Baculoviruses biopesticides for fruit tree pests: overcoming the shortcomings and improving efficacy

Abstract: Baculoviruses have been used for control of tree fruit Lepidoptera for several decades, with the first being Cydia pomonella granulovirus (CpGV) for Cydia pomonella (codling moth) control. Subsequently, pest species, such as Grapholita molesta (oriental fruit moth) and Thaumatotibia leucotreta (false codling moth) have been targeted. Despite the obvious efficacy and benefits of virus-based biopesticides, they do present certain shortcomings. For example, although host specificity is an advantage, so is it a disadvantage; baculoviruses are UV-sensitive and degrade rapidly in direct sunlight; although not common, pest resistance can occur; and speed of kill is slow. Consequently, a multi-faceted research programme is being driven to develop solutions to these deficiencies. Bioprospecting for new baculoviruses has identified alternative CrleGV isolates in the event that resistance by T. leucotreta may develop. A novel CpGV isolate with potential to overcome codling moth resistance to CpGV has also been found. A novel virus species, the Cryptophlebia peltastica nucleopolyhedrovirus (CrpeNPV), with a relatively broad host range, being virulent against several species of tortricids, has also been found and characterized. We have also successfully selected a UV-resistant CrleGV isolate, with more than 1000-fold improved virulence after UV-exposure, compared to the wild-type isolate. Combining different species of virus has also resulted in a synergistic response, increasing virulence. Lastly, passaging of a virus through a closely related heterologous host can result in selection of more virulent genotypes, thus improving virulence against the heterologous host. These and other strategies present tremendous opportunities for improvement of efficacy of baculovirus biopesticides.