Invasive plants have a significant detrimental effect on ecosystems globally, with impacts estimated at millions of dollars per invasive species each year. Biological control has long been used as a management tool for invasive plants, as it is considered a long–term cost–effective control strategy. Surprisingly, the impact of biological agents is rarely quantified. Any form of impact evaluation is generally conducted soon after agent release and establishment; with few studies examining the impact of the agents on the population dynamics of the invader, particularly once the agents have been established for a long time. The aim of the research in my thesis is to evaluate the biological control program of groundsel bush (Baccharis halimifolia L. Asteraceae) in Australia. The groundsel bush biological control agents were released up to 40 years ago and no quantitative assessment of agent impact has ever been conducted, despite the fact that the program has cost about $9.6 million. More specifically, the overall aim of this thesis is to investigate the impact of the released biological control agents on individual plants and populations of groundsel bush. In addition, my thesis aims to examine the impacts of climate as a potential confounding factor of the biological control program. My thesis provides a unique example of biological control evaluation by using a combination of observational damage studies, insect exclusion experiments, and statistical, population and climate modelling to assess, a posteriori, the effectiveness of biological control. This is the first time a long term biological control program has ever been evaluated. To assess the efficacy of the agents, I conducted a large field survey to examine whether the agents were distributed throughout the entire range of groundsel bush and if any biotic or abiotic factors influenced their effectiveness. In addition to this, I assessed the effect of the agents on the growth, survival and fecundity of individual plants under field conditions, and subsequently population growth rate. To do this, I used statistical models of observed effects of biological control agent damage and insect exclusion experiments on plant growth and fecundity to parameterise matrix population models. My results indicate that the groundsel bush biological control agents may be patchy in their effectiveness due to factors such as rainfall and plant size. At their current rate of damage, the groundsel bush biological control agents do not reduce plant growth or fecundity significantly. However, simulation models demonstrated that the agents have the potential to reduce individual plant and population growth when damage is at high levels. A reduction in an invader’s population growth rate, following the introduction of biological control agents, does not necessarily signify that the agents were responsible for the reduction. Factors such as land clearing, chemical and mechanical control, ecosystem health and climate may reduce populations of invasive plant species. With this in mind, I developed a series of climate models to examine how the favourability for growth of groundsel bush may change under different climate scenarios. The climate simulations demonstrated that the distribution and abundance of groundsel bush populations may have contracted in the past 50 years (post–biological control agent release) due to changing rainfall and temperature patterns. The results of the research in my thesis clearly show the need for thorough biological control evaluations, and for detailed data to be collected on the target plant’s demography and population sizes pre- and post-agent release. At a minimum, this should enable biological control practitioners to determine some level of agent impact and demonstrate support for further agent releases or integrative management strategies if necessary. Groundsel bush is a significant invader in Europe where biological control has not yet been carried out. Lessons from the evaluation of the Australian biological control program could be applied to new biological control programs elsewhere such as Europe. Overall, my research findings contribute to a better understanding of how to best evaluate a post-release biological control program, using groundsel bush as a case study. This is the first study to demonstrate an effective set of strategies and quantitative tools to evaluate a biological control program, which can be similarly applied to any biological control program and contributes significantly to an area of biological control which has only recently received significant attention.

Brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), has become an important pest of soybean in the Mid-Atlantic US. To assess the influence of tree borders on BMSB infestations in soybean, twelve fields were sampled weekly using five 3-min visual counts of BMSB on tree of heaven (TOH) (Ailanthus altissima) and other host trees along a wooded border, on the adjacent soybean edge, 15 m and 30 m into the soybean field. At all locations, BMSB densities increased on TOH wooded borders in July, then, gradually moved into adjacent soybean borders later in the summer. BMSB did not move far from the field edge, with approximately half as many bugs being present at 15 m into the field and very few being detected 30 m into the field. These results validate the use of border sprays for BMSB control in soybean. Additional studies conducted in 2013 and 2014 compared a visual plant inspection method with a standard sweep net strategy for sampling BMSB. Overall, the two methods were highly correlated with a correlation coefficient of R=0.83. Visual inspection appears to be an effective method for assessing BMSB populations in soybean. One of the major factors affecting the distribution and establishment of invasive species is climate. The CLIMEX modeling software uses climatic and biological factors of species to predict the geographic risk for pest outbreaks. A climate simulation model was run with CLIMEX to determine the potential distribution of BMSB in Virginia based on temperature. To develop a more accurate model, factors like resource availability and source population would need to be considered. / Master of Science in Life Sciences / Brown marmorated stink bug (BMSB) is a major pest of many crops, including soybean. Before moving into soybean the bug has been observed on other preferred hosts (primarily tree of heaven) in neighboring forest edges. To determine the relationship of these hosts to BMSB and its movement into soybean fields we sampled these forest edges, the neighboring field edge, 15 m into the field, and 30 m into the field. Results showed that BMSB populations were high on the forest edges early in the season and increased rapidly on neighboring field edge when soybeans begin developing pods and seeds. Bugs rarely moved past the 15 m sample zone. These results validate the use of border sprays for BMSB control in soybean. Sampling for BMSB with a sweep net has proven to be a challenge as the insect has a strong “startle response” where it will drop from the plant after slight disturbance. To assess the relationship between a standard sweep net sampling strategy and a new 2-min visual inspection method we sampled soybean fields in Virginia, Maryland and Delaware in 2013 and 2014. Data suggested that the 2-min visual inspection method can be used as an alternative to sweep net sampling. Climate plays a critical role in the geographic distribution of species. We ran a climate simulation model with CLIMEX (modeling software) to determine the potential distribution of BMSB in Virginia based on temperature. To develop a more accurate model, additional factors like resource availability and distance from source population would need to be considered.

The invasion of natural environments by alien species is a significant threat to the ecological integrity of these systems. Senna obtusifolia is an aggressive invasive weed recently introduced to Australia that is having significant impacts on grassland ecosystems on the Cape York Peninsula. Currently the species is inadequately managed and so range expansion continues. The invasion potential of S. obtusifolia in Australia remains unknown, as does much about its behaviour and management in natural systems. This project undertakes extensive mapping and modelling of the current and future distributions and the invasion dynamics of S. obtusifolia in Australia to facilitate early detection of outbreak populations and the development of appropriate management strategies. The mapping and modelling of S. obtusifolia was conducted at three different scales: continental, landscape and local (population). To address these spatial scales, eco-climatic modelling, remote sensing analysis, field experimentation and creation of a model of seed fate was undertaken. Using the climatic preferences of S. obtusifolia displayed internationally, an eco-climatic model (using CLIMEX software) ascertained that S. obtusifolia has a very large invasive potential in Australia. The predicted geographic distribution comprised the entire eastern and northern Australian coastlines, with spread further inland being largely restricted by a lack of moisture. The regional distribution of S. obtusifolia was not successfully delineated using remote sensing technology. Despite possessing favourable traits for detection by remote sensors, poor data quality and inappropriate image scales prevented the weed from being distinguished from other vegetation by multi-spectral satellite imagery and aerial photography. However, the results indicated that refining the data and the techniques used, single S. obtusifolia populations may be detectable in the future. Investigation of the invasion dynamics of S. obtusifolia at the local scale involved multiple field surveys and manipulative experiments during 2002-2005. Field work indicated that little variation in population characteristics (e.g. stem density, soil seed reserve, seed production) existed within populations, but there was variability across populations and between years: the variation between years was very significant. The vegetation type adjacent to the weed population did not affect population attributes; however less competitive, more open and disturbed environments may better facilitate the invasion. The compartment model of seed fate reflecting S. obtusifolia population dynamics demonstrated that change in annual rainfall was unlikely to explain the variation evident between populations and years. Instead, the rate at which dormancy is broken in seeds and the intensity and regularity of fire provided a better explanation of the weed's population dynamics. Early detection of invaders and the prediction of likely sites of invasion provide the most effective means of preventing future invasions. How best to achieve these goals still remains largely unknown. The process undertaken in this study was a relatively quick and reliable method for assessing the seriousness of S. obtusifolia, predicting future outbreaks and for providing clues to long term management. The appropriate use of fire, maintaining high interspecific competition and shade, as well reducing the rate at which dormancy is broken in seeds are all possible methods of managing S. obtusifolia.

Parthenium hysterophorus (Asteraceae), classified as an emerging weed in South Africa, has become abundant throughout large parts of southern and eastern Africa. In South Africa it has invaded areas in KwaZulu-Natal, Mpumalanga, the North West Province and Limpopo. A biological control programme against parthenium weed was launched in South Africa in 2003, based on the success achieved in Australia. Zygogramma bicolorata, a leaf-feeding beetle native to Mexico, was imported into South Africa via Central Queensland, Australia where it was released in the 1980s. This thesis examines aspects of the thermal physiology of Z. bicolorata which, in conjunction with its native and exotic geographical distribution, was used to predict the potential distribution of the agent in South Africa, in relation to climate. To determine Z. bicolorata’s physiological capability, several physiological parameters were examined for mechanistic modelling purposes. These parameters included the beetle’s lethal thermal limits, critical thermal limits, lethal humidities (Chapter 2) and developmental rate at constant temperatures (Chapter 3). In Chapter 4, these physiological parameters were entered into the dynamic modelling program CLIMEX (CLIMEX programme ver. 2, CSIRO Entomology ©) and a map of the areas that are acceptable for the establishment of Z. bicolorata was produced. The CLIMEX model predicted that most of South Africa is favourable for the establishment of the beetle, except in the west of the country and in the north of Lesotho, extending into South Africa. All areas in which parthenium currently occurs were predicted to be very favourable for Z. bicolorata establishment and proliferation. Optimal release sites aimed at initial establishment were earmarked at three areas in the northeastern part of South Africa (Jozini, Ndumu Game Reserve and along the road from Swaziland to Mozambique). It is concluded that Z. bicolorata is climatically suited to South Africa, increasing the likelihood that populations will establish and proliferate when released. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

To refine our knowledge and to adequately test hypotheses concerning theoretical and applied aspects of invasion biology, successful and unsuccessful invaders should be compared. This study investigated insect establishment patterns by comparing the climatic preferences and biological attributes of two groups of polyphagous insect species that are constantly intercepted at New Zealand's border. One group of species is established in New Zealand (n = 15), the other group comprised species that are not established (n = 21). In the present study the two groups were considered to represent successful and unsuccessful invaders. To provide background for interpretation of results of the comparative analysis, global areas that are climatically analogous to sites in New Zealand were identified by an eco-climatic assessment model, CLIMEX, to determine possible sources of insect pest invasion. It was found that south east Australia is one of the regions that are climatically very similar to New Zealand. Furthermore, New Zealand shares 90% of its insect pest species with that region. South east Australia has close trade and tourism links with New Zealand and because of its proximity a new incursion in that analogous climate should alert biosecurity authorities in New Zealand. Other regions in western Europe and the east coast of the United States are also climatically similar and share a high proportion of pest species with New Zealand. Principal component analysis was used to investigate patterns in insect global distributions of the two groups of species in relation to climate. Climate variables were reduced to temperature and moisture based principal components defining four climate regions, that were identified in the present study as, warm/dry, warm/wet, cool/dry and cool/moist. Most of the insect species established in New Zealand had a wide distribution in all four climate regions defined by the principal components and their global distributions overlapped into the cool/moist, temperate climate where all the New Zealand sites belong. The insect species that have not established in New Zealand had narrow distributions within the warm/wet, tropical climates. Discriminant analysis was then used to identify which climate variables best discriminate between species presence/absence at a site in relation to climate. The discriminant analysis classified the presence and absence of most insect species significantly better than chance. Late spring and early summer temperatures correctly classified a high proportion of sites where many insect species were present. Soil moisture and winter rainfall were less effective discriminating the presence of the insect species studied here. Biological attributes were compared between the two groups of species. It was found that the species established in New Zealand had a significantly wider host plant range than species that have not established. The lower developmental threshold temperature was on average, 4°C lower for established species compared with non-established species. These data suggest that species that establish well in New Zealand have a wide host range and can tolerate lower temperatures compared with those that have not established. No firm conclusions could be drawn about the importance of propagule pressure, body size, fecundity or phylogeny for successful establishment because data availability constrained sample sizes and the data were highly variable. The predictive capacity of a new tool that has potential for eco-climatic assessment, the artificial neural network (ANN), was compared with other well used models. Using climate variables as predictors, artificial neural network predictions were compared with binary logistic regression and CLIMEX. Using bootstrapping, artificial neural networks predicted insect presence and absence significantly better than the binary logistic regression model. When model prediction success was assessed by the kappa statistic there were also significant differences in prediction performance between the two groups of study insects. For established species, the models were able to provide predictions that were in moderate agreement with the observed data. For non-established species, model predictions were on average only slightly better than chance. The predictions of CLIMEX and artificial neural networks when given novel data, were difficult to compare because both models have different theoretical bases and different climate databases. However, it is clear that both models have potential to give insights into invasive species distributions. Finally the results of the studies in this thesis were drawn together to provide a framework for a prototype pest risk assessment decision support system. Future research is needed to refine the analyses and models that are the components of this system.