Impact of the invasive rust Puccinia psidii (myrtle rust) on native Myrtaceae in natural ecosystems in Australia

The invasive rust Puccinia psidii (myrtle rust) was detected in Australia in 2010 and is now established along the east coast from southern New South Wales to far north Queensland. Prior to reaching Australia, severe damage from P. psidii was mainly restricted to exotic eucalypt plantations in South America, guava plantations in Brazil, allspice plantations in Jamaica, and exotic Myrtaceous tree species in the USA; the only previous record of widespread damage in native environments is of endangered Eugenia koolauensis in Hawai’i. Using two rainforest tree species as indicators of the impact of P. psidii, we report for the first time severe damage to endemic Myrtaceae in native forests in Australia, after only 4 years’ exposure to P. psidii. A 3-year disease exclusion trial in a natural stand of Rhodamnia rubescens unequivocally showed that repeated, severe infection leads to gradual crown loss and ultimately tree mortality; trees were killed in less than 4 years. Significant (p < 0.001) correlations were found between both incidence (r = 0.36) and severity (r = 0.38) of P. psidii and subsequent crown loss (crown transparency). This provided supporting evidence to conclude a causal association between P. psidii and crown loss and tree mortality in our field assessments of R. rubescens and Rhodomyrtus psidioides across their native range. Assessments revealed high levels of damage by P. psidii to immature leaves, shoots and tree crowns—averaging 76 % (R. rubescens) and 95 % (R. psidioides) crown transparency—as well as tree mortality. For R. psidioides, we saw exceptionally high levels of tree mortality, with over half the trees surveyed dead and 40 % of stands with greater than 50 % tree mortality, including two stands where all trees were dead. Tree mortality was less prevalent for R. rubescens, with only 12 % of trees surveyed dead and two sites with greater than 50 % mortality. Any alternative causal agents for this tree mortality have been discounted. The ecological implications of this are unclear, but our work clearly illustrates the potential for P. psidii to negatively affect Australia’s biodiversity.

The biology and natural history of Tripogon loliiformis (Poaceae, Chloridoideae), an Australian resurrection grass

Tripogon loliiformis is a desiccation-tolerant grass that occurs throughout mainland Australia. There has been recent interest in this species as a model system for understanding desiccation tolerance in a native grass at the structural, molecular and physiological levels. However, not much is known about the biology and natural history of this species, despite its widespread geographic distribution and remarkable capability of withstanding prolonged drying. We provide an overview of the genus by consolidating information from a wide variety of sources. We report a variety of new and interesting observations on the general biology, ecology and desiccation response of T. loliiformis and conclude by highlighting areas for future research.

The upper respiratory tract is a natural reservoir of haemolytic Mannheimia species associated with ovine mastitis

Lamb suckling has been suggested to be an important way of infecting a ewe's udder with different bacteria, including Mannheimia haemolytica. To test the potential role of lambs in transferring Mannheimia species to the ewe’s udder, the restriction endonuclease cleavage patterns of isolates obtained from nasopharyngeal swabs were compared with those obtained from cases of mastitis. Sterile cotton swabs were used to collect nasopharyngeal samples from 50 ewes and 36 lambs from three flocks. M. haemolytica and Mannheimia glucosida as well as haemolytic Mannheimia ruminalis-like organisms were detected in the upper respiratory tract of lambs and ewes. Comparison of the restriction endonuclease cleavage patterns of the isolates suggested that the M. haemolytica isolates obtained from different milk samples from ewes with mastitis were more clonal than those obtained from the nasal swabs. However, some nasal isolates within both Mannheimia species had restriction endonuclease cleavage patterns identical to those obtained from milk samples from ewes with mastitis, indicating that lambs may have a role in transferring these organisms to the udder. More clonality was observed between the M. glucosida isolates than between M. haemolytica isolates.

Natural Hendra Virus Infection in Flying-Foxes - Tissue Tropism and Risk Factors

Hendra virus (HeV) is a lethal zoonotic agent that emerged in 1994 in Australia. Pteropid bats (flying-foxes) are the natural reservoir. To date, HeV has spilled over from flying-foxes to horses on 51 known occasions, and from infected horses to close-contact humans on seven occasions. We undertook screening of archived bat tissues for HeV by reverse transcription quantitative polymerase chain reaction (RT-qPCR). Tissues were tested from 310 bats including 295 Pteropodiformes and 15 Vespertilioniformes. HeV was detected in 20 individual flying-foxes (6.4%) from various tissues including spleen, kidney, liver, lung, placenta and blood components. Detection was significantly higher in Pteropus Alecto and Pconspicillatus, identifying species as a risk factor for infection. Further, our findings indicate that HeV has a predilection for the spleen, suggesting this organ plays an important role in HeV infection. The lack of detections in the foetal tissues of HeV-positive females suggests that vertical transmission is not a regular mode of transmission in naturally infected flying-foxes, and that placental and foetal tissues are not a major source of infection for horses. A better understanding of HeV tissue tropism will strengthen management of the risk of spillover from flying-foxes to horses and ultimately humans.

Spatiotemporal aspects of Hendra Virus infection in Pteropid Bats (Flying-Foxes) in Eastern Australia

Hendra virus (HeV) causes highly lethal disease in horses and humans in the eastern Australian states of Queensland (QLD) and New South Wales (NSW), with multiple equine cases now reported on an annual basis. Infection and excretion dynamics in pteropid bats (flying-foxes), the recognised natural reservoir, are incompletely understood. We sought to identify key spatial and temporal factors associated with excretion in flying-foxes over a 2300 km latitudinal gradient from northern QLD to southern NSW which encompassed all known equine case locations. The aim was to strengthen knowledge of Hendra virus ecology in flying-foxes to improve spillover risk prediction and exposure risk mitigation strategies, and thus better protect horses and humans. Monthly pooled urine samples were collected from under roosting flying-foxes over a three-year period and screened for HeV RNA by quantitative RT-PCR. A generalised linear model was employed to investigate spatiotemporal associations with HeV detection in 13,968 samples from 27 roosts. There was a non-linear relationship between mean HeV excretion prevalence and five latitudinal regions, with excretion moderate in northern and central QLD, highest in southern QLD/northern NSW, moderate in central NSW, and negligible in southern NSW. Highest HeV positivity occurred where black or spectacled flying-foxes were present; nil or very low positivity rates occurred in exclusive grey-headed flying-fox roosts. Similarly, little red flying-foxes are evidently not a significant source of virus, as their periodic extreme increase in numbers at some roosts was not associated with any concurrent increase in HeV detection. There was a consistent, strong winter seasonality to excretion in the southern QLD/northern NSW and central NSW regions. This new information allows risk management strategies to be refined and targeted, mindful of the potential for spatial risk profiles to shift over time with changes in flying-fox species distribution.

Maximum likelihood estimation of natural mortality and quantification of temperature effects on catchability of brown tiger prawn (Penaeus esculentus) in Moreton Bay (Australia) using logbook data

It is common to model the dynamics of fisheries using natural and fishing mortality rates estimated independently using two separate analyses. Fishing mortality is routinely estimated from widely available logbook data, whereas natural mortality estimations have often required more specific, less frequently available, data. However, in the case of the fishery for brown tiger prawn (Penaeus esculentus) in Moreton Bay, both fishing and natural mortality rates have been estimated from logbook data. The present work extended the fishing mortality model to incorporate an eco-physiological response of tiger prawn to temperature, and allowed recruitment timing to vary from year to year. These ecological characteristics of the dynamics of this fishery were ignored in the separate model that estimated natural mortality. Therefore, we propose to estimate both natural and fishing mortality rates within a single model using a consistent set of hypotheses. This approach was applied to Moreton Bay brown tiger prawn data collected between 1990 and 2010. Natural mortality was estimated by maximum likelihood to be equal to 0.032 ± 0.002 week−1, approximately 30% lower than the fixed value used in previous models of this fishery (0.045 week−1).

Estimation of higher natural frequencies of polar orthotropic annular plates

A method based on an assumption that the radial bending moment is zero at a nodal circle is shown to yield accurate estimates of natural frequencies corresponding to higher modes of transversely vibrating polar orthotropic annular plates for various combinations of clamped, simply supported and free edge conditions. This method is found to be convenient for the determination of locations of nodal circles as well. Numerical investigations revealed that for small holes, nodal circles tend to move towards the outer edge with increasing number of nodal diameters. For large holes, it has been shown that the plate behaves like a long rectangular strip.

Temporal Variation in Physiological Biomarkers in Black Flying-Foxes (Pteropus alecto), Australia

Bats of the genus Pteropus (Pteropodidae) are recognised as the natural host of multiple emerging pathogenic viruses of animal and human health significance, including henipaviruses, lyssaviruses and ebolaviruses. Some studies have suggested that physiological and ecological factors may be associated with Hendra virus infection in flying-foxes in Australia; however, it is essential to understand the normal range and seasonal variability of physiological biomarkers before seeking physiological associations with infection status. We aimed to measure a suite of physiological biomarkers in P. alecto over time to identify any seasonal fluctuations and to examine possible associations with life-cycle and environmental stressors. We sampled 839 adult P. alecto in the Australian state of Queensland over a 12-month period. The adjusted population means of every assessed hematologic and biochemical parameter were within the reported reference range on every sampling occasion. However, within this range, we identified significant temporal variation in these parameters, in urinary parameters and body condition, which primarily reflected the normal annual life cycle. We found no evident effect of remarkable physiological demands or nutritional stress, and no indication of clinical disease driving any parameter values outside the normal species reference range. Our findings identify underlying temporal physiological changes at the population level that inform epidemiological studies and assessment of putative physiological risk factors driving Hendra virus infection in P. alecto. More broadly, the findings add to the knowledge of Pteropus populations in terms of their relative resistance and resilience to emerging infectious disease.

Area-wide releases and evaluation of the parasitoid Eretmocerus hayati(Hymenoptera:Aphelinidae) for silverleaf whitefly control

Silverleaf whitefly (SLW), Bemisia tabaci biotype B, is a major horticultural pest that costs Queensland vegetable growers millions of dollars in lost production and control measures each year. In the Bowen and Burdekin districts of North Queensland, the major cultivated SLW host crops are tomatoes, melons, green beans, pumpkins, eggplants, and cucumbers, which cover a total production area of approximately 6500 ha. Eretmocerus hayati, an effective SLW parasitoid, was imported into Australia by CSIRO in 2002 and released from quarantine in 2004. In 2006, DAFF established a mass-rearing unit for E. hayati at Bowen Research Station to provide E. hayati for release on vegetable farms within its SLW integrated pest management research program. A total of 1.3 million E. hayati were released over three seasons on 34 vegetable farms in the Bowen and Burdekin districts (October 2006 to December 2008). Post-release samplings were conducted across the release area over this time period with parasitism levels recorded in tomatoes, melons, beans, eggplants, pumpkins, and various SLW weed hosts. Sample data show that E. hayati established at most release sites as well as some non-release sites, indicating natural spread. Overall results from these three years of evaluation clearly demonstrated that E hayati releases played a significant role in SLW control. In most crops sampled, E hayati exerted between 30 and 80% parasitism. Even in regularly sprayed crops, such as tomato and eggplant, E. hayati was able to achieve an overall average parasitism of 45%.

Natural disasters have unexpected impacts on mental health

Radical circumstances (bushfires and natural disasters) flush out the mental illness in society. Whenever there’s a disaster, there’s a rush on hospital admissions for psychiatric problems. But on the whole, the illness is already there. Emergencies naturally make fodder for delusions and the emergency efforts, for mania. Obviously, there are direct mental health consequences – a small rise in post-traumatic stress disorder inevitably follows disaster. This correlates with the severity of the consequences of the disaster (loss of family, friends, animals and property). And there’s usually a big rethink, with about a third of those affected leaving the area permanently. But, for the most part, this isn’t driven by mental health issues, it results from the very real fears about whether living in a fire (or other disaster) zone is worth it.

Natural convection in rectangular cavities at high Rayleigh number

Natural convection in rectangular two-dimensional cavities with differentially heated side walls is a standard problem in numerical heat transfer. Most of the existing studies has considered the low Ra laminar regime. The general thrust of the present research is to investigate higher Ra flows extending into the unsteady and turbulent regimes where the physics is not fully understood and appropriate models for turbulence are not yet established. In the present study the Boussinesq approximation is being used, but the theoretical background and some preliminary results have been obtained[1] for flows with variable properties.

A computer code for enclosed natural convection in the boundary layer regime

A computer code is developed for the numerical prediction of natural convection in rectangular two-dimensional cavities at high Rayleigh numbers. The governing equations are retained in the primitive variable form. The numerical method is based on finite differences and an ADI scheme. Convective terms may be approximated with either central or hybrid differencing for greater stability. A non-uniform grid distribution is possible for greater efficiency. The pressure is dealt with via a SIMPLE type algorithm and the use of a fast elliptic solver for the solenoidal velocity correction field significantly reduces computing times. Preliminary results indicate that the code is reasonably accurate, robust and fast compared with existing benchmarks and finite difference based codes, particularly at high Rayleigh numbers. Extension to three-dimensional problems and turbulence studies in similar geometries is readily possible and indicated.

The laminar boundary layer regime for natural convection of air in a square cavity

Numerical predictions are obtained for laminar natural convection of air in a square two dimensional cavity at high Rayleigh numbers. Proper resolution of the core reveals weak multi-cellular structure which varies in a complex manner as the effects of convection are increased. The end of the steady laminar regime is numerically estimated to occur at Ra=2.2x10^8.

Laminar and turbulent natural convection in rectangular cavities

A computer program has been developed for the prediction of buoyancy-driven laminar and turbulent flow in rectangular air-filled two-dimensional cavities with differentially heated side walls. Laminar flow predictions for a square cavity and Rayleigh numbers from Ra = 10^3 up to the onset of unsteady flow have been obtained. Accurate solutions for Ra = 5 x 10^6, 10^7, 5 x 10^7 and 10^8 are presented and an estimate for the critical Rayleigh number at which the steady laminar flow becomes unsteady is given for this geometry. Numerical predictions of turbulent flow have been obtained for RaH~0(10^9 -10^11 ) and compared with existing experimental data. A previously developed second moment closure model (Behnia et al. 1987) has been used to model the turbulence. Results indicate that a second moment closure model is capable of predicting the observed flow features.

Laminar and turbulent natural convection in rectangular cavities

"This chapter discusses laminar and turbulent natural convection in rectangular cavities. Natural convection in rectangular two-dimensional cavities has become a standard problem in numerical heat transfer because of its relevance in understanding a number of problems in engineering. Current research identified a number of difficulties with regard to the numerical methods and the turbulence modeling for this class of flows. Obtaining numerical predictions at high Rayleigh numbers proved computationally expensive such that results beyond Ra ∼ 1014 are rarely reported. The chapter discusses a study in which it was found that turbulent computations in square cavities can't be extended beyond Ra ∼ O (1012) despite having developed a code that proved very efficient for the high Ra laminar regime. As the Rayleigh number increased, thin boundary layers began to form next to the vertical walls, and the central region became progressively more stagnant and highly stratified. Results obtained for the high Ra laminar regime were in good agreement with existing studies. Turbulence computations, although of a preliminary nature, indicated that a second moment closure model was capable of predicting the experimentally observed flow features."--Publisher Summary