Bioassay experiments for investigating the potential of recombinant nucleopolyhedroviruses expressing a scorpion toxin (AaIT), and a juvenile hormone esterase from Manduca sexta (Linnaeus) (AcMsJHE) in killing first instar larvae of Agrotis ipsilon (Hufnagel) were tested in comparison with the wild type virus (AcMNPV). Protein expression and viral replication in insect were determined using SDS-PAGE and agarose gel electrophoresis. Results of lethal concentrations indicate that AaIT was the most efficient virus compared with AcMsJHE or AcMNPV. Median lethal concentration of AaIT was 4.0 × 10⁵ PIBs/ml compared with 7.0 × 10⁵ and 7.6 × 10⁵ PIBs/ml for AcMsJHE and AcMNPV, respectively. AaIT killed the treated first instar larvae of A. ipsilon markedly faster than AcMsJHE or AcMNPV, and significantly affected third instar larval weight after 96 hours post-infection (h.p.i.), which the LT₅₀s of AaIT were 94 and 89 h.p.i. when 1 × 10⁶ and 1 × 10⁸ PIBs/ml were used, respectively. SDS-PAGE for protein separation and agarose gel electrophoresis for DNA fragment visualization after restriction enzymes cut indicate that recombinant viruses might be replicated and expressed the inserted genes in A. ipsilon larvae. Protein profile showed differences among larval homogenate samples infected with recombinant viruses and wild type virus compared with control. DNA fragments of recombinant viruses run on 1% agarose gel indicate that there are different size and absence fragments when the total genome cut with EcoRI or PstI. Data of this work illustrated the efficiency of recombinant virus with a scorpion toxin gene on A. ipsilon, which indicate that the use of this virus within integrated pest management programme for A. ipsilon control may be useful.