Construction and Characterization of Immediate Early Baculovirus Pesticides

Recombinant baculoviruses that express insect-specific toxins under the control of viral late gene promoters can kill susceptible lepidopteran hosts faster than the wild-type virus. In an effort to improve the efficacy of genetically engineered baculovirus pesticides, we have produced a recombinant that contains an insect specific toxin gene (AaIT) under the control of the promoter from an immediate early gene (ie1) ofAutographa californicanuclear polyhedrosis virus (AcNPV). AaIT protein was detected as early as 4 h postinfection in cultured insect cells infected with this recombinant. The protein continued to accumulate as the infection progressed and, even as late as 24 h postinfection, the amount of AaIT was about equal to that provided by a recombinant that expressed AaIT under the control of the very latep10promoter. Similar results were obtained with a recombinant that expressed a modified insect juvenile hormone esterase (JHE–KK) underie1control, confirming the ability of this promoter to provide early and abundant expression of gene products with potential pesticidal activity. Bioassays showed that theie1–AaIT recombinant killedHeliothis virescenslarvae faster than wild-type virus, but not faster than thep10–AaIT recombinant. However, larvae infected with theie1–AaIT recombinant were smaller than those infected with thep10–AaIT recombinant, suggesting that expression of AaIT earlier in infection enhanced the ability of the virus to reduce the feeding activity ofH. virescenslarvae.