ARS | Publication request: Genetic variation and virulence of Autographa californica multiple nucleopolyhedrovirus and Trichoplusia ni single nucleopolyhedrovirus isolates

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 2012
Publication Date: May 1, 2012
Citation: Harrison, R.L., Popham, H.J., Breitenbach, J.E., Rowley, D.L. 2012. Genetic variation and virulence of Autographa californica multiple nucleopolyhedrovirus and Trichoplusia ni single nucleopolyhedrovirus isolates. Journal of Invertebrate Pathology. 110(1):33-47.

Interpretive Summary: A group of moth species called loopers are serious pests of many crops around the world. The use of chemical insecticides to kill these pests is no longer desirable due to negative ecological, environmental, and health consequences. Baculoviruses are a group of insect viruses that can be used to kill insect pests without the problems of chemical insecticides. In this study, a large number of baculoviruses isolated from different species of loopers were examined. A method for quickly identifying and gathering information on baculoviruses was used to document genetic differences among these viruses. Doses of the viruses required to kill a looper species called the cabbage looper was determined. The length of time that the cabbage loopers survived after being infected with the different viruses was also determined. The information in this study contributes to progress towards developing and registering baculoviruses that can be used as biopesticides against looper pests. Baculoviruses have a wide range of applications in addition to their use as biopesticides, and this study will be of interest to scientists in academia, government, and industry who work with this group of viruses.

Technical Abstract: To determine the genetic diversity within the baculovirus species Autographa calfornica multiple nucleopolyhedrovirus (AcMNPV; Baculoviridae: Alphabaculovirus), a PCR-based method was used to identify and classify baculoviruses found in virus samples from the lepidopteran host species A. californica, Autographa gamma, Trichoplusia ni, Rachiplusia ou, Anagrapha falcifera, Galleria mellonella, and Heliothis virescens. Alignment and phylogenetic inference from partial nucleotide sequences of three highly conserved genes (lef-8, lef-9, and polh) indicated that 45 of 74 samples contained isolates of AcMNPV, while six samples contained isolates of Rachiplusia ou multiple nucleopolyhedrovirus strain R1 (RoMNPV-R1) and 25 samples contained isolates of the species Trichoplusia ni single nucleopolyhedrovirus (TnSNPV; Alphabaculovirus). One sample from A. californica contained a previously undescribed NPV related to alphabaculoviruses of the armyworm genus Spodoptera. Data from PCR and sequence analysis of the ie-2 gene and a region containing ORF ac86 in samples from the AcMNPV clade indicated to a distinct group of viruses, mostly from G. mellonella, that are characterized by an unusual ie-2 gene previously found in the strain Plutella xylostella multiple nucleopolyhedrovirus CL3 (PlxyMNPV-CL3) and a large deletion within ac86 previously described in the AcMNPV isolate 1.2 and PlxyMNPV-CL3. PCR and sequence analysis of baculovirus repeated ORF (bro) genes revealed that the bro gene ac2 was split into two separate bro genes in some samples from the AcMNPV clade. Comparison of sequences in this region suggests that ac2 was formed by a deletion that fused the two novel bro genes together. In bioassays of a selection of isolates against T. ni, significant differences were observed in the insecticidal properties of individual isolates, but no trends were observed between isolates of AcMNPV, TnSNPV, or RoMNPV. This study expands on what we know about the variation of AcMNPV, AcMNPV-like and TnSNPV viruses, provides novel information on the distinct groups in which AcMNPV isolates occur, and contributes to the knowledge required for the registration, evaluation, and improvement of AcMNPV, AcMNPV-like, and TnSNPV isolates as biological control agents.