Cryptophlebia peltastica Nucleopolyhedrovirus Is Highly Infectious to Codling Moth Larvae and Cells

Abstract

Cydia pomonella granulovirus (CpGV) is a cornerstone of codling moth (Cydia pomonella) control in integrated and organic pome fruit production, though different types of resistance to CpGV products have been recorded in codling moth field populations in Europe for several years. Recently, a novel baculovirus named Cryptophlebia peltastica nucleopolyhedrovirus (CrpeNPV) was isolated from a laboratory culture of the litchi moth, Cryptophlebia peltastica, in South Africa. Along with CpGV, it is the third known baculovirus that is infectious to codling moth. In the present study, parameters of infectiveness of CrpeNPV, such as the median lethal concentration and median survival time, were determined for codling moth larvae susceptible or resistant to CpGV. In addition, the permissiveness of a codling moth cell line with respect to infection by CrpeNPV budded virus was demonstrated by infection and gene expression studies designed to investigate the complete replication cycle. Investigations of the high degree of virulence of CrpeNPV for codling moth larvae and cells are of high significant scientific and economic value and may offer new strategies for the biological control of susceptible and resistant populations of codling moth.IMPORTANCE The emergence of codling moth populations resistant to commercially applied isolates of CpGV is posing an imminent threat to organic pome fruit production. Very few CpGV isolates are left that are able to overcome the reported types of resistance, emphasizing the demand for new and highly virulent baculoviruses. Here we report the recently discovered CrpeNPV as highly infectious to all types of resistant codling moth populations with a high speed of killing, making it a promising candidate baculovirus in fighting the spread of resistant codling moth populations.

Keywords: CpGV resistance; alphabaculovirus; bioassays; biological control; cell culture; survival time analysis; virulence.

FIG 1

Survival time analysis of the uninfected control (A) and CpGV-M (B), CpGV-E2 (C), and CrpeNPV (D) tested on laboratory strains of susceptible CpS (purple), resistant type I CpRR1 (blue), type II CpR5M (red) and type III CpRGO (green) neonate larvae.

FIG 2

Uninfected Cp14R cells (A) and Cp14R cells infected with BV from CrpeNPV (B) viewed under the light microscope at 7 dpi. Polyhedral occlusion bodies are visible as dark aggregations within the nuclei of cells. Bars, 30 μm.

FIG 3

Relative transcription rates of selected CrpeNPV genes after infection of Cp14R cells. Levels of transcripts of ie-1 (blue), lef-8 (red), dnapol (green), vp39 (orange), f-protein (light blue) and polh (purple) genes were measured by reverse transcription-qPCR at 24, 48, 72, and 96 hpi. Analyses of transcription were repeated independently in triplicate. Numbers of replicates (n) with measurable gene transcription are given above the columns. Vertical bars represent standard errors (SE).