Doctor Jennifer Morrow
Candidature
Graduated PhD 2014.
Thesis Title
Molecular studies of Wolbachia and sex-determination genes in Australian Bactrocera species - complementary approaches to improved fruit fly control
Research Project
Bactrocera tryoni is Australia's most destructive horticultural pest due to its extensive host fruit preferences and wide geographic range. Belonging to the family Tephritidae, B.tryoni is one of a number of Tephritid pest species of economic importance, thus control or eradication measures are of great consequence. Besides chemical control, Tephritid species are controlled by reproductive suppression methods including the release of irradiated, sterile individuals; or individuals infected by Wolbachia.
Wolbachia are common symbiotic bacteria of insects, can cause crossing sterility between infected males and uninfected females, and can manipulate the sex determination pathway in some insect species. Wolbachia incompatibility may be used in insect population control by releasing mass reared infected males in uninfected field populations of B.tryoni. The strict release of infected males only is crucial for the success of the Wolbachia incompatibility strategy, and male-only release has demonstrably improved the effectiveness of the sterilisation strategy.
To ultimately achieve a male-only strain of B.tryoni, a thorough understanding of the genes that form the sex determination pathway is necessary. The pathway has been well studied in the model insect Drosophila melanogaster, and this has provided a starting point for characterising genes involved in sex determination in other Diptera, including B.tryoni. A cascade of genetic interactions takes place, beginning with a signal which triggers either female or male development.
Several key genes in sex determination have been identified in B.tryoni, including homologues of transformer and transformer-2, in D.melanogaster. However, the initial signal in male fruit fly is communicated by the dominant male determiner, M, located on the Y chromosome, which is absent in Drosophila species. The mode of action of M, and its direct targets have yet to be characterised in fruit flies or in any other Y-determined insect.
A Y chromosome marker carried in a B.tryoni line can separate male and female embryos with a simple PCR assay, enabling expression studies of important sex determination genes at the earliest stages of development. The introduction of Wolbachia in the same B.tryoni line will enable the assessment of Wolbachia interaction with the expression of sex determination genes. This may provide new insights into the regulation and function of sex determination genes, clarifying more on the timing and operation of M, as well as revealing their manipulation by Wolbachia in early development.
Research Project Supervisors
Dr Markus Riegler, Dr Marian Frommer, Dr Deborah Shearman
Awards / Honours
Received $6,900 for the F G Swain Award for the proposal 'Sex determination genes in Queensland fruit fly, Bactrocera tryoni'. 2011
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