Infectivity studies of a new baculovirus isolate for the control of the diamondback moth (Plutellidae: Lepidoptera)

This study describes a new baculovirus isolate recovered from infected larvae of the diamondback moth, Plutella xylostella (L.), and identified as a multiple nucleopolyhedrovirus (MNPV). The plaque purified isolate designated as PxMNPVCL3 was found to be pathogenic to P. xylostella, Heliothis virescens (F.), Trichoplusia ni (Hubner), H. subflexa (Guenee), Helicoverpa zea (Boddie), Spodoptera exigua (Hubner), and S. frugiperda (J. E. Smith) larvae in decreasing order of susceptibility. The LC(50) for diamondback moth, the most susceptible, was 6 occlusion bodies (OB)/cm(2), whereas the most resistant species, namely S. frugiperda, was 577 OB/cm(2). PxMNPVCL3 was more pathogenic to diamondback moth by 3-4 log cycles as compared with 2 broad-spectrum baculoviruses, namely Autographa californica (alfalfa looper) MNPV and Anagrapha falcifera (celery looper) MNPV. The 3 baculoviruses were compared with each other and characterized by restriction endonuclease (REN) analysis, hybridization, and neutralization tests. Fragmentation profiles generated by REN showed that the 3 baculoviruses shared some fragments in common. Hybridization studies employing digoxigenin labeled PxMNPVCL3 DNA as a probe revealed the close but distinct relationship of these 3 viruses. Neutralization tests confirmed the hybridization studies, namely that the 3 viruses although genetically similar are distinguishable from each other.