Organization of the Structural Protein Region of La Jolla Virus Isolated from the Invasive Pest Insect Drosophila suzukii

Abstract

Drosophila suzukii (Ds) is an invasive pest insect that infests ripening fruit, causing severe economic losses. Control measures based on chemical pesticides are inefficient and undesirable, so biological alternatives have been considered, including native Ds viruses. We previously isolated a strain of La Jolla virus (LJV-Ds-OS20) from Ds in Germany as a candidate biopesticide. Here we characterized the new strain in detail, focusing on the processing of its capsid proteins. We tested LJV growth during Ds development to optimize virus production, and established a laboratory production system using adult flies. This system was suitable for the preparation of virions for detailed analysis. The LJV-Ds-OS20 isolate was cloned by limiting dilution and the complete nucleotide sequence was determined as a basis for protein analysis. The terminal segments of the virus genome were completed by RACE-PCR. LJV virions were also purified by CsCl gradient centrifugation and analyzed by SDS-PAGE and electron microscopy. The capsid proteins of purified LJV virions were resolved by two-dimensional SDS-PAGE for N-terminal sequencing and peptide mass fingerprinting. The N-terminal sequences of VP1 and VP2, together with MS data representing several capsid proteins, allowed us to develop a model for the organization of the LJV structural protein region. This may facilitate the development of new viral strains as biopesticides.

Hunting Drosophila viruses from wild populations: a novel isolation approach and characterization of viruses

“…We used electron microscopy to examine the morphology of LJV and NFV virions. LJV showed an icosahedral viral particle (Figure 2C), consistent with other positive-sense single-stranded RNA viruses in the Iflaviridae family and previous reports of LJV [25]. Surprisingly, NFV repeatably showed elongated and spherical-shaped structures, which is consistent with this virus having pleomorphic virions (Figure 2D).…”

“…We used electron microscopy to examine the morphology of LJV and NFV virions. LJV showed an icosahedral viral particle (Figure 2C), consistent with other positive-sense singlestranded RNA viruses in the Iflaviridae family and previous reports of LJV [25].…”

“…It was able to infect D. suzukii orally and reduce the number of flies that emerged from blueberry fruits, suggesting it merits investigation as a potential biological control agent. Other insect viruses have shown to cause mortality in D. suzukii , including Cricket Paralysis virus (CrPV), FHV, and DCV, DAV and LJV [6, 29, 56, 57] [25]. While these experiments suggest viruses might be suitable as biological control agents, more research is needed to determine whether producing and delivering RNA viruses is practical, or whether their effects on D. suzukii are sufficient to reduce crop damage.…”

Pathogenicity of La Jolla Virus in Drosophila suzukii following Oral Administration

“…Similarly, we have evaluated the ability of specific insect viruses to control Ds [ 17 ], which led to the isolation of La Jolla virus (LJV) from moribund Ds specimens in Germany [ 18 ]. LJV belongs to the family Iflaviridae and has a single-stranded positive-sense RNA genome 10,250 nt in length [ 19 ]. LJV was initially discovered in Drosophila melanogaster [ 20 ] before its isolation from Ds [ 18 , 21 ].…”

“…LJV was initially discovered in Drosophila melanogaster [ 20 ] before its isolation from Ds [ 18 , 21 ]. The intrathoracic injection of LJV caused significant mortality in adult Ds flies, suggesting its potential as a control method [ 18 , 19 ]. However, LJV must also be lethal when delivered orally, particularly to larvae, because this would be the typical administration route and target in the field following the application of a sprayable virus formulation.…”