Determination of baculovirus titers
The baculovirus stock titer was measured with a Baculovirus rapid titer kit (TaKaRa, Tokyo, Japan) according to the manufacturer’s instructions. Briefly, samples diluted from 10-3 to 10-5 were added to Sf9 monolayer cells in a 96-well plate. After incubation at room temperature (RT) for 1 h, the supernatant was replaced with a methyl cellulose overlay. Twenty-seven hours later, the plate was fixed with 4% paraformaldehyde, and blocked with normal goat serum. An Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) envelope glycoprotein (gp64) mAb (1:200) was used as the primary antibody, and an HRP-conjugated goat anti-mouse antibody (1:250) was used as the secondary antibody. Blue peroxidase substrate was added and incubated for 3 h at RT. Blue-stained foci in the wells of the highest dilution that contained a reasonable number of foci were counted, and the titer was determined.