Search Results (7)

The genetic diversity of baculoviruses provides a sustainable agronomic solution when resistance to biopesticides seems to be on the rise. This genetic diversity promotes insect infection by several genotypes (i.e., multiple infections) that are more likely to kill the host. However, the mechanism and regulation of these virus interactions are still poorly understood. In this article, we focused on baculoviruses infecting the codling moth, Cydia pomonella: two Cydia pomonella granulovirus genotypes, CpGV-M and CpGV-R5, and Cryptophlebia peltastica nucleopolyhedrovirus (CrpeNPV). The influence of the order of ingestion of the virus genotypes, the existence of an ingestion delay between the genotypes and the specificity of each genotype involved in the success of multiple infection were studied in the case of Cydia pomonella resistance. To obtain a multiple infection in resistant insects, the order of ingestion is a key factor, but the delay for ingestion of the second virus is not. CrpeNPV cannot substitute CpGV-R5 to allow replication of CpGV-M. Full article

Many steps in the baculovirus life cycle, from initial ingestion to the subsequent infection of all larval cells, remain largely unknown; primarily because it has hitherto not been possible to follow individual genomes and their lineages. Use of ANCHOR^TM technology allows a high intensity fluorescent labelling of DNA. When applied to a virus genome, it is possible to follow individual particles, and the overall course of infection. This technology has been adapted to enable labelling of the baculovirus Autographa californica Multiple NucleoPolyhedroVirus genome, as a first step to its application to other baculoviruses. AcMNPV was modified by inserting the two components of ANCHOR^TM: a specific DNA-binding protein fused to a fluorescent reporter, and the corresponding DNA recognition sequence. The resulting modified virus was stable, infectious, and replicated correctly in Spodoptera frugiperda 9 (Sf9) cells and in vivo. Both budded viruses and occlusion bodies were clearly distinguishable, and infecting cells or larvae allowed the infection process to be monitored in living cells or tissues. The level of fluorescence in the culture medium of infected cells in vitro showed a good correlation with the number of infectious budded viruses. A cassette that can be used in other baculoviruses has been designed. Altogether our results introduce for the first time the generation of autofluorescent baculovirus and their application to follow infection dynamics directly in living cells or tissues. Full article

Cydia pomonella granulovirus, in particular CpGV-M isolate, is used as a biological control against the codling moth (CM), Cydia pomonella. As a result of intensive control over the years, codling moth populations have developed resistance against this isolate. This resistance is now called type I resistance. Isolates, among them, CpGV-R5, have been found that are able to overcome type I resistance. Both CpGV-M and CpGV-R5 are used in orchards to control the codling moth. High resolution melting (HRM) has been adapted to differentiate between CpGV-M and CpGV-R5 isolates. Specific PCR primers have been designed for the CpGV p38 gene, encompassing the variable region responsible for the ability to overcome resistance. Because each amplicon has a specific melting point, it is possible to identify the CpGV-M and CpGV-R5 genotypes and to quantify their relative proportion. This method has been validated using mixtures of occlusion bodies of each isolate at various proportions. Then, the HRM has been used to estimate the proportion of each genotype in infected larvae or in occlusion bodies (OBs) extracted from dead larvae. This method allows a rapid detection of genotype replication and enables the assessment of either success or failure of the infection in field conditions. Full article

To test the importance of the host genotype in maintaining virus genetic diversity, five experimental populations were constructed by mixing two Cydia pomonella granulovirus isolates, the Mexican isolate CpGV-M and the CpGV-R5, in ratios of 99% M + 1% R, 95% M + 5% R, 90% M + 10% R, 50% M + 50% R, and 10% M + 90% R. CpGV-M and CpGV-R5 differ in their ability to replicate in codling moth larvae carrying the type I resistance. This ability is associated with a genetic marker located in the virus pe38 gene. Six successive cycles of replication were carried out with each virus population on a fully-permissive codling moth colony (CpNPP), as well as on a host colony (R_GV) that carries the type I resistance, and thus blocks CpGV-M replication. The infectivity of offspring viruses was tested on both hosts. Replication on the CpNPP leads to virus lineages preserving the pe38 markers characteristic of both isolates, while replication on the R_GV colony drastically reduces the frequency of the CpGV-M pe38 marker. Virus progeny obtained after replication on CpNPP show consistently higher pathogenicity than that of progeny viruses obtained by replication on R_GV, independently of the host used for testing. Full article

The detection of resistance in codling moth (Cydia pomonella) populations against the Mexican isolate of its granulovirus (CpGV-M), raised questions on the sustainability of the use of this biological insecticide. In resistant host cells, CpGV-M is not able to complete its replication cycle because replication is blocked at an early step. Virus isolates able to overcome this resistance have been characterized—among them, the CpGV-R5 isolate. In mixed infections on resistant insects, both CpGV-M and CpGV-R5 viruses replicate, while CpGV-M alone does not induce mortality. Genetically heterogeneous virus populations, containing 50% of each CpGV-M and CpGV-R5 appear to control resistant host populations as well as CpGV-R5 alone at the same final concentration, even if the concentration of CpGV-R5 is only half in the former. The use of mixed genotype virus preparations instead of genotypically homogeneous populations may constitute a better approach than traditional methods for the development of baculovirus-based biological insecticides. Full article

In our article “Progressive Adaptation of a CpGV Isolate to Codling Moth Populations Resistant to CpGV-M.” (Viruses 2014, 6, 5135–5144; doi:10.3390/v6125135) [1] we obtained resistance values of the codling moth, Cydia pomonella, RGV laboratory colony [2], when challenged with Cydia pomonella Granulovirus, Mexican Isolate (CpGV-M), that were lower than those previously published [2]. Careful analysis of both the RGV colony and the CpGV-M virus stock used led to the realization that a low level contamination of this virus stock with CpGV-R5 occurred. We have made new tests with a verified stock, and the results are now in agreement with those previously published. Full article

The NPP-R1 isolate of CpGV is able to replicate on CpGV-M-resistant codling moths. However, its efficacy is not sufficient to provide acceptable levels of control in natural (orchard) conditions. A laboratory colony derived from resistant codling moths was established, which exhibited a homogeneous genetic background and a resistance level more than 7000 fold. By successive cycles of replication of NPP-R1 in this colony, we observed a progressive increase in efficacy. After 16 cycles (isolate 2016-r16), the efficacy of the virus isolate was equivalent to that of CpGV-M on susceptible insects. This isolate was able to control both CpGV-M-susceptible and CpGV-M-resistant insects with similar efficacy. No reduction in the levels of occlusion body production in susceptible larvae was observed for 2016-r16 compared to CpGV-M. Full article