The Baculoviridae is a large family of pathogens that mainly infects lepidopteran insects. Baculoviruseshave a large circular, supercoiled, and double-stranded DNA genome ranging from 80 to 180 kbp. Baculoviruses have been used as bioinsecticides as well as expression vectors for foreign genes, called Baculovirus Expression Vector System (BEVS). In addition to such industrial use, basic researches on baculoviruses such as genome sequencing and gene knockout have progressed rapidly. Functional characterization of baculoviral genes revealed that some of the non-essential auxiliary genes encode proteins controlling behavior, cell death, and molting in host insects. In this review, I describe our research progress on functional analyses of baculoviral genes that are involved in host manipulation.