The major horticultural pests in Australia are of the family Tephritidae, commonly known as fruit flies (the real ones, not Drosophila which is actually called the ‘vinegar fruit fly’ due to its attraction to rotten fruit!). The Queensland fruit fly (Bactrocera tryoni, a.k.a Qfly) and the Mediterranean fruit fly (Ceratitis capita, a.k.a Medfly) are the two major invaders of our agricultural systems. Medfly is a very successful global invader and Qfly is a new emerging one. Indeed, there is anecdotal evidence that Qfly is a very successful competitor against Medfly and therefore may in the future become the new global fruit fly pest.
One of the major concerns in the horticulture industry is safe control. At the moment a grower’s toolbox includes pesticides, biological control and integrated pest management practices. These are considered pre-harvest methods since they are applied while the food is growing. However, one of the major impediments to the industry is the ability to access markets. If a fruit contains an egg or larvae of one of these fruit flies, then rational biosecurity protocols will prevent this fruit (and the entire shipment container it is part of) to be imported by any other country. In other words, we cannot move our fruit. This applies not only between nations but also between states that are fruit fly-free (for example South Australia). For this reason, all fruits that originate from a non-fruit fly-free area must undergo a post-harvest treatment in order to ensure that they are safe to store and transport to other countries.
Post-harvest treatments of insects focus on delivering a lethal stress yet the ability of an organism to survive natural abiotic and biotic stresses is essential to its survival and have evolved – yet unknown – mechanisms to overcome them. We expect the two tephritid mega pests (MedFly and QFly) to have become such successful worldwide invaders partly due to an ability to respond to environmental stresses in a cost-effective manner. Such cost-effective mechanisms can be due to developmental or cellular plasticity: e.g. activate any energetically costly stress response pathways only when necessary. Indeed, cells have a remarkable ability to respond to changes in external conditions by rapidly regulating protein production through a cascade of gene activation and inactivation. Therefore, the best tool for dissecting this phenomenon of stress-induced death and stress resistance is gene expression. This tool was, until recently, the provenance of large biomedical or basic science communities. In recent years a number of technology breakthroughs such as low-cost RNASeq libraries, high-throughput qPCR, bioinformatic software and gene network reconstruction have allowed large advances to be taken in biomedical and livestock science.
In our project, we are in the process of dissecting the biological pathways triggered by disinfestation stressors such as heat, cold, irradiation and others. Our project will enable the refinement of post-harvest disinfestation by learning which stresses can be best combined so that different death pathways are targeted and lower doses can be delivered. We will also learn which stresses are thus arranged in gene networks as to enable the evolution of resistance. With this project acting as a seed fund, our labs will be able to invest in functional genomic assays (e.g. RNAi and CRISPR knockouts) to initiate the validation of our findings.