In Vivo Treatment of a Nuclear Polyhedrosis Virus of Autographa californica (Lepidoptera: Noctuidae) with Chemical Mutagens: Determination of Changes in Virulence in Four Lepidopteran Hosts

Chemical treatment of a nuclear polyhedrosis virus of Autographa californica (Speyer) was carried out initially in Trichoplusia ni (Hübner), Heliothis zea (Boddie), H. virescens (F.), and Spodoptera frugiperda (J. E. Smith), and subsequent effects of treatment on virulence of the virus were assessed in each host. No significant effects were noted in any of the four insect species after treatment with 5-bromodeoxyuridine or nitrosoguanidine. Almost a 100-fold increase in virulence was observed, however, when the virus was treated in T. ni with 3-methylcholanthrene and assayed in S. frugiperda. This isolate also maintained a high degree of pathogenicity for T. ni. Significant changes were also observed in the LT50 of several virus samples, but none of these changes persisted after several serial passages. These observations support use of such low-passage virus isolates, which demonstrate a significant increase in virulence, on crops affected with a particular insect pest.