Selection of a nucleopolyhedrovirus isolate from Helicoverpa armigera as the basis for a biological insecticide

Background: the cotton bollworm, Helicoverpa armigera, is an insect that causes damage in a wide range of crops in Spain.Seven isolates of H. armigera single nucleopolyhedrovirus (HearSNPV) from the Iberian Peninsula were subjected to molecularand biological characterization and compared with a Chinese genotype (HearSNPV-G4). Results: the estimated sizes of the Iberian genomes varied between 116.2 and 132.4 kb, compared to 131.4 kb of theHearSNPV-G4 reference genome. Phylogenetic analysis based on the lef-8, lef-9 and polh genes revealed that the Iberianstrains were more closely related to one another than to other HearSNPV isolates. Occlusion body (OB) concentration-mortalityresponses (LC 50 values) did not differ significantly among Iberian isolates when tested against a Helicoverpa armigera colonyfrom Oxford (UK). Despite being the fastest killing isolate, HearSNPV-SP1 was as productive as isolates with lower virulence,with an average yield of 3.1 × 109 OBs larva−1 . OBs of HearSNPV-SP1 and HearSNPV-G4 were similarly pathogenic against arecently established colony from southern Spain, although HearSNPV-SP1 was faster killing than HearSNPV-G4 against a rangeof instars. Conclusion: the insecticidal properties of HearSNPV-SP1 mean that this strain is likely to prove useful as the basis for abiological insecticide for control of Helicoverpa armigera in Spain.