(27k) Development of a Cell Culture-Derived Viral Insecticide to Control the Spread of Drosophila Suzukii

Drosophila suzukii, also known as spotted-wing drosophila (SWD), is an invasive insect pest native to Southeast Asia. In recent decades, the pest has expanded its range to affect all major orchard regions in Europe and America. The SWD is a highly adaptable insect, able to spread, survive, and thrive under a wide range of environmental conditions. The list of SWD host plants is long, with berries and grapes being the preferred hosts. Unlike other Drosophila species, SWD can penetrate the skin of intact fruit with a toothed ovipositor to lay eggs in ripe and mature fruit. Development of the larvae inside the fruit results in rapid pulp decomposition and rotting of the fruit, causing significant economic damage through yield loss, reduced shelf-life of infested fruit and increased production costs. Fresh markets, frozen berries and fruit export programs have been affected by the pest due to zero tolerance for fruit infestation. Many chemical insecticides cannot be used at these late stages for consumer safety reasons. In addition, various classical broad-spectrum chemical insecticides are banned because they are hazardous to bees and other beneficial insects. The control of SWD is therefore a major challenge and there is a great need for alternative, environmentally friendly and consumer-friendly control strategies. The use of insect-specific viruses is one promising approach for this purpose. Baculoviruses, for example, are naturally occurring insect-pathogenic viruses, which, due to their high virulence and specificity, have been widely used to control insect pests in organic apple production in order to reduce the use of classical insecticides.

The aim of this research project is to develop an innovative and ecologically acceptable method for the control of the SWD.

In field studies, several entomopathogenic viruses such as the Drosophila C virus (DCV), Flock House virus (FHV), Cricket Paralysis virus (CrPV) und La Jolla virus (LJV) were isolated from the SWD larvae and demonstrated to be virulent. Of these, two viruses, the DCV and LJV, were selected for their host specificity and process suitability for the development of an in-vitro production process.

First, we investigated, which of the classical insect cell lines, such as the Spodoptera frugiperda 9 (Sf9) cells or the Drosophila Schneider 2 (S2) cells, could be infected with the respective viruses, which is a prerequisite for the economic production of insect-pathogenic viruses in an insect cell line. We then identified critical process parameters for the production process and started to optimize the space-time yield of the virus. First results indicated virus yields of more than 10⁸ virus particles per milliliter of culture broth for LJV produced in S2 cells. However, the yields for DCV are slightly lower. In addition, assays were developed to monitor the critical process parameters. Finally, the production process was scaled up to a larger laboratory scale, and a purification method based on a steric exclusion chromatography was developed for formulation studies.