School of BioSciences - Theses
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ItemNo Preview AvailableTowards Strategies for the Control of Invasive Liriomyza Pests in Australia: Dispersal Pathways, Parasitoid Wasps and EndosymbiontsXu, Xuefen ( 2022)The Agromyzidae are a family of small, morphologically similar flies whose larvae feed internally on living plant tissue, often as stem and leaf-miners. The genus Liriomyza is the most well-known and more than 20 species are recorded as pests or potential pests of crops worldwide. They are highly polyphagous and have a strong propensity to colonize new plant hosts. Among them, three polyphagous Liriomyza species - Liriomyza sativae, L. huidobrensis, and L. trifolii - are recognized as the most damaging leafmining pests that have spread to many new areas in the world including Australia, imposing additional financial burdens to the agricultural and horticultural industries. Unfortunately, systematic strategies for the management of Liriomyza pests in Australia have been largely unexplored. Therefore, this thesis focuses on the identification of leafmining species, the dispersal pathway of one of the exotic Liriomyza species, and an exploration of biological control methods that can help control the outbreak of Liriomyza in Australia. Firstly, molecular methods based on cytochrome c oxidase subunit 1 (COI) DNA barcodes were deployed to character 13 dipteran leafminer species collected from Australia and overseas. In Australia, there already exist some leafmining species that look similar to exotic Liriomyza pests but with little economic importance. The taxonomy of leafmining flies is often challenging due to the complicated morphological keys as well as putative cryptic species. We here provide a baseline for DNA-based identification of pest Liriomyza incursions spreading across the Australian east coast and other species already present in Australia. Secondly, genome-wide single nucleotide polymorphisms (SNPs) were generated by double-digest restriction-site associated DNA sequencing (ddRAD-seq) to reveal the potential origin(s) of Liriomyza sativae into Australia and contribute to reconstruct its global invasion history, showing that the Torres Strait population is the source of the mainland population and highlighting the mixed origins of the Torres Strait population. Thirdly, 13 dipteran leaf-mining species were examined for Wolbachia infections and the potential for this endosymbiont in biocontrol. The comparison of Wolbachia relatedness relied on the wsp/MLST genes. A colony of Liriomyza brassicae was established and treated with tetracycline for reciprocal crosses and cytoplasmic incompatibility was demonstrated. These findings highlight the potential of Wolbachia to impact the Liriomyza pests based on approaches such as the incompatible insect technique. Fourthly, natural enemies like parasitoid wasps are recognized as effective biological agents worldwide to suppress the outbreak of polyphagous leafmining pests. However, the parasitoid complexes in Australia are poorly studied due to their small body size and challenging morphological diagnostic characteristics. To address the knowledge gap of parasitoid wasps in Australia, molecular methods based on cytochrome c oxidase subunit 1 (COI) DNA barcodes as well as traditional morphological approaches were employed to identify 13 parasitoid species. The status of endosymbionts was also checked in these parasitoid wasps given the limited information available in the literature, and two endosymbionts were identified. These findings provide the foundation for employing parasitoid wasps as biological agents for the management of exotic leafmining pests in the future. Fifthly, thelytokous parasitoid wasps are preferred for mass rearing due to an absence of male wastage, and the possible existence of thelytoky locally was explored. In Japan and China, Neochrysocharis formosa infected with Rickettsia are thelytokous and are suggested to be effective to control the polyphagous Liriomyza pests. In Australia, Neochrysocharis specimens have only been identified to genus but not formally identified. Using five DNA barcodes, we identified N. formosa from Australia and established the presence of Proacrias, a genus of leafminer parasitoid not previously detected in Australia. 16S rRNA sequencing indicated that both species were infected with a Rickettsia bacterium. These findings expand records of parasitoids to attack leafminers in Australia and highlight the potential of applying endosymbionts to produce thelytokous strains to increase the efficiency of biocontrol.