Singapore is a recognized global hotspot for invasive species and many introduced plant species have become major weeds there. Some of the common invasive taxa, such as Asystasia gangetica ssp. micrantha , Mimosa pigra , Neptunia plena , Panicum maximum , and Urochloa mutica , are spread over large areas and dominate the indigenous flora in some habitats. In a study aimed at understanding the relationship between polyploidy and invasiveness, we show that all the investigated invasive taxa are polyploids. A. gangetica ssp. micrantha , N. plena , and P. maximum vary in chromosome number and ploidy level across the world, but we recorded only one chromosome count for each of these species in Singapore. Similarly, the cytology of M. pigra and U. mutica also revealed that these species are polyploid, each with only one chromosome number across all populations. The results indicate that one polyploid line in each of these species has been selected favourably and has become invasive. We also show that all the species exhibit normal male meiosis and possess high percentages of pollen fertility. Based on the present study and an analysis of previously reported ploidy levels, we suggest that these taxa are probably of allopolyploid origin. We conclude that polyploidy and an effective reproductive system are a perfect mix for successful invasion by these species in Singapore. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 395‐403.

Ninety isolates of root nodule bacteria from an invasive Mimosa pigra population in Australia were characterized by PCR assays and by sequencing of ribosomal genes. All isolates belonged to the same bacterial genus (Burkholderia) that predominates on M. pigra in its native geographic range in tropical America. However, the Australian Burkholderia strains represented several divergent lineages, none of which had a close relationship to currently known Burkholderia strains in American M. pigra populations. Inoculation of M. pigra with Australian strains resulted in equal or higher plant growth and nodule nitrogenase activity (measured by acetylene reduction assays) relative to outcomes with bacteria from M. pigra’s native geographic region. The main difference in symbiotic phenotype for bacteria from the two regions involved responses to an alternate Mimosa host species: Central American strains failed to fix nitrogen in association with Mimosa pudica, while most Australian Burkholderia isolates tested had high nodule nitrogenase activity in association with both Mimosa species. Invasive M. pigra populations in Australia have therefore acquired a diverse assemblage of nodule bacteria that are effective nitrogen-fixing symbionts, despite having a broader host range and a distant genetic relationship to bacterial strains found in the plant’s ancestral region.

The effect of manual defoliation and Macaria pallidata (Geometridae) herbivory on Mimosa pigra: Implications for biological control

Evaluating the impact of biological control against Mimosa pigra in Australia: Comparing litterfall before and after the introduction of biological control agents

In Burkina Faso, Glossina palpalis gambiensis Vanderplank and G. tachinoides Westwood (Diptera: Glossinidae) are the main cyclic vectors of trypanosomiasis. The vegetation type along river banks is an important factor determining the distribution and abundance of these tsetse. The following work investigated the relation between the plant species present (including the disturbance level) and tsetse distribution and abundance, using three ecotypes, described by P.C. Morel in 1978. These were the Guinean, Sudano-Guinean and Sudanese gallery forests. In the Mouhoun River basin, these three ecotypes are found successively from upstream to downstream. Berlinia grandiflora, Syzygium guineense and Cola laurifolia and finally Acacia seyal and Mitragyna inermis were the best indicators for the Guinean, Sudano-Guinean and Sudanese gallery forest ecotypes, respectively, as suggested by Morel. However, other species such as Pterocarpus santalinoides and Mimosa pigra were not ecotype specific. Trap catches confirmed that G. palpalis and G. tachinoides are predominant in Guinean and Sudanese gallery forests, respectively, and that both species are well represented in the Sudano-Guinean ecotype. Tsetse densities dropped significantly in disturbed Sudano-Guinean and Sudanese gallery forest sites. However, this was not the case for both species in Guinean or for G. tachinoides in half-disturbed Sudanese gallery forest sites, confirming their high resilience to human-made changes. The importance of a detailed consideration of riverine ecotypes when predicting tsetse densities is discussed.

Summary Evaluation of the success of biological control agents is essential to improve the efficiency and safety of future programmes. This study assessed the impact of Carmenta mimosa, a stem‐mining moth, introduced into northern Australia as a biological control agent of mimosa Mimosa pigra. Litter fall, seed banks, vegetation cover, density and age structure of mimosa stands were compared using data collected at nine sites where Carmenta mimosa was present and eight sites where it was initially absent. Mimosa seed rain was negatively correlated with Carmenta mimosa damage and declined by more than 90% at the highest Carmenta mimosa densities. Seed banks also declined with Carmenta mimosa damage. Percentage cover of competing vegetation was significantly higher under stands defoliated by Carmenta mimosa and this inhibited mimosa seedling establishment and apparently increased the susceptibility of mimosa to fire, by increasing fuel loads beneath stands. Four of the eight stands where Carmenta mimosa was absent expanded and none contracted. In contrast, none of the nine stands where Carmenta mimosa was present expanded and three contracted. Analysis of the age structure of mimosa stands indicated that contracting stands were typified by an absence of seedling regeneration. In contrast to previous studies, no impact could be attributed to the flower feeder Coelocephalapion pigrae or to the stem‐mining moth Neurostrota gunniella, whilst the bruchid Acanthoscelides puniceus consumed up to only c. 10% of seed. However, it is argued that, while these agents are unlikely to suppress dense mimosa thickets, they may reduce the rate mimosa can expand. Synthesis and applications. By preventing stand regeneration, Carmenta mimosa is predicted to cause widespread reductions in mimosa populations and should therefore be redistributed to areas of mimosa where it is absent. Differences between the age structures of stands with Carmenta mimosa present may highlight how biological control could succeed for a suite of woody legume weeds with long‐lived seed banks.

There have been few studies investigating whether predators can affect the survival of insects that have been introduced into new regions. To address this, ants and birds were excluded from mimosa (Mimosa pigra) plants that had larvae of a leaf-feeding geometrid moth, Macaria pallidata placed on them. The moth is used as a biological control agent against mimosa in the Northern Territory. More larvae were observed when ants and birds were excluded. The ants present were generalists, probably attracted to mimosa by the nectar it supplies at the base of the leaves.

A total of 191 rhizobial isolates from the root nodules of three geographically separate populations of the invasive plant Mimosa pigra in Taiwan were examined using amplified rDNA restriction analysis, 16S rDNA sequences, protein profiles and ELISA. Of these, 96% were identified as Burkholderia and 4% as Cupriavidus taiwanensis. The symbiosis-essential genes nodA and nifH were present in two strains of Burkholderia (PAS44 and PTK47), and in one of C. taiwanensis (PAS15). All three could nodulate M. pigra. Light and electron microscopy studies with a green fluorescent protein transconjugant variant of strain PAS44 showed the presence of fluorescent bacteroids in M. pigra nodules. These bacteroids expressed the nifH protein, hence this is the first confirmation that Burkholderia is a genuine symbiont of legume nodules. The predominance of Burkholderia in Taiwanese M. pigra suggests that this species may have brought its symbionts from its native South America, rather than entering into association with the Taiwanese Mimosa symbiont C. taiwanensis which so successfully nodulates Mimosa pudica and Mimosa diplotricha.

Review and analysis of the surveys for natural enemies of Mimosa pigra: What does it tell us about surveys for broadly distributed hosts?

Hydrological and ecological impacts of dams on the Kafue Flats floodplain system, southern Zambia

ABSTRACT The present study assessed the ecological risks of the herbicide tebuthiuron to freshwater fauna and flora of northern Australia's tropical wetlands. Effects characterization utilized acute and chronic toxicity data of tebuthiuron to local freshwater species (three animals and two plants) as well as toxicity data derived from northern hemisphere species. Species sensitivity distributions (SSDs) for four effects scenarios—plant chronic toxicity (NOEC data), plant chronic toxicity (EC/IC50 data), invertebrate and vertebrate chronic toxicity (NOEC data), and vertebrate acute toxicity (LC50 data)—were used to characterize effects and calculate 10, 5, and 1% hazardous concentrations (HCs). Tebuthiuron concentrations affecting 5% of species (i.e., HC5s) for the earlier scenarios were 0.013, 0.093, 9.0, and 97 mg L−1, respectively. Exposure characterization involved the use of historical field monitoring data of tebuthiuron concentrations following application of tebuthiuron to a large infestation of the wetland weed Mimosa pigra (Mimosa). Tebuthiuron concentrations in surface water ranged from below detection to 2.05 mg L−1 and were still measurable up to 10 months following application. A breakpoint regression model was fitted to the field monitoring data, providing a time-dependent estimate of exposure to tebuthiuron. Risk characterization involved the comparison of the SSDs and associated HCs for each of the effects scenarios, with the time-dependent model of tebuthiuron exposure. Modeled tebuthiuron concentrations over the first 12 days post-application were in excess of concentrations required to cause major (i.e., 50% reductions in population numbers) effects to over 85% of freshwater plant species (based on data for phytoplankton and floating macrophytes). Beyond this period and up to 300 d post-application, 10–20% of species were still predicted to be affected. To quantify the probability of prolonged effects, the plant SSDs were compared to a cumulative probability distribution of tebuthiuron measured from 70 d to 293 d post-application. The probability of at least 5% of freshwater plant species experiencing chronic effects due to tebuthiruon at ≥70 d post-application was 58% based on NOEC data and 8% based on EC/IC50 data. Overlap of the 95% confidence limits of the exposure distribution and plant SSDs indicated substantial uncertainty in the risk estimates. Risks of effects to freshwater invertebrates and vertebrates were generally < 1%. It was concluded that tebuthiuron appears to represent a significant and prolonged risk to native freshwater plant species, particularly phytoplankton and floating macrophytes, whereas the risks to freshwater invertebrates and vertebrates appear low. However, from a management perspective, the risks of tebuthiuron (and other herbicides) must be weighed against the known, serious environmental and economic impacts of the target weed, Mimosa. Overall, the outcomes of the risk assessment support the various management options that have been implemented with regard to the use of tebuthiuron to control Mimosa.

Prevalence of Burkholderia sp. nodule symbionts on four mimosoid legumes from Barro Colorado Island, Panama

Malacorhinus irregularis for biological control of Mimosa pigra: host-specificity, life cycle, and establishment in Australia

Summary Methods for floodplain revegetation using native species were investigated, following clearance of the invasive shrub Mimosa pigra L. (Mimosaceae) in the Northern Territory of Australia. Prolific revegetation occurred naturally and several species were identified that have potential for revegetation at sites where natural regeneration is poor, namely: Spiny Mud Grass, Pseudoraphis spinescens, Awnless Barnyard Grass, Echinochloa colona, and an unidentified Panicum species. However, it may still be desirable to plant native perennial grasses, of which most species did not establish naturally. Stolons of the native floodplain grass Hymenachne acutigluma (Steud) Gilliland (Poaceae) established well when planted in wet mud and shallow water during the early dry season, as seasonal floodwaters subsided. Similar plantings during the early wet season were less successful. Sowing seed of several floodplain grasses and Eliocharis dulcis was unsuccessful in both seasons. Planting stolons of H. acutigluma as seasonal floodwaters subside may provide a reliable alternative to exotic floodplain grasses, Para Grass (Urochloa mutica), and Amity Aleman Grass (Echinochloa polystachya), which are also currently propagated vegetatively in Australia. However, planting H. acutigluma stolons had no tangible benefits in terms of suppressing Mimosa establishment, which was low in all treatments. Revegetation should not be considered an alternative to the diligent control of Mimosa seedlings; regenerating following control of Mimosa thickets.

Maigana fish farm (located approximately between latitude 110 7'N and longitude 70 46'E) along Jos Road from Zaria was established in 1970 by the Kaduna State Government for production of fish and fingerlings of Clarias gariepinus, Cyprinus carpio and Oreochromis niloticus . Agricultural activities, and poor management practices over the years have led to high siltation rates and consequent extensive growth of emergent aquatic macrophytes such as Typha australis, Nymphaea lotus, Echinochloa pyramidalis and Leersia hexandra , as well as marginal plants such as Mimosa pigra and Sesbania bispinosa . These plants have been established to varying extents and at least five seral stages of aquatic succession were seen in the production ponds. These seral stages in the pattern of macrophyte community development were seen to be approximately annual. Ponds that had stayed up to one year without clearance were typified by presence of species such as Nymphaea lotus , which gradually accommodated others such as Ludwigia erecta in the second year. Later seral stages were characterized by occurrence of species such as Polygonum lanigerum, Typha australis, Echinochloa pyramidalis etc. Ponds that are not cleared become completely taken over by terrestrial plants within a period of less than five years. In the reservoir area, population of marginal plants such as Neptunia prostrata, Sesbania bispinosa and Mimosa pigra were rapidly expanding towards the open water. Urgent management and control measures are needed. Key Words: Macrophytes, fish farm, Nigeria. Journal of Aquatic Sciences Vol.19(2) 2004: 85-94

Rapid characterisation of host specificity is important both in biological control of weeds and studies in ecology and evolution. A means for doing this was developed and tested on four species of leaf beetles of interest for biological control of the weed Mimosa pigra (Mimosaceae). We identified the most promising for the more detailed tests necessary to obtain release approval. The impact of time-dependent effects and effects of experience were also investigated as part of this study but were not detected. Short-term host specificity tests on adult feeding accurately predicted the results of longer term trials. The long-term trial showed that survival on a plant species depended on feeding on it. Hence short-term feeding trials can predict the longer term survival of adults on other plant species. Different feeding results were obtained in cut foliage versus entire plants but no consistent pattern was shown: of the two insect species tested, one species ate more of the cut material while the opposite was demonstrated for the second species. Species in order of priority for further consideration as biocontrol agents were Syphrea bibiana, Genaphthona sp., Syphrea sp. and Paria sp. The latter three species were probably not sufficiently specific for release. The tests done here allow the identification of the most likely species upon which to conduct the more laborious and difficult larval developmental tests, saving considerable resources.

Summary In Australia, biological control is a promising long‐term management strategy for the woody weed mimosa Mimosa pigra but does not yet provide adequate control. Other management techniques, including herbicides and fire, can be ineffective and their impact on biological control agents is unknown. We investigated the potential of integrating control techniques, including biological control, to provide cost‐effective management. A large‐scale (128‐ha) split‐plot experiment was performed to measure the impact of single and repeated applications of herbicide and crushing by bulldozer, either alone or in combination, on both mimosa and five introduced biological control agents that were abundant at the site. Herbicides were applied over three seasons (1997–99) and all plots were burned in 2000. The impact of control options on mimosa cover, biomass, number of stems per ha, stand size structure and seedling regeneration was determined by aerial photography and by sampling permanent and random quadrats. Biological control agent abundance was also quantified. In isolation, herbicide, bulldozing and fire were not effective, but several combinations of techniques cleared mimosa thickets and promoted establishment of competing vegetation that inhibited mimosa regeneration from seed. Depending on the species, biological control agent abundance on surviving mimosa plants was either unchanged or increased following herbicide and/or bulldozing treatments. All agents recolonized regenerating mimosa within 1 year of the fire treatment, and Neurostrota gunniella increased dramatically. Carmenta mimosa abundance, however, was reduced by fire. The abundance of N. gunniella increased in response to all treatments, which we attribute to attack by this species being most common along stand edges. Control treatments separated monocultures of mimosa into smaller patches, thereby increasing the ratio of ‘edge’ to ‘thicket’ plants. The proportion of plants susceptible to N. gunniella attack increased as a result. Synthesis and applications. We conclude that integrating control techniques can successfully control dense mimosa thickets. Biological control integrates well with other control options and should lead to significant cost reductions for mimosa management. To maximize this benefit, integrated weed management plans should be designed to integrate biological control fully with other methods, rather than separate them spatially or temporarily.

Summary Where biocontrol programmes for invasive plants are in place, only one‐third are fully successful. Integrated weed management (IWM) emphasizes the use of several complementary control measures. We used models of increasing complexity to determine which parameters affect site occupancy of an invasive shrub, Mimosa pigra, in tropical Australia. Two introduced biocontrol agents have spatial effects on both plant fecundity and the probability of recolonization after senescence. We incorporated biocontrol effects into IWM models with small‐scale disturbance, such as grazing and pig‐rooting, and large‐scale disturbance, such as mechanical control, herbicide and fire. The models were parameterized from experimental and field data. The models indicated that reduction in fecundity is not the most important impact of biocontrol; rather it is defoliation at the edges of stands, allowing grasses to out‐compete M. pigra seedlings. We demonstrated that biocontrol alone is only successful at low levels of small‐scale disturbance and seedling survival and, even then, current biocontrol agents would take decades to reduce a stand to &lt; 5% site occupancy. Our model predicts the most successful IWM strategy to be an application of herbicide in year 1, mechanical control + fire in year 2 and herbicide in year 3, with reduction of small‐scale disturbance where possible. The addition of biocontrol improves the success of this strategy. Synthesis and applications. Ascertaining how control measures, including biological methods, will influence persistence of an invasive requires models of the target species’ dynamics and its ecosystem. As in previous applications of this model, disturbance is the most important regulator of population size in M. pigra; moderate to high levels of small‐scale disturbance promotes M. pigra occupancy. We have shown that IWM can control M. pigra and that biocontrol is an effective part of this strategy. Reductions in fecundity alone are unlikely to control invasive leguminous shrubs. However, biocontrol agents affect the probability of recolonization after senescence and enhance control. Our recommended 3‐year treatment programme (herbicide : mechanical control + fire : herbicide, with biocontrol) is justifiable in terms of the biology of the system, making it more likely to be acted upon by risk‐averse farmers and land managers.

Integrated weed management: effect of herbicide choice and timing of application on the survival of a biological control agent of the tropical wetland weed, Mimosa pigra

The impact of a stem-boring moth Neurostrota gunniella and a fungal plant pathogen Phloeospora mimosae-pigrae on Mimosa pigra seedlings was investigated in a shade house. N. gunniella and P. mimosae-pigrae , either alone or in combination, reduced seedling growth by approximately 29-38% which, in field conditions, should be associated with reduced survivorship during wet-season flooding. There was no significant difference in N. gunniella damage between plants inoculated with N. gunniella alone, and plants inoculated with both N. gunniella and P. mimosae-pigrae . However, pathogen symptoms were significantly greater on plants inoculated with P. mimosae-pigrae alone than when N. gunniella was also present. Competition between N. gunniella and P.mimosae-pigrae may be at least partially responsible for the current poor performance of P. mimosae-pigrae in Australia.