The competition for host resources among coexisting parasitoids with varying life history traits necessitates a comprehensive examination of the consequences on fitness and overall efficacy so as to enhance the effectiveness of biological control. Trichogramma sp. and Telenomus sp. co-exists as egg parasitoids of fall armyworm, a global polyphagous pest of grains and horticultural crops. While research has been conducted on the competition between the two parasitoids on some lepidopteran hosts, their interspecific competition on different host densities has been sparsely reported. This laboratory study aimed to assess the outcome of competition when both species share the same resource and the impact of that contest on the fitness of emerged progeny ultimately exploring possible implications for the biological control of the invasive fall armyworm. Laboratory experiments were conducted allowing both parasitoid species to simultaneously exploit an egg patch of 15, 30, and 60 fall armyworm eggs. Observations on parasitism rates, rate of successful development for each parasitoid, developmental times, and sex ratios were recorded. T. remus showed significantly higher parasitism efficiency compared to Tr. pretiosum. Nonetheless, at low-host density, Tr. pretiosum was more

My PhD project focuses on a group of insects with potential to threaten the Australian Citrus industry – psyllids.

Psyllids are small sap-sucking insects, comprising about 4,000 species worldwide, of which Australia hosts a significant proportion of the global diversity.

Citrus industries worldwide are concerned about two species in particular: the African citrus psyllid, Trioza erytreae, and the Asian citrus psyllid, Diaphorina citri. These specific psyllids can transmit Liberibacter species, causing a disease known as Huanglongbing, or citrus greening, which has resulted in losses of billions of dollars worldwide. These psyllids are exotic, and their vectored bacteria are also not present in Australia, but very little is known about Australia’s native species, their diversity, and whether some of these could vector similar pathogens.

I aim to explore the diversity of Australian native psyllids around Australian citrus orchards to better understand what psyllids and bacterial communities are present here, and how they differ from exotic psyllid pests and associated pathogens.

During the first year of my PhD, I have started using different traps and hand sampling techniques to conduct field collections of psyllids across three states and four major citrus growing regions of the east coast of Australia.
I am using traditional morphological diagnostics coupled with molecular techniques, including COI barcoding and metabarcoding, to identify thousands of specimens. Using this integrative taxonomy approach, I aim to identify many different species of psyllids and bacteria (including pathogens, symbionts, and gut bacteria).

Once complete, this will be the first study to contribute significantly towards the compilation of a COI databases for the Australian Psylloidea, allowing future researchers and biosecurity diagnosticians to streamline their identification processes. This project will benefit researchers, diagnosticians, and growers by providing a vast ‘landscape’ of information about Australian psyllids.

Citrus black core rot is a significant and emerging problem in the southern citrus growing regions in Australia. The disease is characterised by pre-harvest fruit drop and internal fruit rot which often goes undetected until fruit reaches the kitchen bench or juicing plant. The occurrence of this disease is erratic between citrus varieties, regions and seasons, resulting in a varied impact across the industry. Alternaria alternata has been reported to be the causative agent of citrus black core rot, however, this fungus is also known to cause another disease in citrus called brown spot, typically a northern Australian growing region issue. While the symptoms and geographical distribution of the two diseases are apparently distinct, the difference between the pathogen identities, biology and the disease cycles remain a significant gap in knowledge which has left the industry with little capacity to effectively manage the disease. We performed multi-locus phylogenetic analyses and found that isolates recovered from both diseases were placed under the A. alternata clade which is polyphyletic. Detached fruit and leaf pathogenicity assays have been established to compare the pathogens that cause black core rot and brown spot. New knowledge on the pathogen identity and pathogenicity from this study will aid improved management of citrus black core rot and will be combined with a multi-year field trial to elucidate the risk of pathogen spread to other citrus growing regions across Australia to prevent impact of the disease to industry.

Myrtle rust caused by the biotrophic fungal pathogen Austropuccinia psidii infects hundreds of plants in the family Myrtaceae. Since the arrival into Australia in 2010, it has caused localised extinction of several keystone plant species. While devastating for selected species, variability in response to the pathogen has been identified within and between species. Resultingly, studies investigating the genetic basis of resistance to A. psidii have been conducted in a range of Myrtaceae species with no model established. Melaleuca quinquenervia (broadleaved paperbark) is a keystone species broadly distributed across the east coast of Australia and displays variable response to A. psidii. Owing to this variable response along with ease of propagation, high seed set, rapidly establishing seedlings, and availability of a high-quality genome, M. quinquenervia is an ideal model for investigation of resistance to A. psidii. To investigate resistance and early response to A. psidii, we conducted transcriptomic analysis on infected resistant and susceptible M. quinquenervia as early as 6-hours post germination. Our results revealed distinct expression signatures prior to A. psidii inoculation in resistant and susceptible hosts, providing an opportunity to investigate the establishment of a diagnostic tool for susceptibility in the absence of the pathogen. Importantly, several disease resistance genes were determined to be upregulated in resistant individuals. To test the utility of M. quinquenervia as a model, we screened 16 Melaleuca species for their susceptibility to A. psidii. Genotyping of resistant and susceptible individuals has revealed the conservation of the disease resistance genes from M. quinquenervia in these Melaleuca species. Testing is now underway to determine expression differences between resistant and susceptible individuals. These findings establish important target genes further investigation, and we anticipate these results will shed light on common mechanisms of resistance to A. psidii and aid in the development of diagnostic tools for susceptibility.