Characterization and in vivo-studies of entomopathogenic viruses for biocontrol of the invasive pest Drosophila suzukii

Abstract

In the past ten years, Drosophila suzukii, a fruit fly native to Eastern and Southeastern Asia, has devel-oped into a serious invasive economically relevant pest of soft and stone fruits. This notorious pest has an economic impact on the agricultural industry that reaches to millions of euros in crop losses. For instance, an estimate of 3 million € in losses in cultivated fruit crops, i.e. cherries, raspberries and blue-berries, was recently recorded only for the Autonomous Province of Trento. This, combined with the rapid global spread of this pest insect, makes SWD one of the most serious threats for modern horticul-ture. There are several features that allowed D. suzukii to become a pest: (i) its ovipositor that possesses the ability to penetrate the skins of a broad range of fruit; (ii) the pest’s high reproduction rate and rapid lifecycle; (iii) and the ability of the three larval instars to develop inside the fruit. Taken together, chem-ical control measures cannot be used to effectively fight SWD. Consequently, effective, ecologically safe, and sustainable strategies for its control are urgently required. To the best of the author’s knowledge, no adequate chemical, biotechnological, or biologically effective measures have been yet described for the control of this invasive pest species. However, it is known from literature that viruses have proven for more than fifty years to be host-specific and environmentally friendly biocontrol agents. The main goal of this thesis was the study of host-specific viruses identified from naturally infected D. suzukii. This was achieved by sampling larvae from orchards and estimating their health status. Subsequently, viruses obtained from collected larva were screened. Finally, four vi-ruses were identified: Drosophila A virus (DAV), La Jolla virus (LJV), Mots Mills-like virus (MMlV) and Teise virus. Of those, DAV and LJV were isolated, functionally studied and compared by using D. suzukii as model insect for the first time. In this thesis, LJV was chosen due to its relatively high virus-host adaptation, which seemed to signifi-cantly impact the lifespan of D. suzukii. Subsequently, a virus-specific ultra-purification protocol was established, followed by LJV genomic structural characterization. Thereafter, the fundamental biologi-cal features of this Iflavirus were studied such as (i) infection across different developmental stages and organs, (ii) a probable transmission route and (iii) host-virus adaptation experiments in vivo. However, formulation and details of the up-scale have to be investigated further on the way towards a sustainable, virus-based insecticide for effective biocontrol of D. suzukii.