Biology and Host Range of the Green-seed Weevil, Sibinia fastigiata , for Biological Control of Mimosa pigra

Aspects of the biology and host range of Sibinia fastigiata Clark (Coleoptera: Curculionidae) were studied to assess its safety for release in Australia as a biological control agent of the weed Mimosa pigra L . (Mimosaceae) . Larvae feed on the seeds and adults on open flowers of their host . Adults oviposit on to immature seeds 3 mm long or less and hence seeds of this length and maturity were used in the host range tests and for rearing . Females are shown to avoid previously attacked seeds enhancing their effectiveness as seed destroyers . Survival of adults was higher when provided with open flowers . The host range was determined using laboratory control - choice oviposition tests on excised plant material and , in the field in the native range , no - choice oviposition tests on living plants , surveys of adults on plants , and breeding of insects from pods of plants of various legume species . The control - choice oviposition tests employed a new design in which the control plant alone was offered to the insects followed by a choice of test plants species . Other than M. pigra, only one plant species was acceptable for oviposition , the closely related M. asperata. Larval development also occurs on M. asperata and this host is occasionally used in the field . This insect was approved for release in March 1997 .     

Weed species and weed communities

Summary With weeds as with many plant species the main or first level factor determining the area of distribution is a (complex) climatic one. As they have an artificially enlarged area of distribution, they have a huge border area (in an ecological sense), where the climate is not optimal for them, and where they have a narrow ecological and sociological amplitude and are especially sensitive to some measures of modern intensified agriculture. In their northern border areas species of southern origin are restricted to calcarcous substrates and to agrestal and finally ruderal communities, while in their optimal climate they are indifferent to that soil factor and able to compete with other species even in natural vegetation types. Species presumably of origin in atlantic areas are restricted with increasing continentality to very poor and acid soils, as they cannot compete with other species on better sites any more, because of their physiological properties. Thus weed distribution demonstrates the complicated reaction of plant species to the complexes of soil-climatic factors and to the competition of other species. As far as weeds are concerned, species may be only relatively calciphilous, but genuinely calcifuge species, the control being climatic in the former case and physiological in the second.The measures of modern agriculture bring about a gradual extinction of sensitive species from the limit of their range towards their centre of distribution, where they can find refuge habitats in the natural vegetation. The sensitivity of such species (also against herbicides) seems to increase towards their limits. Resistant species occur with increasing densities after the removal of their competitors. In addition, they are able to enlarge their area and to invade sites, where they had not been able to compete before, or sites where they could not previously bear the environmental conditions together with the competition of the rich weed flora.As the complex climatic gradients responsible for the ranges of weed species show smooth transitions, the alteration of species composition in weed communities is also a gradual one. This is one of the problems of weed phytosociology briefly discussed.Nomenclature follows Ehrendorfer (1973), Phytosociological units according to Westhoff & Den Held (1969).Contribution to the Symposium on Plant Species and Plant communities, held at Nijmegen, 11–12 November 1976, on the occasion of the 60th birthday of Professor Victor Westhoff.Field studies were partly supported by a grant of the Austrian Federal Ministry of Agriculture and Forestry.     

The history of crops and crop weeds in south-western Germany from the Neolithic period to modern times, as shown by archaeobotanical evidence

The results of more than 100 archaeobotanical investigations from south-western Germany have been arranged into chronological groups and analyzed with a spreadsheet to obtain presence data and the numbers of taxa present in the various time periods. They show an increase in the number of plant taxa cultivated in gardens since the Roman period, a decrease in the crops that were the earliest to be cultivated, especially emmer, and an increase of spelt, rye and oats in the course of time. New crop weeds appear, including an increasing number of southern plants originating from open vegetation. This is more likely to be a result of the intensification of agriculture than from increased human mobility. The crop weeds, grouped together according to their requirements for soil nutrients, show increasing soil acidification through the course of time.     

Riparian zones as havens for exotic plant species in the central grasslands

In the Central Grasslands of the United States, we hypothesized that riparian zones high in soil fertility would contain more exotic plant species than upland areas of low soil fertility. Our alternate hypothesis was that riparian zones high in native plant species richness and cover would monopolize available resources and resist invasion by exotic species. We gathered nested-scale vegetation data from 40 1 m²subplots (nested in four 1000 m² plots) in both riparian and upland sites at four study areas in Colorado, Wyoming, and South Dakota (a total of 320 1 m² subplots and 32 1000 m² plots). At the 1 m² scale, mean foliar cover of native species was significantly greater (P<0.001) in riparian zones (36.3% ± 1.7%) compared to upland sites (28.7% ± 1.5%), but at this small scale there were no consistent patterns of native and exotic species richness among the four management areas. Mean exotic species cover was slightly higher in upland sites compared to riparian sites (9.0% ± 3.8% versus 8.2% ± 3.0% cover). However, mean exotic species richness and cover were greater in the riparian zones than upland sites in three of four management areas. At the 1000 m² scale, mean exotic species richness was also significantly greater (P<0.05) in riparian zones (7.8 ± 1.0 species) compared to upland sites (4.8 ± 1.0 species) despite the heavy invasion of one upland site. For all 32 plots combined, 21% of the variance in exotic species richness was explained by positive relationships with soil % silt (t =1.7, P=0.09) and total foliar cover (t = 2.4, P=0.02). Likewise, 26% of the variance in exotic species cover (log₁₀ cover) was explained by positive relationships with soil % silt (t =2.3, P=0.03) and total plant species richness (t = 2.5, P=0.02). At landscape scales (four 1000 m² plots per type combined), total foliar cover was significantly and positively correlated with exotic species richness (r=0.73, P<0.05) and cover (r=0.74, P<0.05). Exotic species cover (log₁₀ cover) was positively correlated with log₁₀% N in the soil (r=0.61, P=0.11) at landscape scales. On average, we found that 85% (±5%) of the total number of exotic species in the sampling plots of a given management area could be found in riparian zones, while only 50% (±8%) were found in upland plots. We conclude that: (1) species-rich and productive riparian zones are particularly invasible in grassland ecosystems; and (2) riparian zones may act as havens, corridors, and sources of exotic plant invasions for upland sites and pose a significant challenge to land managers and conservation biologists.     

Diet selection by hares (Lepus europaeus) in arable land and its implications for habitat management

Populations of European hares (Lepus europaeus) have experienced a dramatic decline throughout Europe in recent decades. European hares are assumed to prefer weeds over arable crops, and weed abundance was reduced by the intensification of agriculture. Therefore, modern agriculture has been blamed as a major factor affecting European hare populations. However, it is questionable whether European hares select weeds at all, as previous studies had major methodological limitations. By comparing availability and use of plants with Chesson’s Electivity Index, we investigated whether the European hare actually feeds selectively on different plants in arable land. Food availability and use were dominated by cultivated crops (e.g. winter wheat, spring barley and sugar beet). Diet selection analysis revealed that in autumn and winter, European hares predominantly preferred cultivated crops (winter wheat) and food items provided by hunters (tubers of sugar beet and carrot). In spring and summer, apart from soy, only weeds (e.g. clover and corn poppy) were positively selected, especially after cereal crops were harvested. We suggest that the decline in European hare populations throughout Europe was facilitated by the decrease in weed abundance. Wildlife-friendly set-asides in arable land have the potential to reconcile the European Union’s Common Agricultural Policy with wildlife conservation.     

Carboxylesterase activities toward pesticide esters in crops and weeds

Proteins were extracted from maize, rice, sorghum, soybean, flax and lucerne; the weeds Abutilon theophrasti, Echinochloa crus-galli, Phalaris canariensis, Setaria faberii, Setaria viridis, Sorghum halepense and the model plant Arabidopsis thaliana and assayed for carboxylesterase activity toward a range of xenobiotics. These included the pro-herbicidal esters clodinafop-propargyl, fenoxaprop-ethyl, fenthioprop-ethyl, methyl-2,4-dichlorophenoxyacetic acid (2,4-d-methyl), bromoxynil-octanoate, the herbicide-safener cloquintocet-mexyl and the pyrethroid insecticide permethrin. Highest activities were recorded with alpha-naphthyl acetate and methylumbelliferyl acetate. Esters of p-nitrophenol were also readily hydrolysed, with turnover declining as the chain length of the acyl component increased. Activities determined with model substrates were much higher than those observed with pesticide esters and were of limited value in predicting the relative rates of hydrolysis of the crop protection agents. Substrate preferences with the herbicides were typically 2,4-d-methyl>clodinafop-propargyl>fenthioprop-ethyl, fenoxaprop-ethyl and bromoxynil-octanoate. Isoelectric focussing in conjunction with staining for esterase activity using alpha-naphthyl acetate as substrate confirmed the presence of multiple carboxylesterase isoenzymes in each plant, with major qualitative differences observed between species. The presence of serine hydrolases among the resolved isoenzymes was confirmed through their selective inhibition by the organophosphate insecticide paraoxon. Our studies identify potentially exploitable differences between crops and weeds in their ability to bioactivate herbicides by enzymic hydrolysis and also highlight the usefulness of Arabidopsis as a plant model to study xenobiotic biotransformation.     

Composition and diversity of weed communities in Al-Jouf province,northern Saudi Arabia

The aim of this study was to identify the main weed communities in Al-Jouf province in northern Saudi Arabia. Moreover, the composition and diversity of these communities were studied in relation to soil variables and crop type. Some 54 stands representing olive orchards, date palm orchards, wheat crop and watermelon crop were studied, using ten quadrats (1 × 1 m) per stand. A total of 71 species belonging to 22 families and 61 genera were observed. The classification of vegetation using the Two Way Indicator Species Analysis (TWINSPAN) resulted in the recognition of four vegetation groups representing wheat crop, orchards in winter season, orchards in summer season and watermelon crop. These results suggested the importance of both crop and season for the formation of weed community. Detrended Correspondence Analysis (DCA) showed that these groups are clearly distinguished by the first two DCA axes. The species richness was higher in both olive and date palm orchards than in wheat and watermelon crops. This pattern of species richness could be related to farm management practices and habitat micro-heterogeneity. Soil electrical conductivity, organic carbon and soil texture showed significant correlations with species richness and the cover values of some dominant species, suggesting the significant role of soil characteristics in weed community structure and diversity.     

Supplemental risk evaluations and status of Puccinia carduorum for biological control of musk thistle

Tests of seven rare and endangered native North American Cirsium species and four modern artichoke lines were requested in response to a proposal for introduction of Puccinia carduorum into the United States for biological control of musk thistle (Carduus nutans ssp. leiophyllus). These tests were supplemental to an earlier extensive host-range study that established P. carduorum from musk thistle as host specific, useful for biological control, and suitable for limited field tests in Virginia. Test plants in the current study were evaluated in support of a proposal to use the rust in the western United States, and particularly, in California. None of the test plants in this study had been evaluated in previous assessments and all were either rare, endangered or threatened in California. Tests were conducted in both field and greenhouse settings. Field tests were run for two seasons, and test plants were inoculated by natural spread of the pathogen from source plants inside rings of test plants. Greenhouse tests involved direct inoculation under optimal conditions of dew and temperature (18–20 °C, 16 h) for infection. None of the seven Cirsium species or subspecies tested became infected by P. carduorum, either in field or greenhouse tests, compared to infection of 98% of the individual musk thistle plants (n = 102) from all the studies. Modern artichoke cultivars were tested only by direct inoculation under optimal greenhouse conditions. All artichoke plants (n = 115) either were immune (no macroscopic symptoms, n = 69) or at most, resistant (n = 46); pustules on all but two of the resistant plants were very small (0.30 mm diam). Despite infections on artichokes, P. carduorum could not be maintained on artichokes under optimal greenhouse conditions. These results confirm earlier findings from host-range tests and risk assessments of P. carduorum. This information suggests that rare, threatened, or endangered Cirsium spp. and modern artichoke cultivars are not likely to be adversely affected by the use of P. carduorum for biological control of musk thistle. These data have been reviewed by grower groups and regulatory agencies in a proposal for permission to use the rust for musk thistle control throughout the United States.     

The Californian urban butterfly fauna is dependent on alien plants

Abstract. Using the unusually well-documented butterfly fauna of Davis, Yolo County, California, it is shown that the mainly native species commonly observed in gardens breed mostly or entirely on alien plants, especially naturalized weeds. Over 40% of the fauna has no known native hosts in the urban–suburban environment. Were certain alien weeds to be eradicated or their abundance greatly reduced, the urban-suburban butterfly fauna would disappear. This might be regarded as an unfortunate, and perhaps intolerable, side-effect of such programs.     

Hybridization and the evolution of invasiveness in plants and other organisms

Less than a decade ago, we proposed that hybridization could serve as a stimulus for the evolution of invasiveness in plants (Ellstrand and Schierenbeck Proc Nat Acad Sci USA 97:7043–7050, 2000). A substantial amount of research has taken place on that topic since the publication of that paper, stimulating the symposium that makes up this special issue. Here we present an update of this emergent field, based both on the papers in this volume and on the relevant literature. We reevaluate the lists that we presented in our earlier paper of reports in which hybridization has preceded the evolution of invasiveness. We discard a few cases that were found to be in error, published only as abstracts, or based on personal communication. Then we augment the list from examples in this volume and a supplementary literature search. Despite the omissions, the total number of cases has increased. Many have been strengthened. We add a list of cases in which there has been evidence that intra-taxon hybridization has preceded the evolution of invasiveness. We also provide a number of examples from organisms other than plants. We consider how our examples suggest mechanisms whereby hybridization may act to stimulate the evolution of invasiveness. Hybridization does not represent the only evolutionary pathway to invasiveness, but it is one that can explain why the appearance of invasiveness often involves a long lag time and/or multiple introductions of exotics.