The isolation of a novel alphabaculovirus and its potential for microbial control of key tortricid moth pests

Abstract: A laboratory culture of Cryptophlebia peltastica, a major pest of litchis in southern Africa, was established for the first time. During the rearing of C. peltastica, larvae showing symptoms of baculovirus infection were collected and analysed. Occlusion bodies (OBs) were purified from the symptomatic larvae and observed by transmission electron microscopy to be a nucleopolyhedrovirus. Genetic characterisation through creating restriction profiles and sequencing the whole genome, revealed that this was a novel alphabaculovirus, with no close relative, and was thus named the Cryptophlebia peltastica nucleopolyhedrovirus (CrpeNPV). This is the first known record of an NPV naturally infecting any species within the Grapholitini tribe of the Tortricidae. Bioassays were used to determine the virulence of CrpeNPV against C. peltastica, Thaumatotibia leucotreta (false codling moth) and Cydia pomonella (codling moth). The LC90 of CrpeNPV for neonate larvae of these three species was respectively, 3.33 × 105, 9.97 × 104 and 1.26 × 104 OBs/ml. The average speed of kill to cause 90% mortality of each species was 5 days. As the bioassay results indicated superior virulence against T. leucotreta and C. pomonella than against the homologous host, C. peltastica, field trials were conducted against T. leucotreta in citrus and C. pomonella in apples at rates of between 5 × 1011 and 5 × 1013 OBs/ha. Very promising results were achieved. Consequently, CrpeNPV is considered to have significant potential for effective biological control of these, and potentially other, key tortricid pests of agriculture.