifolius. Data analysed by both principal component and hierarchical clustering analyses revealed significant changes in metabolite accumulation. The accumulation of most abundant metabolite oxalate in leaves was affected by both high CO₂ as the carbon source and nutrients. We suggest that the common weed R. obtusifolius may proliferate in cultivated lands under high CO₂ level, a potential cause of global warming.     

Performance and Mortality of Rumex obtusifolius and R. crispus in Managed Grasslands are Affected by Nutrient Availability

The reasons for the greater incidence of Rumex obtusifolius in grasslands compared with R. crispus have never been investigated. In a small-plot field experiment in which seedlings of R. obtusifolius and R. crispus were transplanted into a sward dominated by Dactylis glomerata, the growth and survival of seedlings were monitored over three years under control and P, N, NP and NPK fertilizer treatments. The highest plants of R. obtusifolius and R. crispus were generally recorded in the N, NP and NPK treatments and the lowest in the control and P treatment. The maximum recorded heights of R. obtusifolius were 100?cm and of R. crispus 80?cm. The number of leaves per plant, weight of individual plants, cover and fertility were generally higher for R. obtusifolius than for R. crispus. 30% to 80% of transplanted R. obtusifolius plants flowered in the first (seeding) year and this contrasted with no flowering of transplanted R. crispus plants. After cutting, substantially better regrowth of R. obtusifolius was recorded compared to that of R. crispus and surviving R. crispus plants tended to show a gradual reduction in leaf number. The mortality of R. obtusifolius over three years ranged from 0% in the NPK treatment to 13% in the control, with an average of 8% over all treatments. The mortality of R. crispus ranged from 19% in the control to 94% in the NPK treatment with an average of 64% over all treatments. We concluded that R. obtusifolius is better adapted to growing in highly productive temperate grasslands than R. crispus because of its perennial character, larger plant size and higher fertility.