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Title: Genetic variation and virulence of nucleopolyhedroviruses isolated worldwide from the heliothine pests Helicoverpa armigera, Helicoverpa zea, and Heliothis virescens

Author
item Rowley, Daniel
item Popham, Holly
item Harrison, Robert - Bob

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2011
Publication Date: 6/1/2011
Citation: Rowley, D.L., Popham, H.J., Harrison, R.L. 2011. Classification, genetic variation, and biological activity of nucleopolyhedrovirus isolates from three heliothine pests. Journal of Invertebrate Pathology. 107:112-126.

Interpretive Summary: A group of three moth species called heliothines 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 that potentially can kill heliothine pests were examined. A method for quickly identifying and gathering information on baculoviruses was used to document genetic differences among the viruses. Doses of the viruses required to kill one of the heliothines and the length of time that the insects survived after being infected with the different viruses were also determined. The information in this study contributes to the progress towards developing baculoviruses that can be used as biopesticides against heliothine 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: A PCR-based method was used to classify 90 samples of nucleopolyhedrovirus (NPV; Baculoviridae: Alphabaculovirus) obtained worldwide from larvae of Heliothis virescens, Helicoverpa zea, and Helicoverpa armigera. Partial nucleotide sequencing and phylogenetic analysis of three highly conserved genes (lef-8, lef-9, and polh) indicated that 67 of these samples contained isolates of the H. zea-H. armigera single nucleopolyhedrovirus (Hz/HaSNPV) species group. Eighteen of the samples contained isolates of a multiple NPV from H. armigera, HearMNPV, and five of the samples contained isolates of Autographa californica MNPV (AcMNPV). Sequencing and analysis of an additional seven loci (orf5/orf5b, hr3-orf62, orf26, orf79, orf124/orf117a, orf42, and a part of the region between hr2 and hr3) in the Hz/HearSNPV isolates further classified these viruses into two groups of HearSNPV variants mostly from India and China and a third group of HzSNPV variants. Some of the samples contained isolates of more than one virus; one sample from Colombia, South America contained three distinct NPVs, including an AcMNPV isolate, a HearMNPV isolate, and an isolate of Pseudoplusia includes NPV (PsinNPV). In bioassays of a selection of isolates against H. zea, the commercially available Gemstar' isolate of HzSNPV killed larvae faster than other Hz/HaSNPV isolates, and Hz/HaSNPV isolates killed larvae faster than HearMNPV isolates. Gemstar' and the HearMNPV isolates exhibited higher LC50s than the other Hz/HaSNPV isolates tested. These results reveal the degree of genetic and biological variation among isolates of NPVs to be found in larvae of the heliothine pest complex.