Efficacy of Various Low Temperature and Exposure Time Combinations for Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) Larvae.

A systems approach was developed as an alternative to a standalone quarantine disinfestation treatment for Thaumatotibia leucotreta in citrus fruit exported from South Africa. The systems approach consists of three measures: pre and postharvest controls and measurements, postpacking inspection, and postharvest exposure to low temperatures. Different cold treatment conditions with a range of efficacy levels can be used for this last measure. A series of trials reported here evaluated the efficacy of seven temperatures ranging from 0 to 5°C for durations from 14 d to 26 d. Mortality of the most cold-tolerant larval stages of T. leucotreta was determined. Temperatures of 0, 1, 2, and 3°C for 16, 19, 20, and 24 d respectively, induced 100% mortality of the tested populations. Probit 9 level treatment efficacy was achieved at 0 and 1°C for 16 and 19 d respectively. Mortalities higher than 90% were obtained with temperatures of 4, 4.5, and 5°C, after exposure for the longer durations. We demonstrated a significant difference in cold-induced insecticidal efficacy between 1, 2, 3, and 4°C. There was no significant difference in insecticidal efficacy between 4 and 4.5°C, but both of these temperatures were more efficacious than 5°C. The results of this study are valuable to support the use of cold treatment conditions with lower risk of fruit chilling injury in an effective systems approach, where the cold treatment efficacy can be augmented with other components of the systems approach.

CpGV-M Replication in Type I Resistant Insects: Helper Virus and Order of Ingestion Are Important.

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.

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

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.

Development of a Postharvest Cold Treatment for Cryptophlebia peltastica (Lepidoptera: Tortricidae) for Export of Litchis From South Africa.

The litchi moth, Cryptophlebia peltastica (Meyrick) (Lepidoptera: Tortricidae), is endemic to sub-Saharan Africa and certain Indian Ocean islands. It is an important pest of litchis and to a lesser extent macadamias. Litchis are exported to certain markets that consider C. peltastica as a phytosanitary pest. Consequently, an effective postharvest phytosanitary treatment is required. This study sought to develop a cold disinfestation treatment for this purpose. First, it was established that the fifth instar was the most cold-tolerant larval stage, as it was the only instar for which there was still some survival after 12 d at 1°C. It was then determined that cold treatment trials could be conducted in artificial diet, as there was no survival of fifth instar C. peltastica in litchis after only 9 d at 1°C, whereas it took 15 d at this temperature before no survival of fifth instar C. peltastica was recorded in artificial diet. Consequently, cold susceptibility of fifth instar C. peltastica and the most cold-tolerant larval stages (fourth and fifth instar) of false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), were compared in artificial diet. There was no survival of C. peltastica after 13 d at 1°C, whereas this was only so for T. leucotreta after 16 d. Consequently, it can be concluded that any cold treatment that has been proven effective against T. leucotreta would be as effective against C. peltastica. Finally, it was confirmed that the cold susceptibility of T. leucotreta in artificial diet did not overestimate the effect of cold on T. leucotreta larvae in litchis.

Morphological, genetic and biological characterisation of a novel alphabaculovirus isolated from Cryptophlebia peltastica (Lepidoptera: Tortricidae).

Cryptophlebia peltastica is an agricultural pest of litchis and macadamias in South Africa with phytosanitary status for certain markets. Current control methods rely on chemical, cultural and classical biological control. However, a microbial control option has not been developed. An Alphabaculovirus from C. peltastica was recovered from a laboratory reared colony and morphologically characterised by transmission electron microscopy (TEM). Analysis of occlusion bodies indicated a single NPV (SNPV) varying in size from 421 to 1263 nm. PCR amplification and sequencing of the polh gene region using universal primers followed by BLAST analysis revealed a 93% similarity to a partial polh gene sequence from Epinotia granitalis NPV. Further genetic characterisation involving single restriction endonuclease (REN) digestion of genomic DNA was carried out to generate profiles for comparison against other baculovirus species and potential new isolates of the same virus. The complete genome of the virus was sequenced, assembled and analysed for a more comprehensive genetic analysis. The genome was 115728 base pairs (bp) in length with a GC content of 37.2%. A total of 126 open reading frames (ORFs) were identified with minimal overlap and no preference in orientation. Bioassays were used to determine the virulence of the NPV against C. peltastica. The NPV was virulent against C. peltastica with an LC50 value of 6.46 × 103 OBs/ml and an LC90 value of 2.46 × 105 OBs/ml, and time mortality ranging between 76.32 h and 93.49 h. This is the first study to describe the isolation and genetic characterisation of a novel SNPV from C. peltastica, which has potential for development into a biopesticide for the control of this pest in South Africa.