A preliminary assessment of the response of a native reptile assemblage to spot‐spraying invasive Bitou Bush with glyphosate herbicide

During recent work examining the effects of Bitou Bush (Chrysanthemoides monilifera ssp. rotundata) invasion on native reptile assemblages in coastal heathland vegetation in Eastern Australia, unplanned spot‐spraying of glyphosate occurred at some of our experimental sites invaded by Bitou Bush. We used this unexpected herbicide application as an opportunity to provide a preliminary assessment of the short‐term impacts on reptiles of glyphosate spot‐spraying of Bitou Bush. Using an M‐BARCI design, we compared reptile assemblages among uninvaded (reference) sites, invaded (control) sites and invaded and sprayed (impact) sites before and after spraying. We found no significant short‐term (7 – 10 months) differences in reptile abundance, species richness or assemblage composition among invaded, uninvaded and sprayed sites before and after glyphosate application. We cautiously interpret our results to generate a preliminary finding that spot‐spraying of Bitou Bush with glyphosate appears not to have a deleterious effect on reptile assemblages at seven and ten months following herbicide application. While we would not recommend basing management decisions on the outcomes of our study alone, we suggest that our findings can be used to assist in the development of strategic analyses of glyphosate impacts on native flora and fauna.     

Development of a Pesticide Exclusion Technique for Assessing the Impact of Biological Control Agents for Chrysanthemoides monilifera

Seven biological control agents have been released on the environmental weed Chrysanthemoides monilifera in Australia and two are widely established on infestations of C. monilifera subsp. rotundata in New South Wales. Five pesticides were screened for their impact on seed production of C. monilifera and two on the survival of the agent Comostolopsis germana, a shoot tip-feeding lepidopteran. The insecticides carbaryl, carbofuran, dimethoate, fluvalinate and the fungicide benomyl had no significant effect on seed production of C. monilifera when applied over a period of four months. Numbers of C. germana larvae were readily suppressed after three months by applications of fluvalinate or a mixture of carbaryl, carbofuran and dimethoate. Shoot growth was not affected by applications of carbaryl, dimethoate and benomyl. It is concluded that exclusion by pesticides of biological control agents is a valid method of measuring the impact of agents on C. monilifera.     

Biotic resistance to Chrysanthemoides monilifera ssp. monilifera in Tasmania

Boneseed, Chrysanthemoides monilifera ssp. monilifera (Asteraceae) is concentrated in and near cities and towns on the north and east coasts of Tasmania. Its absence from intervening rural and bushland areas cannot be attributed to environmental conditions or a lack of time for dispersal from introduction points. The hypothesis tested in the present paper is that the range of boneseed in Tasmania is limited by biotic resistance through herbivory. Cafeteria experiments and field observations showed that sheep (Ovis aries), cattle (Bos taurus), Tasmanian pademelons (Thylogale billardierii), Bennett's wallabies (Macropus rufogriseus), garden weevils (Phlyctinus callosus) and native invertebrates all consumed boneseed, while common brushtail possums (Trichosurus vulpecula) did not. A boneseed population subjected to sheep grazing for 168 days suffered high mortality, while an adjacent ungrazed population survived intact. A replicated exclosure experiment showed that 75 days of grazing by cattle reduced the size of boneseed plants. Observations of a population subject to Bennett's wallaby and Tasmanian pademelon grazing over 1 year and 2 months showed consistently high leaf damage to foliage within pademelon reach and a decline in population, with high mortality rates in the driest and coldest times. Leaf loss attributable to invertebrates did not prevent a nearby population without wallabies from growing. The distributions of the taxa were consistent with biotic resistance, with those demonstrating no severe effect on boneseed individuals widespread, while those with evidence of severe effects more common in rural areas than in urban areas. Boneseed seemed unlikely to survive for very long at normal stocking levels. Macropod grazing, particularly that of T. billardierii, may also inhibit the invasion of boneseed. Thus, the recent introduction of foxes to Tasmania may not only cause the extinction of species such as T. billardierii, but also may cause an expansion of the range of boneseed.     

The effects on terrestrial arthropod communities of invasion of a coastal heath ecosystem by the exotic weed bitou bush (<Emphasis Type="Italic">Chrysanthemoides monilifera</Emphasis> ssp. <Emphasis Type="Italic">rotundata</Emphasis> 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.     

Establishment and rapid spread of the bitou seed fly, Mesoclanis polana Munro (Diptera: Tephritidae), in eastern Australia

The establishment and spread of the seed fly Mesoclanis polana Munro, an introduced biological control agent for Chrysanthemoides monilifera (L.) Norlindh, is described. From an initial release of 124 adult flies in August 1996, the species occupied virtually the entire range of bitou bush by October 1998, from Rainbow Beach in the north to Tathra in the south, a distance of over 1200 km. Early data on abundance are provided.     

Selection of Cassida spp. from southern Africa for the biological control of Chrysanthemoides monilifera in Australia

Four species of tortoise beetle (Chrysomelidae, Cassidinae) (Cassida spatiosa Spaeth and three undescribed Cassida species, labelled 1. 2 and 3) from South Africa, were assessed as potential biological control agents against Chrysanthemoides monilifera monilifera (L.) T. Norl. and C. m. rotundata (DC.) T. Norl. These southern African plants are important weeds of conservation areas in Australia. In South Africa, Cassida spatiosa was found feeding on C monilifera subcanescens (DC.) T. Norl., Cassida sp. 1 on Chrysanthemoides monilifera pisifera (L.) T. Norl. and C m. monilifera, Cassida sp. 2 on C m. pisifera and Chrysanthemoides incana (Burm.f.) T. Norl. and Cassida sp. 3 on C. m. rotundata. The life cycle of each species was completed in about three months on the leaves of the host. Cassida species 1, 2 and 3 were tested against eight species of plant and only fed and completed development on Chrysanthemoides species and the related species. Calendula officinalis L. Cassida species 1 and 3 showed no preference between Calendula officinalis and Chrysanthemoides species for oviposition. Cassida species 3 was selected for further assessment as a biological control agent based on match to the host subspecies and target climate in Australia.     

The impact of suburbanization on remnant coastal vegetation in Hobart,Tasmania

Abstract. Changes in vascular species composition and abundance were examined in coastal vegetation at Hobart, Tasmania, Australia over a period of 13 yr, during which suburbanization extended to cover a large proportion of its hinterland. There were significant increases in the richness and cover of exotic vascular plant species, most of which derived from the Mediterranean basin or southern Africa. While most of the introduced species were confined to vegetation with a high exotic component, and close to domestic gardens, some, including the South African coastal shrub, Chrysanthemoides monilifera, expanded in otherwise native vegetation relatively remote from gardens. The impact of proximity to gardens on the relative abundance of exotics and natives in coastal vegetation in 1997 best correlated with the pattern of distance from gardens in 1966, suggesting that there is, at least, a 30‐yr lag period in transformation from largely native to substantially exotic vegetation. This lag period provides an opportunity to reduce exotic invasion problems before they become severe.     

The potential for indirect effects between a weed, one of its biocontrol agents and native herbivores: A food web approach

The safety of biological control is a contentious issue. We suggest that constructing and analyzing food webs may be a valuable addition to standard biological control research techniques, as they offer a means of assessing the post-release safety of control agents. Using preliminary data to demonstrate the value of food webs in biocontrol programs, we quantified the extent to which a key agent has infiltrated natural communities in Australia and, potentially, impacted on non-target species. Using these data, we also demonstrate how food webs can be used to generate testable hypotheses regarding indirect interactions between introduced agents and non-target species. We developed food webs in communities invaded to varying degrees by an exotic weed, bitou bush, Chrysanthemoides monilifera ssp. rotundata, and a key biocontrol agent for this weed in Australia, the tephritid fly, Mesoclanis polana. Three food webs were constructed during springtime showing the interactions between plants, seed-feeding insects and their parasitoids. One food web was constructed in a plot of native Australian vegetation that was free of bitou bush (‘bitou-free’), another in a plot of Australian vegetation surrounded by an invasion of bitou bush (‘bitou-threatened’) and a third from a plot infested with a monoculture of bitou bush (‘bitou-infested’). The bitou-free web contained 36 species, the bitou-threatened plot 9 species and the bitou-infested web contained 6 species. One native Australian herbivore attacked the seeds of bitou bush. M. polana, a seed-feeding fly, was heavily attacked by native parasitoids, these being more abundant than the parasitoids feeding on the native seed feeders. A surprising result is that none of the three species of native parasitoids reared from M. polana were reared from any of the native herbivores. The food webs revealed how a highly host-specific biocontrol agent, such as M. polana has the potential to change community structure by increasing the abundance of native parasitoids. The webs also suggest that indirect interactions between M. polana and native non-target species are possible, these been mediated by shared parasitoids. The experiments necessary to determine the presence of these interactions are outlined.