A novel concept applying baculovirus-mediated gene silencing to study insect gene function and regulation is described in this paper. A recombinant baculovirus, Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV), was constructed with the juvenile hormone esterase (JHE) gene from the tobacco budworm Heliothis virescens in the antisense orientation, driven by the viral p10 promoter. Infection with this recombinant greatly reduced the haemolymph JHE level and resulted in aberrant morphogenesis of final-instar H. virescens larvae. The body organization remained larval, although the cuticle became hard and brown, similar to pupal cuticle. These results demonstrated that baculovirus-mediated gene silencing can be accomplished and utilized to dissect insect development and to design a new class of baculovirus insecticides.