Enhancing insecticidal efficacy of baculovirus by early expressing an insect neurotoxin, LqhIT2, in infected Trichoplusia ni larvae

LqhIT₂, an insect specific neurotoxin from the venom of Leiurus quinquestriatus hebraeus, has been demonstrated to improve insecticidal efficacy of Autographa californica nuclar polyhedrosis virus (AcMNPV). A polyhedrin-positive recombinant AcMNPVvAcP_hsp70EGFP/P_pag90IT₂ was engineered for larvae to express the enhanced green fluorescence protein (EGFP) and LqhIT₂ under the control of P_hsp70 and P_pag90 promoters, respectively. This would allow a visual observation of the viral infection and an improvement of the insecticidal efficacy. The insecticidal activity of this recombinant baculovirus, a wild type AcMNPV and four other recombinant baculoviruses, was evaluated and compared in terms of mortality, body weight, median lethal time (LT₅₀), and median lethal concentration (LC₅₀). Insecticidal efficacy was unaltered when treated with vAcP_hsp70EGFP, moderately improved when infected by vAcP₁₀IT₂ (a P₁₀-promoted LqhIT ₂ gene), and significantly elevated when treated with vAcP_pag90IT₂ or vAcP_hsp70EGFP/P_pag90IT₂. No apparent difference was observed in insecticidal efficacy when additional EGFP was expressed as a visible marker. These results suggest that recombinant AcMNPV vAcP_hsp70EGFP/P_pag90IT₂ may be used as an effective insecticide against Trichoplusia ni and other lepidopterous insect pests.