Characterisation of entomopathogenic nematodes and their symbiotic bacteria across eastern Australia and their potential in controlling Queensland fruit fly

Abstract

Tephritid fruit flies (Tephritidae) include several destructive pest species that attack fruit and fruiting vegetables across many climatic regions of the world. The Queensland fruit fly, Bactrocera tryoni, is Australia's most significant horticultural pest. It lays eggs in the fruit of over 40 plant families, including many important fruit and vegetable crops, making it one of the most polyphagous and most economically important species among all tephritids. So far, one of the most effective control measures is the use of synthetic insecticides. However, many insecticides have been abolished because of their environmental and human health risks and their impact on non-target organisms. Entomopathogenic nematodes (EPNs) of the families Heterorhabditidae and Steinernematidae and their associated bacteria Photorhabdus and Xenorhabdus, found in soils throughout the world, are important biocontrol agents of insect pests with soil-inhabiting stages. They have been commercially used as a safe alternative to chemical pesticides. However, the potential of EPNs to control B. tryoni is largely unknown. This PhD thesis comprises five chapters. Chapter 1 reviews the biology and ecology of the Queensland fruit fly, EPNs and their associated symbiotic bacteria. Chapter 2 comprises a survey and the identification of EPNs and their associated bacteria isolated from soils across eastern Australia. Chapter 3 provides an overview of the virulence of the 32 newly isolated and 4 commercial EPN strains on larval and pupal stages of B. tryoni. Chapter 4 provides the result of the effects of temperature on survival and persistence of 17 EPN isolates against larvae and pupae of B. tryoni under laboratory conditions. Overall, my research expands substantially the previously available information about EPN diversity in Australia and provides the first comprehensive genetic characterization of this Australian diversity. Furthermore, the EPN isolates such as Hi.HRN2, Hz.NAR1, Hi.ECCH, Hi.LMI2, Hi.QF6, Hb.HIE and Sf.ECCS showed traits, such as high virulence and long persistence, that make them potential candidates for the biological control of fruit flies. The survival and virulence of these isolates, even at higher temperature suggest that they could be a good biological control agent of fruit flies in Australian conditions. However, it is necessary to further check their efficacy in the field before development of applications at a commercial scale.

Date of Award	2021
Original language	English