Potential replication of recombinant baculoviruses in nontarget insect species: Reporter gene products as indicators of infection

The assessment of environmental risks associated with genetically engineered baculovirus pesticides depends on an accurate knowledge of the host range of each virus. However, studies of baculovirus host ranges based solely on symptomology may misidentify as nonhosts any species with symptomless infections. This project used recombinant viruses that allowed detection of symptomless as well as pathogenic virus infections. Seven recombinant isolates of Autographa californica nuclear polyhedrosis virus (AcMNPV), Bombyx mori nuclear polyhedrosis virus, Lymantria dispar nuclear polyhedrosis virus (LdMNPV), and Orgyia pseudotsugata nuclear polyhedrosis virus were tested by either hemocoelic injection or per os inoculation for their potential replication in 23 insect species from eight orders and 17 families. The recombinant viruses contained genes coding for beta-galactosidase, secreted alkaline phosphatase (SEAP), or luciferase under the transcriptional control of either the polyhedrin or ETL promoter. Replication was initially assessed based on detection of the reporter gene products. Results obtained with beta-galactosidase or SEAP as indicators were more consistent but less sensitive than those with luciferase. With all insects tested, much higher reporter enzyme activities were found with the beta-galactosidase reporter gene placed under the polyhedrin promoter than under the ETL promoter, As indicated by reporter enzyme activity after injection with the budded virus particles, the AcMNPV replicated in more species than did the other viruses, and the LdMNPV was the most host specific. Most of the insect species tested did not support detectable replication of any of the viruses. While an observation of symptoms of viral infection was usually concurrent with detection of reporter gene activities, with certain insect/virus combinations, little or no reporter gene activity was detected even though the feeding activity and growth rates were significantly reduced relative to those of the sham-injected controls. The results of this project provide a database for the establishment of future environmental risk assessment protocols and guidelines with baculovirus pesticides. (C) 1997 Academic Press.