Nucleopolyhedrovirus from the Western Avocado Leafroller, Amorbia cuneana: Isolation and characterization of a potential viral control agent

Abstract

The western avocado leafroller, Amorbia cuneana (Lepidoptera; Tortricidae), is an increasingly important pest of avocados in the San Joaquin Valley of California and is also known to attack citrus periodically. Present control programs rely heavily on biological control agents, mostly hymenopteran parasitoids, but chemical insecticides are also used. To develop more selective alternative control agents, we isolated a multinucleocapsid nucleopolyhedrovirus from A. cuneana (AmcuMNPV) and report here the characterization of this virus in terms of its identity, general genome characteristics, and efficacy as determined in laboratory bioassays. The AmcuMNPV had a genome of 125 kbp and produced virions approximately 220 nm in length occluded in occlusion bodies (OBs) averaging 1.2 μm in diameter. Virions contained an average of four nucleocapsids per envelope. Phylogenetic analyses based on the polh, lef-8, and lef-9 genes showed that this virus was different from, but related to, the NPVs of other tortricid species, specifically, the CfDefNPV of Choristoneura fumiferana and the EppoNPV of Epiphyas postvittana. Histological studies showed its pathology was typical of lepidopteran NPVs, with the virus attacking most tissues, especially the fat body and epidermis. With respect to activity, the virus was highly efficacious, with 70% of neonate larvae dying within a few days of being exposed to a single polyhedron, with an average LC50 of 184 OBs for third instars. These results indicate that this virus has good potential for use in biological and integrated control programs that target A. cuneana.