Impacts of the biocontrol agent Malacorhinus irregularis (Coleoptera, Chrysomelidae) on Mimosa pigra seedlings and the importance of root nodules

This study investigated the impacts of the biocontrol agent Malacorhinus irregularis Jacoby (Coleoptera, Chrysomelidae) on the weed Mimosa pigra L. (Mimosaceae). We used controlled experiments to determine whether larvae of different developmental stages can destroy mimosa seedlings, whether larvae can survive and develop when feeding on root nodules, whether larvae prefer root nodules or seedlings, and the importance of N₂ fixation to mimosa. One third instar larva destroyed a mean of 1.6 seedlings overall, although this varied with larval density. First instar larvae spent more time on seedlings than on nodules, but final instar larvae spent more time on nodules. Larvae survived and developed on root nodules and on seedlings. Mimosa plants growing in pots only produced high numbers of root nodules when growing in low N conditions, indicating that mimosa responds to soil low N status by increasing symbiotic N₂ fixation. The higher N content in mimosa leaves than leaves of native plants from north Australian wetlands, and the ability to vigorously nodulate in conditions with a low N supply suggest that mimosa relies on N₂ fixation during times of low soil N availability and at sites with low N status. We propose that Malacorhinus below ground herbivory on root nodules and seedlings complements the above ground herbivory of other established biocontrol agents against mimosa.     

Nesaecrepida infuscata: a biological control agent of the invasive plant Mimosa pigra

Mimosa pigra L. is a serious weed of wetlands of Australia, Asia and Africa. A suite of established biocontrol agents have been introduced in Australia and some Asian countries, but better control is needed. Nesaecrepida infuscata (Schaeffer) (Coleoptera: Chrysomelidae) is a common insect on M. pigra in tropical America. The larvae develop on the roots while the adults feed on the leaves. As both roots and leaves of M. pigra are relatively undamaged in the introduced range, this species has potential to limit the growth, survival and seed production. Furthermore, it is abundant in the dry season and so inflicts damage when most other agents are not active. In host specificity tests, larvae did not develop on any of the 65 test plant species other than M. pigra. Adult feeding on test plant species other than M. pigra was minimal. Based on these results, this insect has been released in Australia.     

Revegetation of a wetland following control of the invasive woody weed, Mimosa pigra, in the Northern Territory, 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.     

Observations on the life cycle and establishment ofCochylis atricapitana (Lep: Cochylidae), a moth used for biological control ofSenecio jacobaea in Australia

Larvae of the mothCochylis atricapitana (Stephens) are monophagous leaf, crown, stem or bud borers of ragwort,Senecio jacobaea L. (Asteraceae). In the present investigation, aspects of the life cycle ofC. atricapitana were determined. Moths ofC. atricapitana lay an average of 158 eggs/female with as many as 355 eggs being laid by a single female. The majority of eggs are laid individually along the primary and secondary veins on the underside of ragwort leaves. Egg incubation ranges from 4.2 days at 30°C to 14.4 days at 15°C. At a constant 23°C under a 16 hour photoperiod,C. atricapitana takes approximately 40 days to complete a generation. Caterpillars make their way to young, actively growing ragwort shoots or buds, and begin mining into the plant tissue, boring into the leaf, crown, stem or bud.C. atricapitana has five larval instars and enters diapause as a final instar larva. In southern Victoria, moths ofC. atricapitana fly from late September through to the beginning of February. Adults emerge after overwintering towards the end of spring or beginning of summer.C. atricapitana has established at two sites while larvae, or signs of damage have been observed at approximately 52% of release sites.      

Biological control: Premises,ecological input and Mimosa pigra in the wetlands of Australia's Top End

The adverse impacts of weeds on natural ecosystems, together with the inadequate outcomes from treating weeds as a symptom, have escalated interest in finding efficacious control methods. With the aim of protecting wetlands from invasive weeds, this contribution uses the woody shrub Mimosa pigra L. (mimosa) as a case history to examine the methodology of classical biological control and the reasons for the widely accepted 75% failure rate. Overall objectives are for all biocontrol agents to have the opportunity to fully express their potential and to insure that limited resources are spent wisely on attainable weed control. The three main conclusions were that (1) the premises on which biocontrol is based has restricted advancement of this method; (2) monitoring is the logical first step to improving the selection of agents and release sites; and (3) it may be more cost-effective to introduce fewer agents that have undergone agent/plant and host/home range pre- and post-release ecological studies. Weed control may remain elusive unless advantage is taken of every beneficial result. Innovative assistance to agents and the integration of different control methods may preserve a role for weed biological control and has the potential to be of great importance for future weed management. It is proposed that the climate in the Top End of the Northern Territory and the lack of competition on the floodplains has contributed to mimosa's invasiveness. Climate may also underly the difficulties faced by agents. Agents appear unable to impart effective control in the dry season because of low numbers which relates to mimosa's poor growth; nor in the wet season, when the impact from high numbers of agents is outstripped by mimosa's growth.     

Phytochemical investigation of Mimosa pigra leaves,a sensitive species

Mimosa pigra L. is an invasive species that grows with related species called M. pudica L. M. pudica is a dietary supplement, marketing in the United States, with a claim of supporting the immune system. It is known that M. pudica has been misidentified with M. pigra L. As part of our ongoing research endeavors to identify the chemical constituents of broadly consumed herbal supplements or their adulterants, a detailed phytochemical investigation of M. pigra was undertaken. As a result, seven specialized metabolites, including six flavonoid-O-glycosides were isolated from the leaves of M. pigra. The isolated chemical constituents in this study could be used as chemical markers to differentiate M. pigra-based raw materials in various finished products, including the quality of dietary supplements claimed to contain M. pudica.     

The effects of the herbicide tebuthiuron on seedlings of Mimosa pigra and native floodplain vegetation in northern Australia

Abstract We studied the seedbank of floodplain vegetation in three major tropical river systems in northern Australia, which had been variously invaded by the tropical woody weed Mimosa pigra. The sites selected had not previously been treated with tebuthiuron, a herbicide which is widely used in northern Australia to control Mimosa. We collected soil seedbank samples from two floodplain vegetation types (Melaleuca swamp and sedgeland), and, within each type, from areas in which Mimosa was either present or absent. The effects of treatment with tebuthiuron at 15 kg ha^?1, twice the usual recommended rate, was subsequently assessed in die laboratory on the soil-seedbank samples. Ordination of the species composition of seedlings which emerged from the soil seedbank samples showed no effect of (i) the vegetation community from which the samples were collected, (ii) the presence of adult Mimosa, or (iii) treatment with tebuthiuron. The effect of tebuthiuron on the emergence and mortality of seedlings from four functional groups (grasses, sedges, forbs and Mimosa) was also tested on the seed bank samples. Emergence was significantly decreased by tebuthiuron only for forbs from Melaleuca swamps. The mortality of Mimosa was significantly higher than that of the other functional groups, but there was some mortality of forb and grass seedlings. Sedges, however, were unaffected. The impact of tebuthiuron on Mimosa depended on soil clay content—in the soils with lowest clay content, tebuthiuron was the most effective in killing Mimosa seedlings. Mortality in forb and grass seedlings, in contrast, was not affected by soil clay content. Tebuthiuron was therefore selective against Mimosa seedlings. However, even at twice the recommended rate of application for killing adult Mimosa, under ideal conditions for distribution of the herbicide through the soil, 43% of Mimosa seedlings survived. Given the size of the Mimosa seedbank under field conditions (～10 000 seeds/m²), tebuthiuron can therefore not be considered an effective herbicide against Mimosa seedlings.     

Establishment,distribution and abundance of <Emphasis Type="Italic">Mimosa pigra</Emphasis> biological control agents in northern Australia: implications for biological control

Mimosa pigra L. is one of the most troublesome weeds in northern Australia, and is the target of a large biological control program, with 14 agents released to date. This paper describes surveys conducted between 1997 and 2004, for eight of these biological control agents. Surveys assessed the establishment of key agents. Both distribution and abundance of the most damaging agent, the stem-borer Carmenta mimosa Eichlin and Passoa (Lep.: Sesiidae), increased during the eight year period and the moth is now present in all catchments with major M. pigra infestations. The tip-borer, Neurostrota gunniella Busck (Lep.: Gracillariidae) is present in all M. pigra infestations, attacking 94% of tips. The leaf and flower-feeder, Coelocephalapion pigrae Kissinger (Col., Curculionidae) is widespread and its abundance is stable. Neither Acanthoscelides puniceus Johnson (Col., Bruchidae) nor Chlamisus mimosae Karren (Col., Chrysomelidae) were widespread or abundant when surveys commenced and populations declined during the survey period. The nocturnal beetle Malacorhinus irregularis Jacoby (Col., Chrysomelidae) was not found during these surveys, but later searches using different methods found it at three sites. Six other agents appeared not to have established, or are present at densities too low to be detected. How the results of these surveys affect management of M. pigra, and projections for future impacts against this weed are discussed. Using survey results and published literature we concluded that (1) seed and flower feeders must be capable of surviving periods of low food availability; (2) some climate matching may be beneficial before fungal biocontrol agents are released and (3) even in well studied systems such as M. pigra, the failure of an agent to establish cannot always be explained.     

Beta-rhizobia from Mimosa pigra, a newly discovered invasive plant in Taiwan

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.     

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 .     

Mimosa pigra in eastern and southern Africa: Distribution and socio‐ecological impacts

The semiaquatic weed Mimosa pigra has negative impacts on biodiversity, fishing, crop and livestock production, and tourism in most places where it has been introduced, established and proliferated. Many of the ecological impacts are well known, but its impacts on rural livelihoods are less well documented, especially in Africa. We mapped the distribution of M. pigra in eastern and southern Africa, and then compared that with its potential distribution based on an ecoclimatic niche model. Household interviews were conducted to assess the impacts of this weed on local livelihoods. Mimosa pigra was found to be invasive in western Ethiopia, around the shores of Lake Victoria and Lake Tanganyika, and along the Tanzanian coastline, northern Malawi, parts of Mozambique and along the Kafue River and in the Barotse floodplain on the Zambezi River in Zambia. According to respondents living along the Kafue River floodplains in Zambia, it has a negative impact on biodiversity, wildlife, livestock, crop production, fishing and mobility. Dense stands prevented the movement of people and livestock, limiting access to croplands, grazing lands and fishing areas. Fish catches have been reduced and fishing equipment damaged. All respondents agreed that their livelihood options would be considerably enhanced if M. pigra was removed from the landscape. Based on its current and potential impact, we therefore recommend that an integrated management plan be developed and implemented, including the appropriate use of biological control agents to reduce the negative impacts of the weed.     

Post-dispersal seed predation of an exotic weed,Mimosa pigra L., in the Northern Territory

The removal of seeds of the exotic shrub Mimosa pigra from the ground beneath a thicket of the plant and from the open floodplain surrounding the thicket was studied experimentally. Seeds placed beneath the canopy of the M. pigra thicket were taken predominantly by vertebrates (probably omnivorous rodents) while those on the open floodplain were taken predominantly by ants. After 14 days exposure with no barriers to seed removal, less than half of the seeds placed in either habitat had disappeared. Of the seeds that were removed, over 75% had disappeared from both habitats within 5 days. It is unlikely that post-dispersal seed predation appreciably inhibits the spread or maintenance of stands of this weed in tropical Australia.     

Effect of defoliation treatment on Mimosa pigra L. seedling survivability and resilience

Current advancements in the study of the theoretical basis of species interactions are helping scientists understand the basic parameters governing the dynamics of the interactions between generalist herbivores and their target plants. In practice, however, both inter- and intra-specific interactions between plants (as well as between herbivores and plants) within multispecies systems that are under the influence of interrelated biotic and abiotic variables are difficult to predict. Here, we discuss our findings on the effect of simulated herbivory on Mimosa pigra L. leaves on seedling survivability. In Malaysia, M. pigra, a semi-aquatic invasive plant introduced from the South American region, is already creating an ecological problem, especially in wetland habitats. To better understand the impact of herbivores on the M. pigra population, a simulated experiment of the herbivory effect on Mimosa seedlings was conducted. This experiment combined two treatments of simulated herbivory on the leaves of established Mimosa seedlings, that is, a two-level intensity treatment (50 and 100 % defoliation) and a seven-level frequency treatment (one to seven defoliations). The data suggest that Mimosa is highly resilient against herbivory. This plant was able to compensate for repeated losses, thus suggesting that the introduction of herbivores in an effort to totally eradicate the Mimosa population is unlikely to be successful.     

Life cycle and host range of Phycita sp. rejected for biological control of prickly acacia in Australia

Prickly acacia (Vachellia nilotica subsp. indica), a native of the Indian subcontinent, is a serious weed of the grazing areas of northern Australia and is a target for classical biological control. Native range surveys in India identified a leaf webber, Phycita sp. (Lepidoptera: Pyralidae) as a prospective biological control agent for prickly acacia. In this study, we report the life cycle and host‐specificity test results Phycita sp. and highlight the contradictory results between the no‐choice tests in India and Australia and the field host range in India. In no‐choice tests in India and Australia, Phycita sp. completed development on two of 11 and 16 of 27 non‐target test plant species, respectively. Although Phycita sp. fed and completed development on two non‐target test plant species (Vachellia planifrons and V. leucophloea) in no‐choice tests in India, there was no evidence of the insect on the two non‐target test plant species in the field. Our contention is that oviposition behaviour could be the key mechanism in host selection of Phycita sp., resulting in its incidence only on prickly acacia in India. This is supported by paired oviposition choice tests involving three test plant species (Acacia baileyana, A. mearnsii and A. deanei) in quarantine in Australia, where eggs were laid only on prickly acacia. However, in paired oviposition choice trials, only few eggs were laid, making the results unreliable. Although oviposition choice tests suggest that prickly acacia is the most preferred and natural host, difficulties in conducting choice oviposition tests with fully grown trees under quarantine conditions in Australia and the logistic difficulties of conducting open‐field tests with fully grown native Australian plants in India have led to rejection of Phycita sp. as a potential biological control agent for prickly acacia in Australia.     

The life history and host range of Ectagagarcia, a biological control agent for Lantana camra and L. montevidensis in Australia

The life cycle and host specificity of Ectaga garcia were investigated. Moths emerge in the morning and are inactive during the day. Eggs are laid and larvae feed on the undersurface of leaves of Lantana camara and L. montevidensis. Larvae spin protective cocoons from which they feed and in which they pupate. Development from egg to adult takes approximately 48 days. Forty-five plant species were tested to determine host specificity. Females laid eggs only on L. camara and L. montevidensis. In no-choice trials, neonate larvae fed but failed to complete development on nine test species. E. garcia was subsequently approved for release in Australia.