Major Environmental Weed Research Articles

Comparison of growth traits between abundant and uncommon forms of a non-native vine, Dolichandra unguis-cati (Bignoniaceae) in Australia

Cat’s claw creeper vine, Dolichandra unguis-cati (L.) Lohmann (syn. Macfadyena unguis-cati (L.) Gentry) (Bignoniaceae), is a major environmental weed in Australia. Two distinct forms of this weed (‘long’ and ‘short’ pod), with differences in leaf morphology and fruit size, occur in Australia. The long pod form has only been reported in less than fifteen localities in the whole of south-east Queensland, while the short pod form is widely distributed in Queensland and New South Wales. This study sought to compare growth traits such as specific leaf area, relative growth rate, stem length, shoot/root ratio, tuber biomass and branching architecture between these forms. These traits were monitored under glasshouse conditions over a period of 18 months. Short pod exhibited higher values of relative growth rates, stem length, number of tubers and specific leaf area than long pod, but only after 10 months of plant growth. Prior to this, long and short pod did not differ significantly. Higher values for these traits have been described as characteristics of successful colonizers. Results from this study could partly explain why the short pod form is more widely distributed in Australia while long pod is confined to a few localities.

Germination Biology and Occurrence of Polyembryony in Two Forms of Cats Claw Creeper Vine, <i>Dolichandra unguis-cati</i> (Bignoniaceae): Implications for Its Invasiveness and Management

Cat’s claw creeper vine, Dolichandra unguis-cati (L.) Lohmann (syn. Macfadyena unguis-cati (L.) Gentry), is a major environmental weed in Australia. Two forms (“long” and “short” pod) of the weed occur in Australia. This investigation aimed to evaluate and compare germination behavior and occurrence of polyembryony (production of multiple seedlings from a single seed) in the two forms of the weed. Seeds were germinated in growth chambers set to 10/20°C, 15/25°C, 20/30°C, 30/45°C and 25°C, representing ambient temperature conditions of the region. Germination and polyembryony were monitored over a period of 12 weeks. For all the treatments in this study, seeds from the short pod form exhibited significantly higher germination rates and higher occurrence of polyembryony than those from the long pod form. Seeds from the long pod form did not germinate at the lowest temperature of 10/20°C; in contrast, those of the short pod form germinated under this condition, albeit at a lower rate. Results from this study could explain why the short pod form of D. unguis-cati is the more widely distributed form in Australia, while the long pod form is confined to a few localities. The results have implication in predicting future ranges of both forms of the invasive D. unguis-cati, as well as inform management decisions for control of the weed.

Influence of Shade on the Persistence ofGargaphia decoris(Tingidae), a Biological Control Agent ofSolanum mauritianum(Solanaceae) in South Africa

Solanum mauritianum Scop. (bugweed, woolly nightshade; Solanaceae), a small perennial tree from South America, is a major environmental weed in South Africa and elsewhere in the world (see review by Olckers 2011). Bugweed populations persist in a variety of habitats in South Africa, ranging from sunny, exposed habitats (e.g. grasslands, savanna and roadsides) to partially shaded and fully shaded habitats (e.g. forest/plantation margins and understoreys, respectively). The lace bug Gargaphia decoris Drake (Hemiptera: Tingidae) was released in South Africa in 1999, and later in New Zealand in 2010, for the biological control of S. mauritianum (Olckers 2000, 2011; Olckers & Borea 2009). As is typical of lace bugs (e.g. Buntin et al. 1996), high levels of sap-sucking by the adults and nymphs can reduce the plant's growth rate as a result of leaf chlorosis, reduced rates of photosynthesis and transpiration, as well as premature leaf abscission.

Corynespora cassiicola f. sp. schinii, a Potential Biocontrol Agent for the Weed Schinus terebinthifolius in the United States

Schinus terebinthifolius (Anacardiaceae), Brazilian peppertree (BP), is a major environmental weed in many tropical and subtropical areas of the globe, including Florida, Hawai'i, and Australia. This plant has been the target of a classical biocontrol project in the United States involving pathogens collected in Brazil for several years. A fungus was found in the Brazilian state of Espírito Santo causing leaf spots and severe foliage blight on BP. Examination of the morphology and internal transcribed spacer sequence analysis confirmed that the fungus is a strain of Corynespora cassiicola. Preliminary host-range tests involving 24 species, including 11 species in the family Anacardiaceae, were conducted with the fungus, and specificity toward BP was confirmed. Plants of Brazilian pepper tree from populations in Florida and Hawai'i included in the tests became severely diseased. Therefore, the recognition of a new forma specialis-Corynespora cassiicola f. sp. schinii-is proposed. The specificity of this forma specialis and the severity of the disease it caused in the field and under controlled conditions indicate that it has the potential for use as a biocontrol agent for BP in areas where it is an exotic invasive species.

Cat's claw creeper leaf‐mining jewel beetle Hylaeogena jureceki Obenberger (Coleoptera: Buprestidae), a host‐specific biological control agent for Dolichandra unguis‐cati (Bignoniaceae) in Australia

AbstractCat's claw creeper, Dolichandra unguis‐cati (L.) L.G. Lohman (syn: Macfadyena unguis‐cati (L.) A.H. Gentry) (Bignoniaceae), a major environmental weed in Queensland and New South Wales, is a Weed of National Significance and an approved target for biological control. A leaf‐mining jewel beetle, Hylaeogena jureceki Obenberger (Coleoptera: Buprestidae), first collected in 2002 from D. unguis‐cati in Brazil and Argentina, was imported from South Africa into a quarantine facility in Brisbane in 2009 for host‐specificity testing. H. jureceki adults chew holes in leaves and lay eggs on leaf margins and the emerging larvae mine within the leaves of D. unguis‐cati. The generation time (egg to adult) of H. jureceki under quarantine conditions was 55.4 ± 0.2 days. Host‐specificity trials conducted in Australia on 38 plant species from 11 families supplement and support South African studies which indicated that H. jureceki is highly host‐specific and does not pose a risk to any non‐target plant species in Australia. In no‐choice tests, adults survived significantly longer (>32 weeks) on D. unguis‐cati than on non‐target test plant species (<3 weeks). Oviposition occurred on D. unguis‐cati and one non‐target test plant species, Citharexylum spinosum (Verbenaceae), but no larval development occurred on the latter species. In choice tests involving D. unguis‐cati, C. spinosum and Avicennia marina (Avicenniaceae), feeding and oviposition were evident only on D. unguis‐cati. The insect was approved for field release in Australia in May 2012.

Population dynamics of the invasive weedLupinus arboreusin Tasmania, and interactions with two non‐native pollinators

GoulsonD & RotherayEL (2012). Population dynamics of the invasive weedLupinus arboreusin Tasmania, and interactions with two non‐native pollinators.Weed Research52, 535–541.SummaryThe factors that determine which plant species become invasive weeds are not well understood and there have been few studies of population dynamics in the early stages of invasion. Here, we examine changes in population size, pollinator visitation and seed set of the tree lupin,Lupinus arboreus, in Tasmania between 1999 and 2010.Lupinus arboreusis a native of California that has become a major environmental weed in New Zealand and Chile, but has not yet become a serious weed in Tasmania. Our data suggest that the main pollinators ofL. arboreusare honeybees and the bumblebee,Bombus terrestris, which invaded in 1992. There was no clear evidence for an impact of the arrival of bumblebees.Lupinus arboreuspopulation size increased by 76% between 1999 and 2010, despite weed control programmes. Populations appeared to be unstable; 43% of populations detected in 1999 were extinct by 2010, but this was more than offset by establishment of new populations. Inland populations tended to be smaller and were more likely to go extinct, compared with coastal populations, and some coastal populations had increased fourfold in 11 years. Large populations in 2010 tended to have higher seed set than smaller populations. The overall rate of increase suggests thatL. arboreusmay become a major environmental weed in Tasmania. Control of expanding populations is likely to become more difficult if, as we observed, seed set increases with population size.

Cat's claw creeper vine, Macfadyena unguis-cati (Bignoniaceae), invasion impacts: comparative leaf nutrient content and effects on soil physicochemical properties

Macfadyena unguis-cati (L.) Gentry (Bignoniaceae) is a major environmental weed in coastal Queensland, Australia. There is a lack of quantitative data on its leaf chemistry and its impact on soil properties. Soils from infested vs uninfested areas, and leaves of M. unguis-cati and three co-occurring vine species (one exotic, two native) were collected at six sites (riparian and non-riparian) in south-eastern Queensland. Effects of invasion status, species, site and habitat type were examined using univariate and multivariate analyses. Habitat type had a greater effect on soil nutrients than on leaf chemistry. Invasion effect of M. unguis-cati on soil chemistry was more pronounced in non-riparian than in riparian habitat. Significantly higher values were obtained in M. unguis-cati infested (vs. uninfested) soils for ~50% of traits. Leaf ion concentrations differed significantly between exotic and native vines. Observed higher leaf-nutrient load (especially nitrogen, phosphorus and potassium) in exotic plants aligns with the preference of invasive plant species for disturbed habitats with higher nutrient input. Higher load of trace elements (aluminium, boron, cadmium and iron) in its leaves suggests that cycling of heavy-metal ions, many of which are potentially toxic at excess level, could be accelerated in soils of M. unguis-cati-invaded landscape. Although inferences from the present study are based on correlative data, the consistency of the patterns across many sites suggests that M. unguis-cati may improve soil fertility and influence nutrient cycling, perhaps through legacy effects of its own litter input.

Invasion impacts on biodiversity: responses of ant communities to infestation by cat’s claw creeper vine, Macfadyena unguis-cati (Bignoniaceae) in subtropical Australia

Ants are the dominant soil faunal group in many if not most terrestrial ecosystems, and play a key role in soil structure and function. This study documents the impacts of invasion by the exotic cat’s claw creeper vine, Macfadyena unguis-cati (L.) Gentry (Bignoniaceae) on surface-situated (epigaeic) and subterranean (hypogaeic) ant communities in subtropical SE Queensland Australia where it is a major environmental weed of riparian areas, rainforest communities and remnant natural vegetation, smothering standing vegetation and causing canopy collapse. Soil ants were sampled in infested and uninfested areas at eight sites spanning both riparian and non-riparian habitats in subtropical SE Queensland. Patterns of ant species composition and functional grouping in response to patch invasion status, landscape type and habitat stratum were investigated using ANOVA and non-metric multidimensional scaling ordination. The epigaeic and subterranean strata supported markedly different ant assemblages, and ant communities also differed between riparian and non-riparian habitats. However, M. unguis-cati invasion had a surprisingly limited impact. There was a tendency for ant abundance and species richness to be lower in infested patches, and overall species composition was different between infested and uninfested patches, but these differences were relatively small, and did not occur consistently across sites. There were changes in functional group composition that conformed to known functional group responses to environmental change, but these were similarly limited and inconsistent across sites. Our study has shown that ant communities are surprisingly resilient to invasion by M. unguis-cati, and serves as a warning against making assumptions about invasion impacts based on visual appearances.

What lies beneath? The pattern and abundance of the subterranean tuber bank of the invasive liana cat's claw creeper, Macfadyena unguis-cati (Bignoniaceae).

Cat’s claw creeper, Macfadyena unguis-cati (L.) Gentry (Bignoniaceae) is a major environmental weed of riparian areas, rainforest communities and remnant natural vegetation in coastal Queensland and New South Wales, Australia. In densely infested areas, it smothers standing vegetation, including large trees, and causes canopy collapse. Quantitative data on the ecology of this invasive vine are generally lacking. The present study examines the underground tuber traits of M. unguis-cati and explores their links with aboveground parameters at five infested sites spanning both riparian and inland vegetation. Tubers were abundant in terms of density (~1000 per m2), although small in size and low in level of interconnectivity. M. unguis-cati also exhibits multiple stems per plant. Of all traits screened, the link between stand (stem density) and tuber density was the most significant and yielded a promising bivariate relationship for the purposes of estimation, prediction and management of what lies beneath the soil surface of a given M. unguis-cati infestation site. The study also suggests that new recruitment is primarily from seeds, not from vegetative propagation as previously thought. The results highlight the need for future biological-control efforts to focus on introducing specialist seed- and pod-feeding insects to reduce seed-output.

Assessing the risks of releasing a sap-sucking lace bug, Gargaphia decoris, against the invasive tree Solanum mauritianum in New Zealand

The South American tree Solanum mauritianum Scopoli (Solanaceae), a major environmental weed in South Africa and New Zealand, has been targeted for biological control, with releases of agents restricted to South Africa. The leaf-sucking lace bug, Gargaphia decoris Drake (Tingidae), so far the only agent released, has become established in South Africa with recent reports of severe damage at a few field sites. To evaluate the insect’s suitability for release in New Zealand, host-specificity testing was carried out in South Africa in laboratory and open-field trials, with selected cultivated and native species of Solanum from New Zealand. No-choice tests confirmed the results of earlier trials that none of the three native New Zealand Solanum species are acceptable as hosts. Although the cultivated Solanum muricatum Aiton and S. quitoense Lam. also proved unacceptable as hosts, some cultivars of S. melongena L. (eggplant) supported feeding, development and oviposition in the no-choice tests. Although eggplant was routinely accepted under laboratory no-choice conditions in this and previous studies, observations in the native and introduced range of G. decoris, open-field trials and risk assessment based on multiple measures of insect performance indicate that the insect has a host range restricted to S. mauritianum. These results strongly support the proposed release of G. decoris in New Zealand because risks to non-target native and cultivated Solanum species appear to be negligible. An application for permission to release G. decoris in New Zealand will be submitted to the regulatory authority.

The leaf‐tying moth Hypocosmia pyrochroma (Lep., Pyralidae), a host‐specific biological control agent for cat's claw creeper Macfadyena unguis‐cati (Bignoniaceae) in Australia

Abstract: Cat's claw creeper, Macfadyena unguis‐cati, a major environmental weed in coastal and sub‐coastal areas of Queensland and New South Wales, Australia is a target for classical biological control. Host specificity of Hypocosmia pyrochroma Jones (Lep., Pyralidae), as a potential biological control agent was evaluated on the basis of no‐choice and choice larval feeding and survival, and adult oviposition preference tests, involving 38 plant species in 10 families. In no‐choice tests, larval feeding and development occurred only on cat's claw creeper. In choice tests, oviposition and larval development was evident only on cat's claw creeper. The results support the host‐specificity tests conducted in South Africa, and suggest that H. pyrochroma is a highly specific biological control agent that does not pose any risk to non‐target plants tested in Australia. This agent has been approved for field release by relevant regulatory authorities in Australia.

Specificity of Carvalhotingis visenda (Hemiptera: Tingidae) as a biological control agent for cat’s claw creeper Macfadyena unguis-cati (Bignoniaceae) in Australia

Biological control is considered the most suitable management option for cat's claw creeper, Macfadyena unguis-cati, a major environmental weed in coastal and sub-coastal areas of Queensland and New South Wales, Australia. The potential host range of the leaf-sucking bug, Carvalhotingis visenda (Hemiptera: Tingidae) was evaluated on the basis of nymphal survival and development, adult feeding and survival, and oviposition preference using choice and no-choice tests involving 38 plant species in 10 families. In no-choice tests, although adults survived on a few of the non-target plants, no eggs were laid on any of the non-target plants. In no-choice condition, the tingid oviposits and completes nymphal development only on M. unguis-cati. There was also no visible feeding damage on any of the non-target plants. In choice tests, adults showed distinct preference for M. unguis-cati, and the preference level increased over time as the tingids moved away from the non-target plants. At the end of the trial no adults were evident on any of the non-target plants. Host specificity tests confirm that the tingid is a highly host specific biocontrol agent, and does not pose risk to any non-target plants in Australia. This agent has been approved for field release by the relevant regulatory authorities in Australia.

The effects on terrestrial arthropod communities of invasion of a coastal heath ecosystem by the exotic weed bitou bush (Chrysanthemoides monilifera ssp. rotundata L.)

Bitou bush (Chrysanthemoides monilifera ssp. rotundata) is a major environmental weed of littoral habitats on the southeastern coast of Australia. This study investigates the impacts upon selected arthropod assemblages of habitat invasion by this weed. Sixteen sites were placed at four geographic localities within nature reserves between Forster and Budgewoi on the coast of New South Wales. The sampling design included two spatial scales (between and within localities) and eight repeat samples (taken at two scales of temporal separation). Arthropods were collected from both arboreal and epigaeic micro-habitats. Specimens of ants (Hymenoptera: Formicidae), beetles (Coleoptera), true bugs (Heteroptera) and spiders (Araneae) were identified to species level. Differences in α diversity and species abundance distributions between the taxonomic assemblages are described, along with comparisons of data contrasts between bitou bush-free (“control”) and bitou bush-invaded (“impact”) habitats and between geographic localities. A subsidiary impact associated with herbicide application for control of the weed is also examined. Analysis of environmental differences indicates that bitou bush acts as a dampening agent, reducing the degree of seasonal fluctuation in factors such as leaf litter cover. Arboreal Heteroptera were the only group to show consistent evidence of significant differences in taxon richness or abundance between control and impact treatments within a locality, seen as a disruption of normal seasonal variation in diversity in bitou bush-impacted sites. Significant differences between geographic localities were more common, suggesting an effect at broader spatial scales. Evidence for arthropod assemblages characteristic of specific vegetation types was detected for several groups, as were changes in arthropod assemblage composition following application of herbicide for bitou bush control.

Harnessing nature to improve sustainability

Harnessing nature to improve sustainability

Biology, host specificity and risk assessment of the leaf-mining flea beetle, Acallepitrix sp. nov., a candidate agent for the biological control of the invasive tree Solanum mauritianum in South Africa

The South American tree Solanum mauritianum, a major environmentalweed in the high-rainfall regions of SouthAfrica, has proved to be a difficult target forbiological control. Artificially expanded hostranges of candidate agents during quarantinehost-specificity tests, have resulted in therelease of only one agent species which has sofar had a negligible impact on the weed. Thenecessity for additional agents resulted in theimportation of a leaf-mining flea beetle, anunidentified species of Acallepitrix,from Brazil in 1997. No-choice tests inquarantine showed that potential host plantsare confined to the genus Solanum.Although several non-target plants, includingcultivated eggplant (aubergine) and some nativeSouth African Solanum species, sustainedfeeding, oviposition and the development oflarval leaf mines, most of these were inferiorhosts. These results were confirmed by pairedchoice tests, where Acallepitrix sp. nov.displayed significant feeding and ovipositionpreferences for S. mauritianum and where,with few exceptions, more larval leaf mineswere initiated on S. mauritianum.Interpretation of the host-specificity testswas facilitated by a risk assessment matrixwhich suggested that the risk of feeding andoviposition on non-target Solanum plants,including eggplant cultivations, was relativelylow. These and other considerations, such asthe lack of evidence of damage inflicted oncultivated Solanaceae in South America, suggestthat Acallepitrix sp. nov. could beconsidered for release against S. mauritianum in South Africa. However, the results of the host-specificity tests remain ambiguous and until more compelling evidence is obtained from field surveys and open-field trials in Brazil, an application for permission to release the flea beetle in South Africa will not be considered.

The Essential Oil of Cinnamomum camphora (L.) Nees and Eberm.—Variation in Oil Composition Throughout the Tree in Two Chemotypes from Eastern Australia

The camphor tree, Cinnamomum camphora (L.) Nees et Eberm., is a major environmental weed in parts of eastern Australia, particularly in northeastern New South Wales. It occurs in this region in two chemotypic forms, discriminated on the basis of leaf oil: camphor and 1,8-cineole. Oil was extracted from various parts of trees of each of these chemotypes: leaf, fruit, branch, trunk and root. Analysis of the oil revealed that, for the camphor-type, camphor content was greater in leaves than in other tree parts, where cineole and safrole were also present in substantial proportions; and, for the cineole-type, 1,8-cineole, which with lesser quantities of sabinene and citronellol dominated the leaf oil, is reduced in significance in the trunk where camphor is also an important constituent.

The Essential Oil of Cinnamomum camphora (L.) Nees and Eberm.—Variation in Oil Composition Throughout the Tree in Two Chemotypes from Eastern Australia

The camphor tree, Cinnamomum camphora (L.) Nees et Eberm., is a major environmental weed in parts of eastern Australia, particularly in northeastern New South Wales. It occurs in this region in two chemotypic forms, discriminated on the basis of leaf oil: camphor and 1,8-cineole. Oil was extracted from various parts of trees of each of these chemotypes: leaf, fruit, branch, trunk and root. Analysis of the oil revealed that, for the camphor-type, camphor content was greater in leaves than in other tree parts, where cineole and safrole were also present in substantial proportions; and, for the cineole-type, 1,8-cineole, which with lesser quantities of sabinene and citronellol dominated the leaf oil, is reduced in significance in the trunk where camphor is also an important constituent.

Assessing the risks associated with the release of a flowerbud weevil, Anthonomus santacruzi, against the invasive tree Solanum mauritianum in South Africa

Abstract Biological control of Solanum mauritianum Scopoli, a major environmental weed in the high-rainfall regions of South Africa, is dependent on the establishment of agents that can reduce fruiting and limit seed dispersal. The flowerbud weevil, Anthonomus santacruzi Hustache, is a promising fruit-reducing agent, despite ambiguous results obtained during host-specificity evaluations in quarantine. Adult no-choice tests showed that although feeding is confined to Solanum species, normal feeding and survival occurred on the foliage (devoid of floral material) of cultivated eggplant (aubergine), potato, and several native South African Solanum species. During paired-choice tests, involving floral bouquets in 10-liter containers, A. santacruzi oviposited in the flower buds of 12 of the 17 test species, including potato and eggplant, although significantly more larvae were recovered on S. mauritianum than on eight other species. Larvae survived to adults on all 12 species, with survival significantly lower on only four species than on S. mauritianum . However, during multi-choice tests, involving potted plants in a large walk-in cage, A. santacruzi consistently displayed significant feeding and oviposition preferences for S. mauritianum over all of the 14 Solanum species tested. Analyses of the risk of attack on nontarget Solanum plants suggested that, with the possible exception of two native species, none is likely to be extensively utilized as a host in the field. Also, host records and field surveys in South America have suggested that A. santacruzi has a very narrow host range and that the ambiguous laboratory results are further examples of artificially expanded host ranges. These and other considerations suggest that A. santacruzi should be considered for release against S. mauritianum in South Africa, and an application for permission to release the weevil was submitted in 2003.

Biology and host range of the stem-boring beetle Aphanasium australe , a promising agent for the biological control of Hakea sericea in South Africa

The invasive Australian shrubHakea sericea Shrader is a majorenvironmental weed in the Western and EasternCape Provinces of South Africa. Dense,impenetrable thickets severely threaten theunique endemic vegetation of the Cape FloristicKingdom, increase fire hazards and reduce wateryields in catchments. Biological control,initiated in the 1970s, is largely confined tothe use of seed-feeding insect agents. Becausenone of these agents reduce the density ofexisting hakea populations, a stem-boringbeetle, Aphanasium australe (Boisduval) (Cerambycidae),was imported into quarantine in South Africa in1975. During multichoice oviposition tests,involving 12 Australian and six South Africanproteaceous species, in a walk-in cage, A. australe only oviposited on four species ofHakea and two exotic species of Grevillea. However, culturing difficultiesresulted in the suspension of host-specificitytesting after three years. Testing was resumedfollowing re-importations in 1995, also becauseA. australe also attacks Hakeagibbosa (Sm.) Cav., which is not attacked byany of the existing biocontrol agents. Duringno-choice survival tests, involving 66test plant species from 15 families, A. australe only developed on H. sericea, H. gibbosa and one exoticspecies of Grevillea. The contention thatA. australe is confined to the genus Hakea was confirmed by host records andsurveys in Australia which provided no evidenceof attacks on crop, pasture or related plants.The regulatory authorities accepted theseresults and A. australe was cleared forrelease in South Africa during 2001.

Replacement of littoral native vegetation with the ponded pasture grass Hymenachne amplexicaulis: effects on plant, macroinvertebrate and fish biodiversity of backwaters in the Fitzroy River, Central Queensland, Australia

Changes in plant and macroinvertebrate communities were found following replacement of extensive zones of floating-attached/submergent native vegetation within Fitzroy River backwaters by the major environmental weed Hymenachne amplexicaulis (Poaceae). Impacts of H. amplexicaulis on native littoral flora and fauna (macroinvertebrates and fish) were assessed by comparing three sites previously supporting native vegetation and now invaded by H. amplexicaulis with nearby stands of native backwater vegetation. Plant biomass of Hymenachne plant beds was 30-fold greater than native plant beds, whereas plant species diversity (richness) was significantly less. Macroinvertebrate communities of Hymenachne beds were significantly lower in abundance of insect orders Ephemeroptera, Hemiptera and Odonata, while Coleoptera were more abundant in Hymenachne beds. Non-metric multidimensional scaling ordination of macroinvertebrate family abundance and composition data showed that Hymenachne plant beds had a different assemblage to that in native plant beds. In common with other studies of weed invasions, an increased abundance of some vertebrate fauna was observed (in this case an introduced fish species Xiphophorus maculatus comprised 75% of fish captured in Hymenachne beds compared with 0% in native plant beds). Change in vegetation structure was implicated as an important factor influencing macroinvertebrate and fish faunal composition, and with potential to impact on waterbird habitat values of wetlands.